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8 STEMscopes Georgia Student Notebook

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a part of STEMscopes NGSS Georgia_8th_Book.indd 1

8th grade

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developed by Accelerate Learning, Inc. & Rice University

Notebook

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GEORGIA Student Notebook – Eighth Grade ISBN: 978-1-946725-78-3

Published by Accelerate Learning Inc., 5177 Richmond Ave, Suite 800, Houston, TX 77056. Copyright © 2017, by Accelerate Learning Inc. All rights reserved. No part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without prior written consent of Accelerate Learning Inc., including, but not limited to, in any network or other electronic storage or transmission, or broadcast for distance learning. To learn more, visit us at www.acceleratelearning.com

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GEORGIA

This Student Notebook is designed to be used as a companion piece to our online curriculum. The pages of this book are organized and follow the 5E model.

Student Handout

ENGAGE

A short activity to grab students’ interest

Student Journal

EXPLORE

A hands-on activity in which students get experience with the concept being taught

STEMscopedia

EXPLAIN

A reference material that includes parent connections, technology, and science news

Reading Science A reading passage about the concept that includes comprehension questions

ELABORATE Math Connection

A set of grade-level appropriate math problems that address the concept

Writing Science

EVALUATE

A writing prompt based on the concept studied in which the students can demonstrate what they have learned

Only student pages are included in this book and directions on how to use these pages are found in our online curriculum. Use the URL address and password provided to you by your district to access our full curriculum.

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Eighth Grade Student Notebook Table of Contents Physical Science Lesson 8P1A

Pure Substances and Mixtures 8P1B

Particles in States of Matter

8P1CD

Physical and Chemical Properties and Changes

8P1E

Patterns in the Periodic Table

8P1F

Conservation of Mass

8P2AB

Kinetic and Potential Energy

8P2C

Energy Transformations Within a System

8P2D

Heat Transfer and Molecular Motion

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Page

1 23 47 69 105 125 157 179 iii

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Eighth Grade Student Notebook Table of Contents

Physical Science Lesson

Page

8P3A

205

Speed, Distance, Velocity, and Acceleration 8P3BC

Forces On and Motions of Objects

8P4A

Similarities and Differences Bewtween Electromagnetic and Mechanical Waves 8P4BF

8P4C

301

Practical Applications of the Electromagnetic Spectrum 8P4D

321

Light and Sound Waves 8P4E

Wave Behavior in Different Media

Lenses 8P5A

Fields and Forces iv

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253 279

Waves and Energy

8P4G

229

349 369 389

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Eighth Grade Student Notebook Table of Contents

Physical Science Lesson

Page

8P5B

411

Causes of Electrostatic Forces 8P5C

Strength of Electric and Magnetic Forces

429

Appendix Glossary

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8th Grade Physical Science

8P1A

Pure Substances and Mixtures

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8P1A Pure Substances and Mixtures

Student Handout Name:

Date:

Separation Experiment Sketch a picture of sample (A) below.

Examine your sketch and write down your observations.

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8P1A Pure Substances and Mixtures

Student Journal Name:

Date:

Group:

Part I: Washers, Nuts, and Bolts Answer the questions about the following combinations of washers, nuts, and bolts. Container A 1. What is in this container? 2. Is this a pure substance or mixture? 3. Justify your answer for #2: Container B 1. What is in this container? 2. Is this a pure substance or mixture? 3. Justify your answer for #2: Container C 1. What is in this container? 2. Is this a pure substance or mixture? 3. Justify your answer for #2: Container D 1. What is in this container? 2. Is this a pure substance or mixture? 3. Justify your answer for #2: Container E 1. What is in this container? 2. Is this a pure substance or mixture? 3. Justify your answer for #2: © Accelerate Learning Inc. - All Rights Reserved

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8P1A Pure Substances and Mixtures

Student Journal Part II: Element, Compound, or Mixture? Answer the questions about the objects at each station. Station A (Aluminum foil; Formula: Al) 1. Is this an element, a compound, or a mixture? 2. Can the parts be separated physically or chemically or is it the smallest it can be?

Station B (Salt water; Formula: NaCl+H2O) 1. Is this an element, a compound, or a mixture? 2. Can the parts be separated physically or chemically or is it the smallest it can be?

Station C (Sand) 1. Is this an element, a compound, or a mixture? 2. Can the parts be separated physically or chemically or is it the smallest it can be?

Station D (Wax candle) 1. Is this an element, a compound, or a mixture? 2. Can the parts be separated physically or chemically or is it the smallest it can be?

Station E (Chalk; Formula: CaCO3 ) 1. Is this an element, a compound, or a mixture? 2. Can the parts be separated physically or chemically or is it the smallest it can be?

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8P1A Pure Substances and Mixtures

Student Journal Part II: Element, Compound, or Mixture? Continued Station F (Water; Formula: H2O) 1. Is this an element, a compound, or a mixture? 2. Can the parts be separated physically or chemically or is it the smallest it can be?

Station G (Copper wire; Formula: Cu) 1. Is this an element, a compound, or a mixture? 2. Can the parts be separated physically or chemically or is it the smallest it can be?

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STEMscopedia: PURE SUBSTANCES AND

MIXTURES

8P1A

Reflect To understand pure substances and mixtures, you must first know what role atoms and molecules play. An atom is defined as the basic unit of a chemical element. Atoms are millions of tiny particles that make up a solid, liquid, or gas. The best way to describe an atom is its comparison to an egg. The yolk of the egg would make reference to the nucleus. The nucleus is made up of positively charged protons and neutrally charged neutrons. The egg whites would represent the negatively charged electrons, which rotate around the nucleus. A molecule is a group of two or more atoms that stick together. Molecules are so small that nobody can see them. Pretty much everything on Earth and other planets is made of molecules. We, as humans, are made up of trillions and trillions of different types of molecules. The difference between atoms and molecules are that atoms are the smallest units possible and a molecule is a combination of atoms. What Is the Difference Between Pure Substances and Mixtures? First, it is important to mention that pure substances are considered compounds and elements. An element is defined as a substance that is made from one type of atom and cannot be broken down into simpler components by chemical or physical means. A mixture is defined as two or more substances that are chemically different and are not chemically joined. And finally, a compound is defined as a substance formed when two or more elements chemically react with each other to form chemical bonds between their atoms. To make things more simple, the difference between elements and compounds is elements are made of only one thing, but compounds are made of more than one thing. Compounds are a combination of elements. Elements are what make up the periodic table of the elements; these are in their simplest forms. A good example is a single atom of sodium would still be sodium, but sodium chloride, salt, is sodium and chlorine and broken down it would be a single atom of sodium and a single atom of chlorine.

Periodic Table of Elements

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STEMscopedia: PURE SUBSTANCES AND

MIXTURES

Look Out

There are millions of different substances but only about 100 atoms. Molecules are made up of many different ratios of atoms. Some of these ratios make some dangerous substances—never mix substances that you don’t know about. Sugar is made of: C6 – 6 carbon atoms H12 – 12 hydrogen atoms O6 – 6 oxygen atoms It takes this exact combination of atoms to make up a sugar molecule. Facts About Molecules • 66% of the human body is made up of oxygen atoms. • Molecules can have many different shapes. • Organic compounds always contain carbon. • DNA is a molecule. It is the molecular makeup that makes each person unique.

What Do You Think? What Are the Parts of an Atom? Atoms have three parts: protons, neutrons, and electrons. The protons and neutrons are found in the center of the atom called the nucleus. The electrons are found on the outside of the nucleus and are much smaller. Electrons move very fast; they could be compared to a superfast racing car that is going so fast, they just sort of turn into a blur. That is called an orbital. In all atoms, the number of protons and the number of electrons is always the same. The number of neutrons is very roughly the same as the number of protons, but sometimes it’s rather more. The number of protons in an atom is called the atomic number, and it tells you what type of atom you have.

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STEMscopedia: PURE SUBSTANCES AND

MIXTURES

How Do Atoms Make Molecules and Compounds? Atoms are more stable when they are joined with other atoms. A molecule is made up of any combination of atoms. Compounds are made up of two or more atoms. All compounds are molecules, but not all molecules are compounds. Molecules can’t be compounds if they are only made from one element.

Molecules and compounds can be really confusing, so the easiest way to remember the difference is compounds are elements joined together and molecules are atoms joined together. Look up different molecules and see how they are made. Are they made up of one element? Or more than one element? Can you see a pattern?

Example of an atom.

Example of a water molecule.

Try Now Color markers have molecules that make up the different pigments. The different color pigment molecules are different sizes. A black marker is made up of many different color pigments. Try this experiment to see what color pigment molecules can be found in black ink. You will also be able to see how different pigments travel different distances and at different rates based on their size. Developed in 1910 by Russian botanist Mikhail Tsvet, chromatography is used to separate the pigment molecules of plant dyes. This technique is also known as “color writing.” Materials • Scissors • White paper coffee filter • Black marker (not permanent) • Water • Coffee cup or mug

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STEMscopedia: PURE SUBSTANCES AND

MIXTURES

Directions 1. Cut a circle out of the coffee filter. 2. Draw a black line across the circle, about 1 inch up from the bottom. 3. Put just enough water in the coffee cup to cover the bottom.

4. Put the paper circle in the bottom of the cup, making sure the black ink is in the water. 5. As the filter absorbs the water and it reaches the black line, you’ll start to see the different colors. 6. Leave the paper in the water until the colors go all the way to the top edge. How many colors can you see? If you have another brand of black marker, do the experiment again. Does this marker make different colors than the first one? Compare your results. There are many different types of chromatography. They all work the same way as this experiment. Because the colors have different sized molecules, they travel at different rates and end up in different places on the coffee filter; therefore, you are able to see what was used to make the mixture of a black marker. What colors made up the black marker? How Does a Combination of Many Colors End Up Turning Black? Depending on the makeup of atoms and electrons in colors, they are going to do one of several things when exposed to light: either absorb, reflect, do nothing, or refract light. The mixture of the colors absorbs the light of many colors, and therefore it cannot reflect any light, and the result is the color black.

Connecting With Your Child Your child has been learning about atoms and molecules. Also, they have learned about elements, compounds, and mixtures. They have learned that everything on Earth is made of molecules. The purpose of this unit is to help your child distinguish between atoms and molecules and describe the difference between pure substances (elements and compounds) and mixtures. Some things will not always mix together. There are certain compounds that will just not work together. Take water and oil for instance—they do not mix. Try this experiment with your child. What can you find out about how water and oil are made up? What about their makeup makes them repel each other?

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STEMscopedia: PURE SUBSTANCES AND Materials

MIXTURES

• Vegetable or baby oil • Pie tin • Food coloring • 3 Cups • Dropper Directions 1. Cover the bottom of the pie tin with oil. 2. Put food coloring in 3 separate cups of water. 3. Use a dropper to put the colored water into the oil. What happens? What happens if you stir the mixture? Can you push the bubbles together? Why won’t the oil mix with the water?

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8P1A Pure Substances and Mixtures

Reading Science Name:

Date:

Group:

Few Elements, Many Compounds 1

Think of the English alphabet. Millions of words can be made from only 26 letters! The same thing is true of elements and compounds. It takes a few common elements (the basic form of matter that cannot be broken down any further) to make most of the planet’s many compounds, including rocks (solid earth), air, water, and even people.

Let’s take a trip to Maui in the Hawaiian Islands. When you cross the Pacific Ocean, you are traveling across seawater that is made of hydrogen, oxygen, sodium, chlorine, and traces of other elements. Pure water has only hydrogen and oxygen. When you first get to the island, you will probably walk on sand, which is actually tiny bits of worn-out rock composed largely of oxygen and silicon. A nice tropical breeze hits your face; it consists of nitrogen, oxygen, a little argon and carbon dioxide, and small amounts of other gases.

As you walk around, you will notice volcanic rocks and mountains on the island that are made up of mixtures of oxygen and silicon with magnesium, aluminum, potassium, iron, and small amounts of other elements. Green volcanic rock, which is also in abundance on the island, has a heavy concentration of iron and magnesium.

You are sure to notice all the plants and animals. The Hawaiian Islands contain much diversity, and your focus rests on the beautiful trees, bushes, and flowers. A Hawaiian tree, a beautiful purple orchid on that tree, and a beetle crawling on the ground—these are all examples of living matter composed of the elements hydrogen, oxygen, carbon, and nitrogen, with hydrogen being the most abundant.

As you leave Hawaii, you marvel at what you’ve seen and how so many compounds can be made from so few elements. Through chemical changes, a few simple elements can be turned into many, many different things.

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8P1A Pure Substances and Mixtures

Reading Science 1.

What is the basic form of matter that cannot be broken down any further? A

A compound

An element

A chemical reaction

An organism

Which of the following elements do living things have that volcanic rocks do not have? A

Oxygen

Silicon

Magnesium

Carbon

Which of the following best summarizes the passage? A

Volcanic rocks and mountains are on Hawaiian islands.

Green volcanic rock has a heavy concentration of iron and magnesium.

Sand is tiny bits of worn-out rock made mostly of oxygen and silicon.

A few common elements make most of the planet’s many compounds.

What is the main point of the reading? A

A few elements combine to make many compounds.

Many elements combine to make a few compounds.

Elements cannot be combined except by artificial means.

Hawaii is made up of only a few types of compounds.

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8P1A Pure Substances and Mixtures

Reading Science

Argon Oxygen

Nitrogen Carbon dioxide and trace gases

This chart shows the compounds that make up the air. The rectangle on the right is an expanded view of the smallest wedge of the pie chart. What percentage of air is oxygen? A

0.07%

0.93%

21%

78%

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8P1A Pure Substances and Mixtures

Math Connections Name:

Date:

Group:

Elements are pure substances composed of only one type of atom that cannot be broken down into any other substances by chemical or physical means. The periodic table of elements is a way of organizing all known elements by their physical and chemical properties. Compounds are formed when atoms of different elements are combined by chemical bonds. Example: Water covers about 70% of Earth’s surface, and it can be in the form of a solid, liquid, or gas. Water (H2O) is composed of 2 hydrogen atoms and 1 oxygen atom. What is the total atomic mass of water? Variable Definition: x=mass of hydrogen atoms, y=mass of oxygen atoms Equation: 2x+y=total atomic mass of 1 water molecule Total atomic mass of H2O: 2(1.007)+(15.9994)=18.0134u 1.

Write a function for the number of water molecules in terms of the number of oxygen atoms.

If you had 4×10² oxygen atoms, how many water molecules would you have?

Write a function for the number of water molecules in terms of hydrogen atoms.

If you have 9×103 water molecules, how many hydrogen atoms would you have?

Oxygen is in the air we breathe in, while carbon dioxide is the air we breathe out. Carbon dioxide (CO2) is composed of 1 carbon atom and 2 oxygen atoms. What is the total atomic mass of carbon dioxide? Variable Definitions: Equation: Total atomic mass of CO2 :

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8P1A Pure Substances and Mixtures

Math Connections 6.

Write a function to describe the number of oxygen atoms in terms of carbon atoms.

Graph the function on the grid below.

If you have 6 molecules of CO2, how many oxygen atoms do you have?

Zinc carbonate (ZnCO3) is composed of 1 zinc atom, 1 carbon atom, and 3 oxygen atoms. What is the total atomic mass of zinc carbonate? Variable Definitions: Equation: Total atomic mass of ZnCO3 :

10. One source of energy is glucose (C6H12O6), which is composed of 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms. Find the total atomic mass of glucose. Variable Definitions: Equation: Total atomic mass of C6H12O6 :

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8P1A Pure Substances and Mixtures

Writing Science Name:

Date:

Group:

LOOK

THINK Think about the differences and similarities between the characteristics of a pure substance and a mixture.

WRITE As you compare and contrast pure substances to mixtures, describe whether the beans in the picture are representative of a mixture or a pure substance such as an element or a compound. Be sure to • clearly state your central idea; • organize your thoughts; • develop your essay in detail; • choose your words carefully; and • use correct spelling, capitalization, punctuation, and grammar.

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8P1A Pure Substances and Mixtures

Writing Science

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8th Grade Physical Science

8P1B

Particles in States of Matter

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8P1B Particles in States of Matter

Student Handout Name:

Date:

Moving Molecules Sketch each of the three containers in the boxes below.

_______________________

What differences do you notice between the three containers?

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8P1B Particles in States of Matter

Student Journal Name:

Date:

Group:

Changes in State 1.

In the space below, sketch and write your observations about the molecules in the solid.

As the heat increases, sketch, and write your observations about the behavior of the molecules.

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8P1B Particles in States of Mattert

Student Journal 3.

Once the highest point has been reached, sketch and write your observations about the behavior of the molecules.

As the temperature drops, sketch and write your observations about the behavior of the molecules.

When the temperature has decreased to its lowest point, sketch and write your observations about the behavior of the molecules.

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8P1B Particles in States of Matter

Student Journal Reflections and Conclusions 1.

The substance started out as a solid. How did the molecules behave?

What happened to the molecules as heat was added?

When the heat was at its highest point, how did the molecules behave?

Since the substance started as a solid, what other states of matter did you observe?

When you started to remove heat from the container, how did the molecules behave?

When all the heat had been removed from the container, how did the molecules behave?

When you first started removing heat, the substance was a gas. What states of matter did you see as all the heat was removed?

Knowing what you know about states of matter and their particles, draw what the particles would look like in plasma.

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STEMscopedia: PARTICLES IN STATES OF MATTER

8P1B

Reflect

How do you describe the movement of particles in solid, liquid, gas, and plasma states? Matter is the “stuff” of the universe, it’s the atoms, molecules, and ions that make up all physical substances. Matter is anything that has mass and takes up space. Energy is the capacity to cause change. Energy cannot be created or destroyed; it can only be conserved and converted from one form to another. “Potential energy” is the energy stored in an object due to its position. There are four known phases, or states, of matter: solids, liquids, gases, plasma. The main difference of each state is in the density of each one. In a solid, particles are packed tightly together so they are unable to move about very much. Particles of a solid have very low kinetic energy. The electrons of each atom are in motion, so the atoms have a small vibration, but they are fixed in their position. Solids have a definite shape. They do not conform to the shape of the container in which they are placed. They also have a definite volume. The particles of a solid are already so tightly packed together that increasing pressure will not compress the solid to a smaller volume.

In the liquid phase, the particles of a substance have more kinetic energy than those in a solid. The liquid particles are not held in a regular arrangement, but are still very close to each other so liquids have a definite volume. Liquids, like solids, cannot be compressed. Particles of a liquid have just enough room to flow around each other, so liquids have an indefinite shape. A liquid will change shape to conform to its container. Force is spread evenly throughout the liquid, so when an object is placed in a liquid, the liquid particles are displaced by the object. Particles of a liquid tend to be held by weak intermolecular attraction rather than moving freely as the particles of a gas will. This cohesive force pulls the particles together to form drops or streams.

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STEMscopedia: PARTICLES IN STATES OF MATTER

Gas particles have a great deal of space between them and have high kinetic energy. If unconfined, the particles of a gas will spread out indefinitely; if confined, the gas will expand to fill its container. When a gas is put under pressure by reducing the volume of the container, the space between particles is reduced, and the pressure exerted by their collisions increases. If the volume of the container is held constant, but the temperature of the gas increases, then the pressure will also increase. Gas particles have enough kinetic energy to overcome intermolecular forces that hold solids and liquids together, thus a gas has no definite volume and no definite shape.

Plasma is not a common state of matter here on Earth, but may be the most common state of matter in the universe. Plasma consists of highly charged particles with extremely high kinetic energy. Gases such as helium, neon, argon, krypton, xenon, and radon are often used to make glowing signs by using electricity to ionize them to the plasma state. Stars are essentially superheated balls of plasma.

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STEMscopedia: PARTICLES IN STATES OF MATTER

Look Out Description of Phase Change

Term for Phase Change

Heat Movement During Phase Change

Solid to liquid

Melting

Heat goes into the solid as it melts

Liquid to solid

Freezing

Heat leaves the liquid as it freezes

Liquid to gas

Vaporization, which includes boiling and evaporation

Heat goes into the liquid as it vaporizes

Gas to liquid

Condensation

Heat leaves the gas as it condenses

Solid to gas

Sublimation

Heat goes into the solid as it sublimates

Can you go from a gas to a solid? Deposition occurs when a gas becomes a solid without going through the liquid state of matter. On winter mornings you may notice those little frost crystals on plants that build up when water vapor from the air becomes a solid on the leaves of plants. How is Plasma made? Plasma can be made from a gas if a lot of energy is pushed into the gas. In the case of neon, it is electrical energy that pulls the electrons off. When it is time to become a gas again, just flip the neon light switch off. Without the electricity to energize the atoms, the neon plasma returns to its gaseous state. We have an environment where you don’t find a lot of everyday plasma. Once you leave the planet and travel through the universe, you will find plasma everywhere. It’s in stars and all of the space in between.

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STEMscopedia: PARTICLES IN STATES OF MATTER

What Do You Think? Where do you think plasmas can be found? flames lightning Northern lights The Sun is an example of a star in its plasma state What state of matter are these substances? • Jelly • Paper • Toothpaste • Flour • Foam • Sponge Cake • Ice Cream

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STEMscopedia: PARTICLES IN STATES OF Try Now

MATTER

Solid to Liquid to Solid Watch the transition from solid to liquid to solid in this science project on states of matter – and make something good to eat. Solids can change into liquids, and liquids can change into solids. Make ice pops with orange juice, and you can see both transformations. What You Need: • Can of frozen orange juice • Pitcher • Large spoon • Water • Paper cups • Wooden craft sticks Step 1: Open a can of frozen orange juice, and spoon it into a large pitcher. Touch the frozen juice to feel that it is both solid and cold. Step 2: Add water according to the package directions to make orange juice. Step 3: Fill several paper cups about 2/3 of the way with orange juice. Step 4: Put a craft stick into the liquid in each paper cup. Step 5: Being careful not to spill, put the cups of juice into the freezer. Step 6: Check them after two hours. Can you gently pull out the craft stick, or has the liquid orange juice frozen solid around the stick? Step 7: Once the orange juice has frozen, peel off the paper cups. You and your friends can enjoy a frozen treat!

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STEMscopedia: PARTICLES IN STATES OF MATTER

Connecting With Your Child Cooking that Matters Cooking is a great way to help children learn the differences between states of matter. Ask your child to help you make pizza, a food that is a great example of all three states of matter. You can find many different recipes online; here is a summary of the main steps. 1. Put a tea-kettle on high, and when the water boils, show the steam to your child. Explain this is water vapor—the gaseous form of water. Be careful not to place your hands directly in the steam, though—it is extremely hot! 2. Let your child pour a packet of yeast into a bowl, and then ask if the powder is a solid, liquid, or gas. This is a tough question because powder pours into the container like a liquid. Explain it is actually many small kernels of a solid. 3. Add 1 cup of the hot water—the liquid—to the yeast and mix. 4. In another bowl, have your child mix 2.5 cups of flour, 1 teaspoon of sugar, and 1 teaspoon of salt. As with the yeast, all of these ingredients are solids made up of many tiny particles. 5. Add the yeast mixture and 2 tablespoons of olive oil to the mixture of flour, sugar, and salt, and form the resulting dough into a ball. Emphasize to your child that even though the dough is gooey and easy to mold, it is still a solid. 6. Let the balled dough rise for about 30 minutes. 7. After the dough rises, pat it into a pizza crust on a greased, large cookie sheet. Add spaghetti sauce (a liquid that sometimes contains solid chunks of vegetables), shredded cheese (a solid), and any toppings of your choice (solids). 8. Bake the pizza in an oven at 425°F for 20 minutes, and observe the solid nature of the crust. 9. Enjoy! Here are some questions to discuss with your child: • Is flour a solid or liquid? Why? • Why does water turn into a gas in the teakettle? • Why does the moist dough turn into a hard solid?

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8P1B Particles in States of Matter

Reading Science Name:

Date:

Group:

Plasma Televisions 1.

The Sun is made of plasma, the fourth state of matter, which is created when gas atoms are stripped of their electrons and form charged ions. In plasma, the bare nucleus moves with their stripped electrons. Plasma looks like a gas because both states of matter have indefinite shape and volume. However, plasma is made up of electrically charged ionized gases that conduct electricity, while gases are made of intact neutral atoms. Plasma TV screens, which are filled with this ionized stuff, became very popular in the 1990s for their crisp, brilliant color. However, several major differences exist between the plasma in the Sun and the plasma used in TVs.

The first major difference is longevity. The Sun is a slow-burning nuclear furnace made of hydrogen plasma that will last for billions of years. In stark contrast, none of the major TV companies still produce plasma TVs. You can wake up to a glorious sunrise for eons to come, but plasma TVs are a thing of the past. The Sun has perfected plasma production, but TV plasma technology ended up with major problems.

A second difference is the temperature or energy level of the plasma. The Sun is an enormous ball of super-hot plasma radiating enough energy to illuminate the entire solar system and fry anything near it. The plasma in a TV, on the other hand, is “cold plasma” created by passing an electrical current through xenon or neon gas at very low density. The TV plasma just has enough energy to create an entertaining, crisp, colorful image. The only way a plasma TV could hurt you is if someone threw it at you! In plasma TVs, although electrons are hot (have higher kinetic energy), the gas is actually made up mostly of ions, which have less energy. Thus, the overall average kinetic energy in a TV plasma is relatively low and, therefore, cold.

Another difference between the plasma in the Sun and in TVs is how the plasma is produced. In stars, like the Sun, tremendous heat and pressure in the core of the star strip the gases of their electrons to ionize the atoms of hydrogen. To create man-made cold plasma, a gas is pumped with electrical energy that strips the gas of its electrons and creates particles constantly bumping into each other. These collisions of xenon or neon ions release ultraviolet light photons. The photons strike the flat screen pixels of three fluorescent red, green, and blue lights. Just like a traditional television, the plasma display varies the light intensities. This creates a full range of colors to produce a crisp, brilliant image.

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8P1B Particles in States of Matter

Reading Science 5.

So why did plasma TVs decline if their image was so superior to traditional TVs? The plasma technology was not perfect. Many models had screen reflection where the room reflected off the screen and interfered with viewing the image. Also, power consumption was unreasonably large, previous images were often left on the screen (screen burn), the plasma TVs were very heavy, and they had a short screen life. When the LCD (liquid crystal display) TV came into existence in 2009 without these problems, the plasma TV became an undesired technology.

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8P1B Particles in States of Matters

Reading Science 1.

How does plasma, the fourth state of matter, differ from gas? A.

Plasma has indefinite shape and volume; gas does not.

Plasma has definite shape and volume; gas does not.

Plasma conducts electricity; gas does not.

Plasma cannot conduct electricity; gas can.

Plasma is produced when gas is ionized, which means gas atoms ___________. A.

are stripped of their nucleus and become charged ions

are stripped of their electrons and become charged ions

become neutrally charged

are stripped of their protons and become ions

Cold plasma used in TVs is different from the solar plasma because ___________. A.

it has much less kinetic energy than solar plasma

it has much more kinetic energy than solar plasma

it is made from ionized gas, while solar plasma is not

it is not made from ionized gas, while solar plasma is

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8P1B Particles in States of Matter

Reading Science 4.

According to the image at the top of the article, what do you think the problem is with plasma televisions? A.

The crisp, bright image was expensive.

The cold plasma screen illuminated colorful fluorescent pixels.

The plasma TV consumed too much electricity.

The cold plasma screen became hot to the touch.

How is cold plasma produced? A.

Gas is pumped with magnetism, which strips electrons.

Gas is pumped with high temperatures, which strips electrons.

Gas is depressurized, which strips electrons.

Gas is pumped with electricity, which strips electrons.

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8P1B Particles in States of Matter

Math Connections Name:

Date:

Group:

Measuring and Observing State Changes in Matter Solids, liquids, and gases have different properties that describe their state. When heat is applied to a substance, it causes the state to change, and thus the properties of the substance change as well. It can be hard to see the tiny particles that make up a solid, liquid, or gas. However, we can use our observations of a substance’s volume and how it looks to infer how the particles in the substance are acting. A student used the following procedures to heat a sample and collect time and temperature data. Procedure 1.

Heat 80.0 grams of ice in a 200 mL beaker.

The ice starts at −12°C when it is placed in the beaker.

Chart the time and temperature of the water for 20 minutes.

Create a graph to describe the data collected.

Data Time (minutes)

Temperature (°C)

Time (minutes)

Temperature (°C)

−12

−8

−4

100

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8P1B Particles in States of Matter

Math Connections 1.

Plot the time versus temperature data on the graph below.

Temperature (oC)

State Changes in Matter of H2O

Time (minutes) 2.

Use a red colored pencil to create a line that represents the temperature from the start of the experiment until the ice reaches its melting point. Label the melting point with the letter A.

Describe the state of the water from 0–3 minutes. How are the particles spaced and what is their energy level?

What is the equation of the line from 0 –3 minutes?

Use a blue colored pencil to represent the part of the graph that shows the ice melting.

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8P1B Particles in States of Matter

Math Connections 6.

What is the equation of the line that represents the ice melting?

Use an orange colored pencil to represent the water from the time it’s completely melted to the time it boils and starts to evaporate. Label the boiling point with the letter B.

What is the equation of the line from 5-15 minutes?

Describe the state of the water from 5–15 minutes. How are the particles spaced and what is their energy level?

10. Use a green colored pencil to represent the part of the graph that shows the water boiling. 11. What is the equation of the line that represents the boiling water?

12. Are the the boiling point and melting point of water extensive or intensive properties?

13. Which colors represent the phase changes from solid to liquid and from liquid to gas in your graph?

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8P1B Particles in States of Matter

Writing Science Name:

Date:

Group:

LOOK

THINK Think about the states of matter.

WRITE Describe the ways in which particles move in solids, liquids, gases, and plasma, and explain why particles move in the ways that they do.

Be sure to • clearly state your central idea; • organize your thoughts; • develop your essay in detail; • choose your words carefully; and • use correct spelling, capitalization, punctuation, and grammar.

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8P1B Particles in States of Matter

Writing Science

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8th Grade Physical Science

8P1CD

Physical and Chemical Properties and Changes

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8P1CD Physical and Chemical Properties and Changes

Student Handout Name:

Date:

Decomposition of Hydrogen Peroxide Experiment Complete this page as your teacher performs the demonstration. Physical Properties

Yeast

Hydrogen Peroxide

Make at least two observations when the hydrogen peroxide and yeast are mixed.

Is this a physical or chemical change? How do you know?

How did the properties of the splint change once it was lit?

What do you think caused the splint to relight?

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8P1CD Physical and Chemical Properties and Changes

Student Journal Name:

Date:

Group:

Part I: Physical and Chemical Properties and Changes Stations At each station, describe your observations or task, which chemical or physical property is being observed or tested, and whether a physical or chemical change is occurring.

Observations

Which chemical or physical property is being observed?

Is a chemical or physical change occurring?

Station 1

Station 2

Station 3

Station 4

Station 5

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8P1CD Physical and Chemical Properties and Changes

Student Journal Part I: Physical and Chemical Properties and Changes Stations, continued

Observations

Which chemical or physical property is being observed?

Is a chemical or physical change occurring?

Station 6

Station 7

Station 8

Station 9

Station 10

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8P1CD Physical and Chemical Properties and Changes

Student Journal Part II: Design Your Own Investigation Using the designated supplies, plan your own investigation on physical and chemical properties and changes.

Criteria and Constaints: •

All materials must be used somehow.

•

A physical change must be observed.

•

A chemical change must be observed.

Procedure: Write your step-by-step procedure(s) below.

Perform your investigation(s). Answer the following questions regarding your investigation(s). 1. What are the physical properties of the following materials: •

water:

•

food coloring

• 2.

Alka-Seltzer tablet Which part of your investigation proved a physical change had taken place?

Which part of your investigation proved a chemical change had taken place?

What chemical property was observed?

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STEMscopedia: PHYSICAL AND CHEMICAL

PROPERTIES AND CHANGES

8P1CD

Reflect What do ice cream, root beer, and carbon dioxide gas have in common? Not only do these ingredients combine to make a good treat on a hot summer day, but they are also made of matter. Matter can be found in many different shapes, sizes, and forms. For example, the ice cream, the root beer, and the gas that makes the root beer fizz are all types of matter. Even your body is made of matter. What other things in your life contain matter? What Is Matter? Simply put, matter is the stuff that every physical thing is made of. Matter can be described and classified by its properties. A property is a characteristic or feature of a substance or an object. Matter has both physical properties and chemical properties. Physical Properties Physical properties can be observed and measured. Some physical properties of matter—such as size, color, and shape—can be observed using your senses. Measurements made using science tools can be used to describe other physical properties of matter. Most matter can be found in three phases; solid, liquid, or gas. Both melting points and boiling points are examples of physical properties. Different substances have different melting points; this is one way scientists can classify matter. Chemical Properties A chemical property is how matter reacts or behaves when it undergoes a chemical change. Some examples of chemical properties are flammability, oxidation, and toxicity. A substance must undergo some kind of a chemical reaction to observe a chemical property. Some substances react with other substances—this is a chemical property called reactivity.

Flammability: the ability of a substance to burn or ignite

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STEMscopedia: PHYSICAL AND CHEMICAL

PROPERTIES AND CHANGES

What Do You Think? Observe the following pictures. Can you list the physical properties about each substance? Research and find at least one chemical property of each substance.

Match Wood Physical properties:

Physical properties:

Chemical properties:

Rocks

Vinegar

Physical properties:

Chemical properties:

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STEMscopedia: PHYSICAL AND CHEMICAL

PROPERTIES AND CHANGES

Look Out J ust like matter has physical and chemical properties, all forms of matter can undergo both physical and chemical changes. These two types of changes should not be confused because they are very different. Physical changes do not change the chemical makeup of a substance, but a chemical change is caused by a chemical reaction and it does change the substance into an entirely new substance with different chemical properties. Anytime you change the physical properties of a substance, you are causing a physical change. The chemical makeup is the same. If you crush a can, you have changed its appearance, but it is still a can. When you melt an ice cube, you are changing the state of matter, but chemically it is still H2O, or water. On the other hand, chemical reactions cause a change that creates an entirely new form of matter. Burning wood is an example of a chemical change. When some sort of fuel is added to wood and then exposed to oxygen and heated to wood’s combustibility temperature, the wood catches fire and begins to burn. As it burns, it is breaking down into ashes, and is no longer wood.

Reactant: a substance that takes part in and undergoes change during a reaction

Let’s look at an example showing the difference. Suppose you have a glass of water and a spoonful of sugar. If you dissolve the sugar in the water, the resulting product seems different than the original reactants, but it is just a mixture of sugar and water. No new substance has formed. However, if you place antacid tablets in water, the tablets dissolve through a chemical reaction. This is readily observed by the bubbling of gas in the glass. The antacid tablets contain the substances sodium bicarbonate (NaHCO3 ) and citric acid (C6H8O7). When these substances are placed in water, the atoms rearrange and carbon dioxide gas is produced. The picture below shows the gas bubbles that you observe in the glass. The gas is an entirely new substance created during the chemical reaction.

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STEMscopedia: PHYSICAL AND CHEMICAL

PROPERTIES AND CHANGES

Evidence of Chemical Reactions There are several ways you can observe whether or not a chemical change has occurred due to a reaction. You will always observe one or more of these changes in a chemical change. Production of a Gas As previously discussed, mixing antacids with water creates the gas carbon dioxide. Anytime molecules rearrange to form a gas as a by-product of a chemical reaction, you can be sure that a chemical change has occurred.

Production of Light The burning of logs in a fireplace is the reaction of the wood and oxygen along with a heat initiation source. Wood is made of cellulose, a combination of different substances that contain carbon, hydrogen, and oxygen. When this reaction occurs, a large amount of energy is produced. This energy is in the form of both heat and light. This type of reaction is a combustion reaction. It is similar to the reaction that produces the bright light and heat in fireworks. Change in Temperature Chemical reactions can either give off heat or use heat. Perhaps you have had an injury and applied a chemical heat pack to the area. A chemical heat pack is an example of a reaction that produces heat. A common substance in a heat pack is magnesium sulfate (MgSO4 ). When the heat pack is activated, the magnesium sulfate reacts with water. The result is the production of heat, which you use to soothe your injury. Chemical cold packs work in an opposite way to use heat when they mix with water. They may feel very cool to the touch. These temperature changes are evidence of a chemical reaction. Formation of a Precipitate A precipitate is a solid substance that forms and separates from a solution. A precipitate often settles to the bottom of a liquid reaction. One common chemical reaction that forms a precipitate is the reaction of solutions of lead nitrate (Pb(NO3 )2 ) and potassium iodide (KI). Each of these substances in a solution is clear and colorless. But if you mix a solution of each substance, lead iodide (PbI2 ) and potassium nitrate (KNO3 ) form as products. Lead iodide is insoluble, so it separates from the solution as a yellow precipitate (shown in the image on the right). The potassium nitrate remains in the solution. Change in Color You may have seen rust form on a steel object, such as a chain or an automobile. In this chemical reaction, iron (Fe) in the steel reacts with oxygen (O2 ) in the air as well as water (H2O) to produce rust (Fe(OH)3 ). The properties of steel are different than the properties of rust. Steel is a shiny, silver metal made from iron and other elements. Rust is a flaky, reddish-colored substance. The change in color from silver to red provides evidence that a chemical reaction has happened. Rusting is a complex reaction that happens in stages, and it is easy to observe these changes as they happen.

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STEMscopedia: PHYSICAL AND CHEMICAL

PROPERTIES AND CHANGES

Try Now What Do You Know? Tell whether each property is a chemical property or a physical property. 1. Color 2. Density 3. Combustibility 4. Melting point 5. Reactivity Label each picture as a chemical change or a physical change. 1.

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STEMscopedia: PHYSICAL AND CHEMICAL

PROPERTIES AND CHANGES

Connecting With Your Child Investigating Chemical Reactions To help your child learn more about chemical reactions, work together to determine how to identify the evidence that may be observed when a chemical reaction occurs. To do so, gather the following materials: • 3 glasses of water • 2 effervescent tablets • 1 tablespoon of sugar • 1 tablespoon of Epsom salts • Thermometer While performing the chemical reactions, encourage your child to record all observations. Let the first glass contain the control sample in which no chemical reaction occurs. Add a tablespoon of sugar to the water in the glass and stir until the sugar dissolves completely. Record all observations until the sugar dissolves. Remember that this control sample does not involve a chemical reaction because sugar dissolving in water is only a physical change. Then, have your child add both of the effervescent tablets to the second glass of water. Record any observations for at least two minutes while the tablets dissolve. Finally, place the thermometer in the third glass and record the initial water temperature. If a thermometer is not available, feel the outside of the glass and record if it feels hot, warm, or cold. Then, add a tablespoon of Epsom salt and gently stir the liquid using the thermometer. Make sure to watch the temperature closely and determine how the temperature changes when the salt is added. After performing the reactions, discuss the following questions with your child: • In which of the glasses did a chemical reaction take place? How do you know? • Why can you assume that a chemical reaction did not take place in all three glasses? How could you confirm that a chemical reaction took place in the glasses? • Can you write a chemical equation to describe each chemical reaction that occurred?

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8P1CD Physical and Chemical Properties and Changes

Reading Science Name:

Date:

Group:

Signs of Chemical Change 1

Hundreds of years ago, early scientists began to systematically explore the way that different compounds behaved when mixed together. Over and over again, they combined various substances to see what would happen. Researchers made observations of the properties of the starting compounds and what occurred when the substances initially touched one another. They ran tests on the resulting mixtures to see if the chemical properties had changed. At every step, they took careful notes, which were shared with other scientists.

When many observations were compiled, scientists noticed patterns that led to the development of a set of rules on how to determine when a chemical change had happened. Five signs that early scientists indicated would signal a chemical change are as follows: • Production of light • Production of a precipitate • Production of a gas • Change in color • Change in temperature

Even though these rules are old, they are still used today to determine when a chemical change happens. Each of these relies on empirical evidence—a property that can be directly seen or measured in an experiment.

Maria was assigned to investigate several pairs of compounds to determine whether a new substance is formed when they are mixed. To find the answers, she designed an experiment using these five rules as the criteria for whether a chemical change has occurred.

Maria developed a procedure that she used for each mixture. First, she measured equal portions of each of the two compounds to be combined and put one of them into a test tube. She examined them carefully and wrote what she observed in her notebook. Watching closely, she put the second compound into the test tube, swirling to mix the two substances together. Still watching, she put the test tube into the rack, let it sit for one minute, and then recorded her observations.

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8P1CD Physical and Chemical Properties and Changes

Reading Science Continued 6

A summary of the mixtures Maria tested and the observations she made is as follows: a) Two clear liquids began to glow with a yellow light after mixing. b) Two clear liquids were mixed but did not look any different afterward. c) A piece of metal was dropped into a clear liquid. Before long, small bubbles began to float to the surface. d) A clear liquid was added to a dark blue liquid. The resulting mixture was light blue. e) A clear liquid was added to a pale yellow liquid, forming a white powder that settled on the bottom. f) A clear liquid was poured onto a white powder. Immediately, it fizzed and foamed. After one minute, the bubbles were gone and only a clear liquid remained.

After the tests were complete, Maria reviewed her observations and analyzed her results to see if a chemical change had occurred. Soon Maria knew which combinations had produced a new substance. Will your conclusions match hers?

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8P1CD Physical and Chemical Properties and Changes

Reading Science 1.

Identify the flaw in the way that Maria set up her experiment. A

She did not take pictures.

She did not wait long enough.

She did not measure the temperature.

She did not mix the substances well enough.

Which of these describes Maria making an observation? A

Maria measured the compounds.

Maria let the test tube sit for one minute.

Maria wrote her results in her lab notebook.

Maria saw that bubbles formed on the metal in mixture (c).

What is the best summary of this passage? A

Early scientists studied the way substances behaved when they were combined. They developed rules to identify when a chemical change occurred. Maria used those rules to create an experimental procedure and test six mixtures.

Maria was curious about how several compounds acted when mixed. She put them into test tubes and swirled them together. She could tell if a chemical change had occurred by watching for signs like bubbles or light.

Maria mixed compounds together to test for chemical change. One mixture produced light, two mixtures had bubbles, two mixtures had changes of color, and one mixture did not change.

You can tell if a chemical change has occurred because there will be a production of light, precipitate, or a gas, or there will be a change in color or temperature.

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8P1CD Physical and Chemical Properties and Changes

Reading Science 4.

Using Maria’s results, determine how many mixtures produced a new substance. A

Which is the best definition of empirical in paragraph 3? A

Can be seen or measured

From a currently used procedure

Collected in an old, reliable method

Related to whether a chemical change has occurred

Maria made a mistake in the analysis of her results. Which of the following conclusions is incorrect? A

A chemical change occurred in mixture (a) because there was a production of light.

A chemical change occurred in mixture (d) because there was a color change.

A chemical change occurred in mixture (e) because there was a production of a precipitate.

A chemical change occurred in mixture (f) because there was a production of a gas.

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8P1CD Physical and Chemical Properties and Changes

Math Connections Name:

Date:

Group:

A physical change to matter will not alter the composition or identity of a substance. A chemical change to matter will always result in the formation of a new substance. During science class, students created different solutions with water and a solid. They recorded the temperature in degrees every minute, seen in the chart below: Time elapsed (minutes)

Solid

Calcium chloride

78.5

81.5

84.5

87.5

90.5

Citric acid

76.3

72.3

68.3

64.3

60.3

Magnesium sulfate

76.6

75.1

73.6

72.1

70.6

Sodium carbonate

77.5

78.75

81.25

82.5

Create a scatterplot below using the data recorded for the calcium chloride solution. 2. Is the relationship linear? Why or why not? 3. Determine the rate of change of the solution in degrees per minute (slope). 4. Determine the temperature of the solution when no time had elapsed. Add this data to your scatterplot (y-intercept). 5. Write the equation of the line created by the data.

What is the limitation for the equation you created? Is there a point at which the solution will stop heating or cooling?

Which other solution will have a similar graph to the calcium chloride solution? a. Determine the rate of change of the solution in degrees per minute. b. Determine the y-intercept for the data. c. Write the equation of the line created by the data.

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8P1CD Physical and Chemical Properties and Changes

Math Connections 8.

Create a scatterplot below, using the data recorded for the citric acid solution. 9. Determine the temperature of the solution when no time had elapsed. Add this data to your scatterplot. 10. Determine the rate of change of the solution in degrees per minute (slope).

11. Write the equation of the line created by the data. 12. Which other solution will have a similar graph to the citric acid solution? a. Determine the y-intercept for the data. b. Determine the rate of change of the solution in degrees per minute. c. Write the equation of the line created by the data.

13. How are the two scatterplots different?

14. How do the equations reflect this difference?

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8P1CD Physical and Chemical Properties and Changes

Writing Science Name:

Date:

Group:

LOOK

THINK Think about physical and chemical properties of matter. WRITE Explain the difference between physical and chemical properties, and describe what types of evidence suggest a chemical change has taken place. Be sure to clearly state your central idea; organize your thoughts; develop your essay in detail; choose your words carefully; and use correct spelling, capitalization, punctuation, and grammar.

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8P1CD Physical and Chemical Properties and Changes

Writing Science

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8th Grade Physical Science

8P1E

Patterns in the Periodic Table

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8P1E Patterns in the Periodic Table

Student Journal Name:

Date:

Group:

The Atom Part I: Modeling Atoms

Helium Atom Hydrogen Atom

Nucleus

Electron Cloud

Key Symbol

Subatomic Particle proton (p +) neutron (n 0) electron (e-)

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8P1E Patterns in the Periodic Table

Student Journal Part I: Modeling Atoms, continued 1. Fill in the data table below. Properties of Subatomic Particles Subatomic Particle

Symbol ( )

Electrical Charge

Mass in AMU

Proton Neutron Electron

2. Where is the mass of an atom found? Explain.

3. Look at the diagrams to determine what contributes the most to the volume of an atom, the nucleus or the electron cloud? Explain.

4. Since protons (p+) with a positive charge and neutrons (n0) without a charge are located in the nucleus, what is the overall charge of the nucleus portion of an atom: positive, negative, or no charge at all? Explain.

5. What is the overall charge of the electron cloud of the atom? Explain.

6. What similarities do you see when comparing the hydrogen atom diagram to the helium atom diagram?

7. Compare the numbers of each subatomic particle found in both diagrams, and then list what makes hydrogen different from helium.

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8P1E Patterns in the Periodic Table

Student Journal Part II: Atom Patterns Lithium Atom.

Nucleus

Electron Cloud

Beryllium Atom

Nucleus

Electron Cloud

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8P1E Patterns in the Periodic Table

Student Journal Part II: Atom Patterns, continued 1.

Use all four atom diagrams to complete the data table below. Use your diagrams and the information in the Student Guide to answer the questions. Hydrogen has been completed for you. Characteristics of the First Four Elements Atom

Proton number

Neutron number

Mass of atom

Electron number

Charge of atom

Hydrogen

1 p+

----

1 amu

1 e-

Helium Lithium Beryllium

Explain why the charge is 0 (zero) for each of the four atoms that you built on the diagrams

Use the periodic table to look up the atomic numbers for the elements of hydrogen, helium, lithium, and beryllium. Complete the data table below and answer the follow-up question below the table. Atomic Number and Protons Element

Atomic number

Number of protons

Hydrogen Helium Lithium Beryllium

What statement can be made about an element’s atomic number and the number of protons in one atom of the element?

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8P1E Patterns in the Periodic Table

Student Journal Part II: Atom Patterns, continued 5.

Use the trend that you see in the previous table to predict how many protons will be found in an atom of each of the following elements. Then predict the number of electrons found in a single, neutral atom of each element. Protons and Electrons in Atoms of Neutral Elements Atom

Atomic number

Copper

Boron

Uranium

Gold

Neon

Number of protons

Number of electrons

What statement can be made about an electrically neutral atom’s number of protons and electrons?

Look at the example, and then complete the rest of the data table below using the atoms that you built on the diagrams. Total Mass from Protons and Neutrons Typical atom of:

Mass in amu

Number of protons Number of neutrons contributing to the contributing to the mass mass in the nucleus in the nucleus

Hydrogen (H)

Helium (He)

Lithium (Li)

Beryllium (Be)

Copper (Cu)

Boron (B)

(Uranium (U)

238

Gold (Au)

197

Neon (Ne)

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8P1E Patterns in the Periodic Table

Student Journal Reflections and Conclusions 1.

If we know an atom’s mass in amu and we know the number of protons of the atom, can we calculate the number of neutrons that contribute to the mass? Explain.

Electrons have a

The atomic number of an atom is also the number of

Protons have a

charge and are found in the area of an atom called

in an atom.

charge and are found in the area of an atom called

do not have a charge and are found in the area of an atom called .

Circle the correct word: Protons and neutrons contribute (mass or volume) to the atom.

Circle the correct word: Electrons contribute to an atom’s (mass or volume).

Each proton and each neutron contribute

amu to an atom. Amu means

. 9.

If we know the total mass of an atom in amu, we can subtract the number of to calculate the number of neutrons found in the nucleus of the atom.

10. In a neutral atom, the number of 11. Atomic numbers for atoms across the periodic table.

is the same as the number of in increments of

as you move

12. In your own words, summarize the atom’s structure in terms of subatomic particles.

13. Explain what makes one atom different from another atom.

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8P1E Patterns in the Periodic Table

Student Journal Name:

Date:

Group:

Part I: Patterns and Codes

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8P1E Patterns in the Periodic Table

Student Journal Part I: Patterns and Codes, continued 1. How many periods are shown on the periodic table? 2. How is the number of energy levels in an atom related to the period number? 3. To which period does the lanthanide series belong?

actinide?

4. Use the observed pattern to predict the number of energy levels in a neutral atom: Rb – Rubidium (atomic number 37) Cs – Cesium (atomic number 55) Fr – Francium (atomic number 87) Ni – Nickel (atomic number 28) Hg – Mercury (atomic number 80) Kr – Krypton (atomic number 36) 5. What pattern do you see as you compare elements that belong in groups 1A to 8A on the periodic table?

6. Use this observed pattern to predict how many valence electrons would be found in the following neutral atoms: I – Iodine (atomic number 53) Ra – Radium (atomic number 88) Ga – Gallium (atomic number 31) Sn – Tin (atomic number 50) Sb – Antimony (atomic number 51) Rn – Radon (atomic number 86)

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8P1E Patterns in the Periodic Table

Student Journal Part II: Putting It All Together, Continued Periodic Table

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8P1E Patterns in the Periodic Table

Student Journal Part II: Putting It All Together, continued Use this example to answer questions 1 and 2.

X 1. The example shown would be a member of group 2. Use the periodic table to list the chemical symbols for each member of the group that is represented by the example. 3. Use a red marker to draw valence electrons as dots for a member of group 4A on the X.

4. Use a red marker to draw valence electron dots around each member of the group 4A elements using their chemical symbols below instead of the X.

C Si

Sn Pb

5. Use the periodic table and a red marker to draw valence electron dots around the chemical symbols for each of the following elements:

K O

N Ca

6. When moving from left to right in a period, the number of valence electrons

7. When moving down a group, the number of energy levels

8. When moving down the periodic table within a specific group, all element group members have the same number of .

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Paste three elements with similar properties in a row along this line.

8P1E Patterns in the Periodic Table

Student Journal

Part III: Properties!

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8P1E Patterns in the Periodic Table

Student Journal Part III: Properties!, continued 1. What chemical properties can be predicted about the elements rubidium, cesium, and francium based on the matching characteristic found with the other three elements of group 1A (potassium, lithium, and sodium)?

2. What is the number of valence electrons for these group 1A elements? 3. What chemical properties can be predicted about the elements strontium, barium, and radium based on the matching characteristic found with the other three elements of group 2A (calcium, magnesium, and beryllium)?

4. What is the number of valence electrons for these group 2A elements? 5. What chemical properties can be predicted about the elements iodine and astatine based on the matching characteristic found with the other three elements of group 7A (fluorine, chlorine, and bromine)?

6. What is the number of valence electrons for these group 7A elements? 7. What chemical properties can be predicted about the elements krypton, xenon, and radon based on the matching characteristic found with the other three elements of group 8A (argon, neon, and helium)?

8. What is the number of valence electrons for these group 8A elements?

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8P1E Patterns in the Periodic Table

Student Journal Part IV: Studentium Elements Element name: __________Symbol: ______ Element name: __________Symbol: ______ __(p+)+__(n0)=__ __ atomic mass of 1 atom __(p+)+__(n0)=__ __ atomic mass of 1 atom __(p+)+__(n0)=__ __ atomic mass of 1 atom __(p+)+__(n0)=__ __ atomic mass of 1 atom __(p+)+__(n0)=__ __ atomic mass of 1 atom __(p+)+__(n0)=__ __ atomic mass of 1 atom __(p+)+__(n0)=__ __ atomic mass of 1 atom

__(p+)+__(n0)=__ __ atomic mass of 1 atom __(p+)+__(n0)=__ __ atomic mass of 1 atom __(p+)+__(n0)=__ __ atomic mass of 1 atom __(p+)+__(n0)=__ __ atomic mass of 1 atom __(p+)+__(n0)=__ __ atomic mass of 1 atom __(p+)+__(n0)=__ __ atomic mass of 1 atom __(p+)+__(n0)=__ __ atomic mass of 1 atom

Find the average for the above column. Average atomic mass=

If found on the periodic table, the box would look like: the atomic number the chemical symbol the atomic mass the name of the element

Element name: __________Symbol: ______ Element name: __________Symbol: ______ __(p+)+__(n0)=__ __ atomic mass of 1 atom __(p+)+__(n0)=__ __ atomic mass of 1 atom __(p+)+__(n0)=__ __ atomic mass of 1 atom __(p+)+__(n0)=__ __ atomic mass of 1 atom __(p+)+__(n0)=__ __ atomic mass of 1 atom __(p+)+__(n0)=__ __ atomic mass of 1 atom __(p+)+__(n0)=__ __ atomic mass of 1 atom

Find the average for the above column. Average atomic mass=

If found on the periodic table, the box would look like: the atomic number the chemical symbol the atomic mass the name of the element

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8P1E Patterns in the Periodic Table

Student Journal Part IV: Studentium Elements, Continued 1. What subatomic particle remained the same in number within each atom of the Studentium elements? 2. What subatomic particle varied in number within each neutral atom of the Studentium elements? 3. Explain why average atomic mass is not a whole number for the Studentium elements.

4. Based on the Studentium activity, explain why the atomic mass numbers listed for elements on the periodic table are not whole numbers.

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8P1E Patterns in the Periodic Table

Student Journal Reflections and Conclusions 1. Within the nucleus of individual atoms of the same element, the proton number . Within the nucleus of individual atoms of the same element, the number of may vary. This is why the is shown on the periodic table as an average number. 2. Why are elements within the same group on the periodic table considered “family members”?

3. Use the X to represent any element member of group 6A and draw a representation of the valence electrons around the X below.

4. What happens to the number of energy levels in the electron cloud with increasing period number?

5. Which of the following three elements—carbon, nitrogen, and phosphorous—do you predict would exhibit similar properties? Explain your answer.

6. What does the number of valence electrons have to do with properties of elements within a group?

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8P1E Patterns in the Periodic Table

Student Journal Name:

Date:

Group:

Combining Atoms Complete the data table as you create your molecule models. Understanding Chemical Formulas and Substance Compositions Chemical Name of Substance composition: Drawing of model using formula substance this key: number and type of oxygen = white each atom in a molecule hydrogen = blue of the substance carbon = black nitrogen = red sodium = yellow

hydrogen gas

oxygen gas

ozone

H2O

water

CH4

methane

NaOH

sodium hydroxide

N2O

nitrous oxide

H2CO3

carbonic acid

Write a statement that explains the meaning of a subscript in a chemical formula.

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STEMscopedia: PATTERNS IN THE PERIODIC TABLE

8P1E

Reflect Suppose you wanted to organize your locker at school. How could you separate and arrange everything in an organized way? You could place the books, notebooks, and folders on a shelf that is separate from the pencils, pens, and erasers. You might order the books from smallest to largest with the notebooks and folders on the end. Or you might arrange the books and folders by subject. Scientists use properties to organize things, too. The elements are organized in a specific way on the Periodic Table of Elements (Periodic Table for short). What properties do scientists use to organize the Periodic Table? What does this tell us about the elements? Atomic Number Elements are organized on the Periodic Table according to atomic number. The atomic number of an element refers to the number of protons in the nucleus of that atom. Each atom of an element always has the same number of protons, therefore, the same atomic number. Here is a version of the Periodic Table.

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STEMscopedia: PATTERNS IN THE PERIODIC TABLE

Moving across (left to right) each row of the Periodic Table, the atomic number increases sequentially (in order.) For example, the atomic number of carbon (C) is 6 and the atomic number of nitrogen (N) is 7. These two elements are next to each other in the second row of the Periodic Table. Cesium (Cs) has an atomic number of 55 and Barium has an atomic number of 56. They are found next to each other in the sixth row. The atomic number increases as you go to the right across and as you go down the Periodic Table. Atomic Mass Because elements are arranged according to their atomic number, the atomic mass of each element also increases when moving to the right and down the Periodic Table. Atomic mass is the average mass of one atom of an element.

Look Out As you move across the Periodic Table from left to right, the atomic number of each element increases by one. Typically, this number is written as a whole number above the chemical symbol (the one- or two-letter code that represents an element). Be careful not to confuse this with the number below the chemical symbol, which is the atomic mass. Take a look at the illustration on the right. The element helium (He) has an atomic number of 2, which is the number above the symbol He. The average atomic mass of helium is 4.00260. The average atomic mass is written below the He symbol. Groups and Periods There are additional patterns of arrangement on the Periodic Table. The vertical columns are known as groups. If you look at the Periodic Table on the previous page, you will notice that numbers and letters are used to identify groups. For example, the first group from the left is 1A. Elements in the same group have the same number of valence electrons. Valence electrons are the electrons in the outer energy level. They determine the chemical behavior of an element. So, elements in the same group have similar chemical properties because they have the same number of valence electrons. There are some exceptions to this order. These exceptions are shown by the unshaded elements in the diagram at the right. Let’s discuss the elements in the first column, or group 1A, of the Periodic Table. Each element in this group has one valence electron. Sodium (Na) and potassium (K) are two elements in this group.

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STEMscopedia: PATTERNS IN THE PERIODIC TABLE

The electron arrangements of these two elements are shown in the figures below. These elements are metals and tend to donate their single valence electron to other elements in order to have a full outer energy level. The other elements in this group also tend to donate their single valence electron.

Elements in other groups also have the same number of valence electrons as other elements in that group. For example, elements in the second column, or group, have two valence electrons and tend to donate these two electrons. Elements in group 17, the second to last column from the left, have seven valence electrons. They need one electron to fill their outer energy level. They tend to react with other elements to gain one electron. Alternatively, the elements in the last column are known as the noble gases. These elements have a complete outer energy level, so they tend to keep their electrons and are very stable elements. They do not react easily with other elements. You learned earlier in the lesson that atomic number increases as you move from left to right across rows and down the rows of the Periodic Table. These rows are called periods and they correspond to the number of energy levels in an element. Energy levels are the different orbits in which electrons move around the center of an atom. For example, every element in the top row (first period) has the same number of energy levels. This period contains only two elements, hydrogen (H) and helium (He). These elements have only one energy level. The elements in the second period (Li, Be, B, C, N, O, Cl, and Ne) have two energy levels. This pattern continues as you move down the rows of the Periodic Table. The arrangement of elements in the Periodic Table is based on atomic number, reactivity and valence electrons and allows you to predict reactivity and behavior of elements based on their locations on the table.

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STEMscopedia: PATTERNS IN THE PERIODIC TABLE

What Do You Think? Take a look at the diagram below. For each element, identify the group and period to which each element belongs. Use a Periodic Table for reference. What can you determine about each element based on its location on the Periodic Table?

Metals, Non-metals, and Metalloids Because elements are arranged on the Periodic Table according to similar chemical properties, three main types of elements are arranged in a pattern on the table as well. The three main types are metals, non-metals, and metalloids. Most of the elements on the Periodic Table are metals. Metals are usually shiny solids that are malleable and ductile. They are good conductors of heat and electricity. Examples include gold (Au), iron (Fe), lead (Pb), and silver (Ag.) The metals are shaded in gray on the Periodic Table on the next page. Non-metals are typically dull and brittle. Brittle materials break or crack easily. Non-metals are generally poor conductors of heat and electricity. There are only 18 non-metals on the Periodic Table, including hydrogen (H), carbon (C), and nitrogen (N.) The non-metals are un-shaded (white) on the Periodic Table on the next page. Metalloids have properties of both metals and non-metals. Some metalloids have a metallic luster, such as silicon (Si). Silicon is also brittle; therefore, it has characteristics of both the metals and the non-metals. Some metalloids are semi-conductors, meaning they carry an electrical charge under certain conditions. The metalloids are located along the “steps” that separate metals from nonmetals on the Periodic Table. They are shaded orange on the Periodic Table on the next page.

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STEMscopedia: PATTERNS IN THE PERIODIC TABLE

Discover Science: Development of the Periodic Table In the 1800s, a professor named Dmitri Mendeleev developed one of the first tables to arrange the elements. First, Mendeleev ordered the elements by increasing atomic mass, and then further separated them based on their chemical properties. This work was the basis for our current Periodic Table of Elements. At the time, there were only 63 known elements. However, Mendeleev was able to theorize about new elements, which were identified after his table of the elements was created. In the years following Mendeleev’s development, the elemental table was revised slightly. A scientist named Henry Moseley ordered the elements based on atomic number. This is the current method in which the elements are ordered.

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STEMscopedia: PATTERNS IN THE PERIODIC TABLE

Try Now The Periodic Table of Elements is arranged based on the properties of elements. The chart below lists five elements. For each element, find a “matching” element in the box below the chart. A matching element is one that is in either the same group or the same period as the element in the chart. Then, write whether the elements are in the same group or the same period. Finally, write at least two characteristics that are shared by the matching elements based on their locations on the Periodic Table. You will need to refer to a Periodic Table to complete this activity. Element

Matching Element

Matching Group or Period?

Shared Characteristics

Calcium (Ca)

Fluorine (F)

Iodine (I)

Argon (Ar)

• Oxygen (O) • Neon (Ne) • Magnesium (Mg) • Xenon (Xe)

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STEMscopedia: PATTERNS IN THE PERIODIC TABLE

Connecting With Your Child Organization of the Periodic Table To help your child learn more about the Periodic Table, work together to create an “element” game. For this activity, you or your child will need to make 10 flash cards. You will also need a copy of a Periodic Table, which can be found in science textbooks or on the Internet. Decide who will be the “reader” and who will be the “guesser.” The reader should spend some time making the flash cards by choosing 10 elements and writing information about each element on a single card. On one side of the card, write the chemical symbol for the element. On the other side, describe its location on the Periodic Table (group and period), its atomic mass, and its classification as a metal, non-metal, or metalloid. This information is to help the reader answer the questions asked by the guesser. Have the reader choose a flash card to start the game. Make sure the guesser does not see the card. The guesser should begin by asking a series of questions until he or she correctly guesses the element. The only questions the guesser may ask are those that require a “yes” or “no” answer. For example, the guesser could ask, “Is the element a metal?” The guesser cannot ask, “What is the atomic number of the element?” Make sure the copy of the Periodic Table is available for the reader to use as a reference during the game. Here are some questions to discuss with your child after you play the game: 1. Which questions were most helpful to the guesser in identifying the element on each flash card? 2. Were there any questions that were not helpful? If so, what were they? 3. How does organizing the elements help scientists use the Periodic Table?

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8P1E Patterns in the Periodic Table

Reading Science Name:

Date:

Group:

Mendeleev and His Periodic Table 1

Russian chemist Dmitri Mendeleev realized the need for scientists to be able to know an element’s identity quickly and efficiently. Although earlier scientists had organized elements, their tables did not satisfy Mendeleev. He felt they had left out important information.

Early in his studies, Mendeleev saw patterns in the chemical and physical properties of some elements. He grouped the elements into a neat, logical manner according to these patterns. He developed the periodic table of elements in 1869. This table arranged elements according to increasing atomic mass. Groups of elements that have similar physical and chemical properties are arranged into rows and columns.

The table later proved to be a bit flawed, but Mendeleev expected this. He left some blank spots in his table for undiscovered elements. These were, indeed, later discovered. His table also did not consider the importance of protons that had not yet been identified. Protons are important in grouping elements, since they strongly influence the physical and chemical properties of elements. The table also did not take into account the noble gases, which do not have properties like those near them on the table.

Today’s periodic table looks much like Mendeleev’s table of 130 years ago. More elements have been identified and classified. The inert gases now have been placed on the table. The table now is arranged according to increasing atomic number, showing each element’s physical and chemical properties, rather than according to atomic mass as Mendeleev’s did. The periodic table of elements remains a valuable tool for chemists and other scientists.

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8P1E Patterns in the Periodic Table

Reading Science 1.

In the same way that today’s periodic table is organized by atomic number, Mendeleev organized his periodic table by – A

protons.

neutrons.

atomic mass.

atomic number.

The modern periodic table is different from Mendeleev’s in several ways. In which way are the two tables the same? A

The inert gases occupy one column of the table.

Elements are arranged by increasing atomic number.

There are blank spots in the middle for undiscovered elements.

Elements are put into columns based on similar chemical properties.

Mendeleev’s periodic table lacked – A

noble gases.

chemical property trends.

neutrons.

atomic mass.

How does the periodic table used today classify elements? A

According to chemical properties alone

According to atomic number

According to atomic mass

According to radioactive properties

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8P1E Patterns in the Periodic Table

Reading Science

The diagram shows a portion of the periodic table. Elements that were unknown during Mendeleev’s time have been removed. Using Mendeleev’s rules for arranging elements, which box would contain the metal gallium that has an atomic number of 31 and an atomic mass of 70? A

Box 5

Either box 2 or box 3

Only box 2

Only box 3

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8P1E Patterns in the Periodic Table

Math Connections Name:

Date:

Group:

Periodicity: Atomic Radius and Effective Nuclear Charge The atomic radius is a measure of the distance from the center of the nucleus to the outward boundary of the electron cloud. The effective nuclear charge (Zeff ) is the net positive charge felt by the valence electron that affects the atomic size. Look up the atomic number for each element on the periodic table and record it in the chart below. Plot the atomic radius and the calculated Zeff for the highest-energy electron versus the atomic number on the graph below the chart. Use this graph to answer the following questions. (Use a red pencil to mark the atomic radius and a blue pencil to mark the points for Zeff. ) Atomic radius (pm)

Effective nuclear charge, Zeff

Sodium

186

Magnesium

160

109

Aluminum

143

130

Silicon

111

138

Phosphorous

107

150

Sulfur

100

163

Chlorine

180

Argon

195

Element

Atomic number

xplain the relationship between atomic E radius and Zeff. Provide rationale for your response, using data from the table and graph you created.

Zeff

Atomic radius (pm)

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Math Connections 2.

Write an inequality statement that compares the atomic radii for each atom, using the symbol <, >, or=in each blank below.

a. Mg

b. W

c. Si

d. Ce

e. Na

f. V

g. V

h. Li

The amount of energy that must be added to remove an electron from a neutral atom to give a cation is called the atom’s ionization energy. Which element would you expect to have the larger ionization energy: Na, or Mg? Provide rationale for your response.

As you look at the periodic table of elements, what trend or pattern do you notice about the size of the atomic radius?

The picometer is an extremely small unit of measurement used to measure atomic structures. One (1) picometer is equal to 1⁄1,000,000,000,000 meters. Element

Atomic radius (pm)

Aluminum

143

Magnesium

160

Silicon

111

Sulfur

100

Argon

Atomic radius (meters)

Use scientific notation to represent the atomic radius of the elements in the table above in meters.

How much larger is aluminum’s atomic radius than argon’s? Use scientific notation to provide your answer in meters.

What are some benefits of using a smaller unit of measurement?

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8P1E Patterns in the Periodic Table

Writing Science Name:

Date:

Group:

LOOK

THINK Think about the arrangement of the periodic table and the information it provices.

WRITE Explain how you can use properties to identify elements.

Be sure to clearly state your central idea; organize your thoughts; develop your essay in detail; choose your words carefully; and use correct spelling, capitalization, punctuation, and grammar. © Accelerate Learning Inc. - All Rights Reserved

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Writing Science

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8th Grade Physical Science

8P1F

Conservation of Mass

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8P1F Conservation of Mass

Student Handout Name:

Date:

Conservation of Matter Observations Record the mass of the materials before and after the experiment.

Before: ____________________________________________________________ After: ______________________________________________________________

Answer the following questions in complete sentences. During the experiment, was there an indication that a reaction took place? Explain.

How can you relate the law of conservation of mass to the balancing equations and counting atoms?

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8P1F Conservation of Mass

Student Journal Name:

Date:

Group:

Where Did It Go? Data Table Part I Open System Object (Reactants)

Initial Mass (g)

Final Mass (g)

Initial Mass (g)

Final Mass (g)

Water and water bottle Alka-Seltzer tablet Total system (water and water bottle, and Alka-Seltzer) Observations

Part II Closed System Object (Reactants) Water and water bottle Alka-Seltzer tablet Balloon Total system (water and water bottle, Alka-Seltzer, and balloon) Observations

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8P1F Conservation of Mass

Student Journal Where Did It Go? 1. In which part(s) was the law of conservation of matter verified (confirmed, proven)? Explain your answer.

2. Why was there a difference between the mass of the reactants and the mass of the products in Part I?

3. The container in Part II was covered (with the balloon). Offer an explanation as to where the discrepancy (difference) arose between the mass of the reactants and the mass of the products.

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STEMscopedia: CONSERVATION OF MASS 8P1F

Reflect What is the law of conservation of mass? It is when an object is broken into smaller pieces, when a solid is dissolved in a liquid, or when matter changes state (solid, liquid, gas)... BUT the total amount of matter remains constant. Who was Antoine Lavoisier and what is his connection to the law of conservation of mass? Between 1772 and 1794, the first French chemist, Lavoisier, found that mass is conserved in a chemical reaction. Thus, he discovered the law of conservation of mass. Important Vocabulary: matter: anything that has mass and takes up space mass: the amount of matter in an object volume: the amount of space something takes up solid: the state of matter that has a definite shape and volume liquid: the state of matter that has no definite shape but takes up a definite amount of space (volume) and takes the shape of its container gas: the state of matter that has no definite shape and does not take up a definite amount of space The law of conservation of mass states that matter can be changed from one form to another, mixtures can be separated or made, and pure substances can be decomposed, but the total amount of mass stays the same. The law of conservation of matter states that matter (mass) can neither be created nor destroyed. It can, however, be rearranged. In a chemical reaction, the mass of the reactants must equal the mass of the products. So, in other words, when matter goes through a physical or chemical change, the amount (or mass) of the substances that you begin with must equal the amount (or mass) of the substances that you end with. The before and after must balance. Why, you ask? It’s the law!

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STEMscopedia: CONSERVATION OF MASS Look Out What are the macroscopic and microscopic differences between physical and chemical changes? Macroscopic Definitions physical change: The matter remains the same. The original matter can be recovered. chemical change: The matter is different. The original matter is no longer present and cannot be recovered. Microscopic Definitions physical change: The particles of the substance are rearranged. chemical change: The particles of the substance are broken apart and the atoms are rearranged into new particles, forming a new substance.

physical change

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chemical change

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STEMscopedia: CONSERVATION OF MASS What Do You Know? What is the difference between a physical change and a chemical change? If you change something physically, you still have what you started with. For example, if you tear a piece of paper, you still have paper. If you change something chemically, you end up with something very different than what you started with. For example, if you burn a piece of paper, you end up with carbon—the paper is essentially gone. But these are obvious examples. Is it always that simple? What if you put sugar into water? Is that a physical or a chemical change? How about if you freeze water? Is that physical or chemical? For these examples, we have to examine what it would take to get the original substances back after we have made the change. With the sugar and the water, we could evaporate the water, which would reveal no change to the sugar except in how it looks. It is still sweet, and it can be remixed in water. The frozen water can be melted, and we would have the same water we started with. If we take that same sugar and water, mix it with flour, eggs, vanilla, and chocolate chips, and bake cookies, we will have performed a chemical change. No matter what you do to the cookies, you will never get the sugar and the water out of them as before. So in summary, there are really only two questions that determine whether a change is chemical or physical: 1) After the change, does it look the same? and 2) Can you change it back? If the answer to both questions is yes, the change is physical every time. If the answer is no, the change is chemical every time. Five Examples of a Physical Change • Crushing a can • Melting an ice cube • Boiling water • Mixing sand and water • Breaking a glass Five Examples of a Chemical Change • Baking cake • Rusting nails • Burning wood or lighting a match • Exploding fireworks • Ripening and rotting bananas

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STEMscopedia: CONSERVATION OF MASS How do you know if a chemical reaction has occurred? You walk into your science lab and notice that there is an actual lab set up for you to conduct today. As you perform the various tasks, you notice on the board that it states you are looking to prove that a chemical reaction has occurred. How do you know if a chemical reaction, and not just a physical change, is occurring? There are some reactions to take note of, but you must remember that water is an exception to most of these examples. At the first station, you begin by adding an unknown liquid to an unknown solid. As you add the liquid, you notice that the solid dissolves and the test tube becomes warm to the touch. You have to determine if a chemical reaction is occurring. This is an example of a reaction that you can witness with the sense of touch. The heat produced is an indicator that a chemical reaction is occurring, because it is a change in temperature. If the solution was cold to the touch or light is emitted, these could also be indicators. Look at the formula below. CaCl2 (s) + 2H20 → Ca(OH)2 (aq) + 2HCl (g) + heat The formula shows when calcium chloride and water are mixed, the ending products release heat from the reaction. Due to the conservation of mass, no matter is created or destroyed but only rearranged into new substances. At the second station, you are given two test tubes with unknown liquids. You are asked to mix both liquids into a third test tube. As you slowly pour the two liquids, you notice that some solid particles appear at the bottom of the test tube. The solid particle is called a precipitate, which is an indication that a chemical reaction has occurred. Precipitates are solids that form from aqueous, liquefied solutions. Look at the formula below. CdSO4 (aq)+K2S (aq) → CdS (s)+K2SO4 (aq) The formula shows that on the reactant side, left, there are two aqueous solutions. On the product side, right, you should notice the (s) for solid, but it still has one aqueous (aq) solution. Again, the matter has just been rearranged. At the third station, you are given an unknown, powdery, solid substance and an unknown liquid. As you slowly pour the liquid over the powdery substance, you notice that the powdery substance seems to be dissolving as you notice bubbles forming in the test tube. The production of gas is another indicator to show that a chemical reaction is occurring. Look at the formula below. C2H4O2 (aq) + NaHCO3 (s) → NaC2H3O2 (aq) + H2O (l) + CO2 (g) The formula shows that there is an aqueous solution and solid on the reactant side. On the product side, there is now an aqueous solution, liquid, and gas. The production of a gas, carbon dioxide, demonstrates that a chemical reaction has occurred.

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STEMscopedia: CONSERVATION OF MASS At the last station, you are instructed to mix the two aqueous solutions into a beaker. As you pour the two solutions, you notice that the clear solutions, when combined, have changed to a black color. Color change is an indicator that is used to determine if a chemical reaction has occurred. Look at the formula below. S2O8 2− (aq) + 2 I− (aq) → I2 (aq) + 2 SO4 2− (aq) The formula does not show the change in color; only your observation of the reaction will demonstrate this change. The formula is again used to demonstrate that matter is not created or destroyed during this chemical reaction. Summary These four reaction types are used to determine if a chemical reaction has occurred. However, there are always exceptions to these examples. • Change in temperature or light emitted • Precipitate forms • Gas formed • Color change

Try Now The law of conservation of mass indicates that mass cannot be created nor destroyed. This means the total mass of reactants in a chemical reaction will equal the total mass of the products. If a gas is produced during a reaction, its mass is often forgotten when calculating the final mass because the students are unable to see the gas. For this reason, balloons or Ziploc® bags may be used to collect the gas and preserve the mass. When balancing chemical equations, the law of conservation of mass is also demonstrated because the total number of atoms that goes into the reaction must be produced. Materials: • 1 Ziploc® bag • 2 Small plastic cups • Vinegar (acetic acid) • Baking soda (sodium bicarbonate) • Triple beam balance

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STEMscopedia: CONSERVATION OF MASS Directions: Drop an Alka-Seltzer™ tablet into a beaker of water. Discuss the law of conservation of mass. Why is it hard to prove the law when a gas is produced? Try this: 1. Fill one cup halfway with vinegar. 2. Fill a second cup halfway with baking soda. 3. Put both cups in the plastic bag. Be careful NOT to spill the contents of either cup. 4. Determine and record the mass of the cups, the plastic bag, and their contents. 5. Seal the plastic bag. 6. Without opening the bag, pour the vinegar into the cup of baking soda. 7. Without opening the bag, record the mass of the contents of the plastic bag 8. Take care not to break the seal of the plastic bag. What happens when the vinegar was poured into the cup of baking soda? There was a release of gas, correct? This is a typical chemical reaction in which an acid (vinegar) reacts with a base (baking soda) to produce a new chemical (a salt). What do you remember about chemical reactions? This experiment is a chemical reaction, and the gas produced in this reaction can put out fires. Can you make a guess about its identity? What is the name of the gas? It is called carbon dioxide. What do you remember about the conservation of mass? How does it relate to this experiment? As long as the carbon dioxide was not allowed to escape, the change in mass that occurred during the reaction should be zero.

Connecting With Your Child Help your child explore the law of conservation of mass of a physical change by using a sheet of cardboard, heavy paper, or file folder. The purpose of this experiment is to observe events and report observations, measure mass, plan an experiment, predict results of investigations, and to record data. • Using the balance, record the weight of the sheet of cardboard. • Tear or cut the cardboard into small pieces. • Using the balance, again record the weight. Is the weight the same or different? How would you explain this? [Mass is conserved.] Have your child explain the following based on what he or she has learned.

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8P1F Conservation of Mass

Reading Science Name:

Date:

Group:

The Birth of Chemical Formulas and Equations 1

Around 2,000 years ago, the Roman poet Lucretius said, “Things cannot be born from nothing.” Even then, people knew that all the matter that we see is all the matter we would ever have. It wasn’t until the 1700s that several scientists proved the theory.

In the 1700s, several scientists made chemical compounds and formulas easier to understand. In 1748, Russian scientist Mikhail Lomonosov first came up with the idea of the law of conservation of mass. In 1789, French scientist Antoine Lavoisier proved this law. His experiments showed how two reactants (tin and lead) combined with oxygen. Swedish scientist Jöns Jacob Berzelius and British scientist John Dalton also get credit. They created a simpler way to explain how chemical reactions happen.

Because Berzelius worked with chemical compounds with several different elements, he needed a way to simplify chemical notations and make them easier to manipulate. He worked up a system of one- or two-letter symbols along with a smaller-sized number (subscript). The chemical formula pictured above is NH3 (1 nitrogen and 3 hydrogen atoms.) It would be much harder to write if chemical symbols and subscripts were not used.

John Dalton came up with his atomic theory that scientists still use. The theory explains chemical formulas and has four major points: • All matter is made of atoms that cannot be divided or destroyed. • All atoms of a given element are the same in mass and properties. • New compounds are formed when two or more elements combine. • A chemical reaction changes how atoms are arranged. He and other scientists knew that the chemical properties of a molecule are related to the arrangements of the atoms in that molecule.

Without the early work of chemists from many different countries, chemical formulas would be hard to work with. Their methods give us an easy way to represent complex chemicals by using formulas and subscripts.

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8P1F Conservation of Mass

Reading Science 1.

Complete the following analogy: MIKHAIL LOMONOSOV : LAW OF CONSERVATION OF MASS :: JOHN DALTON :

ATOMIC THEORY

SUBSCRIPTS

CHEMICAL COMPOUNDS

FORMULAS

What is the purpose of subscripts in chemical formulas? A

So the chemist can multiply the chemical formula by that number

To let the chemist know that the element is a noble gas

To indicate that the element has an isotope

To indicate an element’s proportions within a formula

Ammonium carbonate has the chemical formula (NH4)2CO3. How many hydrogen atoms (H) are in ammonium carbonate? A

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8P1F Conservation of Mass

Reading Science 4.

Which of the following is one component of John Dalton’s atomic theory? A

All matter can be divided by chemical reactions.

All matter is made of indivisible, indestructible atoms.

Chemical reactions can only occur by means of a particle accelerator.

Elements cannot be combined to form new compounds.

What is the meaning of the word manipulate in paragraph 3? A

Chance

Confuse

Work with

Free

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8P1F Conservation of Mass

Math Connections Name:

Date:

Group:

In a chemical change, bonding of atoms changes, and new substances are formed. The law of conservation of matter states that the number and type of atoms in the reactants is exactly equal to the number and types of atoms in the products. The total mass of the reactants is also equal to the total mass of the products. Chemical equations are used to describe the reaction and how the atoms combine with one another to form new molecules. 1.

Propane, C3H8, is a colorless, odorless gas often used to power gas-cooking grills. Write a balanced equation for the combustion reaction of propane with oxygen to yield carbon dioxide and water. Unbalanced equation: C3H8 + O2

CO2 + H2O

Step 1: Balance the carbon atoms. Step 2: Balance the carbon and hydrogen atoms. Step 3: Balance the carbon, hydrogen, and oxygen atoms. Balanced Equation: 2.

Potassium chlorate (KClO3 ), an ingredient in kitchen matches, can act as a source of oxygen in combustion reactions. When it reacts with ordinary table sugar (sucrose, C12H22O11), the reaction yields potassium chloride, carbon dioxide, and water. Write a balanced equation for the reaction. Unbalanced equation: KCIO3 + C12H22O11

KCI + CO2 + H2O

Step 1: Balance for C. Step 2: Balance for C and H. Step 3: Balance for C, H, and O. Step 4: Balance for K and Cl Balanced Equation:

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8P1F Conservation of Mass

Math Connections 3.

Fermentation occurs when making bread dough. Balance the equation for the fermentation of sugar to yield ethyl alcohol. C6H12 O6

C2H6O + CO2

Plants use photosynthesis to make food. Balance the equation for the photosynthesis. CO2 + H2O

Hydrazine is a component of rocket fuel. Balance the equation for the synthesis of hydrazine. NH3 + Cl2

C6H12O6 + O2

N2H4 + NH4Cl

Which of the following equations are balanced? a. The development reaction in photography: 2AgBr + 2NaOH + C6H6O2

2Ag + H2O + 2NaBr + C6H4O2

b. The preparation of household bleach: 2NaOH + Cl2

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NaOCl + NaCl + H2O

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8P1F Conservation of Mass

Writing Science Name:

Date:

Group:

LOOK

THINK Think about the law of conservation of matter. WRITE Explain the law of conservation of matter, and include why it is considered a scientific law.

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8P1F Conservation of Mass

Writing Science

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8th Grade Physical Science

8P2AB

Kinetic and Potential Energy

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8P2AB Kinetic and Potential Energy

Student Handout Name:

Date:

Craft Stick Explosion Activity 1.

With your group, create a craft stick chain. Follow the instructions in the Student Handout: How to Build a Craft Stick Chain.

Put on goggles for this activity.

Be sure to keep pressure on the top stick in the chain as you go along.

When the chain is completed and you are ready, let go!

Record your observations of what happens next in the space below.

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8P2AB Kinetic and Potential Energy

Student Journal Name:

Date:

Group:

Part I: Types of Energy 1. Use the information you have learned to fill in the chart below by cutting out and gluing in the pictures given to you. When you have finished, you should have six pair of examples. Potential and Kinetic Energy Pairs Within a System Potential

Kinetic

Potential

Kinetic

2. Think about two pictures that could be added to the chart above for a child swinging on a swing. Describe how the picture of the child on a swing would look when placed under the potential energy column.

3. Describe how the picture of the child on a swing would look when placed under the kinetic energy column.

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8P2AB Kinetic and Potential Energy

Student Journal Part II: Potential and Kinetic Energy 1.

Complete the data table below as you perform the investigation.

Mass, Speed, and Kinetic Energy Data Travel Distance:____________ Ball/Trial

Mass (kg)

Speed (m/s)

Kinetic Energy (joules)

Ball A – Trial 1 Ball A – Trial 2 Ball A – Trial 3 Average for Ball A Ball B – Trial 1 Ball B – Trial 2 Ball B – Trial 3 Average for Ball B Ball C – Trial 1 Ball C – Trial 2 Ball C – Trial 3 Average for Ball C

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8P2AB Kinetic and Potential Energy

Student Journal Part III: Kinetic Energy 2.

Create a graph for Kinetic Energy and Mass based upon the data. Label the x-axis and the y-axis, and include a title.

Make a general statement about the results shown in the graph. Identify linear and nonlinear relationships in the constructed graph.

What is the relationship between mass and kinetic energy?

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8P2AB Kinetic and Potential Energy

Student Journal Part III: Potential Energy 1.

Complete the data table below as you perform the investigation. Bounce Height in cm Starting Height

Trial 1

Trial 2

Trial 3

Average

50 cm 100 cm 2.

Create a graph based upon the data. Label the x-axis and the y-axis, and include a title. For each data set, mark the height at which the potential energy is at 100% and where it is zero. Then mark the height at which the kinetic energy is at 100% and where it is zero.

Make a general statement about the results shown in graph.

Write a scientific explanation of how potential energy is affected by position.

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8P2AB Kinetic and Potential Energy

Student Journal Part IV: Potential and Kinetic Energy Transformation 1. Use the table below to collect data from the investigation. Release Height of Pendulum Bob Versus Distance Traveled by Block Distance Block Moved from Block-Start to Block-Stop Positions Height of Pendulum Bob

Trial 1 (cm)

Trial 2 (cm)

Trial 3 (cm)

Average (cm)

10 cm 20 cm 30 cm 40 cm 2. Graph the data results using these guidelines: • Graph only the averages. • Label the x-axis and the y-axis. • Include a title and a legend for the graph.

Legend:

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8P2AB Kinetic and Potential Energy

Student Journal Part IV: Potential and Kinetic Energy Transformation, continued 3. List the parts of the system that you explored in the activity. 4. What happened to the block of wood after the pendulum bob struck it? Explain by stating what type of energy was demonstrated. 5. Which release height of the pendulum bob caused the wood block to move the farthest distance? 6. Which release height of the pendulum bob caused the wood block to move the shortest distance? 7. Describe the pattern in the data. In other words, how did the changes in the starting height of the pendulum bob affect how far the block moved?

8. How does raising the height of the pendulum bob affect its potential energy?

9. As the pendulum is let go from increasing heights, how is the resulting kinetic energy affected? What is the evidence?

10. Use the constructed graph to predict how far the block could travel if the pendulum bob’s release height is 50 cm.

11. Explain how the initial height of a wrecking ball is directly related to its ability to demolish a very thick concrete wall. Use the words potential and kinetic energy in your explanation.

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8P2AB Kinetic and Potential Energy

Student Journal Part V: Compare and Contrast Potential and Kinetic Energy 1. Use the information you have learned to fill in the chart below. Characteristics of Potential and Kinetic Energy Potential Energy

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Kinetic Energy

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8P2AB Kinetic and Potential Energy

Student Journal Part V: Compare and Contrast Potential and Kinetic Energy, continued 2. Define potential energy and then explain what factors, or variables, cause potential energy to change.

3. Define kinetic energy and then explain what factors, or variables, cause kinetic energy to change. 4. Provide an everyday example of kinetic energy transferring from one object to another object.

5. Provide an everyday example of an increase in the total energy of a system due to an increase in potential energy.

6. If you put your backpack in the car and then drive to the mall, is your backpack in motion when comparing it to the system of the car? Does the backpack have kinetic energy while you are on your way to the mall?

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8P2AB Kinetic and Potential Energy

Student Journal Reflections and Conclusions 1. What is energy?

2. What is a system?

3. What are the two types of energy within a system?

4. What is the unit of measure for energy? 5. How are potential and kinetic energy alike?

6. How are potential and kinetic energy different?

7. Look at the diagram below. Describe the transformation between potential and kinetic energy within this system.

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STEMscopedia: KINETIC AND POTENTIAL

ENERGY 8P2AB

Have you ever used a swing at a playground? Can you describe your motion while swinging? Do you ever feel like the swing stops or goes faster at certain points? What do you think causes these changes in speed? Do you think your energy is also changing as you swing? Energy can change within a system. Energy can take many forms. What do these forms have in common? They all have the ability to cause changes to a system, or a set of connected things that work together. As you swing on the playground, you and the swing form a system. The increase or decrease of energy in a system has a direct effect upon the system’s physical variables. These variables include temperature, speed, position, pressure, and motion. If someone turns on a stove burner under a pot of water, energy from the burner will cause the pot to heat up. The heat will cause the water to come to a boil. This shows the relationship between energy and the system of the water-ﬁlled pot. Energy can be classiﬁed as potential or kinetic. There are two Physical variable: something main forms of energy in a system: potential and kinetic. Potential measurable that can change energy (PE) is stored energy. Kinetic energy (KE) is energy in the form of motion. The total amount of potential energy and kinetic energy in a system is known as mechanical energy. Think back to the swing example. This diagram shows how the swing moves back and forth as a person rides it. When the person has swung all the way back (position A), the swing pauses a moment. At this moment, the swing has only potential energy. The swing then falls forward, gradually gaining speed. As it falls, its potential energy changes to kinetic energy. At position B, the swing has only kinetic energy. As the swing continues forward, it gradually slows down. Its kinetic energy changes back to potential energy until it reaches the farthest point in its arc (position C). Here, the swing pauses again for a moment. At this moment, the swing has only potential energy. It then falls backward through its arc. Its potential energy changes to kinetic energy, and the cycle is repeated.

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STEMscopedia: KINETIC AND POTENTIAL

ENERGY

Reflect At every point in this cycle, the system of swing and person has the same amount of mechanical energy. In other words, when the system has less potential energy, it has more kinetic energy. And when the system has more kinetic energy, it has less potential energy. At each moment, the system’s kinetic energy and potential energy add up to the same value.

Look Out You may think that, as a swing gains speed, its potential energy is destroyed and kinetic energy is created. In fact, energy can only change forms. It cannot be created or destroyed. This is called the law of conservation of energy. Why can’t you swing forever? Where does the energy go? As you swing, your body collides with particles of air. These particles are tiny, but there are a lot of them. Each time you collide with air particles, a little of your kinetic energy is transferred to the particles. This force, called air resistance, gradually slows you down. Another force that slows you down is called friction. As the swing moves, its parts rub against each other. As this happens, some of the swing’s energy changes to heat and leaves the system. If there were no friction or air resistance, you could swing forever!

As air particles collide with the parachute, the force of air resistance slows down the skydiver.

Potential energy and kinetic energy are similar but not the same. Scientists measure both potential energy and kinetic energy in joules (J). A joule describes the amount of energy needed to do a certain amount of work or cause a certain amount of change. So more joules of energy can perform more work or cause more change. Scientists can use the same unit to measure both types of energy because kinetic energy and potential energy are related. Remember, a system’s mechanical energy equals its potential energy plus its kinetic energy.

There are also differences between potential energy and kinetic energy. Potential energy is stored energy. In other words, it has the potential to become kinetic energy. The chemicals that make up food, batteries, and fuel all contain potential energy. When you eat food, your body converts the food’s potential energy into kinetic energy that you can use to move and function. When fuel is burned in a car engine, the fuel’s potential energy is converted to kinetic energy that powers the car.

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STEMscopedia: KINETIC AND POTENTIAL

ENERGY

Look Out Potential energy depends on gravity. The higher an object is, the more potential energy the object will have. The force of gravity is stronger on an apple high in a tree than an apple low in a tree. So the higher apple will have greater potential energy than the lower apple. Kinetic energy is the energy of motion. It depends on an object’s mass or velocity. A large car will have greater kinetic energy than a small car. What if two cars have the same mass but are moving at different speeds? The car moving faster will have greater kinetic energy.

What Do You Think? Look at this picture of an apple tree. Which apples have the most potential energy? Which apples have the least potential energy? Everyday Life: Energy and Roller Coasters Mechanical energy is part of everyday life. Have you ever ridden a roller coaster at an amusement park? Engineers who design roller coasters must understand the relationship between potential and kinetic energy. For example, engineers take advantage of potential energy when the coaster car is at the top of the ﬁrst hill of the roller coaster. This hill is usually the highest point on the coaster. So a car atop the hill will have the greatest potential energy. As the coaster car rolls down the hill, its potential energy is converted to kinetic energy. At the bottom of this hill, the car’s velocity is very high. The car has lots of kinetic energy. This kinetic energy propels the car up the next hill. As the car climbs this hill, its kinetic energy decreases. Where does it go? It is converted to potential energy.

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STEMscopedia: KINETIC AND POTENTIAL

ENERGY

Try Now What Do You Know? A student sets up the pendulum system shown below. He holds the pendulum at the top of its arc.

Draw the path of the pendulum after the student releases it. Label the following points in the pendulum’s path. If the total mechanical energy of the system is 100 J: • Where does the pendulum have 100 J of kinetic energy? How many joules of potential energy does the pendulum have at this point? • Where does the pendulum have 100 J of potential energy? (Label both points.) How many joules of kinetic energy does the pendulum have at each of these points? • Where does the pendulum have 50 J of potential energy? (Label both points.) How many joules of kinetic energy does the pendulum have at each of these points?

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STEMscopedia: KINETIC AND POTENTIAL

ENERGY

Try Now What do you know? A student designs a rollercoaster track to test the relationship between kinetic energy to mass and speed. The data collected is shown below. Graph the data and determine how kinetic energy is related to mass and speed. 1. The student first tested a car with 100 kilograms of mass at various speeds, and the kinetic energy was calculated. Graph the data.

Speed m/hr.

Kinetic Energy J

500

2000

4500

8000.

The student then tested four cars of different mass on the rollercoaster track. They were held to a speed of 10 miles per hour, and the kinetic energy was calculated. Graph the data.

Mass kg

Kinetic Energy J

100

500

200

1000

300

1500

400

2000

What does the graph tell us about the relationship between speed and kinetic energy?

What does the graph tell us about the relationship between mass and kinetic energy?

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STEMscopedia: KINETIC AND POTENTIAL

ENERGY

Try Now A student designs a rollercoaster track to test the relationship between potential energy to mass and height. The data collected is shown below. Graph the data and determine how potential energy is related to mass and height. 5.

The student tested four cars of different mass on the rollercoaster track. Only the force of gravity was used to create speed. Then the potential energy was calculated. Graph the data.

Mass kg

Potential Energy J

100

4,900

200

9,200

300

14,700

400

19,600

For the last test, the student tested a car with a mass of 100 kilograms at different heights. Only the force of gravity was used to create speed. Then the potential energy was calculated. Graph the data.

Height m

Potential Energy J

980

1960

2940

3920

7. What does the graph tell us about the relationship between mass and potential energy? 8. What does the graph tell us about the relationship between height and potential energy?

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STEMscopedia: KINETIC AND POTENTIAL

ENERGY

Connecting With Your Child Egg Drop Experiment This can be a messy experiment but a fun way to see how gravitational potential energy is converted to kinetic energy. As a family, you can design a compartment to safely protect an egg so that it does not break when you drop it from a height of several meters. You may want to perform this experiment outdoors. Be careful when dropping the eggs—make sure you are standing on a sturdy foundation so that you will not slip or fall. You may construct your compartments from a wide variety of materials including egg cartons, milk cartons, cereal boxes, newspapers, and bubble wrap. You will also need eggs and a meter stick or tape measure. You may need to test many different designs (and break many different eggs!) before you design a compartment that successfully protects an egg. Record which designs and materials have the most success. Suggest possible reasons why these types of material were most successful in protecting an egg. Have your child explain when the potential energy and kinetic energy were the highest and lowest during each test. After completing the experiment, you can discuss how these concepts may apply to other areas in life—for example, designing cars to safely withstand a crash or sneakers to cushion a runner’s feet. Here are some questions to discuss with students: 1. Which materials were the most successful in protecting an egg? Why do you think so? 2. Did you use friction or air resistance to your advantage in your design? 3. How do you think engineers use models and tests similar to this activity when they design safety features for cars? What would be the advantages of using models instead of actual cars? 4. Can you apply what you learned in this activity to other areas of your life?

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8P2AB Kinetic and Potential Energy

Reading Science Name:

Date:

Group:

An Amazing Ride 1

Josie and her father heard a distant rumble as they stood in the middle of the amusement park. It steadily grew louder as a screeching rush of warm air blew through their hair. They looked up to see the giant Turbo roller coaster race at top speed over their heads. They watched it zoom through the loop-the-loop. Screams and cheers echoed in the evening air as it soared around the next bend and out of sight.

“Wow! That was awesome!” Josie shouted with excitement. “Can we ride the Turbo now?”

“Sure,” her dad answered, “but I imagine we will have quite a wait.”

“That’s okay. I can explain the physics involved in the roller coaster as we wait.”

Josie’s father was impressed. He always was when Josie shared what she had learned in her science class.

The cars of the roller coaster began clicking and clanking as they ascended the first giant hill. Josie began her explanation, “Here, the chain that pulls the train of cars up the hill works against the force of gravity. The cars are acquiring potential energy, or stored energy.”

They watched as the cars reached the peak of the initial hill, and Josie continued, “At the top of this first hill, there is maximum potential energy because the train is as high as it gets.” Suddenly, a chorus of screams took them by surprise. The train of cars descended the other side of the hill picking up speed as it flew.

“What’s happening now?” her father asked.

“Well, as the train starts down the hill, the potential energy is converted into kinetic energy, or the energy of a moving object, and the train speeds up.”

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8P2AB Kinetic and Potential Energy

Reading Science 10

Josie’s father watched the coaster and proudly listened to his daughter. She explained how at the bottom of the hill there was maximum kinetic energy and little potential energy. The kinetic energy propelled the train up the second hill building up the potential energy level. As the train entered the loop-the-loop, it had a lot of kinetic energy but not much potential energy. The potential energy level continued to build as the train sped to the top of the loop. It was soon converted back to kinetic energy as the train left the loop.

They watched the roller coaster in awe as the transformation between potential energy and kinetic energy continued. Finally, the cars pulled into the station.

They got into the car, and the attendant secured their safety bar over each of them. “It’s our turn, and I’m sure this will be an amazing ride!” Josie’s father exclaimed.

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8P2AB Kinetic and Potential Energy

Reading Science 1.

In paragraph 6, what is the meaning of the word ascended? A

Go downward

Go upward

Go to the side

Go around

What word in paragraph 10 means “pushed something forward”? A

Maximum

Kinetic

Propelled

Transformed

Based on the passage, what would be another example of potential energy? A

A ball resting on a shelf.

A ball spinning on a finger.

A ball rolling on the ground.

A ball flying through the air.

Based on the passage, what would be another example of kinetic energy? A

A hammer hanging from a peg.

A hammer resting on a table.

A hammer falling off a table.

A hammer lying on a board.

Which of the following shows kinetic energy being converted into potential energy? A

A boulder rolling across the ground.

A rock being tossed high into the air.

A boulder falling off the edge of a cliff.

A rock sitting in the grass.

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8P2B Kinetic and Potential Energy

Math Connections Name:

Date:

Group:

Potential energy is energy that is stored in a system. Kinetic energy is energy of motion. Energy can be transformed from potential energy to kinetic energy, or vice versa. Energy is a quantity that can be measured. The joule is the unit used to measure energy, represented by J. Potential energy (PE)=9.8 (m/s2)×mass (kg)×height (m) (where 9.8 is the acceleration due to gravity) Kinetic energy (KE)=0.5×mass (kg)×speed2 (m/s) 1.

Delaney is getting ready to race her soapbox car down a hill. The car weighs 60 kg. Delaney weighs 35 kg. The height of the hill is 3.5 meters. Write and solve the equation for the potential energy of the car, with Delaney in it, before sliding down the hill.

After she starts the race, she is traveling at a speed of 8.9 m/s. Write and solve the equation for the car’s kinetic energy.

Dr. Francis conducted several trials to compare the kinetic energy of a hollow tube to a solid cylinder. He knows that the kinetic energy of each object is 1,152 J. The speed of the hollow tube is 12 m/s, and the speed of the solid cylinder is 8 m/s. What is the difference between the mass of the tube and the mass of the cylinder?

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8P2B Kinetic and Potential Energy

Math Connections 4.

Write a word problem involving potential energy, using the following variables: • Potential energy=16 J • Acceleration due to gravity on Earth=9.8 m/s2 • Mass=7 kg Think about what information you are missing and what the problem could be asking you to solve. Make sure to include the solution to your problem.

Write a word problem involving kinetic energy, using the following variables: • Kinetic energy=316 J • Speed=10 m/s Think about what information you are missing and what the problem could be asking you to solve. Make sure to include the solution to your problem.

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8P2B Kinetic and Potential Energy

Math Connections Meli and Jarvis are comparing potential and kinetic energy. They have a ball weighing 0.08 kg that they will drop from various heights. Help these two students by determining the kinetic energy and potential energy at each point. Use the following formulas. (Read the ball’s height from the bottom of the ball.) PE=9.8 m/s2×mass×height KE=0.5×mass×speed×speed Speed 1

a. 0 meters/second

b. 10 meters/second 0.8

c. 0 meters/second

e. 1.5 meters/second

Meters

d. 6 meters/second

0.6 0.4

E 0.2 B

Position 6.

10.

Potential Energy

Kinetic Energy

11. At what position would potential and kinetic energy be equal?

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8P2AB Kinetic and Potential Energy

Writing Science Name:

Date:

Group:

LOOK

THINK Think about everyday examples that illustrate either potential or kinetic energy.

WRITE Explain the difference between potential and kinetic energy. Be sure to • clearly state your central idea; • organize your thoughts; • develop your essay in detail; • choose your words carefully; and • use correct spelling, capitalization, punctuation, and grammar.

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8P2AB Kinetic and Potential Energy

Writing Science

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8th Grade Physical Science

8P2C

Energy Transformations within a System

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8P2C Energy Transformations within a System

Student Journal Name:

Date:

Group:

Background 1. What is energy?

2. What are the two main forms of energy? Describe them.

3. Match each form of energy to the correct description. a. chemical

a. energy of the movement of charged particles

b. electrical

b. energy of the moving particles in an object

c. mechanical

c. energy stored within the matter of the element

d. radiant

d. energy of vibrating particles

e. sound

e. energy that moves in electromagnetic waves

f. thermal g. nuclear

f. the sum of energy due to position and movement g. energy stored in substances

4. What is the law of conservation of energy?

5. What is an energy transformation?

6. What happens to the amount of energy during an energy transformation? Use the terms energy source and energy receiver.

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8P2C Energy Transformations within a System

Student Journal Part I: Plan Your Investigation 1. Question of inquiry:

2. What do you need to do to answer this question? Consider the setting, scale, and time frame that will be needed to observe the naturally occurring system to make observations and to answer the question of inquiry.

3. What are the variables that you will observe? Consider the boundaries of the naturally occurring system that will be observed.

4. What materials, equipment, and technology will you need for this investigation?

5. What safety precautions must be taken in this investigation?

6. Procedures. Record your procedure on the back of this worksheet or in your lab journal if needed.

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8P2C Energy Transformations within a System

Student Journal Part II: Implement Your Investigation Collect, Record, and Organize Your Data 1. Data Table: Energy Transformation Observations

Station

Energy Source

Energy Form and Type of Source

Energy Receiver

Energy Transformations Observed

Evidence of Energy Transformation

Hair dryer Battery powered fan Lamp Solar powered calculator Crumpling paper Paper spiral Diagrams of Natural Settings 1 Diagrams of Natural Settings 2

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8P2C Energy Transformations within a System

Student Journal Part II: Implement Your Investigation, continued Analyze Your Data 1. Describe the energy transformations that occur in a hair dryer.

2. Describe the energy transformations that occur in a battery-powered fan.

3. Describe the energy transformations that occur after you turn on a lamp.

4. Describe the energy transformations that occur in a solar-powered calculator.

5. Describe the energy transformations that occur when you crumple paper.

6. Describe the energy transformations that occur when turning on a lamp and holding a paper spiral over it.

7. Describe the energy transformations that occur when energy is transferred from the Sun to plants and to a deer.

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8P2C Energy Transformations within a System

Student Journal Part II: Implement Your Investigation, continued 8. Use your data from any station of the investigation to support the law of conservation of energy. 9. Use your data from the investigation to support the following statement: In energy transformations, energy decreases in some parts of the system and increases in other parts, but the total amount of energy remains the same.

10. Identify the energy transformations occurring in the following situations: A. A hot oven

B. A burning match

and

C. Playing a guitar

D. Melting snow E. Exploding fireworks

to to

and

11. The illustration below shows a wind turbine system. Identify the energy transformations that are occurring in the wind turbine system.

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8P2C Energy Transformations within a System

Student Journal Reflections and Conclusions 1. Was there a relationship between the variables you observed?

2. Where could errors have been made while collecting or organizing data?

3. What do you conclude about this investigation?

4. What would you do differently if you were to conduct this experiment again?

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STEMscopedia: ENERGY TRANSFORMATIONS

WITHIN A SYSTEM

Reflect

8P2C

Do you know what energy is? Scientists usually define energy as the ability to do work. That makes sense because you can’t get much work done if you’re low on energy. A good way to expand on this definition is to name different forms that energy can take. You have already learned about many of these forms: heat, light, and sound are three different forms of energy. Electricity, or electrical energy, is another form. So is mechanical energy—the energy of moving (kinetic energy) and of keeping still (potential energy). Energy is even in the particles that make up all matter—including us. The energy that holds, or bonds, these particles together is called chemical energy. Chemical energy is a form of potential energy. How can electrical energy be transformed to light energy and sound energy? How can light energy be transformed to heat energy? Take a few moments to think about all the different ways that one form of energy can be transformed into another.

Look Out Before we can learn about energy transformations, we need to clarify something. Sometimes energy may seem to come out of nowhere, or we may do something that seems to create energy. On the other hand, sometimes energy may seem to disappear, or we may do something that seems to destroy energy. In fact, none of these things actually happens. Energy is never created and never destroyed. This statement is the law of conservation of energy. The law of conservation of energy is true throughout the universe! The same amount of energy that exists now has always existed. It is constantly changing form, but it never increases or decreases.

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STEMscopedia: ENERGY TRANSFORMATIONS

WITHIN A SYSTEM

Energy transformations demonstrate the law of conservation of energy. You may wonder how the law of conservation of energy applies to the world around you. Energy allows an animal or a machine to move faster. Where does the energy of motion come from? Over time, the animal slows down. Where does the energy go? In every instance above, the energy has been transformed. When energy seems to come out of nowhere, it is usually because we are converting a stored form of energy to a form that can do work. When energy seems to be used up, it has usually been changed into a stored form that we cannot easily use.

We need the energy stored in food to climb a mountain.

When we turn on a For example, we eat food to computer it heats get energy to climb a mountain. up. Heat is a form of The energy was stored in the energy—where does it chemical bonds that make up come from? When we the food. As we move up and turn off the computer it down the mountain, this chemical cools down. Where does energy changes to kinetic energy. the heat energy go? As we move we get hot. This is our kinetic energy changing to heat energy. Climbing the mountain makes the air around us slightly warmer because heat being produced by our bodies is moving into the air.

This increase in heat energy equals the chemical energy stored in the food we ate. Energy has neither been created nor destroyed—it has simply changed form! The chemical energy (food) was transferred into kinetic energy (hiking), which was transferred into heat energy (warming air). The Sun is the source of most of Earth’s energy. Solar energy—or energy from the Sun—travels to our planet as light waves. Thus, the first benefit we get from solar energy is light. The second benefit we get is warmth: light energy transforms into heat energy. (We call heat from the Sun radiation.) Most of the energy that supports life on Earth comes from the Sun.

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STEMscopedia: ENERGY TRANSFORMATIONS

WITHIN A SYSTEM

Everyday Life: Energy Transformations in Flashlights and Windmills Most flashlights are powered by batteries. Batteries contain certain chemicals in which energy may be stored. So, the energy stored in batteries is a form of chemical energy. When we use batteries in a flashlight, the chemical energy is transformed into electrical energy. Wires in the flashlight carry the electrical energy to the light bulb. There, the electrical energy is transformed into light energy that we use to see. Electrical energy can also be generated from kinetic energy. This is the transformation that happens in windmills. Because wind is the motion of air particles, wind is a form of kinetic energy. This energy is transferred to the blades of the windmill. The motion of the blades spins a turbine. Here you can see the wires that carry electrical energy from batteries to the bulb of a flashlight.

A turbine is a machine that transforms kinetic energy into electrical energy. Underground wires carry the electricity away from the windmills to buildings where people can use it. The result is that kinetic energy enters the windmill system and electrical energy leaves the system.

What Do You Think? A system is an arrangement of parts that work together to perform a task. Flashlights and windmills are open systems. Energy enters the system in one form (from a battery or the wind) and leaves the system in another form (as light energy or electrical energy). In a closed system, energy does not leave the system, though it may change its form many times. If the energy in one part of a closed system increases, what do you think happens to the energy in another part of the system? Does it increase, decrease, or stay the same? (HINT: The universe is a closed system. As the Sun sends energy to Earth, the amount of energy on Earth increases. According to the law of conservation of energy, what must be happening to the amount of energy in the Sun?)

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Wind spins the windmill blades, which spin a turbine that generates electrical energy.

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STEMscopedia: ENERGY TRANSFORMATIONS

WITHIN A SYSTEM

Try Now What Do You Know? The boxes on the left describe a long series of energy transformations. These transformations occur in the order shown from top to bottom. The boxes on the right show different forms of energy. Draw lines between boxes to match each step on the left with the appropriate form of energy on the right. Some forms of energy may be used more than once. Some steps may show several forms of energy. Sunlight travels to Earth.

Sunlight warms air. Chemical Energy Hot air rises and cool air sinks, creating winds (convection).

As wind blows, it spins blades on a windmill.

The spinning blades produce electricity.

Electricity powers an oven to bake bread.

The particles that make up the bread have energy.

Electrical Energy

Heat Energy

Kinetic Energy

Potential Energy

Solar Energy

We eat the bread to get energy to work.

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STEMscopedia: ENERGY TRANSFORMATIONS

WITHIN A SYSTEM

Connecting With Your Child Identifying Everyday Energy Transformations With your child, look around your home and neighborhood for examples of energy transformations. It is important to understand how each transformation demonstrates the law of conservation of energy. The goal is to find as many types of transformations as possible. The transformation from electrical to other forms of energy is an easy place to start. You should be able to find electricity transformed into most of these forms of energy: • Heat (e.g., toaster, oven, range) • Light (e.g., light bulbs, computer monitor, TV screen) • Sound (e.g., radio, TV, stereo) • Mechanical (e.g., motors in fans, washing machine, blender) • Chemical (e.g., battery charger) You can see kinetic and potential energy—the two components of mechanical energy—being transformed back and forth in any pendulum system, such as a playground swing. There are many examples of chemical energy being transformed into heat, light, and kinetic and potential energy. Any movement by an animal (including people) or use of a combustible fuel transforms chemical energy into at least one other form. Remind your child that people usually want to transform energy into a specific form to do a specific kind of work, but all energy transformations produce energy in unwanted or “wasted” forms as well. The wasted energy is usually transformed into heat. For example, the heat given off by a tungsten filament bulb greatly reduces its efficiency in providing light. An electric stove burner produces some light that reduces its efficiency in providing heat. In general, heat energy is the final result of all series of energy transformations. Unfortunately, this “waste” heat dissipates into the universe and cannot be reused by humans. If you want to tabulate your study of energy-transforming devices, you could use a table like this. (An example is provided.) Energy-Transforming Device

Energy Transformed

Desired Energy Form(s)

Unwanted Energy Form(s)

Television

Electrical

Light, Sound

Heat

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STEMscopedia: ENERGY TRANSFORMATIONS

WITHIN A SYSTEM

Here are some questions to discuss with your child: 1. Compare your body temperature (almost 100°F) to a comfortable room temperature. What does this tell you about how your body transforms the chemical energy stored in food? 2. When the chemical energy in gasoline is transformed in the engine of a car, it is eventually transformed into many other forms of energy. What are some examples of the energy transformations that happen in a car? 3. Where in your home does energy appear to be created or destroyed? Use the law of conservation of energy to explain how energy is not actually created or destroyed in each instance.

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8P2C Energy Transformations within a System

Reading Science Name:

Date:

Group:

Flashlights 1

A flashlight is a portable, battery-operated device that produces light. A typical handheld flashlight consists of one or more batteries inside a compartment that forms the handle of the light. There is a switch between the batteries and the bulb. The switch controls the flow of electricity between the batteries and the bulb.

Flashlights have multiple uses. We use them during emergencies such as power outages or when our car breaks down. Our parents may use them while searching through the attic, the basement, or a dark closet. You may have used one on a camping trip or when you walked down the street while trick-or-treating. Everyone has used a flashlight at one time or another. When we do, energy is transformed.

Energy is the ability to do work or cause a change. The law of conservation of energy states that energy cannot be created or destroyed, but it can be transformed from one form to another. There are many different forms of energy, such as chemical energy, electrical energy, and light energy.

What energy transformations occur when we use a flashlight? First, the batteries contain chemical energy. This is energy that will be released during a chemical change. When chemical bonds are formed or broken, electrons are rearranged. This movement of electrons produces chemical energy. Batteries can convert stored chemical energy into electrical energy.

Electrical energy is the energy of electricity. When electrical charges move through a conductor, it is called electricity. Electricity moves through wires to places where it is needed. Then it can be converted into other forms of energy. In a flashlight, the electrical energy becomes light energy and thermal energy in the bulb.

Light energy moves by wave motion. That is, light is a form of energy caused by electromagnetic waves. It enables us to see, since objects are only visible when they reflect light into our eyes. Our eyes convert the light energy back to electrical energy. They make a nerve signal that our brain can convert into an image we see.

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8P2C Energy Transformations within a System

Reading Science Continued 7

Thermal energy is the energy of heat. When energy transforms from one form into another, a small amount is often converted into thermal energy as a by-product. The bulb transforms electrical energy into both light energy and thermal energy. It makes more light than heat, however. This is why the light bulb starts to feel warm after the flashlight has been on for a while.

The last time you looked at a flashlight, it probably looked pretty simple. You flip the switch, and light comes out. Now you know that there is a lot more happening. Energy must first be converted from chemical energy in the batteries into electrical energy. Then this energy moves to the bulb to be transformed into the light you see.

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8P2C Energy Transformations within a System

Reading Science 1.

Which of the following sentences is the best short summary for a flashlight? A

A flashlight has many uses.

A flashlight is able to create light energy, allowing us to see in the dark.

A flashlight is a necessary tool for every household.

A flashlight is a portable, battery-operated device that makes light.

Much like a battery, wood contains stored energy. What energy transformations occur when wood is burned? A

Thermal energy transforms to chemical energy and light energy.

Biological energy transforms to electrical energy and light energy.

Chemical energy transforms to thermal energy and light energy.

Chemical energy transforms to thermal energy and heat energy.

In paragraph 5, what does converted mean? A

Transferred

Changed

Transported

Current

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8P2C Energy Transformations within a System

Reading Science 4.

Identify the correct order for the energy transformations in a flashlight. A

Electrical to chemical to thermal

Light to electrical to chemical

Thermal to electrical to light

Chemical to electrical to light

In an ideal situation where no heat energy is produced, what is the relationship between the chemical energy provided by the battery and the electrical energy produced according to the law of conservation of energy? A

The chemical energy should be less than the electrical energy.

The chemical energy should be equal to the electrical energy.

The chemical energy should be more than the electrical energy.

None of the above.

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8P2C Energy Transformation within a System

Math Connections Name:

Date:

Group:

When energy flow occurs in a system, measurable changes to parts of that system may occur, such as speeding up, slowing down, or getting warmer or cooler. The total amount of energy within the system remains the same, yet the forms of energy can change. A flashlight demonstrates energy transformation when the energy in a battery changes from chemical energy to electrical energy to light energy. The data below shows the results from an investigation designed to see whether different brands of batteries store different amounts of chemical energy. To complete the investigation, 10 flashlights with new Bear lithium batteries and 10 flashlights with new Rotar nickel batteries were turned on. The investigators observed the amount of time each flashlight produced light energy and recorded when each flashlight turned off. Flashlights Powered by Batteries Trial number

Bear lithium (hours)

2.5

3.7

2.2

4.1

2.8

4.7

0.5

Rotar nickel (hours)

6.1

5.7

2.4

3.7

3.2

4.8

4.33

3.6

2.8

Using the data above, create a box and whisker plot by following the steps below. 1.

Order each set of data from least to greatest, and calculate the median (known as Q2) number of hours. • Bear lithium: • Rotar nickel:

Divide the data in half, and find the medians of the first half and the second half.

Bear lithium

Rotar nickel

First half:

Sub-median (known as Q1):

Second half:

Sub-Median (known as Q3):

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8P2C Energy Transformation within a System

Math Connections For future reference, fill in the chart below, using data from the previous page. Bear lithium

Rotar nickel

Minimum time Maximum time Median (Q2) Sub-median (Q1) Sub-median (Q3) Use the number line below to complete steps 3 and 4 for each of the battery types. (Both box and whisker plots will use the same number line.)

0.5

1.0 1.5

2.0 2.5

3.0 3.5

4.0 4.5 5.0 5.5

6.0 6.5

7.0

Mark off the minimum, maximum, Q1, Q2, and Q3 values on the number line. (Use the example below to help you.)

Draw a box from Q1 to Q3, and then extend the “whiskers” to the maximum and minimum values.

Describe the distribution of the two graphs. Consider the interquartile range (the length of the boxes) of the data and where the median lies.

What are the mean, median, mode, and range of the data for each battery type? Bear lithium

Rotar nickel

Mean Median Mode Range 7.

What conclusions can you draw about the differences in the brands of batteries?

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8P2C Energy Transformations within a System

Writing Science Name:

Date:

Group:

LOOK

THINK Think about energy transformations.

WRITE Describe all the energy transformations that take place in a car, and explain how these transformations exemplify the law of conservation of energy. Be sure to • clearly state your central idea; • organize your thoughts; • develop your essay in detail; • choose your words carefully; and • use correct spelling, capitalization, punctuation, and grammar.

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8P2C Energy Transformations within a System

Writing Science

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8th Grade Physical Science

8P2D

Heat Transfer and Molecular Motion

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8P2D Heat Transfer and Molecular Motion

Student Handout Name:

Date:

Where in the picture do you see heat moving?

Conduction is a direct type of heat transfer where two objects are in contact with each other. Where in the picture do you see this happening? (Label and explain.)

Convection is a type of heat transfer that happens in liquids and gases where the movement of heat occurs through a current. Where in the picture do you see this happening? (Label and explain.)

Radiation is a type of heat transfer that happens when heat energy travels through space or the atmosphere. Where in the picture do you see this happening? (Label and explain.)

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8P2D Heat Transfer and Molecular Motion

Student Journal Name:

Date:

Group:

Part I: Temperature and Thermal Energy Transfer 1. What is temperature?

2. What is thermal energy?

3. How does the temperature of the ice chip compare to the temperature of your hand?

4. In the example of holding ice, what evidence indicates that thermal energy transfers?

5. In the example of holding ice, where does the thermal energy come from? 6. In the example of holding ice, where does the thermal energy go? 7. Using the example of holding ice, explain when the thermal energy transfer stops.

8. Can you summarize how thermal energy moves from one object to another? Thermal energy always moves from substances with with

temperatures.

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temperatures to objects

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8P2D Heat Transfer and Molecular Motion

Student Journal Part II: Conduction 1. Data Table: Melting Wax Chips by Conduction Chip

Time

2. Use the drawing below to illustrate what you observed. Use labels and arrows to identify the transfer of energy.

3. What type of heat transfer occurs along the aluminum foil? 4. What pattern was evident in the movement of thermal energy?

5. What evidence did you observe that showed heat transfer?

6. In your own words, define conduction.

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8P2D Heat Transfer and Molecular Motion

Student Journal Part III: Convection 1. Draw a lava lamp and show what happens to the blob you observe. Use arrows and labels to identify the parts of the lamp and the heat transfer.

2. Draw the can of cooking fuel and what you observed on the wall or board. Use arrows and labels to identity the setup and the heat transfer. Be sure to show where the heat near the ceiling went.

3. In which state of matter did the transfer of thermal energy occur in the lava lamp? 4. In which state of matter did the transfer of thermal energy occur when you observed the cooking fuel? 5. When observing the cooking fuel demonstration, the shadow eventually disappeared. What happened to the heat in this system?

6. In your own words, define convection.

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8P2D Heat Transfer and Molecular Motion

Student Journal Part IV: Radiation 1. Record your data in the tables below. Radiometer at 20 cm

Radiometer at 15 cm

Radiometer at 10 cm

Did the vane move?

Beginning temperature

Temp. after 3 minutes

2. Graph the ending temperatures for each location of the radiometer.

3. Fill in the blanks using the data you recorded. a. As the distance increased, the temperature b. As the distance decreased, the temperature

. .

4. In your own words, define radiation.

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8P2D Heat Transfer and Molecular Motion

Student Journal Reflections and Conclusions 1. Identify the type of energy transfer (conduction, convection, or radiation) for each description below. Example of Heat Transfer

Conduction, Convection, or Radiation

Hot chocolate is stirred with a spoon and the spoon gets hot. The Sun warms your skin on a cold day.

Macaroni rises and falls in a pot of heated water.

You burn your hand by touching a hot stove.

Warming your feet in front of a fire.

Hot air balloon rises. The air near the ceiling in a room is warmer than the air near the floor. The material in a lava lamp rises and falls. The sidewalk increases in temperature on a sunny day. The sidewalk burns your bare feet in the summertime.

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8P2D Heat Transfer and Molecular Motion

Student Journal Reflections and Conclusions, continued 2. When particles of matter are in direct contact, conduction of thermal energy occurs in which states of matter?

3. When particles of matter are in direct contact and movement occurs in the substance due to convection, thermal energy transfers in which states of matter?

4. Which states of matter are required for energy transfer to occur when radiant energy is the source?

5. Use your data from Part II to draw a conclusion: In thermal energy transfer by conduction, how does heat move between objects that are touching?

6. Use your data from Part III to draw a conclusion: In thermal energy transfer by convection, what is the pattern of heat transfer through fluids?

7. Use your data from Part IV to draw a conclusion: In thermal energy transfer by radiation, how does distance from the thermal energy source affect the amount of thermal energy transfer occurring in a substance?

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STEMscopedia: HEAT TRANSFER AND

MOLECULAR MOTION 8P2D

Reflect What kinds of things flow? Water flows in rivers. Air flows as winds blow across the planet. What about heat? Water and air are fluids, which means they are substances. It is easy to imagine how they flow. Heat is not a substance; it is a form of energy. However, heat does move from place to place. How do you think heat moves or “flows”? In this companion you will learn three different ways. Heat is different than thermal energy. Often people talk about heat and thermal energy as though they are identical. However, there is an important difference. Heat is thermal energy that is being transferred from one place to another. So what is thermal energy? All matter is made of tiny particles, much too small to be seen. These particles are always in motion, and motion is a form of energy. An object’s thermal energy equals the total energy of all its moving particles. Heat transfer happens when some of this energy moves from one object to another object. Energy is never created and never destroyed; it simply changes form. This is the law of conservation of energy. Most forms of energy are eventually transformed into thermal energy, which then flows away into nature. This is what we mean when we say that a system loses energy as heat. In most cases, we cannot capture and reuse this energy. For example, a fire gives off heat as it burns. Eventually, the fire burns itself out. Its energy has not been destroyed, even though we can no longer use it. It has simply been transformed into heat.

Look Out Temperature does not measure heat or thermal energy. Temperature measures the average energy of motion of an object’s particles. Thermal energy is a measure of the total energy of motion of an object’s particles. Suppose a glass of water and a lake of water have the same temperature. The average water particle in the lake and the average water particle in the glass have the same energy of motion. However, the lake has much greater thermal energy because it contains many more particles.

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A thermometer measures the average energy of particle motion in an object.

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STEMscopedia: HEAT TRANSFER AND

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Thermal energy is transferred by three main processes. How does thermal energy move as heat from one object to another? Think of the different ways you experience heat. You feel heat as the Sun shines on you and as you sit by a fire. You can use a microwave oven to heat cold food. If you place a pot of water on a hot stove, you can see the water begin to boil. The stove can burn you if you touch it. Each of these processes involves the transfer of heat. How are they similar? How are they different? Thermal energy can transfer by conduction. Try to imagine the tiny, constantly moving particles that make up an object. In a solid object, these particles vibrate back and forth without changing position. Now imagine placing a metal frying pan on a hot burner on a stovetop. The burner transfers heat to the pan, and the pan gets hot. The bottom of the pan gets hot before the pan’s handle. Why does this happen? Before the pan is placed on the burner, its particles are moving at the same average speed. The whole pan is at the same temperature. The hot burner is at a much higher temperature. In other words, the particles that make up the burner are moving at a greater average speed and therefore have greater thermal energy.

When the burner is turned on, the handle of the pan will get hot last.

When the pan is placed on the stove, the burner’s particles collide with the particles in the bottom of the pan. Some of the energy in the burner’s particles moves to the pan’s particles. As a result, the particles in the bottom of the pan begin to move faster. These particles collide with nearby particles in the pan, which collide with other particles. Each collision passes energy from particles moving quickly to particles moving slowly. In this way, the energy spreads throughout the pan and finally reaches the handle. This process is called conduction. Conduction is the transfer of heat that happens when particles collide with each other. It can happen in solids, liquids, and gases. Thermal energy can transfer by radiation. You don’t actually have to touch a hot frying pan to know it is hot. If you hold your hand a few inches from the pan, you can feel the heat. How is it possible to feel heat without touching a hot object? The answer is that hot objects emit radiation. Radiation is energy that travels as electromagnetic waves. You do not need to touch an electromagnetic wave to feel it. Sunlight is another form of radiation. Light from a light bulb and heat from our bodies are also examples of radiation. Microwaves use radiation to heat food.

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STEMscopedia: HEAT TRANSFER AND

MOLECULAR MOTION

Like light, heat waves can travel through air—they can even move through empty space! Think about standing around a campfire or in front of a fire in a fireplace. Most of the heat you feel reaches you by radiation. If a large group of people is gathered around a campfire, only the people in the front row will feel the heat. If someone is standing in front of you, they will block the heat from reaching you. The campfire warms people by transferring heat through radiation.

Thermal energy can transfer by convection. Let’s talk more about the frying pan. Many kitchen stoves have hoods several feet above the burners. The purpose of the hood is to carry smoke and other fumes away from the stovetop. But why is the hood above the stove? Why isn’t it on the side? Similarly, why are chimneys above fireplaces? You never see a chimney next to or beneath a fireplace. The answer is that hot air rises. This brings us to the third type of heat transfer: convection. During conduction, heat energy moves between particles that touch. During convection, however, the particles themselves move. This happens only in liquids and gases because the particles in solids are stuck in place and cannot move. Particles that move more quickly are “hotter.” As hot particles move into a new area, they increase the area’s thermal energy. This makes the area hotter as well.

In solids (left), particles are stuck in place. In liquids (center) and gases (right), particles flow easily around each other. Note that a drop of liquid contains more particles than an equal amount of gas. Particles in gases have more energy and move greater distances.

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STEMscopedia: HEAT TRANSFER AND

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As particles increase their speed, they also move farther apart. As the particles in a group move apart, the whole group becomes lighter than the surrounding, “colder” particles. As a result, the “hotter” particles rise. As particles rise, they gradually lose energy, cool, and sink. This creates a cycle of rising and sinking particles. This circular motion is called a convection cycle.

Hot air balloons rise because of convection. A flame heats air particles inside the balloon. The heated air rises because it is lighter than the surrounding air outside the balloon. As the heated air rises, the balloon rises as well.

As sunlight heats the ground, air above the ground warms and rises. As the air rises it cools and sinks back to the ground, where it heats and rises again. This results in a convection cycle—and causes wind. Also, convection cycles in seawater power ocean currents.

Heat flows in a predictable pattern. Remember this important rule about heat flow: When objects of different temperatures are in contact, heat always moves from the warmer to the cooler object until their temperatures are equal. If you accidentally touch a hot burner, the heat moves from the burner to your hand because your hand is cooler. What happens if you touch a piece of ice? Heat moves from your hand, which is warmer, to the ice, which is cooler. In other words, your body loses heat—that is why ice feels cold.

What Do You Think? A metal hammer has been lying in the sunlight on a hot day. When you pick up the hammer, it feels very warm in your hand. Explain the different ways that heat is moving in this situation.

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STEMscopedia: HEAT TRANSFER AND

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Getting Technical: How a Refrigerator Works A refrigerator relies on the properties of gases to stay cool. Inside a refrigerator is a part called a compressor and another part called an expansion valve. Metal coils connect these two parts. Inside these coils is a substance called tetrafluoroethane (HFC). Depending on the amount of pressure put on it, HFC can be either a liquid or a gas. As the HFC flows through the compressor, it is squeezed into a gas. This causes the HFC to heat up. The heat is released into the air outside the refrigerator. The HFC then flows through the expansion valve. There, the pressure is decreased and the HFC expands back into a liquid. When this happens, it gets very cold. The cold liquid flows through the refrigerator, cooling it.

This is the compressor of a large industrial refrigeration unit. Kitchen refrigerators have a smaller part that performs the same function.

This process requires a lot of energy. Most refrigerators are powered by electric motors.

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What Do You Know? A pot is placed on a gas flame, and the water inside the pot begins to boil. Heat moves in three different ways, as shown in the image below.

Which part of the image shows conduction? Which part shows convection? Which part shows radiation? Write your answers below. .

A. Heat is carried away from the pot in all directions. This shows .

B. Warm water rises within the pot. This shows C. Heat moves from the flame to the pot’s bottom. This shows

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STEMscopedia: HEAT TRANSFER AND

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Connecting With Your Child Comparing Thermal Insulators and Conductors For this experiment, you and your child will need eight identical plastic bottles filled with water. (You can complete the activity with fewer water bottles, but it will take longer.) Place a thermometer in one bottle, and then put all the bottles in the refrigerator. Wait about an hour for all the bottles to cool to the refrigerator’s temperature; then, remove the bottles and record the temperature using the thermometer in one bottle. Next, your child should follow this procedure: • Wrap four bottles in these materials (one per bottle): • A wool sweater • A cotton T-shirt • Aluminum foil • Bubble wrap • Pour the water from one bottle into a metal container. • Pour the water from one bottle into an insulated container. • Place one bottle in an ice chest. • Leave one bottle sitting at room temperature. After 30 minutes, record the temperature of the water in each container. List the materials from lowest temperature to highest temperature. Which material prevented the most heat loss? (This material is a good insulator or a poor conductor.) Which material prevented the least heat loss? (This material is a good conductor or a poor conductor.) Your child should note that aluminum foil was the best conductor. Explain that aluminum is a metal, and most metals are good conductors. Here are some questions to discuss with your child: 1. If you want to stay warm on a cold day, should you wear a wool sweater or a cotton shirt? Why? 2. What are some things made of insulating materials to prevent heat flow? 3. What are some things made of conducting materials to encourage heat flow? 4. If you place the bottles of water in the sunlight, the water will become warmer. Which process of heat transfer warms the water: conduction, convection, or radiation? Explain. 5. If you pour the water into a metal pot and heat it on a stove, the water will become warmer. Which process of heat transfer warms the water? Explain.

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8P2D Heat Transfer and Molecular Motion

Reading Science Name:

Date:

Group:

Thermal Transformations 1

Long ago, scientists believed that heat was an invisible fluid. In the late 1700s, Benjamin Thompson, an American inventor as well as a physicist, showed that heat is a form of energy. Energy is a natural force that can do work or cause change. Energy cannot be made or destroyed. It can, however, be transferred from one object to another. This is known as the conservation of energy. Thermal energy is one of these types of energy. Thermal energy is the energy of heat that transfers from hotter objects to colder objects. It will continue to move from one object to another until all objects have reached the same temperature. Thermal energy can move in three different ways: by conduction, convection, and radiation.

Conduction is the transfer of heat that occurs when two objects of different temperatures touch. Conduction occurs in solids such as metals. For example, the handle of a metal spoon left in a hot bowl of soup warms up as the molecules at the heated end move faster and collide with other molecules getting them moving. The heat travels through the metal spoon, which is a good conductor of heat. Pretty soon, the handle of the spoon is just as hot as the end of the spoon in the soup.

In liquids and gases, convection is usually the most efficient way to transfer heat. Convection occurs when substances of different temperatures mix. When a liquid or a gas is heated, it expands. It rises because it has become less dense. The cooler, denser liquid or gas sinks. Convection is responsible for making macaroni rise and fall in a pot of heated water. The warmer portions of the water are less dense and therefore they rise. Meanwhile, the cooler portions of the water fall because they are denser. Movements like this in liquids or gases are called convection currents.

Both conduction and convection require a medium to transfer heat. Radiation is the transfer of heat through electromagnetic waves that move through empty space. Sunlight is a form of radiation that is radiated through space to our planet without the aid of solids or fluids. We feel the heat from the Sun even though we are not touching it. Imagine it! The Sun transfers heat through 93 million miles of space. There are no solids (like a huge spoon) touching the Sun and our planet. There are no fluids (like a pot of water) in space. Radiation brings heat to Earth. Let’s think of it on a smaller scale. When you stand near a campfire, you can feel the heat, but you are not touching the fire. The heat is transferring by radiation.

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8P2D Heat Transfer and Molecular Motion

Reading Science 1.

Which of the following is a FALSE statement? A

Heat moves through solids by conduction.

Molecules move faster in warmer substances.

Warm water is denser than cold water.

Heat moves through liquids and gases by convection.

What is an example of conduction? A

Touching a stove and burning your hand

An old-fashioned radiator

Heat from a fire

Batteries

What is an example of convection? A

A heater in a fish tank warming the water at the bottom of the tank

Batteries in a flashlight converting chemical energy into light

Touching a stove and burning your hand

Warming up next to a fire on a cold night

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8P2D Heat Transfer and Molecular Motion

Reading Science 4.

What is an example of radiation? A

Heat from a fire

An old-fashioned radiator

Batteries

Touching a stove and burning your hand

The word medium is used in paragraph 4. Which of the following could be the definition of medium? A

A vacuum

Empty space

Anything with molecules; matter

The absence of molecules in an area

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8P2D Heat Transfer and Molecular Motion

Math Connections Name:

Date:

Group:

Thermal energy can transfer within a system by means of conduction, convection and/ or radiation. Thermal energy will continue to move in a predictable pattern from a warmer site to a cooler site until all sites have reached the same temperature. Types of Thermal Energy Transfer Type of Transfer

Definition

Example

Convection

transfers thermal energy through circular motion caused by heating and cooling in fluids

• boiling soup • a lava lamp

Conduction

transfer of thermal energy that occurs in solids, liquids and gases when two substances of different temperatures touch

• metal cup containing hot cocoa • ironing clothes

Radiation

transfer of thermal energy by electromagnetic rays

• energy emitted by a light bulb • energy from the Sun • body heat

In the following experiment a pan of ice was placed on a hot plate set for 100°C. Every 3 minutes the temperature of the water was recorded in the chart below. Minutes

Temp of Water in °C

100

Which type of thermal energy transfer occurred during the experiment?

Create a scatterplot of the the data on the graph below. Label the graph with a title and correct variables on each axis.

100 80 60 40 20 0 0

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8P2D Heat Transfer and Molecular Motion

Math Connections 3.

What was the rate of change in the temperature of the water per minute between 0 and 18 minutes?

Create a function to describe the rise in temperature of the water from 0 to 18 minutes in terms of degrees celcius.

Create a function to describe the temperature after 21 minutes.

When did the water achieve thermal equilibrium? Why did the temperature stop rising?

Think about what would happen if the water continued to boil for 45 minutes. Describe the particle movement and what would occur in the water.

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8P2D Heat Transfer and Molecular Motion

Writing Science Name:

Date:

Group:

LOOK

THINK Think about what happens when ice melts.

WRITE Explain the meaning of thermal energy transfer, and give specific examples of conduction, convection, and radiation.

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8P2D Heat Transfer and Molecular Motion

Writing Science

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8th Grade Physical Science

8P3A

Speed, Distance, Velocity, and Acceleration

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8P3A Speed, Distance, Velocity, and Acceleration

Student Journal Name:

Date:

Group:

Background 1. What is speed?

2. Show the formula and calculate the speed of a car that traveled 100 km in 2 hr.

3. What is velocity?

4. Show the formula and calculate the velocity of a runner that runs south 10 km in 1 hr.

5. What is acceleration?

Read the description of Juan’s motion during a race. When the race started, Juan’s speed increased until he was running at a constant speed of 6 m/s. After 17 seconds, Juan’s velocity changed to 5 m/s to the northwest and remained constant for 20 s. Finally, Juan’s velocity changed to 7m/s north, and he crossed the finish line. Juan then walked back to the starting line at a slow constant speed of 1 m/s. 6. What are examples of speed from the description of Juan’s race?

7. What are examples of velocity from the description of Juan’s race?

8. What are examples of acceleration from the description of Juan’s race?

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8P3A Speed, Distance, Velocity, and Acceleration

Student Journal Part I: Plan Your Investigation 1. My Question of Inquiry:

2. What is the setting and scale of this investigation?

3. What is the time frame of this investigation?

4. What will you observe in this investigation?

5. Tools, equipment, and technology: Identify what you need to complete the investigation and why. Use additional paper as necessary.

6. List all safety precautions that must be taken.

7. Procedure: Outline the steps of your procedure. Use additional paper as necessary.

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8P3A Speed, Distance, Velocity, and Acceleration

Student Journal Part II: Implement Your Investigation Collect, Record, and Organize Data Record distance data for each walk in the tables below. After you complete the four walks, you will calculate the speed and velocity for each interval of the walk and add to the data table. Walk 1

Walk 2

Distance

Time

Speed for This Interval

Velocity for This Interval

Distance

Time

Speed for This Interval

Velocity for This Interval

0 m/s

Velocity for This Interval 0 m/s

10 s

15 s

20 s

Walk 3

Walk 4

Distance

Time

Speed for This Interval

0 m/s

Velocity for This Interval

Distance

Time

Speed for This Interval

0 m/s

10 s

15 s

20 s

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8P3A Speed, Distance, Velocity, and Acceleration

Student Journal Part II: Implement Your Investigation, continued

Speed (m/s)

Distance (m)

Analyze Data Use your data to create distance versus time graphs and speed versus time graphs. Walk 1 Distance v. Time Walk 1 Speed v. Time

Time (s)

Legend

Legend Walk 2 Speed v. Time

Speed (m/s)

Distance (m)

Walk 2 Distance v. Time

Time (s) Legend 210

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8P3A Speed, Distance, Velocity, and Acceleration

Student Journal Part II: Implement Your Investigation, continued Analyze Data, Continued Walk 3 Speed v. Time

Speed (m/s)

Distance (m)

Walk 3 Distance v. Time

Time (s)

Legend

Legend Walk 4 Speed v. Time

Speed (m/s)

Distance (m)

Walk 4 Distance v. Time

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Time (s) Legend 211

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8P3A Speed, Distance, Velocity, and Acceleration

Student Journal Part II: Implement Your Investigation, continued Analyze Data 1. Describe the speed, velocity, and acceleration of the walker in Walk 1.

2. Compare the distance versus time graph and the speed versus time graph for Walk 1.

3. Describe the speed, velocity, and acceleration of the walker in Walk 2.

4. Compare the distance versus time graph and the speed versus time graph for Walk 2.

5. Describe the speed, velocity, and acceleration of the walker in Walk 3.

6. Compare the distance versus time graph and the speed versus time graph for Walk 3.

7. Describe the speed, velocity, and acceleration of the walker in Walk 4.

8. Compare the distance versus time graph and the speed versus time graph for Walk 4.

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8P3A Speed, Distance, Velocity, and Acceleration

Student Journal Part II: Implement Your Investigation, continued Analyze Data 9. Which graph(s) shows movement at the highest rate of speed? How do the graphs show you this?

10. Which graph(s) shows a change in speed? Explain.

11. Which graph(s) shows the walker changing direction? How do you know?

12. Which graph(s) shows the walker stopping? How is this shown in the graphs?

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8P3A Speed, Distance, Velocity, and Acceleration

Student Journal Reflections and Conclusions 1. Define the following in your own words. (a) Speed (b) Velocity (c) Acceleration 2. How is speed shown on a distance v. time graph?

3. How can you determine if an object is accelerating by looking at a distance v. time graph?

4. How can you determine if an object is accelerating by looking at a speed v. time graph?

Use the graphs below to answer questions 5–8.

Time

Graph D Speed

Distance

Distance Time

Graph C Speed

Graph B

Graph A

Time

5. Which graph(s) demonstrate(s) an object traveling at a constant speed for the entire period of time?

6. Which graph(s) demonstrate(s) an object changing velocity (i.e. changing speed or direction)?

7. Which graph(s) demonstrate(s) an object stopping for a period of time? 8. Which graph(s) demonstrate(s) an object accelerating for the entire period of time?

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STEMscopedia: SPEED, DISTANCE, VELOCITY,

AND ACCELERATION

8P3A

Reflect Look at the picture of people running across a field. What words come to mind? Maybe you think about the word speed to describe how fast the people are running. You might think of the word acceleration to describe the way in which the runners gain speed. Some people might even use the word velocity to explain the direction in which the people are running. But what do these words actually mean? They all relate to motion, but what is the difference between speed, acceleration, and velocity? Frame of Reference When discussing terms that relate to motion, it is important to begin by discussing what is called a frame of reference. Motion describes a change in an object’s position, direction, or location. Speed, velocity, and acceleration all describe the motion of an object relative to some other point. This point is the frame of reference. For example, suppose you are sitting in a motionless vehicle and looking out the window at another motionless vehicle. One of the vehicles starts to move, and for an instant, you cannot tell which vehicle is moving. The experience is especially confusing in the case of side-by-side trains. You might resolve the confusion by looking across to the windows on the other side of the train car and seeing the train station. In this situation, the train station is the frame of reference. Without a frame of reference, it is impossible to determine which of two objects is moving. They are simply moving relative to each other. In general, our frame of reference is Earth’s surface. If you are sitting in a chair, you are motionless because Earth’s surface is motionless. But, what happens if you choose the solar system as your frame of reference? Now, you are traveling in orbits around Earth’s axis as you travel around the Sun in a larger orbit.

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When looking at a passing train from the window of another train, it is hard to tell which train is moving unless you have a frame of reference.

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STEMscopedia: SPEED, DISTANCE, VELOCITY,

AND ACCELERATION

Speed Speed is used to measure how fast an object moves. It is calculated by the distance an object travels divided by the time it takes the object to travel that distance. The formula for speed is s=d/t, where s represents speed, d represents distance, and t represents time. In the United States, speed is usually measured in miles per hour (mph) or feet per second (ft/s.) The “/” symbol represents the word “per.” For scientific purposes, we will use metric units for distance: meters (m) and kilometers (km.) For perspective, 1 m/s=2.24 mph, and 1 km/hr=0.62 mph. Motion often occurs at varying speeds. In these situations, average speed can be calculated if the distance traveled and the time elapsed are known. Suppose you rode in a car across town in stopand-go traffic. The distance traveled was 40 km, and the trip took 2 hr. The average speed of the car was 40 km divided by 2 hr, or 20 km/hr. Average speed of car =distance/time =40 km/2 hr =20 km/hr Graphs are often used to represent speed. Distance is typically plotted on the y-axis and time is plotted on the x-axis. The steeper the line on the graph, the greater the speed of the object. A horizontal line represents an object that has stopped moving since its distance on the graph does not change. Take a look at the graph below. It represents the speed of a car traveling through a city. The steepest part of the line is between points D and E. This represents the time at which the car was moving at the greatest speed.

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STEMscopedia: SPEED, DISTANCE, VELOCITY,

AND ACCELERATION

What Do You Think? If a car is moving at a constant speed of 100 km/hr, how far does the car travel each hour? If the car moves for three hours, what is the total distance it will travel? You can check your answer on page 219. Velocity Velocity is measured in the same units as speed, but the direction of motion is also given. Direction may be described, for example, as north, south, east, west, left, or right. Velocity is said to be a vector quantity, meaning both magnitude (distance from one point to another) and direction are specified. Speed is said to be a scalar quantity, meaning it is a number with no indication of direction. An arrow on a grid often represents a vector quantity. The length of the arrow indicates the magnitude, and the point of the arrow shows the direction; the vector on the graph on the right shows that a car is traveling northeast at 80 km/hr.

Look Out If the speed of a moving object changes, its velocity also changes. The reverse statement, however, is not true. Velocity can change while speed remains unchanged. This is true because a change in direction at constant speed is a change in velocity. A car turning a corner at constant speed is changing its velocity. Acceleration Acceleration is the rate of velocity change during a certain period of time. Since the unit for velocity has time in the denominator (m/s for example), and velocity is divided by units of time (s for example) to calculate acceleration, the unit of time is given in the denominator twice. So, the units for acceleration are m/s2, which is stated as “meters per second per second” or “meters per second squared.” In everyday usage, acceleration is usually thought of as change in speed. However, it is important to remember that acceleration is change in velocity. So, even if an object is moving at a constant speed, if it changes direction, the object is accelerating.

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STEMscopedia: SPEED, DISTANCE, VELOCITY,

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Most people think of acceleration as an increase in speed. However, slowing down is also considered acceleration. In everyday terms, this is called deceleration, but the scientific term is negative acceleration. An object traveling in a perfect circle at constant speed has uniform acceleration, called radial acceleration. The object is constantly changing direction as it travels around and around. Acceleration can be calculated if the change in velocity and time for the velocity to change are known. For example, if a car moving south accelerates from 25 m/s to 50 m/s over a time of 10 seconds, the change in velocity is 25 m/s (50 m/s – 25 m/s) and the time period is 10 seconds. Divide 25 m/s by 10 s, and the acceleration of the car is 2.5 m/s2. Acceleration of car =change in velocity/time period of velocity change =(50 m/s – 25 m/s) /10 s =25 m/s /10 s =2.5 m/s2 south

What Do You Think? The graph on the right shows the acceleration of a student as she walked home from soccer practice. During which time frame did the student travel with positive acceleration? When did she travel with negative acceleration? You can check your answer on page 219. Getting Technical: Escape Velocity Rockets were invented long before the first satellite was launched into space. Why was this the case? The answer has to do with escape velocity, which refers to the minimum velocity an object must reach before it can break free of Earth’s gravitational pull. An object traveling at escape velocity can orbit Earth at the same velocity or head off into space. Escape velocity for Earth is approximately 11,100 m/s (25,000 mph) in a direction away from Earth’s surface. This means that an object, like a rocket, must move away from Earth’s surface at a velocity of at least 11,100 m/s in order to travel into space. The main factor that postponed space exploration was the amount of time it took to develop a rocket that could exert enough force to accelerate an object to such an enormous velocity. In 1959, the Russian satellite, Luna 1, was the first object made by humans to attain escape velocity. This was the beginning of the space age!

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This stamp commemorates Luna 1, the first humanmade object to reach escape velocity.

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STEMscopedia: SPEED, DISTANCE, VELOCITY,

AND ACCELERATION

What Do You Think? Check your answers to the previous problems: 1. A car moving at a constant speed of 100 km/hr (km per hr) travels 100 kilometers each hour. In 3 hours, the car will have traveled 100 km/hr × 3 hr = 300 km. 2. The student traveled with positive acceleration from 0–4 min; during this interval, her speed continually increased. The student traveled with negative acceleration from 4–7 min; during this interval, her speed continually decreased. What Do You Know? The chart below lists examples of different types of motion. Choose one of the following terms that best describes each example. Note there may be more than one possible answer, but you may only use each word once: • Negative acceleration • Velocity • Average speed • Constant speed Motion

Matching Description

A truck traveled southward on a road at 60 km/hr. A student rode her bike to a friend’s house. She traveled 30 meters in 5 minutes and stopped one time along the way. A dog ran at a speed of 5 m/s for 5 min. Then, the dog changed its speed to 3 m/s. A car traveled at the same speed of 110 km/hr around an oval track.

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STEMscopedia: SPEED, DISTANCE, VELOCITY,

AND ACCELERATION

Connecting With Your Child Design a Velocity Experiment To help your child learn more about speed, velocity, and acceleration, work together to design an experiment that can be used to test factors that affect an object’s velocity. Begin by brainstorming ideas for the experiment, focusing on everyday equipment you can use. Develop a question that you and your child will attempt to answer. Suggestions include, “How does the mass of a toy car affect its velocity?” or “How does the surface of a ramp affect the velocity of a rubber ball?” Once you have decided on a question, make a list of materials needed and have your child make a prediction. For example, if you are going to test the effect of mass on velocity, your child should predict how greater mass will affect velocity. Next, gather the materials and set up the experiment. Make sure you are only changing one variable in your experiment. For instance, if you are testing the effect of mass on velocity by using toy cars and a ramp, make sure that the only thing you change in the experiment is the mass of the car. Keep the ramp and all other factors the same. If possible, conduct multiple trials, and find the average velocity for each mass you test. Once you have completed the experiment, have your child write a conclusion, such as, “Objects with greater mass move with greater velocity.” Here are some questions to discuss with students after the experiment: 1. How did you calculate the velocity of the objects in your experiment? 2. What other factors could you test to determine their affect on velocity? 3. How might these kinds of experiments with velocity be useful to engineers and other scientists?

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8P3A Speed, Distance, Velocity, and Acceleration

Reading Science Name:

Date:

Group:

Watch Your Velocity! 1

Motion of an object can be determined by its speed, velocity, and/or acceleration. The distance an object travels over a certain period of time is its speed. An object’s speed and the specific direction it is traveling is its velocity. A change in an object’s velocity over a specific period of time is called acceleration.

To measure velocity, you must know the speed and direction of a given object. Imagine riding in the car with your family taking a trip to the mall. As you head down the street, your mother applies pressure to the gas pedal to move the car forward. The car that was previously moving at 25 miles per hour is now proceeding ahead at 45 miles per hour. Pushing the gas pedal causes the car to accelerate, or speed up. Because the constant rate of speed or the velocity of the car increases, your family will get to your destination much faster. In this case, the velocity and the acceleration of the car are in the same direction.

Velocity can be constant, or it can change. Once your family reaches the main highway, your car is stuck in weekend traffic. Because of this, your mother now applies pressure to the brake pedal causing the car to slow down, or decelerate. The car slows back down from 45 miles per hour to 25 miles per hour. In this case, the velocity of the car and its acceleration are in opposite directions. When you accelerate or decelerate, you change your velocity by a specific amount over a specific amount of time.

For motion to be described accurately, it needs to be described relative to a point of reference. A point of reference is just an object or position near the object in motion. During your trip to the mall, there are several ways to describe your motion. Assume that you are sitting in the car and it is moving at a speed of 25 miles per hour. Here, the ground is your point of reference. Both you and the car are moving 25 miles per hour relative to the ground. If the car is the point of reference, then you are not moving relative to the car. If you pass a car that is driving 20 miles per hour, then you are moving 5 miles per hour relative to the other car. Three different points of reference result in three different descriptions of your motion. For this reason, it is important to indicate your point of reference when measuring velocity. Most often, speed is determined with respect to the ground. However, there are instances when the speed or velocity may be determined with respect to an object or an observer.

Remember, you need to know two things to truly describe how fast an object is going. You need to know its velocity and the point of reference. How else can the officer tell if your mother is speeding?

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Reading Science 1.

The term acceleration was used in paragraphs 1–3. Which of the following could be a definition of acceleration? A

A change in an object’s speed

An object at rest

A change in an object’s direction

Both A and C

In which of these three situations is the object accelerating? 1. A trash truck takes off from the curb. 2. A book rests on a shelf. 3. An airplane banks to circle around the airport.

Only 1

Only 2

Both 1 and 3

1, 2, and 3

When a police officer is trying to decide if a driver is speeding, what is his point of reference? A

The ground

His car

The speed limit

All of these

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8P3A Speed, Distance, Velocity, and Acceleration

Reading Science 4.

Which words help you to determine the meaning of the word decelerate in paragraph 3? A

Velocity can be constant, or it can change

Applies pressure to the brake pedal

The car to slow down

Stuck in weekend traffic

A bowling ball moves 18 meters every 2 seconds down the lane at a bowling alley. What is the speed of the bowling ball? A

18 meters per second

9 meters per second

2 meters per second

36 meters per second

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8P3A Speed, Distance, Velocity, and Acceleration

Math Connections Name:

Date:

Group:

Part I: Speed and Velocity Speed is a scalar quantity that refers to how fast an object is moving. Velocity is a vector quantity that refers to the speed of an object in a specific direction. Essentially, velocity is speed in a specific direction. Average speed is often calculated using the following formula: Average speed (s)=Total distance traveled (d)/Total time of travel (t) Average velocity is often calculated using the following formula: Average velocity (v)=Displacement (meters) / Time (sec) 1.

Based on the units given for displacement and time, what will the units for velocity be?

During summer vacation, Juan traveled a total distance of 400 miles. His trip took 8 hours. What was the average speed during the trip?

An alert driver can apply the brakes fully in about 0.5 seconds. How far would the car travel moving at a rate of 29.06 m/s?

In 2013, the average time men in the United States could run a marathon was about 4 hours and 16 minutes. If a marathon is 26.2 miles, what was the average speed?

In the same year, the average finishing time for U.S. women was 4 hours and 41 minutes. What was the average female speed in miles per hour?

Part II: Acceleration Acceleration is the rate an object changes its velocity. It is a vector quantity, meaning it has a direction. The average acceleration of an object is the change in velocity over a given amount of time. It can be calculated using the formula: Average acceleration=Change in velocity (Δv) / Time (t) 1.

If the velocity of a moving car increases from 9 m/s to 25 m/s in the span of 5 seconds, what is the average acceleration during this time period?

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8P3A Speed, Distance, Velocity, and Acceleration

Math Connections 2.

Usain Bolt, the Olympian from Jamaica, is the fastest human ever recorded. Determine his average rate of acceleration if he achieved a speed of 10.4 m/s in 9.58 seconds. (Think about what the initial speed of a sprinter is.)

Use the following information to answer questions 3 –5. The following data was taken from a manufacturer’s test for a car’s ability to accelerate and brake. Plot the following sets of data on the graph provided. Time (s)

Speed (m/s)

Time (s)

Speed (m/s)

Write a short description about what the graph shows.

What was the average acceleration during the time between 24 seconds and 40 seconds?

What was the average acceleration from 40 seconds to 46 seconds?

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8P3A Speed, Distance, Velocity, and Acceleration

Writing Science Name:

Date:

Group:

LOOK

THINK Think about the motion experienced on a roller coaster ride.

WRITE Explain the difference between speed, velocity, and acceleration.

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8P3A Speed, Distance, Velocity, and Acceleration

Writing Science

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8th Grade Physical Science

8P3BC

Forces on and Motions of Objects

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8P3BC Forces on and Motions of Objects

Student Handout Name:

Change in Motion

Description of Force

Date:

Draw a Picture (use an arrow to represent the force and the direction the ball is moving)

Move Faster

Change Direction

Slow Down

Stop

Define speed.

Define balanced force.

Define unbalanced force.

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8P3BC Forces on and Motions of Objects

Student Journal Name:

Date:

Group:

Part I: Newton’s Law of Inertia 1.

Record your observation from Activity 1 and Activity 2. Observations Activity 1 Activity 2

Use Newton’s law of Inertia to explain why the car stopped when it hit the book.

Use Newton’s law of Inertia to explain why the penny continued to move forward after the car stopped moving.

The penny on the car represents a passenger in a vehicle. How would a seat belt change the motion of a passenger in a collision?

How do the washers in Activity 2 demonstrate Newton’s law of Inertia?

List the following objects in order from lowest Inertia to highest Inertia: Earth, desk, baseball, fork, house, feather, tow truck, cow, Sun. Explain your answer.

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8P3BC Forces on and Motions of Objects

Student Journal Part II: Newton’s Law of Force and Acceleration 1.

Complete the data table.

Car

Car with 5 washers

9.81 m/s2

Force Mass Acceleration 2.

How does the force of the car change as the mass of the car is increased?

How must the force applied to an object change as the mass of an object increases? Solve the following three problems to draw a conclusion. Show your work. A. What force is required to cause a 5-kg bowling ball to accelerate at 4 m/s2?

B. What force is required to cause a 6-kg bowling ball to accelerate at 4 m/s2?

C. What force is required to cause a 7-kg bowling ball to accelerate at 4 m/s2?

D. How does the force required to accelerate an object change as the mass increases?

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8P3BC Forces on and Motions of Objects

Student Journal Part II: Newton’s Law of Force and Acceleration, continued 4.

How does the acceleration of an object change as the force applied to the object increases? Solve the following three problems to draw a conclusion. Show your work. A. What is the acceleration of a 5-kg bowling ball when a 10 newton force is applied?

B. What is the acceleration of a 5-kg bowling ball when a 15 newton force is applied?

C. What is the acceleration of a 5-kg bowling ball when a 20 newton force is applied?

D. How does the acceleration of an object change as the force applied to the object increases?

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8P3BC Forces on and Motions of Objects

Student Journal Part III: Newton’s Law of Action-Reaction 1.

Complete the data table with observations on the action and reaction forces in the activities.

Activity

Action Force

Reaction Force

Stand up. Push a toy car across a table. Press your hand against your neighbor’s hand. Lean against a wall. Blow up a balloon and release it in the classroom. 2.

When you applied the action force, when did the object apply the reaction force?

In the balloon example, the balloon’s air pushing out of the balloon was the action force. The reaction force was the balloon flying in the opposite direction of the air. It was believed for a long time that the air coming out of the balloon hit air molecules that propelled it forward. Newton’s third law states that just the action of the air coming out of the balloon pushed it forward. How does this apply to rockets in the vacuum of space?

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8P3BC Forces on and Motions of Objects

Student Journal Reflections and Conclusions 1.

Write Newton’s law of inertia.

Write Newton’s law of force and acceleration.

Write Newton’s law of action-reaction.

Describe how each of Newton’s three laws applies to the motion of a car on a roller coaster. A. Newton’s law of inertia

B. Newton’s law of force and acceleration

C. Newton’s law of action-reaction

Describe how each of Newton’s three laws applies to the motion of a rocket. A. Newton’s law of inertia

B. Newtons law of force and accelaration

C. Newton’s law of action-reaction

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STEMscopedia: FORCES ON AND MOTIONS OF OBJECTS

8P3BC

Reflect Have you heard the story about Isaac Newton sitting under an apple tree? According to the story, an apple fell from a tree and hit him on the head. From that event, it is said that Newton discovered the force of gravity. No one knows for sure whether the story is true or not. What is certain is that Newton’s ideas about gravity and other forces have explained some of the most signiﬁcant scientiﬁc phenomena related to motion in the universe. How do forces, such as gravity, affect motion? How is motion measured? Answers to these important questions may have begun with a falling apple!

Look Out Different Forces Act on Objects In order to understand motion, we must begin by talking about forces. A force is a push or a pull exerted on an object. Every force has a magnitude and a direction. Magnitude, or the strength of the push or pull on the object, is measured in newtons (N). Examples of direction include east, west, north, south, toward the left, or toward the right. Below, the force the man is exerting on the cart can be described as having a magnitude of 25 newtons and a direction to the right. At any given time, all objects have a variety of forces acting upon them. For example, a laptop computer sitting on a desk has at least two forces acting upon it. Earth’s gravitational force pulls the laptop down toward the center of the planet. Earth’s gravity is what keeps everything on Earth, including people, from drifting off into space. It literally keeps us grounded!

The second force acting on the laptop is the normal force. The normal force is the force of the desk pushing up on the laptop, keeping it from falling through the desk and to the ground. When someone sits on a chair or leans against a wall, the normal force pushes back against that person, preventing a fall through the chair or wall. The normal force acts in the opposite direction of gravity.

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STEMscopedia: FORCES ON AND MOTIONS OF OBJECTS

Together, gravity and the normal force combine to be the net force acting on the laptop. Net force is the total of all forces acting on an object at once. When calculating net force, any forces acting in the same direction are added together. Those acting in opposite directions are subtracted. The direction of the net force is the direction of the greatest force. For example, if a force of 10 newtons to the left and a force of 8 newtons to the right are acting on an object, the net force is 2 newtons to the left. Friction is a force that always acts in the opposite direction of movement. Friction occurs when two surfaces are in contact, such as the bottom of a person’s shoes walking on the ground. The amount of friction between two surfaces depends on the material of the surfaces and the amount of force pressing them together. Smooth surfaces, such as an ice rink or a wood ﬂoor, have less friction than rough surfaces, such as sandpaper or cement. Also, surfaces that have less force pressing them together have less friction; surfaces that have more force pressing them together have more friction.

What is the net force acting on the television? Remember to include both its magnitude and direction.

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STEMscopedia: FORCES ON AND MOTIONS OF OBJECTS

What Do You Know? Matching: Match the correct net force to the diagram: 1.

_____45 newtons right

_____0 newtons

_____12 newtons right

_____20 newtons left

_____5 newtons left

Speed and Direction When an object moves, it travels over a distance in a certain period of time. This is the object’s speed. Speed is calculated by dividing the distance traveled by the time the object took to travel, or s = d/t. For example, suppose a dog runs 88 meters in 2 minutes to fetch a ball. To ﬁnd the dog’s speed, divide 88 meters by 2 minutes, which equals 44 meters per second or 44 m/s. Units of speed include a “/” symbol pronounced as “per” because they are a division of distance and time units. (Dog’s speed) = d/t = 88 meters/2 minutes = 44 m/s To gain a better understanding of how an object moves, a direction is often included along with the speed. Together, speed and direction are an object’s velocity. Balanced and Unbalanced Forces When the net force on an object equals zero, it is said that the forces are balanced. Balanced forces do not change an object’s motion. This means that an object in motion stays in constant motion at the same speed and direction. However, what happens if the net force is balanced on an object at rest? Recall the laptop sitting on the desk. Gravity and the normal force were balanced for a net force of zero. The laptop did not move. Objects at rest stay at rest when their forces are balanced. Many people believe that the only time forces are considered balanced is when an object is at rest. But remember Newton’s first law: An object at rest stays at rest, and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

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Look Out On Earth, we rarely see a situation where the forces are balanced and the object is in motion, due to gravity and friction interacting with all things on Earth. If you were to throw a baseball in space, the baseball would continue to move at the same speed and same direction forever, unless a force is added to the baseball that would cause the ball to change its speed or direction. Have you ever tried to pull a wagon with a small child inside? How about with four children inside? What is the difference in the two experiences? Did one require more muscles or effort to get the wagon to move? Absolutely! The wagon with more children required much more effort to pull or push.

Reflect Inertia Inertia is a term used to describe an object’s ability to change its motion at rest or in motion. To overcome an object’s inertia, a force must be added. For example, if you have two boxes at rest, one box with a mass of 600 kilograms and another box with a mass of 100 kilograms, the box with the greater mass will require a much greater force to move, to overcome the box’s inertia. This example shows that the more mass an object has, the greater its ability resist change. The same applies to an object in motion. If you take the same two boxes mentioned above and slide them down an incline plane, which box would require the greatest force to stop? The heavier box would require much more force to stop than the lighter box. Therefore, it is easy to conclude that an object’s inertia—its ability to resist change—is directly correlated to the object’s mass. The more mass an object has, the harder it is to change its motion.

What Do You Know? Rank the boxes below from the greatest to the least inertia.

_______ _______ _______ _______

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STEMscopedia: FORCES ON AND MOTIONS OF OBJECTS

Connecting With Your Child To help your child learn more about forces and motion, set up a series of simple events in your backyard or at a park where you can demonstrate motion. If you are unable to travel to an outside area, you can spend time looking through books or magazines together to ﬁnd examples of unbalanced forces and motion. Suggestions for events include: • Compete in a game of tug of war where you and your child pull on opposite ends of a rope. Ask your child to determine when the forces are balanced, when they are unbalanced, and the direction of the net force. • Participate in a challenge to push an exercise ball across a line. Set up two lines of masking tape approximately 12 meters apart. Place a large exercise ball in the middle between the lines. Stand on one side of the ball and ask your child to stand on the opposite side of the ball. You both must try to push the ball over the line behind your opponent. Encourage your child to shout out when the forces are balanced. • Try to push a rolling chair with no one on the chair. Then try to push the same chair with an adult sitting in it. Encourage your child to discuss which situation has the greatest inertia. Have your child discuss why. Discuss the following questions with your child: 1. How do you know when forces are balanced on an object? 2. What are some ways to create an unbalanced net force on an object? 3. What determines the inertia of an object?

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8P3BC Forces on and Motions of Objects

Reading Science Name:

Date:

Group:

A Winning Force 1

Everything in our world moves. Although you may not notice it, the world around you is constantly in a state of motion. The whirling wind causes the leaves on a tree to quiver. The ocean waves lift the surfer high above the tide. The baseball flies into the stands after being knocked out of the park by the batter. An object’s motion will always change when acted upon by an unbalanced force.

For an object to move, forces need to act upon it. The force can either speed up (accelerate), slow down (decelerate), or make the object stationary. Take the force of gravity, for example. Gravity keeps your textbook from floating off your desk. It keeps you from floating away into space when you do jumping jacks during physical education class.

An example of acceleration is bike riding. When you push down on the bike pedal, your weight forces the wheels to turn. You accelerate and go full speed ahead. Likewise, when a football player punts a ball, the force that he uses to make a powerful kick causes the ball to fly high in the air. A force that pulls or pushes in a different direction is called an opposing force. These cause an object to decelerate or stop. An example is when you take a dog for a walk. If the dog started to chase a cat, his forward motion would be stopped by your pull on the leash. This principle is true with a tennis match as well. Both players are trying to keep the ball from going out over the back line. They stop the forward movement of the ball by hitting it with their racket. The rest of the force of the swing makes the ball change direction and fly back over the net.

A change in an object’s movement as a result of a force can be described in terms of inertia. Inertia is an object’s tendency to resist a change in motion. This concept of inertia is also referred to as Sir Isaac Newton’s first law of motion. All objects have inertia. As an object’s mass increases, its inertia increases. You need a larger force to overcome this larger inertia. For example, when you push a shopping basket, the basket will move in the direction of the force. It will continue to move as long as you push it. The greater the force used, the greater the change in the basket’s motion. The greater the mass of the basket, the greater the force needed to cause a change in its motion.

Think about forces the next time you are playing softball or football with your friends. Remember that if you exert a greater force upon the ball, it will move faster and harder. Share this with your entire team, and you will be sure to win!

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8P3BC Forces on and Motions of Objects

Reading Science 1.

Complete the following analogy: PEDALING A BIKE : ACCELERATION :: PULLING A DOG’S LEASH : _____.

ENERGY

GRAVITY

INERTIA

DECELERATION

What is the meaning of the word stationary as used in paragraph 2? A

To shake

To fall

To remain in place

To pull down

The greater the mass of an object, the more of what is needed to move it? A

Help

Force

Energy

Time

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8P3BC Forces on and Motions of Objects

Reading Science 4.

Which of the following is an example of an opposing force? A

Gravity pulling a ball down a hill

Wind blowing a leaf off of a tree

Gravity holding a rock still on the ground

Water pushing against someone as they wade through a pool

During a game of tug-of-war, the first team exerts a force of 3,500 N to the left. The second team exerts a force of 3,800 N to the right. Which of the following statements is true about the game? A

The forces are balanced, and there will not be a winner.

The forces are balanced, and the first team will win.

The forces are unbalanced, and the first team will win.

The forces are unbalanced, and the second team will win.

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8P3BC Forces on and Motions of Objects

Math Connections Name:

Date:

Group:

Part I: Newton’s First Law—Unbalanced Forces Newton’s first law of motion states: “An object at rest tends to stay at rest and an object in motion tends to stay in motion unless acted upon by an unbalanced force.” All objects on Earth have forces acting on them. Sometimes the forces are balanced, and sometimes they are unbalanced. Balanced forces are equal in size and opposite in direction. Unbalanced forces are not equal in size, nor are they acting in the same direction. Consider the scenarios below. Draw a free-body diagram for each scenario, label the forces, label the directions of the forces, and calculate the unbalanced force and direction if there is one. 1.

A bicycle is hanging from the ceiling of the garage by a tension rod with an upward force of 1,400 Newtons (N). A 700 N gravitational force is pulling downward on the bicycle.

A boy throws a rock off a cliff. Air is pushing upward on the rock with a force of 500 N, and gravity is pulling down on the rock with a force of 700 N.

A wagon is traveling east with a frictional force of 30 N. It experiences a 60 N gravitational force pulling downward, and counteracts that force with a 60 N normal force pushing upward.

Look at the forces represented by the diagrams below. Calculate the unbalanced forces, and include the direction in which the object will move.

–12

–6

= = = =

What do the negative signs indicate in the diagrams above?

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8P3BC Forces on and Motions of Objects

Math Connections Part II: Newton’s Second Law of Motion Newton’s second law of motion, the law of force and acceleration, states that the acceleration of an object depends upon the object’s mass and the magnitude of the force acting upon it. The formula below can be used to calculate the force, using the mass and acceleration of an object: Force (F)=Mass (m)×Acceleration (a) 1.

Calculate the amount of horizontal force needed to make a 0.5 kg football accelerate at 200 m/s2 when kicked.

On Earth, the acceleration due to gravity is 9.8 m/s2. If a person has a mass of 65 kg, how much force does that person exert in Newtons? In pounds? (Note: 1 lb=4.448 N)

A force of 250 N is exerted on an object with a mass of 45 kg located on a smooth surface. a.

Calculate the acceleration of the object.

b. In a second trial, a second object, identical to the first, is placed on top of the first object. What acceleration would the 250 N force produce?

c. What is the effect of increase mass on the acceleration of an object if the same force is being applied? 4.

A 6 kg brick is pulled across the flat sidewalk by a horizontal force of 35 N. The brick is experiencing a frictional force of 7 N in the opposite direction. Calculate the acceleration of the brick.

A 5×10−3 kg feather is in free-fall in a vacuum tube. If the acceleration due to gravity is 9.8 m/s2, what force is the feather exerting?

250

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8P3BC Forces on and Motions of Objects

Writing Science Name:

Date:

Group:

LOOK

THINK Think about the change in position, direction, and speed of a baseball being struck by a bat at a baseball game.

WRITE Explain what happens when an object is acted upon by unbalanced forces.

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8P3BC Forces on and Motions of Objects

Writing Science

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8th Grade Physical Science

8P4A

Similarities and Differences Between Electromagnetic and Mechanical Waves

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8P4A Similarities and Differences Between Electromagnetic and Mechanical Waves

Student Handout Name:

Waves All Around

Date:

Separation Experiment

In the space below, brainstorm as many examples as you can of waves you experience in everyday life.

Now decide whether each of these examples would be able to move through matter or move through the vacuum of space. Moves Through Matter

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Moves Through Space

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8P4A Similarities and Differences Between Electromagnetic and Mechanical Waves

Student Journal Name:

Date:

Group:

Background 1. What is a wave?

2. If a transverse wave is transporting energy from east to west, which direction will the particles of the medium move?

3. Describe the difference between mechanical and electromagnetic waves.

4. Describe the three types of mechanical waves in relation to the direction of movement.

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8P4A Similarities and Differences Between Electromagnetic and Mechanical Waves

Student Journal Part I: Wave Movement Use the materials listed in the Student Guide to simulate both transverse and longitudinal waves. You do not have to use all of the supplies. 1. What materials will you use to simulate a transverse wave?

2. What steps will you take to carry out the investigation?

3. Draw a labeled diagram of your transverse wave simulation. Be sure to label the wavelength, crest, and trough. Transverse Wave

4. What materials will you use to simulate a longitudinal wave?

5. What steps will you take to carry out the investigation?

6. Draw a labeled diagram of your longitudinal wave simulation. Be sure to include compressions and rarefactions. Transverse Wave

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8P4A Similarities and Differences Between Electromagnetic and Mechanical Waves

Student Journal Part II: Mechanical Waves 1. What happened to the candle when you thumped on the end of the bottle?

2. Describe how the sound wave lab demonstrates longitudinal wave movement.

3. In the ocean wave demonstration, describe the movement of the cork.

4. Describe how this ocean wave demonstration shows surface wave movement.

5. Explain why sound waves and ocean waves are both examples of mechanical waves.

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8P4A Similarities and Differences Between Electromagnetic and Mechanical Waves

Student Journal Part III: Electromagnetic Waves Type of Wave

Description

Wavelength Drawing

Radio waves

Microwaves

Infrared waves

Visible light

Ultraviolet rays

X-rays

Gamma rays

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8P4A Similarities and Differences Between Electromagnetic and Mechanical Waves

Student Journal Reflections and Conclusions 1. In which wave do the particles vibrate in the same direction as the wave? 2. In which wave do the particles vibrate perpendicularly to the direction of the wave? 3. List the following types of waves in order from the least amount of energy to the greatest: gamma rays, microwaves, infrared waves, ultraviolet rays, radio waves, visible light, and X-rays.

4. Summarize the similarities and differences between mechanical and electromagnetic waves.

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STEMscopedia: SIMILARITIES & DIFFERENCES

BETWEEN ELECTROMAGNETIC AND MECHANICAL WAVES

8P4A

Reflect Have you ever watched waves ﬂow against the shore at a beach? As the wave approaches the shore, the water moves up and down in a continual cycle. Each up-and-down cycle makes up a single wave. Another type of wave you may have seen travels along the length of a spring. If you compress and release one end of a spring quickly, a pulse travels along the spring. This pulse causes the spring to become compressed in some parts and stretched in others. The up-and-down motion of water at a beach and the compressed pulse that travels along a spring are both examples of waves. How are they similar? How do they differ? Of course, they travel through different substances—water versus metal— but think about how else these wave types are different.

How would you describe the waves that form along the ocean surface?

Electromagnetic Versus Mechanical Waves A wave is a disturbance or oscillation that travels through space or matter and transfers energy from one place to another. Waves that travel through a medium like air or water are called mechanical waves. As the wave travels, the molecules of the medium are temporarily displaced as the energy is transferred. Waves created by charged particles that are made up of alternating electric and magnetic fields are called electromagnetic waves. Because of their dual composition, electromagnetic waves do not require a medium and can travel through the vacuum of space. How Waves Travel Waves travel in two distinct ways: either perpendicular to the displacement (transverse waves) or in the same direction as the displacement (longitudinal waves). This classifies waves by comparing the direction the wave moves to the direction of the particles that transmit the wave. Electromagnetic waves travel only as transverse waves, while mechanical waves can travel either as a transverse waves or as longitudinal waves. Transverse waves are waves vibrating at right angles to the direction of its propagation. To understand transverse waves, think again about a wave that travels through the water at a beach. You can think of the up-and-down motion of the water as the wave disturbance. This means the wave is propagating in the horizontal direction. However, the water molecules move up and down. This means the particles that transmit the wave are moving in the vertical direction. Thus, the wave travels perpendicular to the displacement. It is a transverse wave. You can create transverse waves on a long rope by tying one end to a tree and shaking the other end up and down perpendicular to the rope’s length, as shown at the top of the next page. A pulse will travel up and down at a right angle to the length of the rope as the wave travels. © Accelerate Learning Inc. - All Rights Reserved

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BETWEEN ELECTROMAGNETIC AND MECHANICAL WAVES

In contrast, longitudinal waves travel in the same direction as the displacement. Consider the spring mentioned earlier. When you compress one end quickly, the compressed pulse oscillates back and forth along the length of the spring. In this case, the spring pulse displacement oscillates horizontally along the spring, and the wave also travels horizontally. Thus, the wave travels in the same direction as the displacement. As the pulse propagates, it creates regions where the particles of the medium are very close together. These regions are called compressions. In between these compressions are regions where the particles are stretched farther apart. These regions are called rarefactions.

A longitudinal pulse travels along the length of a spring. The areas of the spring that are close together are called compressions. The areas that are farther apart are called rarefactions.

All longitudinal waves are made of alternating compressions and rarefactions. Some common examples of longitudinal waves are sound waves and seismic waves.

What Do You Think? Look at the chart to the right. Compare and contrast transverse and longitudinal waves.

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BETWEEN ELECTROMAGNETIC AND MECHANICAL WAVES

Mechanical Waves Mechanical waves are waves that travel through a material known as a medium. A medium is a solid, liquid, or gas made up of a particular type of particle. For example, air, water, and Earth’s crust are three different types of media. The vibrations of particles in the medium produce the mechanical wave.

Both longitudinal and transverse mechanical waves can travel though a solid medium. Earthquakes, for instance, create both longitudinal and transverse waves that travel through the solid structure of Earth. Only longitudinal mechanical waves, however, can travel through fluids such as liquids and gases. (As you will learn, electromagnetic waves are transverse waves that can travel through fluids, but this is because electromagnetic waves are not mechanical—they do not require a medium at all.) Sound is a longitudinal wave that can travel through a fluid or a solid. You can hear voices in another room even with the door closed because the sound waves travel through the air, then through the solid door, and then through the air again to your ears. Why can’t transverse mechanical waves travel through fluids? A transverse mechanical wave can travel only through a medium that is relatively stiff or rigid, such as a rock or a rope. If the medium is not rigid enough, the particles in the medium can slip past each other, and a transverse wave cannot propagate.

Look Out Water is a ﬂuid, so it should transmit only longitudinal waves. However, you have probably seen the motion of a buoy or boat bobbing up and down as waves pass by underneath. This motion seems to come from transverse waves. Are water waves longitudinal or transverse? The answer depends on whether the wave is on the surface of the water. The water below the surface can transmit only longitudinal waves. That is, the particles that transmit waves underwater can move back and forth only along the direction of the wave. Water particles on the surface, however, feel a different net force than particles below the surface. This force is known as surface tension. It causes the surface of the water to be “stiffer” than the water underneath allowing transverse waves to travel along the surface of the water. Both longitudinal and transverse waves can travel across the water surface, but only longitudinal waves can travel beneath the surface.

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The familiar transverse waves on the surface of the ocean hide the longitudinal waves below.

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BETWEEN ELECTROMAGNETIC AND MECHANICAL WAVES Electromagnetic Spectrum and Waves As you have learned, mechanical waves can travel only through a medium. However, some waves do not require a medium through which to travel. That is, Vacuum: a space completely some waves can travel through a vacuum. These waves are (or nearly) empty of matter called electromagnetic waves (also known as radiation). An electromagnetic wave is composed of an oscillating electric field and an oscillating magnetic field. These fields oscillate perpendicular to the direction in which the wave travels. So, electromagnetic waves are transverse waves. The electromagnetic spectrum consists of the range of all possible wave frequencies of electromagnetic waves. The electromagnetic spectrum includes visible light, along with infrared and ultraviolet light, gamma rays, X-rays, microwaves, and radio waves.

Waves in the electromagnetic spectrum are organized by wavelength. A radio wave can be as long as a skyscraper. A gamma ray is smaller than the nucleus of an atom. Electromagnetic waves behave quite differently from mechanical waves. Vibrating particles in a medium transmit mechanical waves. Therefore, mechanical waves are limited by the properties of their medium. If there is no medium, the waves cannot transmit. This is why there is no sound in outer space. However, electromagnetic waves do not rely on the particles in a medium to travel. You can think of an electromagnetic wave as pure energy traveling through space. Because of this, electromagnetic waves can travel through all types of matter—solids, liquids, and gases—as well as empty space.

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BETWEEN ELECTROMAGNETIC AND MECHANICAL WAVES Furthermore, while mechanical waves are caused by disturbances in a medium, vibrating charged particles emit electromagnetic waves. For example, the charged particles in the atoms in our bodies are constantly vibrating. They emit infrared radiation, which is the type of electromagnetic wave commonly associated with the temperature of objects. This is how “night vision” goggles can detect the location of people even when there is no visible light available. Another difference between mechanical and electromagnetic waves is that mechanical waves tend to travel relatively slowly compared to electromagnetic waves. The speed of sound is 343 m/s at 20°C. Electromagnetic waves travel through a vacuum at a speed of 3.00×108 m/s. (This is light speed. Nothing in the known universe travels more quickly than light.) A wave of light from the Sun reaches Earth in about eight minutes.

Special cameras can sense the infrared radiation, or heat, emitted by objects.

Everyday Life: Electromagnetic Waves All Around Us You use electromagnetic waves all the time in your everyday life. Visible light waves are electromagnetic waves, so our vision depends entirely on light waves that travel from objects to our eyes. Cell phones, wireless Internet routers, remote controls, speed detectors, radios, and televisions transmit signals via radio waves and microwaves. Microwave ovens use microwaves to cook food, and many common heaters emit infrared radiation. Furthermore, doctors and dentists use X-rays to take images of their patients during examinations. Electromagnetic waves can also be harmful. Ultraviolet (UV) rays from the Sun can cause our skin to burn and kill bacteria. We take advantage of this property when we use UV rays to sterilize drinking water. Gamma rays and other high-energy waves emitted by radioactive materials can cause serious mutations, cancer, and even death.

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BETWEEN ELECTROMAGNETIC AND MECHANICAL WAVES

What Do You Know? What Do You Know? Compare mechanical waves and electromagnetic waves by writing each description in the correct place in the Venn diagram below. Some terms belong to both types of waves. Descriptions of Waves • longitudinal • transverse • sound wave • wave on a string • visible light • microwaves

Mechanical Waves

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• travels through different media • travels through a vacuum • travels as disturbance of a medium • travels as disturbance of electric and magnetic ﬁelds

Electromagnetic Waves

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STEMscopedia: SIMILARITIES & DIFFERENCES

BETWEEN ELECTROMAGNETIC AND MECHANICAL WAVES

Connecting With Your Child Sound Waves on a Wire Help your child investigate sound waves by experimenting with variations of a simple “tin can telephone.” For materials, you will need two objects to use as telephone “receivers.” (You can use empty cans, each with an opening at one end, or two polystyrene cups.) Your child should connect the two receivers with string, twine, or wire. For example, you can punch a small hole in the closed end of each receiver and pass the line through the holes. Then, secure the line by tying a large knot or by taping the string to the inside of each cup. You and your child can then attempt to communicate with the telephone assembly. For example, you can talk into one receiver while your child listens at the other receiver. You can also attempt to play the line like a guitar string with one person listening at one end. Have your child modify the design of the telephone assembly to observe how the sound transmission changes. For example, your child can experiment with different materials or different lengths of string. Or, your child can try holding the string at different tensions. Here are some questions to discuss with your child: 1. How do the different materials or line tensions affect the transmitted sound? 2. How does the sound travel from one receiver to the other? 3. Do real telephones use similar technology to transmit sound, or is the technology different?

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8P 3C Simple Machines

Writing Science Name:

Date:

Group:

LOOK

THINK Think about simple machines.

WRITE Describe at least four different simple machines, and explain how they make work easier.

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8P 3C Simple Machines

Writing Science

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8P4A Similarities and Differences Between Electromagnetic and Mechanical Waves

Reading Science Name:

Date:

Group:

Waves All Around 1

How long has it been since you watched waves at the beach? Did you pay attention to their shapes? If you are standing at the shore, they look like they are coming right at you. But what if you walk out on a pier jutting into the water? Ocean waves look a bit different if you can see them from their side.

If you watch one spot, you can see that the water rises and dips in a regular pattern. Find something floating on the waves to look at—perhaps a seagull or a jellyfish. You will see that the object moves forward a little bit as the water goes up and then moves backward as the water goes down. The water molecules are not actually being moved to the shore. The waves represent areas of pressure moving through the water, and the water is pushed upward as it is compressed by the higher pressure portions of the wave. The way that the height of the water changes over time follows a pattern physicists call a standing wave. Waves can be described by three properties: wavelength, frequency, and amplitude. Unlike many waves in nature, you can easily observe these properties on your own in ocean waves.

The very highest point of each wave is the peak, and the lowest is the trough. The horizontal distance from peak to peak (or trough to trough) is the wavelength. The frequency is how many peaks go by in a certain amount of time. For waves on the ocean, we might report frequency as waves per minute. A common term for the passing of a wave from one peak to the next is one cycle. For waves with higher frequency, a unit called Hertz (Hz) has been created. One Hz is 1 cycle per second. The last property is amplitude. The vertical distance from the height of the peak to the level of the trough is divided by 2 to give the amplitude. In other words, imagine a line that traveled along the middle height of the wave. The amplitude is the distance from that line to a peak or trough. There are many other waves in nature that are almost the same shape as ocean waves and can be described by the same properties. We can look at a few examples.

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Reading Science Continued, 4

First, imagine that you have tied one end of a rope to a door knob. If you stand so that your arm is pointed at the door knob, the taut rope shows the middle line we use to measure amplitude. If you give the rope some slack and move your arm up and down, you will see a wave in the rope. The amplitude is large on the end that you hold. Closer to the door knob, the rope cannot move up and down as far. The amplitude of the wave decreases to zero at the knot.

Another type of wave is the sound wave. These are also pressure waves that move through matter such as air or water. When sound waves are fed into a device called an oscilloscope, it will show the sound wave as a picture on a screen. A note of a single pitch, like from a flute or an opera singer, will show up as a regular wave. A really low note will have a low frequency. 20 Hz is about the lowest frequency a person can hear. A note of high pitch has a high frequency. When the opera singer hits “high C,” she is producing sound waves at 1,046.5 Hz.

Light can also be described by a wave. We are not able to see the form of these waves, but we can model them mathematically. Visible light does not have a different “pitch” like sound, but it does come in different colors. It is the property of wavelength that changes when we compare light of different colors. The wavelengths of light are very, very small. A special unit of distance called a nanometer (nm) is used to report light wavelengths. There are one billion (1,000,000,000) nanometers in one meter. Violet light has the shortest wavelength at 400 nm. Red light, at 740 nm, has the longest wavelength of visible light. In contrast, the wavelengths of sound waves are measured in centimeters.

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8P4A Similarities and Differences Between Electromagnetic and Mechanical Waves

Reading Science 1.

What is the main point of paragraph 3? A

To define the unit Hertz

To fully describe ocean waves

To explain the three properties of waves

To let the reader know that there are many different types of waves in nature

X 2.

Which property of a wave is labeled X on the diagram above? A

Amplitude

Frequency

Wavelength

None of the above

Which phrase helps the reader understand the meaning of vertical in paragraph 3? A

From the height of the peak

Divided by 2

Imagine a line

Along the middle

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Reading Science 4.

A subwoofer is a type of speaker that plays only the very low notes in a song or movie. Which of the following frequencies would the reader expect to be able to hear from a subwoofer? A

10 Hz

25 Hz

750 Hz

1,050 Hz

Place these waves in order from shortest wavelength to longest. A

Light waves<ocean waves<sound waves

Light waves<sound waves<ocean waves

Sound waves<light waves<ocean waves

Ocean waves<sound waves<light waves

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8P4A Similarities and Differences Between Electromagnetic and Mechanical Waves

Writing Science Name:

Date:

Group:

LOOK

THINK Think about electromagnetic and mechanical waves.

WRITE Describe the characteristics of electromagnetic and mechanical waves, and explain how electromagnetic waves are different from mechanical waves. Be sure to • clearly state your central idea; • organize your thoughts; • develop your essay in detail; • choose your words carefully; and • use correct spelling, capitalization, punctuation, and grammar.

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8P4A Similarities and Differences Between Electromagnetic and Mechanical Waves

Writing Science

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8th Grade Physical Science

8P4BF

Waves and Energy

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8P4BF Waves and Energy

Student Handout Name:

Date:

Part I: Define transverse wave and longitudinal wave in terms of motion of the wave and motion of the medium. Transverse wave: ________________________________________________________________ _______________________________________________________________________________ Longitudinal wave: ________________________________________________________________ _______________________________________________________________________________ Part II: Electromagnetic Spectrum 1. Obtain a set of electromagnetic cards from your teacher. 2. As a team, arrange them from longest wavelength to shortest wavelength. 3. Have your teacher check for accuracy. 4. Complete the questions below. Draw and label the correct order of the electromagnetic spectrum below.

Which part of the electromagnetic spectrum has the longest wavelengths?

Which part of the electromagnetic spectrum has the shortest wavelengths?

Which part of the electromagnetic spectrum do humans see as colors?

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8P4BF Waves and Energy

Student Journal Name:

Date:

Group:

Background 1. What is a wave?

2. What happens to the particles in a medium when waves propagate through the medium?

3. How does a transverse wave differ from a longitudinal wave? Explain and draw an illustration for each.

4. Write the equation for calculating wave velocity. Make sure to identify each variable

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8P4BF Waves and Energy

Student Journal Part I: Plan Your Investigation 1.

My question of inquiry:

What do you need to do to answer this question?

What are the variables that you will observe?

My prediction:

What materials, equipment, and technology will be needed for this investigation?

List all safety precautions that must be taken.

Procedure: Follow the procedures listed in the Student Guide to conduct this investigation.

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8P4BF Waves and Energy

Student Journal Part II: Implement Your Investigation Collect, Record, and Organize Data 1. Qualitative observations: Record your observations of the two wave types.

2. Measuring wave speed: Spring length: LONGITUDINAL WAVE

3. Measuring frequency and wavelength

TRANSVERSE WAVE

TRANSVERSE WAVES ONLY

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8P4BF Waves and Energy

Student Journal Part II: Implement Your Investigation, continued Analyze Data 1.

Do transverse waves and longitudinal waves travel at the same speed? Explain.

Does the amplitude of a wave affect the speed of the wave? Explain.

Was the wave speed the same for all three trials of the same amplitude and type of wave? Why or why not?

Look at the variation in wave speeds determined for all of the trials for transverse waves. Calculate the difference between the highest and lowest speeds found. Is it significant?

Use your data from “Measuring frequency and wavelength” to calculate the frequency of the waves. Then use the wave speed equation, v = fλ, and the average speed for your transverse waves from the previous table to calculate the wavelength of the waves.

Are the values you obtained for wavelength reasonable? Explain.

Recalculate the wavelength for one of your trials using the highest and lowest values you obtained for speed rather than average speed. What is the difference in calculated wavelength? Does it significantly affect your conclusions from the experiment?

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8P4BF Waves and Energy

Student Journal Reflections and Conclusions 1. Was your prediction correct or incorrect? Explain. 2. Was there a relationship between the variables you observed? 3. Where could have errors been made while collecting or organizing data?

4. What do you conclude about this investigation?

What would you do differently if you were to conduct this investigation again?

What are some causes that create uncertainties in your data?

What are some effects of your uncertainties in your data?

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STEMscopedia: WAVES AND ENERGY 8P4BF

Reflect Think about the light energy used in microwaves to heat up meals. What type of energy is used to generate the light in your cell phones? How are we able to see certain light? How does this energy travel through the atmosphere? Does frequency affect the pattern of light? The electromagnetic spectrum describes energy. Electromagnetic radiation, also called photons, is a form of energy that travels in a wavelike pattern and spreads out as it goes. This wide range of radiation can be described using the electromagnetic spectrum. The electromagnetic spectrum includes radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, x-rays, and gamma rays. The energy for all forms of light travels at a speed of 300,000,000 meters per second (mps). Each type of radiation can be characterized by frequency, energy, and wavelength. In the visible ray range, light can be seen. This light is in the form of different colors known as ROYGBIV: red, orange, The image above yellow, green, blue, indigo, and violet. These rainbow-like colors only make represents an up a small portion of the electromagnetic spectrum. One source of energy electromagnetic spectrum that exhibits the full spectrum is our Sun. arranged in order of the longest wavelength to the Wavelength determines the type of radiation. shortest. When energy travels in the form light, it travels in a wavelike pattern. The length of a single wave of energy is called wavelength. This can be measured from the top of one wave (known as the crest) to the top of the next wave. This is also the same for the bottom of the wave, known as the trough. The longer the distance between two waves is, the amount of energy is less. The shorter the distance between two waves, the higher the energy. The units of measurement for wavelength is the nanometer (nm). The effect of amplitude and energy. The amplitude of a wave describes the distance between the point of origin and the top or bottom of a wave. This is also known as the height of the wave. The larger the amplitude or the height, the higher the energy. The shorter the amplitude or height, the lower the energy. Amplitude is important because it can be used to determine the brightness or intensity of a light compared to another light wave.

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In the diagram above, the amplitude is measured from the point of origin to the top of the wave.

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STEMscopedia: WAVES AND ENERGY Frequency and energy have the same characteristics. Another type of measurement used to determine the type of wave is the frequency. The frequency of a wave can be described as the number of waves that pass a given point at a certain time (usually one second). The more waves that pass a given point, the higher the frequency. The opposite would be the fewer the waves that pass a given point, the lower the frequency. If the wave is moving at a higher frequency, the amount of energy is increasing as well. When frequency is compared to wavelength, they are opposites. As one increases, the other decreases. The diagram above displays one high intensity wave and one low intensity wave.

Look Out Photons can be a wave and a particle. The energy given off in the electromagnetic spectrum is known as a photon. When this energy travels at the speed of 300,000,000 meters per second, it moves in a wavelike pattern. Although energy moves as a wave, it still exhibits the properties of a particle. This means that a photon has characteristics that are similar to a proton and electron. The difference between a regular particle and a photon is that a photon has no mass.

What Do You Think? Opposite Relationships Wavelength and frequency are both variables that are used to describe the electromagnetic spectrum. When the variables are compared to one another, they are opposite. This means that as one increases, the other one decreases. The is true because the length between each wave affects frequency. For example, the waves in radio waves take longer to pass a given point compared to the waves in gamma rays. If the frequency is low, so too is the energy. This means they have a direct relationship. The image displayed above shows the relationship between the wavelength and the frequency of a wave.

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STEMscopedia: WAVES AND ENERGY Look Out Visible Light and Color In the electromagnetic spectrum, there is only one type of radiation that can be seen by the human eye, and that is visible light. Visible light ranges in wavelengths from about 400 to 700 nanometers (nm). The colors in the visible light spectrum are red, orange, yellow, green, blue, indigo, and violet (the colors of the rainbow). The order of the colors is from the longest wavelength to the shortest. Using a lens known as a prism, white light can be separated to create a rainbow effect. Image 5 goes with the above paragraph and with the following caption:

The image above represents visible light through a prism that separates into the colors of the rainbow.

Connecting With Your Child Your child has recently learned about the properties of a wave that include wavelength, amplitude, and frequency. He or she has also learned about the relationship between light energy in the electromagnetic spectrum and the frequency of a wave. Investigate the relationship between electromagnetic energy and wavelength with your child by using only one jump rope. Hold one end of the jump rope while your child holds the other end. Create a low frequency wave by moving the rope up and down slowly. Then investigate a high frequency wave by moving the rope up and down quickly. You and your child can communicate about the energy required to move the jump rope at a fast and slow pace.

You can visually display the properties of a wave in an electromagnetic spectrum by using a jump rope.

Here are some questions to discuss with your child: 1. What differences did you see in the length of the wave as you moved the rope slowly and quickly? 2. Did you use more energy moving the rope up and down at a slow pace or a fast pace? 3. How does this activity relate back to the movement of light energy in the electromagnetic spectrum?

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8P4BF Waves and Energy

Reading Science Name:

Date:

Group:

Beauty, Brains, and Bluetooth 1

Most eighth graders are familiar with Bluetooth devices. These inventions automatically make wireless connections using radio waves and very little power over a short distance (less than 10 meters) to devices such as cell phones, computers, digital cameras, etc. Bluetooth technology was named for a 10th century Danish king, Harald Bluetooth. He connected a number of Scandinavian countries under one flag.

However, did you know that 21st century Bluetooth technology was based on a 20th century wireless communication invention developed by a strikingly beautiful female film star, Hedy Lamarr?

Hedy Lamarr’s beauty and talent won the hearts of American moviegoers in the 1940s. While the public knew Hedy for her success in the film industry, few knew of her ability as an inventor. During her first marriage to a Nazi sympathizer, she had to accompany her husband to secret meetings with the Nazis to discuss weapons technology. Hedy was extremely bright. She paid attention to the technical conversations, understood them, and remembered all the details.

After she got divorced, she met an American film producer who was taken by her looks and intelligence. She fell in love, married, moved to the states, and began her movie career. During World War II, Hedy Lamarr was motivated to help with the American war effort. She used her technical savvy and collaborated with George Antheil to develop a wireless “Secret Communications System” to help fight the Nazis.

Their invention changed radio frequencies at irregular intervals between transmission and reception. This formed an unbreakable code and was called “spread-spectrum” frequency hopping. With this communication method, signals are rapidly and randomly changed across a large range of different frequencies. The “hopping” improves the security of wireless communications. It also helps to prevent the interception of classified messages by the enemy.

Lamarr and Antheil received a patent in 1941 for their invention, but it was not used by the military until decades later. Ultimately, the invention Hedy Lamarr created would form the basis for the entire world of wireless connections. Years later, she received the recognition she deserved. Finally, Hedy Lamarr was known as the famous female inventor whose beauty and brains led to the widely popular Bluetooth technology.

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8P4BF Waves and Energy

Reading Science 1.

There are many devices that transmit and receive radio waves, but what makes Bluetooth technology unique? A

Bluetooth transmits wirelessly over great distances with little power usage.

Bluetooth transmits wirelessly over distances of less than 10 meters with little power usage.

Bluetooth uses microwave transmission to transmit wirelessly.

Bluetooth can transmit radio waves over cable connections.

Hedy Lamarr was a film actress, so where did she learn technology to create her Secret Communication System? A

Hedy learned it from listening in on Nazi weapons discussions.

Hedy learned it from attending American colleges.

Hedy learned it from her film-producing husband.

Hedy learned it from library books.

How does spread-spectrum frequency hopping work to protect the security of wireless communications? A

Radio frequencies are kept constant.

Radio wavelengths are changed at regular intervals.

Radio amplitude is changed at regular intervals.

Radio frequencies are changed at irregular intervals.

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8P4BF Waves and Energy

Reading Science 4.

Why is Hedy Lamar’s development of the Secret Communication System so important? A

She was the first female inventor.

Her invention led to the development of modern wireless devices.

She was the first actress to win an Oscar for playing a spy.

She invented Bluetooth.

Why do you think it took so long for her to receive recognition for her invention? A

20th century public attitude about the Cold War

The military’s ability to keep it a secret

Prejudice at the time about a woman’s ability in science

Many female scientists competing for the same award

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8P4BF Waves and Energy

Math Connections Name:

Date:

Group:

Part I: Wavelength, Frequency, Speed, and Period Electromagnetic waves are produced by vibrating, charged particles that result in changes in electric and magnetic fields. Microwave, radio, radar, visible light, ultraviolet, X-rays, and gamma rays are well-known frequencies of electromagnetic waves. Electromagnetic waves are described according to their wavelength, frequency, speed, and period. •

The speed of the wave (v) can be calculated using the equation v = λf, where v is the speed in meters per second, λ is the wavelength in meters, and f is the frequency in Hertz.

•

The period of the wave (T) can be calculated using the equation T = 1 / f, where T is the period in seconds and f is the frequency in Hertz.

A wave cycles up and down 3 times per second, and the distance between each wave is 1.7 m. Calculate the following: a) Frequency of the wave: Hz b) Wavelength: m c) Speed: mps

A sound wave with a frequency of 320 Hz travels through air with a velocity of 300 m/s. Calculate the wavelength.

A gamma ray is a high-energy, high-frequency electromagnetic wave that travels at the speed of light, 3.0 x 108 m/s. If the frequency of the wave is 1020 Hz, what is the wavelength?

The frequency of a longitudinal sound wave is 900 Hz, and its speed is 320 m/s. What is the wavelength of the sound wave?

Which wave has a greater wavelength: red light or blue light?

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Math Connections Part II: Wavelength and Temperature The amount of electromagnetic radiation emitted by an object at a particular wavelength depends on its temperature. Use the data in the table to draw conclusions about the relationship between the temperature and the wavelength of light emitted. 6.

Create a graphical representation of the data using the graph below.

Temperature Peak Wavelength (°C) (microns) 30 9.56 31 9.53 32 9.50 33 9.47 34 9.44 35 9.41 36 9.38 37 9.35 38 9.32 39 9.29 40 9.26

Peak Wavelength (microns)

Infrared Wavelengths and Temperature of Source

Temperature (°C)

Plot a line of best fit on your graph. Is the function linear? Proportional?

What is the rate of change (slope) for the function on the graph?

When you can’t see the y-intercept on the graph, it is still possible to solve the equation of the line using the point slope formula. To use this formula, you will need to know one point on the line and the slope of that line. Use the following formula to solve the equation of the line on your graph: y – y1 = m(x – x1)

10. Use your equation to predict the wavelength of an object with a temperature of 42°C.

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8P4BF Waves and Energy

Writing Science Name:

Date:

Group:

LOOK

THINK String lights give off energy such as heat and light when plugged in. Think about how the energy in the string lights is related to the electromagnetic spectrum.

WRITE Write about the properties of waves, such as wavelength, amplitude, and frequency, as they relate to energy found in the electromagnetic spectrum. Explain how the string lights can be used to illustrate the relationship between energy and the electromagnetic spectrum. Be sure to • clearly state your central idea; • organize your thoughts; • develop your essay in detail; • choose your words carefully; and • use correct spelling, capitalization, punctuation, and grammar.

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8P4BF Waves and Energy

Writing Science

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8th Grade Physical Science

8P4C

Practical Applications of the Electromagnetic Spectrum

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8P4C Practical Applications of the Electromagnetic Spectrum

Student Journal Name:

Date:

Group:

Real-Life Application of the Electromagnetic Spectrum Class Data Collection Directions: As groups present their information, record their data in the chart below. Application

Type of EM Wave Used

Latest Technology

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Advantages of This Technology

Other Uses of This Application

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STEMscopedia: PRACTICAL APPLICATIONS OF THE ELECTROMAGNETIC SPECTRUM 8P4C

Reflect Did you know that when you send a text, tune your radio, heat your pizza in a microwave, or get a dental x-ray, you are using electromagnetic energy? You may not think about it, but you rely on electromagnetic energy every day. Without it, the world as we know it would not exist. Electromagnetic energy is used in the medical field, the military, communication, cooking, and entertainment, just to name a few. Does running a microwave use the same type of electromagnetic energy as sending a text message to your friend? Is one type safer than the other? A Closer Look at the Electromagnetic Spectrum Energy that radiates out from where it is produced is called electromagnetic radiation, and the electromagnetic spectrum is the range of all these types of radiation. Take a look at the spectrum below. The closer the wavelengths are, the higher the amount of energy. Radio waves have the lowest energy and the longest wavelength, while gamma rays have the highest energy and shortest wavelength. Typically, the higher the energy, the more dangerous the electromagnetic radiation. Which type of electromagnetic radiation do you think is the least dangerous? In the next several sections, you will be learning about applications of the electromagnetic spectrum in different fields. Let’s make a prediction. Where would you place the following items on the electromagnetic spectrum? Object

Type of Electromagnetic Radiation

Toaster Television Video Camera Sterilizer for Medical Equipment Cell Phone Signal TV Remote Control

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STEMscopedia: PRACTICAL APPLICATIONS OF THE ELECTROMAGNETIC SPECTRUM

Look Out Just because you can’t see it, doesn’t mean it’s not there. Electromagnetic radiation is made up of photons, and anything made of photons is light. Our eyes can see the part of the spectrum called visible light. Many of the other types of radiation are either too big or too small for our eyes to see, but they are still there! Take a look back at the electromagnetic spectrum diagram and complete the following table. Wavelengths Too Big to Be Seen

Wavelengths Too Small to Be Seen

Electromagnetic Radiation in Communication Radio waves, microwaves, visible light, and infrared are all used for communication. When you tune your car radio, use your mobile phone, or watch television, radio waves are being used. Radio waves have the longest wavelength and can be created by natural sources, such as lightning, or by artificial sources, such as broadcast radio towers. With AM radio, the amplitude of the combined audio frequency and radio frequency waves varies to match the audio signal. However, with FM radio, the frequency of the combined waves change to reproduce the audio signal. There is less interference with FM radio. Microwaves are used to extend TV signals and transmit satellite signals like cell phone calls and texts. Microwave transmitters on buildings communicate with the mobile telephones in their range. Some people believe that mobile phones pose a health risk. This is not accepted by everyone because the intensity of microwaves is too low to damage tissues by heating. Visible light is the light we see. One way it allows us to communicate is by allowing us to create still pictures or movies using video cameras. 306

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STEMscopedia: PRACTICAL APPLICATIONS OF THE ELECTROMAGNETIC SPECTRUM

Infrared is used in communication as well. We cannot see infrared, but it can be felt as heat. It is used to transfer information from place to place, such as your remote for the television or DVD player. Electromagnetic Radiation in the Medical Field Did you know that ultraviolet (UV) waves—the same waves that can be harmful to your skin in sunlight—are also used in medicine? UV rays, x-rays, and gamma rays are all types of electromagnetic radiation that can be used in the medical field. Ultraviolet waves have the ability to inactivate bacteria, and therefore are used to sterilize medical equipment. Ultraviolet light therapy, whether natural or created through medical devices can be used to treat some conditions such as psoriasis and jaundice. It can be given in a clinical setting or at home, and applied over small or large areas from a few minutes to an hour. X-rays are used to diagnose diseases, kill cancer cells, and detect broken bones. They are produced by firing electrons at a metal target. Skin and bone can absorb ionizing radiation. X-rays mostly pass through skin and soft tissue, but Did you know that hanging not easily through bone. your clothes out to dry Gamma rays are also used to treat cancer outside is an effective and as imaging to see inside the body. They way to kill bacteria in your are more energetic than x-rays and therefore laundry? potentially more harmful. Gamma rays, however, can kill living cells, which is an advantage in medicine when killing cancerous cells.

What Do You Think? Both gamma and x-rays have benefits and risks in medicine. They both use ionizing radiation to generate images of the body, which has the potential to cause DNA damage. Do the benefits outweigh the risks? Electromagnetic Radiation in the Military There are endless uses of electromagnetic radiation in the military and defense. Radar (radio waves) is used by pilots to see through clouds and darkness, and in times of war, to detect the presence of enemies. Radar is also important in guiding missile attacks, air defense systems, antimissile systems, marine radars to locate landmarks, and other ships, rendezvous systems, and flight control. Night vision goggles pick up the infrared light emitted by our skin and objects with heat. New military infrared sensors are being developed to improve detection of a wide range of military vehicles. This technology allows helicopters to fly in the darkest of night.

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STEMscopedia: PRACTICAL APPLICATIONS OF THE ELECTROMAGNETIC SPECTRUM

Electromagnetic Radiation into the Future Technology using electromagnetic energy is ever changing and improving. Scientists are working to use infrared technology to predict earthquakes and create new jamming systems that alter incoming signals and send false returns back to the enemy. Others are working to create mini-antennas on a chip. This would allow almost everything in your home or office from toasters and microwaves to washers and dryers to be connected to the Internet! NASA is using x-ray and gamma ray telescopes on orbiting satellites to capture the highest energy light. This may help us one day answer some big questions, such as: What is dark matter? How do massive black holes grow? How did the universe begin and how will it end? The Hubble Space Telescope has been orbiting Earth for over two decades exploring black holes and planets around other stars.

What Do You Know? Draw a diagram of the electromagnetic spectrum and place the following applications on the correct location. Television signal

Radiation therapy

Night goggles

Cell phone

Video camera Radar TV remote Car radio Airport metal detector

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Medical instrument sterilizer

Hubble Space Telescope

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STEMscopedia: PRACTICAL APPLICATIONS OF THE ELECTROMAGNETIC SPECTRUM

Connecting With Your Child Electromagnetic Radiation at Home To help your child gain a better understanding of practical applications of the electromagnetic spectrum, go on a scavenger hunt in your home. Find as many examples as possible of items that use radio, microwave, infrared or visible light energy to function. Have your child identify the item and what type of electromagnetic energy it uses. You can even extend the activity when you go out shopping, driving to practice, or going out to eat. Here are some questions to discuss with your child: 1. Which examples are types of light we can see? 2. Which examples have the longest wavelengths? 3. Which examples have the lowest energy? 4. Which examples have the highest frequency? 5. Why don’t we see as many examples of x-ray and gamma rays in everyday life?

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8P4C Practical Application of the Electromagnetic Spectrum

Reading Science Name:

Date:

Group:

The Electromagnetic Spectrum 1

As the storm clouds roll out and the last of the rain slowly drips to a stop, something magical happens. The Sun peeks through the remaining storm clouds, and a beautiful rainbow appears. Its bright, vivid colors bend in an arch through the sky. The band of light that you see shows you the visible colors of the electromagnetic spectrum. Astronomers, scientists who study space, use the electromagnetic spectrum to learn about the different objects in the universe.

The electromagnetic spectrum can be defined as the electromagnetic waves that are emitted from the Sun and other objects in the universe. To better understand the spectrum, it is broken into smaller categories depending upon wavelength. From the longest to the shortest, the categories are radio waves, microwaves, infrared light, visible light, ultraviolet rays, X-rays, and gamma rays.

Radio waves have the longest wavelength in the electromagnetic spectrum. A single wavelength can span the length of a football field or continue going until it is a mile long. These types of waves have low frequencies and energy. Radio waves bring music to your ears, or a call to your cell phone. Scientists, however, use radio waves to learn about the composition of galaxies, stars, comets, and planets. Astronomers use radio telescopes arranged in an array to collect the waves that are emitted by these astronomical objects.

Microwaves are the next division on the electromagnetic spectrum. Their wavelengths can range from less than an inch in length to as long as a foot. You have probably used microwaves yourself to pop some popcorn or heat up your food. Scientists use microwaves a little differently. These waves can easily pass through different kinds of weather. They are great for sending images back to Earth from space, even on a cloudy day. Astronomers also use microwaves to discover information about the structure of our galaxy and galaxies that are close to us.

Infrared light comes after microwaves on the electromagnetic spectrum. The shortest infrared wavelengths are almost microscopic, while the largest are the size of a pinhead. You experience infrared light every day. The warmth you feel from the Sun, a fire, or a hot metal slide are examples of heat emitted by infrared light. Some of the shorter infrared waves are used by remote-controlled objects like your television or stereo system. Astronomers use infrared light to map the dust between stars. They can also take infrared images of Earth to study cloud structure or ocean temperatures.

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Reading Science 6

In the middle of the spectrum is visible light. Think back to the rainbow that appeared after the storm. The seven colors of light that you see are known as visible light. Visible light is the only electromagnetic light on the spectrum that you can actually see. Red has the longest wavelength, and violet has the shortest. When all of the colors are combined, white light is produced.

Ultraviolet light, or UV light, has a shorter wavelength than visible light. Have you ever been in the Sun for too long? What happened to your skin? The ultraviolet light emitted from the Sun probably gave you a painful sunburn. This type of light cannot be seen by your eye alone. By placing ultraviolet telescopes on satellites, astronomers learn about the structure and evolution of galaxies.

The next electromagnetic wave on the spectrum is X-rays. If you have ever had a broken bone, then you have been exposed to X-rays. X-rays can pass through your skin, but not your bones or teeth. The image produced on the X-ray film will tell the doctor if and where your bone is broken. Astronomers use X-ray telescopes with X-ray detectors placed on satellites to study objects in space. The X-ray telescopes cannot be placed on Earth. Earth’s atmosphere is so thick that it does not allow X-rays to pass through.

Gamma rays are the last electromagnetic wave on the spectrum. Having the shortest wavelength and the most energy, they have the potential to kill cancerous cells. Astronomers use gamma rays to try to understand how the universe began, its age, and how fast it is expanding.

Through the use of the electromagnetic spectrum, scientists find a vast amount of scientific information to study. From radio waves to visible light to gamma rays, each wavelength provides a different answer to the mystery of the universe.

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8P4C Practical Application of the Electromagnetic Spectrum

Reading Science 1.

The statements below compare the similarities of ultraviolet light and microwaves. Which statement does NOT belong in this list? A

Neither can be seen by the human eye.

Scientists use both to study the structure of galaxies.

They both have wavelengths that are longer than visible light.

They are both types of radiation emitted by the Sun.

What is the best wavelength to use if an astronomer wants to study the composition of planets and stars? A

Gamma rays

Radio waves

Visible light

Microwaves

Complete the following analogy: RADIO WAVES : LONGEST WAVELENGTH :: _____ : SHORTEST WAVELENGTH A

INFRARED LIGHT

ULTRAVIOLET LIGHT

X-RAYS

GAMMA RAYS

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8P4C Practical Application of the Electromagnetic Spectrum

Reading Science The term emit is used in the second paragraph. Based on the context, emit means to ___________.

absorb

send out

collapse

review

Wavelength ( ) in meters (m) 104 102 100 10-2

10-4

Wavelength decreasing 10-6 10-8 10-10

Microwaves Radio waves Infrared AM Shortwave FM, TV

104

106

108

1010

X-rays

1012

1014

1016

Frequency R

7.50×10 -7 m 5.

10-14

Gamma rays

Ultraviolet

Frequency (f) in hertz (Hz) Speed of light=3.00×10 8 m/s

10-12

1018

1020

1022

increasing G

Visible Light

V 3.80×10-7 m

Examine the diagram of the electromagnetic spectrum shown above. Which category of electromagnetic waves has a wavelength of 10-8 m? A

Ultraviolet

Radio waves

Microwaves

Red

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8P4C Practical Applications of the Electromagnetic Spectrum

Math Connections Name:

Date:

Group:

Part I: Infrared Wavelengths and Temperature The amount of electromagnetic radiation emitted by an object at a particular wavelength depends upon its temperature. Use the data in the table to draw conclusions about the relationship between the temperature and the wavelength of light emitted. Infrared Wavelengths and Temperature of Source Temperature Peak Wavelength (°C) (microns) 30 9.56 31 9.53 32 9.50 33 9.47 34 9.44 35 9.41 36 9.38 37 9.35 38 9.32 39 9.29 40 9.26 Create a graphical representation of the data using the graph below. Peak Wavelength (microns)

Temperature (°C)

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8P4C Practical Applications of the Electromagnetic Spectrum

Math Connections 2.

Plot a line of best fit on your graph. (Connect the points.)

How does the temperature change with each degree warmer? Write the rate (slope of the line) as a ratio comparing the difference in temperature to one degree.

The y-intercept on the graph at 0 degrees has a peak wavelength of 10.46 microns. You can create an equation for the line by using the formula y = mx + b, where m is the slope and b is the y-intercept. What is the equation for the line on the graph?

Use your equation to predict the wavelength of an object with a temperature of 42°C.

Use your equation to predict the temperature of an object emitting electromagnetic radiation with a wavelength of 9.5 microns.

What can you conclude about the relationship between temperature and wavelength from the information in your graph?

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Math Connections Part II: Reflection, Refraction, and Absorption When rays of light encounter an object, that light can be either reflected, refracted, or absorbed, depending on the makeup of the object. When light hits a surface such as a mirror, it is reflected off the surface. The diagram below shows the angle of reflection and the angle of incidence. Use a protractor to measure the angle of reflection and the angle of incidence. Use the diagram to answer questions 8–10. A

D Mirror 8.

< ADB is the angle of reflection: ______________

< BDC is the angle of incidence: ______________

10. What do you notice about both angles? __________________________________________ When light is transmitted through a surface, the speed of light changes, which causes the angle of the light to change. The extent of the bend in the light ray depends on the material of the surface. Use the diagram below to answer questions 11–13. A

B C

Water D

11. < ACB is the angle of incidence: __________________ 12. < DCE is the angle of refraction: __________________ 13. Are the two the same? _________________

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8P4C Practical Applications of the Electromagnetic Spectrum

Writing Science Name:

Date:

Group:

LOOK

THINK Think about the practical applications of the electromagnetic spectrum.

WRITE Explain the relationship between the electromagnetic spectrum and an x-ray machine as you describe ways the electromagnetic spectrum is applied in our everyday lives.

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8P4C Practical Applications of the Electromagnetic Spectrum

Writing Science

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8th Grade Physical Science

8P4D

Light and Sound Waves

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8P4D Light and Sound Waves

Student Journal Name:

Date:

Group:

Part I: Refraction of Light and Sound Light Procedure 1.

Draw your observations below. Pencil in Empty Glass

Pencil in Glass With Water

Does the pencil appear differently in air than in water? Explain.

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8P4D Light and Sound Waves

Student Journal Part I: Refraction of Light and Sound, continued

2 3

What did you notice about the light as it passed through the lens?

Why did the light behave the way it does as it passes through the lens?

Sound Procedure 5.

Explain what occurred when the toy car rolled from one surface to another.

How does this relate to sound waves refracting?

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8P4D Light and Sound Waves

Student Journal Part II: Diffraction of Light and Sound Light Procedure

1. Draw the path of the light from the flashlight through the prism on the diagram above. 2. Using the map pencils, include the resulting patterns from the light diffracting on the edge of the knife on the above diagram. 3. Read the Background section on your Student Guide. Why did the laser dot change shape?

Sound Procedure 1.

Why were you able to hear your partner even though a book was between you?

Draw how the sound waves would travel in this situation in the space below.

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8P4D Light and Sound Waves

Student Journal Part III: Reflection of Light and Sound Light Procedure

1. Illustrate where the mirrors were placed in the boxes. 2. Draw the path the laser beam took for each trial in the boxes above. 3. What common events occurs in each trial?

4. If light travels in a straight line, how was it possible to strike the target with the beam? Describe the path the light took.

5. Write a list of single words that describe the movement of the light as it strikes the mirror.

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8P4D Light and Sound Waves

Student Journal Part III: Reflection of Light and Sound, continued Sound Procedure 1. Draw a simple diagram that shows the two tubes at an angle. Title the diagram “Sound Waves and the Wall.” Add sound waves to your diagram to represent the event. Label waves that show reflection and/or transmission.

2. Write a statement to predict what you think will happen when using the tubes angled against the other materials as compared to the bare wall.

3. Repeat the process using your chosen materials and add additional diagrams to describe the sound waves during each event. Title and label the diagrams, and then state whether or not your prediction was correct.

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8P4D Light and Sound Waves

Student Journal Part IV: Absorption of Light and Sound Light Procedure 1.

Complete the data table below. Object

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Filter Color/Type

Observations (What color did you see after?)

Drawing of Waves (label absorbed/reflected)

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8P4D Light and Sound Waves

Student Journal Part IV: Absorption of Light and Sound, continued 2.

Diffraction grating works like a prism to break out the color spectrum of light. What color is the light emitted by the flashlight?

When objects appear black, what is happening with the light waves?

When objects appear blue, what is happening with the light waves?

Sound Procedure 1.

Complete the data table for each step of the procedure.

Procedure Step

Observations

Labeled Drawing (include waves)

Describe when and how you were able to detect sound wave absorption.

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8P4D Light and Sound Waves

Student Journal Reflections and Conclusions 1.

Compare and contrast refraction of light and sound.

Compare and contrast diffraction of light and sound.

Compare and contrast reflection of light and sound.

Compare and contrast absorption of light and sound.

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8P4D Light and Sound Waves

Student Journal Name:

Date:

Group:

Part I: Light Transmission

Directions: Fill in the steps below. Review the Student Guide for help, if needed. Step 1: Question

Step 2: Relevance

Step 3: Variables, if applicable independent variable (also known as the manipulated variable) dependent variable (also known as the responding variable) control variable(s) or group (also known as constants) Step 4: Hypothesis Is a hypothesis needed? If so, what is it? How will the responding variable change when the manipulated variable changes? Step 5: Materials

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Student Journal Part I: Light Transmission, continued Step 6: Safety considerations

Step 7: Procedure 1.

Turn on the flashlight and use the light meter to measure the amount of lumens.

Record the amount in the “Lumens From Source” column in your data table with the “Material” as Air and “Lumens Transmitted” as same amount as “Lumens From Source.”

Record any observations of the interaction and draw a diagram of the interaction.

As one person holds the lit flashlight, a second person holds a sheet protector 50 cm away from the flashlight. A third person measures the lumens directly in front of the flashlight and again on the opposite side of the plastic sheet from the flashlight.

Record the lumens in the data table.

Record any observations of the interaction and draw a diagram of the interaction.

Repeat steps 2-6 with the other materials (waxed paper and white copy paper). Record your findings in the data table and draw a diagram.

Step 8: Data collection Use the table to record your data. Material

Lumens From Source

Lumens Transmitted

Diagram

Air Clear Plastic Waxed Paper White Copy Paper

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Student Journal Part II: Sound Transmission Part IIA: How Sound Travels Through Different States of Matter 1.

Fill in the correct state of matter for each material. Rank the materials based on which allowed the loudest and softest sounds to be heard. Material

State of Matter

Rank from 1–3. (1 = Loudest, 3 = Softest)

Sand Water Air 2.

Which material allowed the sound waves to travel the best? Explain your reasoning

Which state of matter allowed the sound waves to travel the worst? Explain your reasoning.

Part IIB: How Sound Travels Through Different Solids 1.

Fill in data table below as you complete the activity.

Material

Listener A

Listener B

Listener C

Success Percentage

Copper Wire Secret Code: _____ Aluminum Wire Secret Code: ______ Cotton String Secret Code: ______ 2.

What material worked best to create a cup telephone?

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Student Journal Reflections and Conclusions 1. What do you notice about the luminosity of light as it transmits through a medium?

2. How does the medium impact how sound vibrations travel?

3. How does the transmission of light and sound compare?

Contrast the transmission of light and sound.

5. Using what you have learned about vibrations, why do you think people sometimes have a hard time hearing when they get off an airplane?

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STEMscopedia: LIGHT AND SOUND WAVES 8P4D Reflect Mention the word waves, and people probably think of ocean waves rhythmically washing over a beach. Or they may think of the rhythmic movement of spectators in a stadium standing and cheering in turn as they do “the wave.” These are just two examples of wavelike behavior that we encounter. They share a wave’s rhythmic movement between a high and low point. They also travel through a substance without really moving the substance from where it started.

Ocean waves wash over a beach.

What are waves? A mechanical wave is an oscillation, or vibration, of the particles in a substance. We call that substance a medium, and it is the stuff that transmits the oscillation. For example, water is the medium through which ocean waves are transmitted. Sounds are also mechanical waves. Sound waves are created by something vibrating. That vibration causes the particles in the medium to be pushed together (compressed) and stretched apart (rarefied). That transmits the vibrations through the medium, which is how sound travels: oscillations moving through a medium. How do sound waves work? The properties of sound waves determine how we hear those sounds. Amplitude is how loud the sound is. A sound with high amplitude is loud, and a sound with low amplitude sounds softer. The pitch is how our ears respond to the sound. For example, to our ears, a flute makes a high-pitched sound while a tuba makes a low-pitched sound. The medium that the wave travels through can affect how the wave travels. For sound waves, this can affect the amplitude and the speed of the wave. You may have noticed that sounds are different underwater compared to in the air. Why is that? We’ll look at how sound waves travel through substances and how the shape of a sound wave affects our perception of that sound.

Look Out Let’s take a look at a sound wave (a longitudinal wave) and how its shape affects the properties of sound. As you can see in the illustration, a sound wave looks like a curvy line. The high points on the line (F) are called the peaks, and the low points (H) are called troughs. How high the peaks are and how deep the troughs are determine the amplitude (G).

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STEMscopedia: LIGHT AND SOUND WAVES You hear differences in amplitude as differences in how loud a sound is. A sound wave with high peaks and deep troughs will sound louder than one with lower peaks and shallower troughs. Remember, the wave is moving, so the peaks and troughs are moving as well. You’ll notice in the illustration to the right that the length of the line is marked as one second. That means that we counted how many waves pass by a given point in one second. The number of waves that pass that point in one second tells us the frequency of the wave. The frequency tells us the pitch of the sound. A high-frequency sound wave has many waves that pass a point in one second. To our ears, we would hear this as a high-pitched sound, like a whistle. Of course, some sounds are too high in pitch for our ears to hear them, like a dog whistle. A low-pitched sound has few waves that pass in one second, or a low frequency. The lowest pitch that humans can hear has a sound wave with 20 waves per second. Some scientists use sounds with frequencies far below that to track earthquakes. For a sound wave to have a high frequency, the peaks have to be close together. For a sound wave to have a low pitch, the sound waves have to be farther apart. The length of the wave is called wavelength. The higher the pitch, the closer together the waves are and the shorter the wavelength. As the wavelength gets longer, the distance between the waves gets larger, and the pitch of the sound goes down. The medium that the sound wave travels through affects how fast the wave can be transmitted. This is determined by the density of the medium. Denser materials allow sound waves to be transmitted faster than less dense materials. Because water is denser than air, sound waves travel faster in water than they do in air. Solids that are denser than water transmit sound waves even faster than water. However, density also affects the amplitude of the wave. Water, being denser, requires more energy to create a sound wave of the same amplitude compared to creating that sound wave in air. For waves of the same amplitude, the lower the density of the medium, the quieter sounds become. The lowest density is in outer space where there is no air. That means there is no medium for the sound waves to travel through. So there is no sound in space!

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STEMscopedia: LIGHT AND SOUND WAVES Try Now You’ve just learned how sounds are caused by mechanical waves moving through a medium. You can make those waves visible by using a glass of water and some earbuds or headphones. Place the glass of water on a countertop or table. Tape the headphones to the outside of the glass. Turn on your music and turn up the volume. Can you see how the surface of the water is vibrating with the music? What happens when you play very low-pitched sounds or very high-pitched sounds?

Look Out Echoes occur as sound waves reflect or bounce off of surfaces. While some sound is absorbed by the surface the waves hit, the remaining sounds continue to move and bounce off of other surfaces until all the sound waves dissipate. Echoes can be heard more easily in an empty room with hard surfaces. Try this. Go into your bathroom and close the door. Call your name out loud and listen for an echo. Then go into your bedroom or other carpeted room and do the same thing. Do you hear an echo as easily as you did in the bathroom? The hard surfaces like tile flooring and bathtub areas do not absorb as much of the sound as carpeting and bed coverings do. Light: Another Type of Wave When you think of light, what do you see? A light bulb? Light from the Sun? Candlelight? We refer to light we see as visible light. Visible light is one type of electromagnetic radiation. While there are many parts of the electromagnetic spectrum, visible light is the only form we use to see. White light can be separated into different colors using a special lens called a prism. When sunlight shines through raindrops, the raindrops can act as a prism and create a rainbow. Visible light is part of the electromagnetic spectrum and is made up of photons having different wavelengths. Visible light ranges in wavelength from about 400 to 700 nanometers (nm). A nanometer is a billionth of a meter. Each of these different wavelengths corresponds to a different color. We see the longest wavelengths of visible light as red light. We see the shortest wavelengths as violet light.

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STEMscopedia: LIGHT AND SOUND WAVES Light Wave Behavior When electromagnetic waves encounter surfaces, they behave differently in the form of reflection (bouncing), scattering (incoming photons going out in all directions), refraction (bending), diffraction (spreading or bending around the edges of an obstacle), or absorption (light energy transferring to another medium). Reflection The most commonly observed wave behavior is reflection. You observe this phenomenon whenever you see your image in a mirror. Reflection occurs whenever a light wave strikes a surface and then bounces back. The angle of incidence equals the angle of reflection. Scattering is different from reflection in that scattered light goes back out in all directions. White surfaces, like many walls, scatter light in all the colors that strike them. Not all light is reflected or scattered. Black absorbs all light. Colored surfaces absorb all wavelengths except for the color reflected. Law of Reflection The reflection of waves from a boundary is similar to the way a billiard ball strikes and bounces away from a wall. If a ball strikes a wall “head on” (meaning it is traveling perpendicular to the wall), the ball will bounce back in exactly the same direction from which it traveled. However, if a ball strikes a wall at an angle to the perpendicular (called the angle of incidence), it will bounce away from the wall at the same angle to the perpendicular (the angle of reflection). Waves behave in the same way, as shown below. In fact, this is called the law of reflection. While a wave’s direction changes during reflection, its speed does not. Refraction A wave can also be transmitted through a boundary, meaning that it passes through the boundary from one medium to another. In fact, at most boundaries, part of the wave is reflected and part is transmitted. Most waves move at different speeds through different media. For example, light moves quickly through air, but more slowly through water. Thus, waves change speeds as they transmit from one medium to another. This change in speed usually causes a wave to refract, or bend, as it passes through the boundary.

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STEMscopedia: LIGHT AND SOUND WAVES Refraction can be thought of as black dots in this diagram that represent a group of students marching across a room. The students represent a light wave. The left side of the room represents air (a relatively fast medium), and the right side represents water (a relatively slow medium). When the students pass from left to right, one student crosses the boundary ﬁrst. This student begins moving slowly, but the rest of the group still travels quickly, causing the students to change direction, or bend, as they move into the new medium. This is known as refraction. Refraction through concave or convex lenses allows correction to poor vision or to magnify objects. Refraction through water bends the image. Refracting telescopes use lenses to gather light from distant sources such as planets, stars, or galaxies, and focus that light through an eyepiece. Diffraction Have you ever watched water waves pass through a narrow slit in a barrier? When the waves pass through, they spread out radially. This is known as diffraction. For example, when a light bulb is turned on in a dark room, light waves spread out radially from the light bulb. However, once the waves have traveled a certain distance, they can be thought of as plane waves that move in parallel “sheets.” When a plane wave passes through a narrow slit or a barrier, the wave will act as though it is originating from a point source again. Thus, the wave spreads out, or diffracts. This can also happen when a wave approaches a solid barrier. In these cases, when the wave passes along any edge of the barrier, it will spread out radially around the barrier. In this way, waves will appear to “bend” around barriers. This is the reason you can hear sounds that are emitted from behind a wall or large building. This also explains how we can see light through curtains in a window.

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STEMscopedia: LIGHT AND SOUND WAVES Connecting With Your Child Building a Periscope A periscope is a tool consisting of several mirrors at opposite ends of a long tube that allows people to see around objects. Designing and building a periscope is an excellent way to learn about the fundamental laws of reflection. Remember, light travels in straight lines, and the angle of incidence (where it hits) equals the angle of reflection (how it bounces off). (In other words, the angle at which a light ray approaches a mirror is the same as the angle the light ray bounces off the mirror.) Plans and instructional videos for building a periscope can be easily found on the Internet. Use the search term “periscope plans.” For most designs, you will need the following items: • A long, square box or enough cardboard to make such a box • Two small pocket mirrors • A protractor • A sharp knife • Duct tape As you and your child position the mirrors at either end of the box, explain the significance of the angles at which the mirrors are set. (The first mirror must reflect light entering the periscope toward the mirror at the other end of the periscope. This mirror must then reflect light toward the eyepiece of the periscope.) Consider watching videos of how a periscope is used on board a submarine. Encourage your child to find other uses for the periscope. For example, a periscope can let someone look around a corner or above a couch.

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8P 4DEF Mechanical Waves and Sound

Writing Science Name:

Date:

Group:

LOOK

THINK Think about sound waves.

WRITE Describe how different mediums (solids, liquids, or gases) affect the behavior of sound waves, and explain how changes in amplitude and pitch affect parts of mechanical waves.

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8P 4DEF Mechanical Waves and Sound

Writing Science

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8P4D Light and Sound Waves

Reading Science Name:

Date:

Group:

Supersonic Ships? 1

Sound waves move differently through different media. In general, they travel faster in liquids and solids than in air. The speed of sound in dry air is 343 m/s at 20ºC. It is faster at sea level than at higher altitude because the air is denser at sea level. Increased humidity also increases sound velocity slightly, by about 0.1–0.6%. Airplane speeds are often reported in Mach numbers. The Mach number depends on the medium that the object travels through. To calculate the Mach number, divide the speed of an object by the speed of sound in that medium.

Sound travels at a much higher speed through water. The speed of sound is 1,533 m/s through seawater. However, it is only 1,493 m/s through fresh water at the same temperature and depth. The speed of sound is increased by increases in temperature and salinity. Sound also travels faster when water pressure increases, such as at greater depth in the ocean. By comparison, sound velocity in steel is about 5,100 m/s. Therefore, you can hear an approaching train from farther away by putting your ear on the railroad track.

If you live near an Air Force base, you might hear an occasional loud boom as a fast-moving fighter jet passes overhead. The boom indicates that the jet has broken the sound barrier. During flight, an airplane pushes the air ahead of it. As it approaches the speed of sound, the air does not have time to get out of the way. A sonic boom is created as the airplane breaks through the sound barrier. The sonic boom wave starts at the nose and sweeps along the plane, as shown in the picture above. The sonic boom travels at the speed of sound away from the aircraft. It will reach your ears after the aircraft has passed overhead.

On October 14, 1947, Charles “Chuck” Yeager flying the Bell X-1 was the first person to break the sound barrier in level flight. Since then, both military and commercial aircraft have broken the sound barrier. Although unmanned aircraft have traveled faster, the fastest manned plane is the SR 71 Blackbird. It has traveled at 936 m/s, or about three times the speed of sound: Mach 3. The SR 71 Blackbird set records for a manned air-breathing flight for both speed and altitude.

The SR 71 Blackbird was retired in 1999. The only supersonic commercial airliner flown to date was the Concorde, which retired in 2003. It crossed the Atlantic between New York and Paris at twice the speed of sound. The Concorde traveled at a cruising speed of Mach 2. Only 20 Concordes were ever built.

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8P4D Light and Sound Waves

Reading Science 6

In contrast, the fastest ship was the Spirit of Alaska, traveling at 142 m/s in 1978. If the Spirit of Alaska traveled in fresh water, its speed would be about 0.1 Mach. Merchant ships carry cargo. They are more concerned about fuel costs than transit time between ports. They travel about 11 m/s. Cruise ships carry passengers. They try to arrive in port in the morning so passengers have time to explore the city. They may travel at slightly higher speeds. The top published speed of Navy vessels is about 26 m/s. During wartime, ships may have to worry about torpedoes. Even torpedoes, which are much smaller and more streamlined than ships, travel below the speed of sound. Maximum torpedo speed is about 103 m/s. Ships and submarines use sonar technology to detect torpedoes with sound waves. If they can detect the torpedo before it arrives, they can take action to avoid being struck.

In summary, several factors combine to make it difficult to build supersonic ships. The first factor involves the motion of an object through water. Water is much more dense than air and thus has much more drag due to friction and turbulence. At the same time, sound travels through water much faster than it travels through air. Combined, these facts make it difficult to build a supersonic ship.

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8P4D Light and Sound Waves

Reading Science 1.

As the temperature of seawater increases from 15ºC to 20ºC, sound velocity through the seawater ____________. A

remains the same

increases

decreases

depends on the distance of the observer from the sound source

The first supersonic flight was in 1947. It was just above the speed of sound. Which altitude would the reader expect Captain Yeager to have used for his flight? A

Sea level

1,000 m

13,700 m (within altitude used by commercial planes today)

85,000 m (where meteor showers originate)

Which plane’s velocity was greatest? A

Yeager’s Bell X-1

Concorde

SR 71 Blackbird

None of the above. They all traveled at the same speed.

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8P4D Light and Sound Waves

Reading Science 4.

A torpedo is launched under water, targeting a naval vessel about 5,000 m away. How can the vessel detect the torpedo before it reaches the vessel? A

By seeing it flying above the water

By listening for it in the air

By listening for it underwater

None of the above. It won’t be able to detect it in time.

A Navy vessel is traveling due north during wartime. A torpedo has been launched by an enemy directly toward the stern (rear) of the vessel. Can the vessel outrun the torpedo if both continue in a straight line due north? A

Yes; the Navy vessel is faster.

No; the Navy vessel is slower.

Maybe; both travel at the same speed.

Maybe; it depends on the temperature of the water.

Why is it harder to build a supersonic ship than a supersonic airplane? A

Sound velocity is greater in water, and it is harder to move through.

Sound velocity is greater in water, and it is easier to move through.

Sound velocity is greater in air, and it is harder to move through.

Sound velocity is smaller in air, and it is harder to move through.

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8P4D Light and Sound Waves

Math Connections Name:

Date:

Group:

Wavelength can be measured as the distance from one crest to the next, or from one trough to the next, on transverse waves. With sound waves, the shorter the wavelength, the higher the frequency and pitch of the sound. Characteristics of Low Octave Piano Notes

C C# D D# E F F# G G# A A# B

Frequency (Hz) 16.35 17.32 18.35 19.45 20.6 21.83 23.12 24.5 25.96 27.5 29.14 30.87

Wavelength (cm) 2110.09 1991.92 1880.11 1773.78 1674.76 1580.39 1492.21 1408.16 1328.97 1254.55 1183.93 1117.59

2500 Wavelength (cm)

Note

2000 1500 1000 500 0

5 10 15 20 25 30 35 40 Frequncy (Hz)

Create a scatterplot of the relationship between the frequency and wavelength of the different notes listed in the table above.

Is the relationship linear? Proportional? Support your answer using evidence from the graph.

If the product of the frequency and wavelength is the speed of sound, what is the speed of sound in m/s? Round to the nearest whole number.

Which note in the chart has the highest pitch? Why?

Which note in the chart has the lowest pitch? Why?

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8P4D Light and Sound Waves

Math Connections The amplitude is the maximum distance that the particles of a wave’s medium vibrate from their rest positions. It is half the vertical distance between the crest and the trough. In sound waves, amplitude indicates the loudness of the sound. The graphs represent three different sounds. Sound A Sound B

Sound C

Order the sounds from loudest to quietest? How do you know?

Sound is produced by the vibration of particles in a medium, and moves relatively slowly through the medium. Sound travels faster in liquids and non-porous solids than it does in air. Speed of Sound and Density of Gases Metal Air Helium Methane Nitrogen Oxygen Carbon Dioxide

Density kg/m3 1.205 0.1664 0.668 1.165 1.331

Speed (m/s) 342 1007 446 349 326

1.842

267

Speed of Sound and Density of Solids Metal Diamond Brass Stainless Steel

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Density kg/m3 3.50 8.48 7.82

Speed (m/s) 12000 3475 5790

How does the density of a gas affect the speed of sound?

About how much faster does sound travel in helium than in air?

Does sound travel faster through solids or gases?

10.

How does the density of a solid affect the speed of sound?

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8P4D Light and Sound Waves

Writing Science Name:

Date:

Group:

LOOK

THINK Think about light waves.

WRITE Explain how manipulation of light waves can cause reflection, refraction, diffusion, and absorption; and describe how different mediums (solid, liquid, or gas) affect wave behavior.

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8P4D Light and Sound Waves

Writing Science

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8th Grade Physical Science

8P4E

Wave Behavior in Different Media

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8P4E Wave Behavior in Different Media

Student Journal Name:

Date:

Group:

Activity: Waves can be categorized as either mechanical or electromagnetic. Mechanical waves are waves that need a medium to travel through to carry energy from one point to another. Mechanical waves cannot travel or carry energy in a vacuum. Examples of mechanical waves include sound waves and water waves. Electromagnetic waves do not need a medium and can transfer energy in a vacuum. Electromagnetic waves form when electromagnetic fields oscillate. Examples of electromagnetic waves include radio waves, x-rays, gamma rays, ultraviolet rays, visible light rays, and microwaves.

Part I Record your findings from dropping the marble into the media.

Data Tables Trial #1

Trial #2

Medium

Distance (cm)

Time(s)

Medium

Distance (cm)

Times(s)

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Speed (cm/s)

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8P4E Wave Behavior in Different Media

Student Journal Part I, continued Trial #3

Medium

Distance (cm)

Time(s)

Speed (cm/s)

Average Speed

Medium

Trial #1

Trial #2

Trial #3

Average Speed

Explain the difference in the speed of the waves in the different media.

Does the time of wave correlate to the speed of the wave? Explain your answer.

In which medium did the wave move the fastest? How was that possible?

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8P4E Wave Behavior in Different Media

Student Journal Part II Rank the different liquids from least dense to most dense and include the actual density of each liquid.

Data Table

Medium

Density

Least Dense

Most Dense

What similarities and differences did you notice in the liquids and their densities?

Were your predictions accurate? Explain why or why not.

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8P4E Wave Behavior in Different Media

Student Journal Part III

Record your observations in the table below. Data Table

Medium

Observation

Conclusions and Analysis 1.

How is density calculated?

How does the density of the media affect the wave speed?

Why do you think scientists need to understand the way that density affects the movement of a wave when predicting the speed of waves during a natural disaster?

What conclusion can you draw from the three parts of this lab when working with waves?

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STEMscopedia: WAVE BEHAVIOR IN DIFFERENT

MEDIA 8P4E

Reflect Have you ever observed fish swimming in an aquarium? Think about the difference between observing the fish through the glass and just looking down into the water from the top of the aquarium. Have you noticed the distortion that makes it look like the fish is somewhere other than where it actually is? This is due to light waves moving from one material––air––to another material–– water and glass. Wave Behavior in Different Media What happens to wave characteristics like wavelength, frequency, and speed when the waves move from one medium to another? A medium is the matter that waves travel through, such as air, water, or wood. It’s important to remember that the media does not travel or move, only the wave energy. When waves cross a boundary from one medium to another, the speed and wavelength will be affected. Refraction of Light Waves When a wave moves from one medium to another, usually its direction will bend slightly. This is known as refraction. Examples of this can be seen by looking into a glass tank full of water, then sticking your hand into it. Your hand will appear to be slightly over from where you actually put it in due to the refraction of light waves traveling from one liquid medium (air) into another (water). The different densities of air and water are what cause this refraction. If you were running along the beach and then ran into the water, you would slow down. This is what happens with light waves, as well. The speed of light is constant only in a vacuum. Since there are no other molecules in the vacuum of space, there is nothing to slow it down. When light waves enter Earth’s atmosphere, they are slowed by air particles.

Notice how the stems that are under water seem slightly offset from where they are above the water. This is due to the light waves bending, or refracting, as they move through different media.

We can calculate how light waves will move through a medium based on the Refractive Index of the particular medium. n = c/v Where n=the refractive index, c=speed of light in a vacuum, and v=velocity of light in the medium.

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Some n values of known substances are: Vacuum

n=1.000

Air at STP

n=1.0003

Water

n=1.54

Polystyrene

n=1.59

Diamond

n=2.42

Application Using the formula n=c/v and the values from table 1, which material has the highest density?

What Do You Think? Based on what you have learned about light waves and density, which material would bend light more noticeably, water or diamond?

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STEMscopedia: WAVE BEHAVIOR IN DIFFERENT

MEDIA

Look Out Is light a wave or a particle? Since Pythagoras and Aristotle, scientists have tried to work out the nature of light. Light both scatters like a particle and bends like a wave. We know that that light exhibits what scientists classified as wave-particle duality. So it is both a wave and a particle. Speed of Sound Like light, sound waves will also be affected by the density of the material it is traveling through. Unlike light waves, sound waves must have some sort of medium to travel. Sound is not something you will encounter in a vacuum.

Sound waves travel from a source to a recipient.

Sound waves are longitudinal waves, meaning they are propagated by one molecule pushing into its neighbor. The closer the neighbor particles are to each other (a denser medium), the quicker the sound will travel. If the neighboring particles are further apart, it will take longer for the sound wave to reach a destination. This is the opposite of what you see in light waves. Temperature can also affect sound wave speed. Warmer air molecules are more excitable, so they transfer the wave energy quicker than cooler air molecules.

What Do You Think? Now that you have learned about sound waves and the media through which they travel, can you answer the age-old question: “If a tree falls in the forest and no one is around to hear it, does it make a sound?”

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STEMscopedia: WAVE BEHAVIOR IN DIFFERENT

MEDIA

Connecting With Your Child It is easy to experiment with sound waves at home! Sound waves can travel through any material or medium. Sound will travel at different speeds depending on the material or even the temperature of different objects. Sound travels fastest in dense materials such as metal and wood. It may seem counterintuitive, but this can be demonstrated with some common household items. Materials: A wooden desk or table Metal spoons of different sizes Yarn or string A wooden ruler Procedure Part I First, just do a simple observation of sound through air versus a solid medium. Have your child stand near the table and knock on it. Have your child describe the sound. Then have your child place their ear on the table while you knock and have them describe the difference in the sound. Part II 1. Cut a length of yarn or string about 2.5 feet long. 2. Make a loop and tie the string to the handle of the spoon halfway along the length of the yarn. (might need a picture or graphic here) 3. Have your child take the two ends of the string and hold them up to the ears while the spoon is left hanging down. 4. Now gently tap the spoon on the round side with the ruler, and have your child describe what he or she hears versus what you hear. 5. Repeat this process with as many different spoons as you like.

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8P4E Wave Behavior in Different Media

Reading Science Name:

Date:

Group:

Seismologist Uses Wave Behavior to Reveal Earth’s Core 1.

In many western movies, a scout would put his ear to the ground to listen for an approaching enemy. They knew intuitively that sound waves travel more clearly and more quickly in solid ground than through the air. Our world is filled with an enormous number of examples where different media affect the behavior of waves by changing their velocity, reflecting/refracting waves, or completely absorbing waves.

Humans have learned to pass sound and light waves through different media for different uses. String, woodwind, and metal instruments produce different sounds from different vibrating media. Acoustic ceilings in auditoriums are made of sound-absorbing materials so the medium will not transmit interfering sound waves. Mirrors are used to reflect light waves, such as bathroom mirrors or tiny mirrors in laser light shows reflecting brilliant laser light shapes. Spectroscopes bend or refract light through a diffraction-grating medium that separates visible light into its component wavelengths. X-rays penetrate soft tissue, change speed through bony tissue, and show up in stark black and white contrast images.

These applications are examples of wave technology used on the surface of Earth where humans live and work. It was not until 1936 that wave behavior was used below the surface of Earth to advance our knowledge of the structure of Earth’s layers. Danish seismologist Inge Lehmann used the idea of the scouts who listen to the ground for sound waves. Seismic waves are produced from slipping tectonic plates along fault lines or plate boundaries.

Instead of observing pounding hooves of approaching horsemen, she used earthquake waves captured on seismographs. She knew that when earthquake waves pass from one medium to another, they change speed and direction. Before Lehmann, geologists thought Earth has only a rocky outer crust, a molten mantle, and a liquid core.

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8P4E Wave Behavior in Different Media

Reading Science 5.

Lehmann studied earthquakes near New Zealand and discovered that some waves did not pass through the core and were actually recorded at different stations. Lehmann wrote her theory that these waves went into the core and then bounced off some sort of boundary that she believed represented two layers in Earth’s center: a solid inner core surrounded by a liquid outer core. This structure was confirmed in 1970 when more advanced seismographs recorded waves deflecting off this solid inner core.

Through her pioneering work on seismic waves, we have learned that P-waves travel as longitudinal (back and forth) compression waves through solids and liquids. P-waves can travel through the liquid outer core and solid inner core. S-waves travel as transverse (up and down) waves and only travel through solids. The liquid outer core blocks S-waves.

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8P4E Wave Behavior in Different Media

Reading Science 1.

Why do you think scouts could hear better through the solid ground rather than through the air? A.

The particles in solids have more kinetic energy and can transfer the sound more easily.

The particles in solids have indefinite volume and shape.

The particles in solids are closer together so the sound waves pass more quickly.

The particle in solids are farther apart so the sound waves pass more quickly.

Acoustical ceilings, musical instruments, and spectroscopes are examples of technology that takes advantage of sound waves that change speeds and make different sounds because __________. A.

the medium has changed

the amplitude has changed

the electromagnetic spectrum has changed

the magnetic fields have changed

Seismic waves are produced from which of the following? A.

Water seeping through cracks in Earth’s surface

The alternating freezing and thawing of Earth’s surface

Earth slipping along faults or plate boundaries

None of the above

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8P4E Wave Behavior in Different Media

Reading Science 4.

Leymann discovered that P-waves pass through all layers but S-waves did not, which revealed the center of Earth has a __________. A.

liquid outer core and solid inner core

solid outer core and liquid inner core

liquid inner and outer core

solid inner and outer core

Which of the following has a similar wave structure to the longitudinal compression P-waves? A.

An outstretched metal coil toy that is pulled alternately back and forth

An outstretched metal coil toy that is pulled repeatedly up and down

An outstretched metal coil toy that is swung around like a jump rope

An outstretched metal coil toy that is held up on one end and dangling downward

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8P4E Wave Behavior in Different Media

Math Connections Name:

Date:

Group:

The speed of a wave is a measure of how fast the crest moves from one position to another. The speed is expressed of as a ratio of distance to time. Sound waves can move through media at different rates due to the characteristics of that medium. The temperature, density, and elasticity of media affect the wave’s speed. Sound waves move differently through gases, liquids, and solids. Below are several charts comparing the density of various media and the speed of sound waves as they travel through them. Sound Waves in Gases Gas Air Hydrogen Helium Krypton Oxygen Methane Propane

Temperature (°C) 20 20 20 20 20 20 20

Density (g/L) 1.205 0.0899 0.176 3.742 1.33 0.668 1.882

Speed of Sound (m/s) 344 1270 1007 221 927 446 258

Graph the relationship between density and the speed of sound on the grid below.

What is the shape of the graph?

What is the relationship between the density of a gas and the speed of sound waves as they travel through it?

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8P4E Wave Behavior in Different Media

Math Connections Sound Waves in Liquids Liquid Alcohol (propyl) Water Glycerine Castor Oil Acetone

Temperature (°C) 25 25 25 25 25

Density (kg/m3) 800 997 1259 956.1 784.6

Speed of Sound (m/s) 1205 1402 1920 1490 1170

Graph the relationship between density and the speed of sound on the grid below. Draw in a regression line.

What is the shape of the graph?

What is the relationship between the density of a liquid and the speed of sound waves as they travel through it?

Compare how the speed of sound changes in gases vs. liquids in relation to the position of the molecules in the substance.

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8P4E Wave Behavior in Different Media

Math Connections Sound Waves in Solids Solid Copper Cast Iron Glass Pyrex Titanium Aluminum Gold

Density (g/cm3) 8.96 6.8 2.23 4.5 2.7 19.32

Speed of Sound (m/s) 2260 2500 3280 3125 3100 1200

Graph the relationship between density and the speed of sound on the grid below. Draw in a regression line.

What is the shape of the graph?

10. What is the relationship between the density of a solid and the speed of sound waves as they travel through it? 11. Compare how the speed of sound changes in solids vs. in liquids in relation to the position of the molecules in the substance.

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8P4E Wave Behavior in Different Media

Writing Science Name:

Date:

Group:

LOOK

THINK Some fishermen rely on fishing poles and bait to catch fish. Bears, on the other hand, use their claws to pin down fish or swat them out of the water and onto the riverbank. Think about light refraction as it applies to fishing.

WRITE Decide whether the fishermen or the bears are more affected by refraction, and describe how different media (solid, liquid, or gas) affect wave behavior. Be sure to • clearly state your central idea; • organize your thoughts; • develop your essay in detail; • choose your words carefully; and • use correct spelling, capitalization, punctuation, and grammar. © Accelerate Learning Inc. - All Rights Reserved

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8P4E Wave Behavior in Different Media

Writing Science

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8th Grade Physical Science

8P4G

Lenses

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8P4G Lenses

Student Journal Name:

Date:

Group:

Background 1.

Compare and contrast concave and convex lenses.

What is a focal point? What is focal length?

Part I: Lens Effects 1.

Draw a picture of your finger when looking through one of the concave and one of the convex lenses in the spaces below. Concave Lens

Convex Lens

How are these lenses similar? How are they different?

Predict what the light will do when it goes through a concave lens.

Predict what the light will do when it goes through a convex lens.

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8P4G Lenses

Student Journal Part I: Lens Effects, continued 5.

Draw a ray diagram of what the light looked like when it went through the same two lenses you used for question 1. Concave Lens

Convex Lens

In what direction does light bend through a concave lens?

In what direction does light bend through a convex lens?

Make observations and models that illustrate what occurs when you combine the lenses in various combinations. Lens Combination

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Observations

Model

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8P4G Lenses

Student Journal Part II: Instruments That Use Lenses 1.

Complete the data table as each group presents their tool. Don’t forget to include your own tool on the table. Depending on the number of groups in your class, you may not use all the rows, or you may need to add rows. Instrument (Tool)

Uses

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Model of Lens(es)

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8P4G Lenses

Student Journal Reflections and Conclusions 1.

Explain what happened to the ray of light as the concave lens moved back and forth.

Explain what happened to the ray of light as the convex lens moved back and forth.

Based on the tools presented in Part II, name four careers that use lenses and describe how they use them.

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STEMscopedia: LENSES 8P4G Reflect Before the first telescopes were invented at the beginning of the 17th century, people looked up at the stars with their naked eyes. The first refracting telescope that Galileo developed in 1609 was likely about as powerful as a pair of binoculars today, but he eventually became the first person to see the rings of Saturn. Sir Isaac Newton developed the reflecting telescope, allowing scientists to see exponentially more stars. Telescopes became increasingly more powerful and sophisticated throughout the centuries, but the launch of the Hubble Space Telescope was a giant step forward. Without Earth’s atmosphere to hinder viewing, the Hubble Space Telescope sights far into deep space, capturing images of galaxies in all stages of evolution, black holes, planets being created, and stars being born and dying. In the works is the James Webb Space Telescope, which is scheduled to launch in October 2018. It will be able to discern even more about our universe by looking through dust that blocks visible light. What wonders will we be able to discover about the past and future of our universe? We can only imagine…

Galileo

Drawing of Isaac Newton’s reflecting telescope

Hubble Space Telescope

View of deep space via telescope

Look Out A common student misconception is that light passes through transparent objects without changing direction. In truth, light always travels in a straight line, but it travels at different speeds through different materials. Generally, the denser the material, the slower light travels. When light travels through air and then hits a glass window, the speed of light changes while traveling through the window so that it is refracted (bent). It travels a constant speed through the window and then is refracted again as it enters the substance on the other side of the window. So light always travels in straight lines, but not the same straight line when it encounters different materials. Characteristics of Light Before investigating lenses, you must understand a few characteristics of light. According to current scientific knowledge, light travels faster than any other known entity. It travels through space at approximately 186,000 miles a second. It could travel around the equator seven times in a second! Light travels in a straight line.

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STEMscopedia: LENSES What happens when light hits an object? It either passes through, is reflected, or is absorbed. When it passes through something, it may be bent (refracted) and will then continue in a new straight line. The angle of refraction is the change in direction of a ray of light as it passes from one material into another. Every material bends light differently. The index of refraction is a value that describes the ability of a material to bend light. Each material has its own index of refraction. Look at the table below to see the index of refraction for some common materials. Index of Refraction for Common Materials Material Vacuum Air Water Glass Vegetable Oil

Index of Refraction 1.0 1.0003 1.33 1.5 1.57

Although there is a broad range of “light,” when we speak of “light,” we are usually referring to white visible light. White light is composed of a spectrum of colors—red, orange, yellow, green, blue, indigo, and violet. Interestingly, the index of refraction varies very slightly depending upon the color of the light. Dispersion describes how the refractive index varies slightly depending upon the color of the light.

What Do You Think? How does a prism work? Look at the image below and try to explain how it breaks white light into its spectrum of colors.

Lenses A lens is made of a transparent material through which you can view images. Because lenses are made of different materials than air, they refract (or bend) light. Variously shaped lenses bend light in different ways and are used for specific purposes.

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STEMscopedia: LENSES A convex lens is curved on both sides. It is thicker in the middle and thinner at the edges. This means the light rays coming out of it come together at a point—they converge. A concave lens is thinner in the middle and thicker at the edges. The light rays that come out of it diverge.

A focal point is an important aspect of lenses that needs to be understood. It is the point at which light rays meet before or after refraction through a lens. The focal points are in different places depending upon whether a lens is convex or concave. When light enters a converging lens, the focal point occurs after the light has entered and exited the lens. When light enters a diverging lens, the focal point is actually located before the light enters the lens and is scattered. In other words, a convex lens bends light in toward a focal point while a concave lens refracts light away from a focal point. Look at the images to contrast the focal points of the two lenses.

Lenses are used to make many tools that help people to see distant objects as if they were closer or microscopic objects as if they were larger. Convex lenses are used in cameras, telescopes, magnifying glasses, and binoculars. Concave lenses are used in flashlights, peepholes, and glasses for nearsightedness. How do these tools use lenses to assist people?

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STEMscopedia: LENSES Telescopes In 1608, Hans Lippershey applied for the first patent for a refracting telescope. Galileo improved upon that model and viewed craters on the Moon the very next year. One century later, Isaac Newton invented the reflecting telescope. Since then, telescopes have gotten larger and more sophisticated to help us see far into the heavens. All telescopes use lenses in some capacity, but reflecting telescopes also use mirrors. Telescopes use the light from distant objects and bring it to a concentrated point called the focal point. The telescope then enhances the light from the focal point using a lens that magnifies the light and image on your eye, which makes the object appear much larger. Refracting Telescopes A refracting telescope uses two lenses to bend light and cause items to appear larger. They are made from a long cylinder and two separate lenses—an objective lens and an eyepiece lens. The function of the objective lens is to retrieve light from something and bend it to the focal point, which is located at the back of the tube near the eyepiece lens. The objective lens is convex so it can direct the gathered light to converge upon the focal point at the back of the telescope. The job of the eyepiece lens is to magnify the image so it appears larger to your eye. Eyepiece lenses can be either convex or concave.

Reflecting Telescopes A reflecting telescope is different from a refracting telescope in that it is constructed in such a way as to direct the flow of light onto a different path. It also uses two mirrors (primary and secondary) instead of an objective lens to gather the light and reflect it to a focal point. Instead of having an eyepiece at the opposite end of where the light enters the telescope, reflecting telescopes have an eyepiece lens on the side. Light enters and travels to the back of the telescope, where the primary mirror reflects it to the secondary mirror. The secondary mirror focuses the light to a focal point right in front of the eyepiece lens. The eyepiece lens magnifies the image onto the retina just like it does in a refracting telescope.

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STEMscopedia: LENSES Microscopes The inventor of the optical microscope remains disputed, but the microscope appears to have been invented around the same time as the telescope in the early 17th century. Optical microscopes have one or more lenses and can work together to magnify objects up to 1250 times. They work in a manner similar to telescopes, with a few minor differences. Because telescopes collect light from dim objects that are far away, they require large objective lenses. Microscopes, on the other hand, only need to gather light from a small area that usually already has a light source, so it uses a very small objective lens. Then, just as with telescopes, an image is magnified by a second lens, called the eyepiece lens. Another variance from telescopes is that microscopes usually have a light source and a condenser, a tool to focus light on the exact area of the sample that will be magnified by the objective lens.

What Do You Know? Have you ever gone to a restaurant and ordered a glass of water with a straw in it? When you look at the glass, the straw seems to be broken! Why does that happen? Write a paragraph and/or draw a diagram explaining what is happening in reference to the light. Hint: Think about the speed of light when it travels through different materials and what might happen when light moves from one material to another.

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STEMscopedia: LENSES Connecting With Your Child Since Hans Lippershey invented the first telescope in 1608, people have been making instruments that contain lenses for a variety of purposes—from telescopes to binoculars to spectacles. To help your child better understand the concept of lenses, create a lens together out of simple household materials. Materials: You will need a tennis ball, a serrated knife, vegetable oil, a small glass, distilled water, and a book. Procedure: • An adult should cut the tennis ball in half. • Pick one-half of the tennis ball and coat the inside with vegetable oil. • Place the half tennis ball in the glass (open side up) and make sure it is level. • Fill the tennis ball half to the top with distilled water. • Put the glass/tennis ball/water carefully in the freezer. • When the lens is frozen, pop it out of the tennis ball and run your warm hands over the flat part of the lens to smooth it out. • Keep the curved side of the ice toward your eye and hold the lens over a page of the book. • Practice focusing the lens by moving it up and down, closer to and farther away from the page. • Try using both sides of the lens to view a variety of objects. • Hint: Try to get the lens out of the freezer as soon as it is thoroughly frozen because it may turn cloudy and be hard to see through if it is left in the freezer for too long. Here are some questions to discuss with your child: 1. Why do you think it was necessary to smooth out the flat part of the lens? 2. What did you notice when you held the ice lens over the book page? 3. What happened when you “focused” the lens by moving it up and down over the book page? 4. What did you observe when you tried both sides of the lens on a variety of objects around the room? 5. Why did the ice lens work?

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8P4G Lenses

Reading Science Name:

Date:

Group:

Telescopes 1.

Galaxies trillions of miles away, stars being born, stars dying, comets crashing into planets, distant solar systems, and black holes––these are all images from the Hubble Space Telescope that we take for granted in the 21st century. The successor to the Hubble Space Telescope, the James Webb Space Telescope, is currently under construction, with a scheduled launch in 2018. It will be capable of looking through particles that block visible light and will perceive infrared light emitted by even more distant objects than we have presently detected. It is hard to imagine that throughout history, until the 17th century, people were only able to stargaze with their naked eyes.

Hans Lippershey is credited with creating the first telescope in 1608. The very next year, Galileo greatly improved upon that refracting telescope by using a combination of convex and concave lenses. A convex lens is also called a converging lens because it is thicker in the middle and thinner on the edges, which causes light to come together at a point. Convex lens are more widely used than concave lenses. A concave lens is also termed a diverging lens because it is thinner in the middle and thicker at the edges, which causes light to spread out as it exits the lens. With his improvements to the telescope, Galileo was able to view craters on the Moon, spots on the Sun, faint bands of stars in the Milky Way, moons orbiting Jupiter, and the rings around Saturn. In the 18th century, Sir Isaac Newton invented a reflecting telescope that combined both mirrors and lenses.

A refracting telescope is a long cylinder that bends light to make items appear larger. It consists of two lenses—an objective lens and an eyepiece lens. The objective lens retrieves light and directs it to the focal point near the back of the telescope. The eyepiece lens at the rear then magnifies the illuminated image at the focal point. The process of double magnification and illumination of the object causes the image to appear much larger on your eye.

A reflecting telescope differs from a refracting telescope in several ways. It bends light on another path using mirrors and a lens. A reflecting telescope is designed to direct light to the primary mirror at the back of the telescope, which reflects the light to the secondary mirror. The function of the secondary mirror is to focus the light in front of the eyepiece lens, which is on the side of the telescope. Because mirrors are much lighter weight than lenses, reflecting telescopes tend to be larger and, thus, more powerful than refracting telescopes.

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8P4G Lenses

Reading Science 5.

Since the invention of the telescope, technology has continued to develop, and telescopes have become more proficient at magnifying very distant objects. Two major obstacles have hindered astronomers in their quest to study the heavens with telescopes. First, the light from distant objects is very dim. Scientists and engineers have overcome this issue by building bigger telescopes and more sensitive cameras. The second problem has been a bigger challenge—blurry images resulting from distortion caused by Earth’s atmosphere. Groundbased telescopes have benefited from a technique called adaptive optics, in which a computer program automatically and continuously adjusts images, correcting for atmospheric distortion. The best solution, however, has been to put a telescope in space, outside of the interference of Earth’s atmosphere. In 1990, scientists did just that with the launch of the Hubble Space Telescope, which is a medium-sized reflective telescope. Images from the Hubble have had greater clarity than any predecessor’s images. The Hubble has taken clear pictures of objects trillions of miles away. With this new technology, learning about our universe has dramatically increased, such as the knowledge that our universe is approximately 14 billion years old. The forthcoming launch of the James Webb Space Telescope should allow us to investigate and learn even more about our universe. The possibilities are vast and exciting.

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8P4G Lenses

Reading Science 1.

The purpose of this passage is to ____________. A.

inform readers of the history, development, and uses of telescopes

convince readers that refractive telescopes are better than reflective telescopes

convince readers that reflective telescopes are better than refractive telescopes

promote continued investment into future telescopes

Which scientist was NOT involved in the development of early telescopes? A.

Sir Isaac Newton

Nicolaus Copernicus

Galileo

Hans Lippershey

What do reflecting and refracting telescopes have in common? A.

The use of mirrors

The location of the eyepiece

The use of lenses

The same inventor

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8P4G Lenses

Reading Science 4.

Which is NOT a reason reflecting telescopes are often preferred for studying astronomy? A.

Mirrors are cheaper than lenses, so larger reflecting telescopes can be constructed for the same price.

The eyepiece in a reflecting telescope is in a more convenient location.

Mirrors reflect all colors of light at the same angle, producing sharper images than lenses.

Mirrors are lighter than glass lenses, so reflecting telescopes are not limited in size by the weight of their lenses.

Why does the Hubble Space Telescope take clearer pictures than other telescopes? A.

It uses adaptive optics to adjust for Earth’s atmosphere.

It is one of the largest telescopes ever manufactured.

It operates outside Earth’s atmosphere.

It is a reflective telescope rather than a refractive telescope.

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8P4G Lenses

Math Connections Name:

Date:

Group:

Image Formation

The position and size of an image reflected from a plane mirror, or refracted from a thin convex lens, can be predicted by drawing a ray diagram and by mathematical calculations. A thin, convex lens is also called a converging lens because it causes parallel light rays to converge to a single point. The image formed by a converging lens can either be real, inverted, and located in the space on the opposite side of the lens from the object, or it can be virtual, upright, and located on the same side of the lens as the object. The location and size of an image can be determined mathematically using the Thin Lens Equation: 1 + 1 = 1 i o f f = the distance from the lens to the focal point i = the distance from the lens to the image o = the distance from the object to the lens 1.

A house is 16 feet from a converging lens with a focal length of 8 feet. How far from the lens does the image of the house appear?

The distance between a vase of flowers and its image in a flat mirror is 40 cm. What is the distance from the vase of flowers to the mirror?

State the type of lenses shown below. a.

b. What does point X represent?

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8P4G Lenses

Math Connections 4.

Four physics students are working on an experiment with a convex lens, placing objects at different distances relative to the focal length (F) of the lens. Below is a table of the results. Filling in the missing information. Object distance Image distance Real or virtual Upright or inverted

Beyond 2F

At 2F

50 cm

35 cm

30 cm

15 cm

30 cm

50 cm

real

inverted

upright

A. _________ B. __________

Between F and 2F Between Lens and F

C. _________ D. ___________ E. __________

How far from a converging lens with a focal length of 25 cm will the image of a vase of flowers appear if the distance between the vase and the lens is 35 cm?

A soap dispenser is 5 cm tall and is placed 45 cm from a double convex lens with a focal length of 17 cm. What is the distance between the soap dispenser’s image and the lens? Round to the nearest hundredth.

Angela is far sighted. She is comfortable reading text at a distance of 70 cm from her eyes. She went to the eye doctor recently for corrective lenses that allow her to read comfortably at a distance of 35 cm. Angela is walking past a few signs in the mall and notices that one of the signs is 70 cm away but appears to be 35 cm away. Find the focal length of the corrective lens.

A glass of water is placed 20 cm from a converging lens with a focal length of 10 cm. How far does the glass of water appear to be from the lens (or what is the distance between the object’s image and the lens)?

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8P4G Lenses

Writing Science Name:

Date:

Group:

LOOK

THINK Think about the effect and the function of lenses when they interact with light waves.

WRITE Explain how the manipulation of light waves can cause reflection, refraction, diffusion, and absorption as they relate to lenses.

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8P4G Lenses

Writing Science

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8th Grade Physical Science

8P5A

Fields and Forces

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8P5A Fields and Forces

Student Handout Name:

Date:

How Strong Is Earth? Activity 1.

Hold a book flat at waist height.

Release the book.

Record what you observed.

Draw a labeled diagram to identify the parts of the system you just observed. Title the diagram.

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8P5A Fields and Forces

Student Journal Name:

Date:

Group:

Mapping Force Fields

Pre-Activity Discussion 1.

What is a force?

Clearly, movement can be seen when I touch an object and apply a push or a pull. I can push the object (push the book) or pull it (hold the band and pull), and the motion of the book as a test object changes. However, we have been studying forces that can act at a distance. What are they?

The ability of these forces to act at a distance depends on fields of force generated by a source object that exist invisibly around the object. We have learned that the strength of these force fields changes based on distance to the source object. How does distance affect the strength of these force fields?

Does gravity demonstrate attraction or repulsion?

Does electromagnetism demonstrate attraction or repulsion?

If we think in terms of an object’s force field, does gravity push or pull?

If we think in terms of an object’s force field, does electromagnetism (both magnetic fields and electric fields) push or pull?

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Student Journal Mapping Force Fields Part I: Mapping Gravitational Force Fields Using a Test Object 8.

Record your observations, and draw a diagram of the gravity well.

Complete the following. 9. The test objects for the force that acts at a distance were... 10. Describe the interaction of the forces using a complete sentence.

11. Draw a labeled diagram to identify the parts of the system. Title the diagram. Under the diagram, record what you observed using complete sentences.

12. Use complete sentences to explain how the plastic wrap allowed you to map the force field of gravity.

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8P5A Fields and Forces

Student Journal Mapping Force Fields Part I: Mapping Gravitational Force Fields Using a Test Object, continued 13. How did you map gravitational force fields with a test object? Did the forces at a distance demonstrate a push, a pull, or both? How did the test object demonstrate the interaction of the force fields?

14. How did you map magnetic force fields with a test object? Did the forces at a distance demonstrate a push, a pull, or both? How did the test object demonstrate the interaction of the force fields?

15. How did you map electric force fields with a test object? Did the forces at a distance demonstrate a push, a pull, or both? How did the test object demonstrate the interaction of the force fields?

Part II: Mapping Magnetic Forces Using a Test Object The paper will look like the diagram below.

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8P5A Fields and Forces

Student Journal Mapping Force Fields Part II: Mapping Magnetic Forces Using a Test Object, continued Setup 1: Magnetic North and a Compass 1.

As a group, agree on a summary statement that describes the interaction between the north end of the bar magnet and the compass pointer.

Chose several positions (at least four) to place and trace around the compass on the circle path. Draw in the positioning of the north end of the compass needle on each tracing of the compass.

Copy the diagram created by the group in the space below. Title the diagram. Write a summary statement that describes the interaction between the north end of the bar magnet and the compass pointer below the diagram.

Setup 2: Magnetic South and a Compass 4.

As a group, agree on a summary statement that describes the interaction between the north end of the bar magnet and the compass pointer.

Chose several positions (at least four) to place and trace around the compass on the circle path. Draw in the positioning of the north end of the compass needle on each tracing of the compass.

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8P5A Fields and Forces

Student Journal Part II: Mapping Magnetic Forces Using a Test Object, continued Setup : Bar Magnet and a Compass 7.

Choose several positions (at least eight) to place and trace around the compass to represent the path around the bar magnet. Draw in the positioning of the north end of the compass needle on each tracing of the compass.

Answer the question set about magnetic force fields using complete sentences. 9.

What is the test object for the forces acting at a distance?

10. Describe the interaction of the forces.

11. How did this activity allow you to map a magnetic force field?

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8P5A Fields and Forces

Student Journal Mapping Force Fields Part III: Mapping Electric Forces Using a Test Object

Observe the movement of the pieces of hair. Record your observations.

Draw a diagram or map of the pattern formed by the pieces of hair.

Answer the question set about electric force fields using complete sentences. 3.

What is the test object for the forces acting at a distance?

Describe the interaction of the forces in this activity.

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STEMscopedia: FIELDS AND FORCES 8P5A Reflect Looking up into the sky, you see a dot. As you continue to gaze, the dot becomes larger and larger. You finally see that it is a skydiver falling toward Earth. The person is falling because of the gravitational pull of the Earth. Wait, the skydiver has just pulled his chute open and he’s still falling but slower—gravity still at work. It doesn’t matter how high something is—even if something is as high as the International Space Station in orbit above Earth—gravity is still pulling it toward Earth. gravity: a force that pulls objects toward other objects Maybe your brother or sister likes to play superheroes, who have special powers that can pull an object toward them or push it away. Maybe you have seen someone blow up a balloon and rub it against his or her hair. When the balloon is pulled away, the person’s hair stands up because it is attracted to the balloon. Maybe you’ve experimented with a magnet, testing it on different objects to see if anything is pulled toward it. force: energy that pushes or pulls

All of these are examples of fields and forces. Electric, magnetic, and gravitational forces all create force fields. Forces that act at a distance can be explained by fields that extend through space. Gravity Gravity is a force that pulls objects toward other objects. That means we all have our own gravity! However, the force of attraction is very weak unless one of the objects is very large. Because Earth is very large, you can feel it pulling on you. This pull is called your weight. You cannot feel the pull between yourself and smaller things, like other people, because the force is too weak. Gravity always pulls; it never pushes. I. Gravity is a force. II. Gravity keeps planets in orbit around the Sun. III. Gravity keeps the Moon in orbit around the Earth.

mass: measurement of the amount of matter in an object weight: measurement of the force of gravity on an object

Instead of saying Earth is large, we should say it has a lot of mass. The more mass an object has, the harder it is to move. Gravity is the attraction between any two masses. The force of gravity is stronger when the masses are greater. The farther apart the masses are from each other, the weaker the force is between them.

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STEMscopedia: FIELDS AND FORCES Magnetism Magnetism, or magnetic force, is a noncontact force exerted by a magnet. A magnet is any material that attracts iron, a metallic element, and a few other metals. A magnetic force exists between a magnet and the object that is attracted to it. The magnetic force is exerted over a distance and includes forces of attraction and repulsion. A magnet can exert a force over a distance because the magnet is surrounded by a magnetic field. Magnetic force and its resultant magnetic field have a direction. A magnet is surrounded by a magnetic field. Both electric and magnetic forces are produced when charges from one piece of matter interact with those of another piece of matter. These forces can be attractive (pulling objects together) or repulsive (pushing objects apart). The concentration of filings near the magnet’s poles indicates areas of strongest force. Magnetic field lines never cross. fields: forces that act across a distance Electric Forces Electric forces are forces that occur due to electric charges. There are two types of electric charges—positive and negative. An electric charge is described by the electric field associated with it. An electric field is produced by all electric charges, whether they are moving or stationary. An electric field can also be produced using varying magnetic fields. Electric forces can be either attractive (if both charges are of different types) or repulsive (if both charges are of the same type). Electric force is an invisible force produced by an electrically charged particle. Objects can have electric charges. Most objects have equal charges. However, if a positive charge builds up, the object becomes positive. If a negative charge builds up, the object becomes negative. Charged particles or objects with more electric charge produce a stronger and larger electric force. The strength of the electric force decreases with distance.

Look Out Many people speak of weight and mass as if they were the same thing. They are not, but it is easy to see why people think they are. Mass is the amount of matter something has. Weight measures the gravitational pull of an object’s mass. What if you were standing on a planet that had more mass than Earth? Would you have the same mass? Would you have the same weight? You would have the same mass because you would be made of the same stuff. You would weigh more because the larger the planet, the larger the gravitational pull. For example, if matter weighs 100 pounds on Earth, the same piece of matter would weigh 236 pounds on Jupiter.

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STEMscopedia: FIELDS AND FORCES When astronauts go to the Moon, their mass doesn’t change. However, they weigh much less. Think about when astronauts are on the Moon. They can jump extremely high! That is because they don’t weigh as much on the Moon. The Moon’s gravity pulls them less. The two ends of a magnet are different. One end is called the north pole. The other end is called the south pole. Any part of a magnet pulls on things made of iron and a few other metals. However, the north pole of one magnet pulls only at the south pole of another magnet. Two north poles push each other away. Two south poles also push each other away. Magnetic force is caused by certain particles that make up an object. When these particles are all arranged in the same way, the object becomes a magnet. The magnetic force of a magnet forms a pattern called a magnetic field. A magnetic field is made up of magnetic lines of force. The lines of force are invisible, but there is a way to see their shape. Put a magnet under a piece of paper and sprinkle small bits of iron on the paper. The iron bits will line up with the lines of force. You can see this in the image above. The strength of an electric field is related to the quantity of the charge and its distance from the source. Therefore, the larger the quantity of charges that are collected in one place, the larger the electrical field will be. Also, the closer charged particles are to each other, the stronger the electric force field will be. Electric forces also act across distances, forming electric fields. Similar to how magnets have north and south poles that can attract or repel each other, there are positive (+) and negative (-) electric charges that attract and repel. Opposite charges, (+) and (-), attract. Like charges, (+) and (+) or (-) and (-), repel. If the electric field source is positive, the field radiates outward from the source. If the electrical field source is negative, the field radiates inward. We use this information to manipulate electric fields in experiments and in real-world applications.

Try Now Fill in the graphic organizer with the correct letter from the following list. A. Static electricity B. Nails C. Planets moving around the Sun D. Vase falling to the floor E. Dried clothes clinging to one another in dryer F. Compass G. Walking across carpeted floor and touching a door handle H. Toddler going down a slide I. Paper clips © Accelerate Learning Inc. - All Rights Reserved

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STEMscopedia: FIELDS AND FORCES

Gravity

Fields and Forces Magnetic

Electric

Connecting With Your Child There are several activities you can do with your child. The first one just requires a balloon. Blow up the balloon and tie it off. Let your child rub the balloon against your hair and pull it away. Your hair will stand straight out as your child pulls the balloon away. Discuss what causes this interaction between the balloon and hair. Try rubbing the balloon on a wool sweater or polyester shirt. Let the balloon go and watch it stay in place. What causes this? Is it the same explanation as the previous activity? The next activity will require a two-pound bag of rice, small metal nails (not copper), a clear plastic food container with a lid, and a magnet (preferable a wand or horseshoe). Place the rice in the plastic food container. Throw in the small metal nails. Place the lid on the container and shake until the nails disappear from sight. Place the magnet against the container and move it around the container and watch what happens to the nails. Discuss this with your child. Now shake the container again. Hold the magnet several inches away from the container and see if it attracts the small nails in the same manner. This final activity will need several items: toothpick, salt crystals, pepper, tacks, marble, penny, belt buckle, and a magnet. With your child, see to which articles the magnet is attracted. If you have two magnets, hold the like poles together and feel what happens. Then try holding the unlike poles together.

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8P5A Fields and Forces

Reading Science Name:

Date:

Group:

Gravity 1

What happens when you throw a basketball up toward the hoop? If you are lucky, the ball sinks into the net, scoring two points before dropping back down to the ground. The basketball isn’t that heavy. Why doesn’t it stay up in the air when you throw it? Have you ever heard the saying, “what goes up must come down”? This saying helps explain what happens to the basketball. It is being acted on by an invisible force called gravity. Gravity is the basic force in the universe that attracts all objects to each other.

Gravity has existed since the beginning of the universe. It is hard to understand how or why it works. We know it is always there because it holds everything in the universe in place. First, you need to understand that there is a gravitational attraction between you and Earth, between Earth and the Moon, and between Earth and the Sun. You can’t feel the gravitational attraction between you and Earth. However, it is what keeps your feet planted firmly on the ground. Imagine spinning around and around on a merry-go-round. As long as you are holding on, you will stay on the merry-go-round. If you ever let go, you will fly off and land on the ground. This analogy helps us visualize the gravitational attraction between Earth and you. Earth is spinning on its axis. Thanks to gravity, you are held to your position on Earth rather than flying out into space.

Focus next on the gravitational attraction between Earth and the Moon. The Moon and Earth are attracted to each other by the same force of attraction between you and Earth. This attraction keeps the Moon traveling in a nearly circular orbit around Earth. Also consider the effect of the Moon’s gravitational force on Earth’s oceans. The gravitational pull of the Moon causes the ocean tides to rise and fall.

There is attraction between you and Earth and between the Moon and Earth. The Sun also has a gravitational pull on Earth. This attraction results in Earth orbiting the Sun. The Sun’s attraction is so strong that all objects in the solar system orbit around this medium-sized star. What would happen if the Sun’s gravitational attraction suddenly disappeared? The comets, asteroids, and all the planets, including Earth, would fly off into space just like you would if you let go of a merry-go-round.

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Reading Science Continued 5

All objects are attracted to each other, so why are some attractions stronger than others? For example, Earth’s gravity has a more powerful effect on you than the Sun’s gravity. With the Sun’s gravitational attraction holding all of the objects in the solar system, how could this be possible? The force of gravity between two objects depends on two things. It depends on the mass of the two objects and the distance between them. The greater the mass of the objects, the greater the gravitational force between them. In other words, the bigger an object is, the more gravity it has. However, when analyzing the effects of gravity, distance also matters. The closer objects are to each other, the greater their gravitational force of attraction. As they get farther apart, the force between them becomes weaker. Even though the Sun is much more massive than Earth, the distance between you and Earth is less. The gravitational pull of the Sun has little effect on you because the distance is so great.

Gravity is the invisible force that attracts all objects, no matter their size or mass. The Sun has the strongest gravitational force of any object in the solar system. It attracts all astronomical objects into orbit around itself. Without this force, everything would fly off in all directions through the universe.

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8P5A Fields and Forces

Reading Science 1.

Which of the following summaries expresses the main points of the passage best? A

Gravity is the most important aspect of our universe. Without it we would all be floating off into the universe. There wouldn’t be any orbits; instead, all planetary bodies would simply float around, running into each other when they crossed paths and just wandering forever.

There is a gravitational force between all objects in the universe. Gravitational force is what keeps all components of our solar system in orbit around the Sun, as well as moons in orbit around planets. The force of gravity affects Earth’s tides and holds us on Earth’s surface. The force of gravity between objects depends on their masses and the distance between them.

Gravity is hard to understand and scientists have little to no understanding of how it works. We know that gravity is out there, but the specifics are often lost on us. Plants, animals, and humans are all able to grow tall due to the pull on Earth from the Sun. Without the Sun, we would all just stretch out along Earth’s surface.

None of the above.

Upon what does the force of gravity between two objects depend? A

The amount of attraction between the two objects

How much each object weighs

How close the objects are to each other

The mass of the two objects and the distance between them

Which best describes why gravity on Earth has a stronger attraction with you than the Sun has? A

Earth has more mass than the Sun allowing a stronger attraction to form.

The Sun has more mass than Earth.

Earth has a smaller mass than the Sun, but it is much closer to you than the Sun allowing for a stronger attraction.

Earth has more magnetism than does the Sun.

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8P5A Fields and Forces

Reading Science 4.

The Sun is to a planet as – A

Earth is to the Moon.

the tides are to the Sun.

a moth is to a flame.

the seasons are to the Moon.

Halley’s comet is a comet that passes close to Earth every 75 years. Based on this passage, which gravitational attraction has the most influence on the movement of this astronomical object? A

Attraction between the comet and Jupiter

Attraction between the comet and the Moon

Attraction between the comet and Earth

Attraction between the comet and the Sun

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8P5A Fields and Forces

Math Connections Name:

Date:

Group:

Newton’s law of gravity states that every particle attracts every other particle with a force that is proportional to the product of their masses and inversely proportional to the distance between the particles. The formula for gravitational force is: F=

(G)(m1)(m2) , where: r2

G=universal gravitational constant = 6.67×10–11 N – m2/kg2 m1=mass of object 1 (kg) m2=mass of object 2 (kg) r=distance between the objects (meters) Use the following information to answer questions 1–5. Celestial body

Mass (kg)

Celestial body

Mass (kg)

Sun

1.98×1030

Earth

5.97×1024

Jupiter

1.89×1027

Venus

4.86×1024

Saturn

5.68×10

Mars

6.41×1023

Mercury

3.30×1023

Neptune

10.24×1025

Moon

7.34×1022

Uranus

8.68×1025

Pluto

1.25×1022

What equation is used to solve for the force Earth exerts on Mars, if the two planets are 7.77×1010 m apart from each other?

What is the force Saturn exerts on a man with a mass of 90 kg standing on Earth, if the man is 1.277 × 1012 m away from Saturn?

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Math Connections 3.

Neptune is 4.18×1010 m from Earth and 4.93×1010 m from Venus. Based on these distances, which planet should have the greater gravitational force on Neptune? When you calculate the gravitational force using their masses, does your conclusion still hold true?

Using the formula provided, create a formula with which you could calculate the mass of Object 1.

If the Eiffel Tower in Paris is 1.21×107 m from the Statue of Liberty in New York and 1.42×106 m from the Trevi Fountain in Rome, which monument would you expect to exert more gravitational force on the Eiffel Tower? (Do not take the masses into account.)

Use the following information to answer questions 6 –7. People have been trying to recreate models with familiar objects to help us understand the scale of the planets in our galaxy. 6.

One person scaled down the solar system so that the Carrier Dome at Syracuse University in Syracuse, N.Y., represented the Sun. If the diameter of the Carrier Dome is 0.16 km and the diameter of the Sun is 1.4 million km, what is the scale for this model?

Another person scaled down the solar system so that Spaceship Earth at Epcot Center at Walt Disney World in Orlando, Florida, represented the Sun. If the diameter of Spaceship Earth is 0.05 km and the diameter of the Sun is 1.4 million km, what is the scale for this model?

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8P5A Fields and Forces

Writing Science Name:

Date:

Group:

LOOK

THINK Think about the effect gravity has on a person.

WRITE Explain the role of gravity in our solar system.

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8P5A Fields and Forces

Writing Science

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8th Grade Physical Science

8P5B

Causes of Electrostatic Forces

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8P5B Causes of Electrostatic Forcess

Student Journal Name:

Date:

Group:

How Does Electricity Flow? Part I: Circuit Closed Circuit Draw the arrangement of your circuit that made the bulb light up. Label the parts in the circuit. This is called a closed circuit.

Open Circuit Draw and explain an open circuit.

In the closed circuit, what keeps the light shining?

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Student Journal Part II: Conductors and Insulators 1.

List the objects you tested and circle the results. Object Tested

Cup used for materials

Conductor

Insulator

Light stayed on

Light turned off

Light stayed on

Light turned off

Light stayed on

Light turned off

Light stayed on

Light turned off

Light stayed on

Light turned off

Light stayed on

Light turned off

Light stayed on

Light turned off

Light stayed on

Light turned off

Name some other items that might be conductors or insulators.

Explain another way that you could test the items for conductivity.

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STEMscopedia: CAUSES OF ELECTROSTATIC

FORCES

Reflect

8P5B

Have you ever noticed that on a cold day you tend to feel an electric shock every time you touch something metal? Have you ever combed your hair and noticed that the strands follow your comb? Have you ever taken a balloon and tried to stick it to the wall? Or have you ever wondered why lightning is attracted to the ground? What do all of these things have in common? Electrostatic forces, of course! Electrostatic Forces: A Shocking Discovery We have all experienced an electrostatic force, whether we knew it was a force or not. So to understand electrostatic forces, we must first understand that the force is electricity at rest. Electricity is an electrical charge caused by the collection or flow of electrons. So you should remember that electrons are the negatively charged particles that are found in atoms. So how can you apply this to your life? Have you ever wondered how two people who are complete opposites are somehow dating? Blame it on electricity. Not the electricity you feel when you are in love, but the flow of electrons. So just like in life, electricity acts similarly. If the charges of the particles are the same, then they will repel each other. If the charges of the particles are opposite, positive and negative, then the charges will attract each other. See, science even mimics life: opposites attract while like charges repel. Electrostatic forces can be transferred. Have you ever rubbed your shoes on the carpet and then touched something metal? Or worse, touched your friend or sibling? You emit an electrical spark, and, if you look closely, you can see the electrical discharge. You may have done it to be funny, but did not think about the science behind your little practical joke. When you rub your shoes on the carpet, you are transferring the electrons from the carpet to your shoes through a force called friction. Friction is a form of conduction, transfer through contact. So friction is the resistance of a substance to the motion created. In other words, the carpet is resisting against the motion you are creating. Since you have negatively charged particles, they are looking for a positively charged surface to release the electrical discharge. Unfortunately for your friend or sibling, he or she happens to be this surface. Can you induce the charge? Speaking of opposites attracting, we cannot leave out a lightning storm. A lightning storm is an example of how opposites attract due to a process called induction. Induction is the movement of charges in an object that result in one side being overly positive or negative due to it coming close to another surface without actually making contact with the surface. During an electrical storm, or lightening storm, the bottom of the clouds are negatively charged. This induces the ground to become positively charged, through a process called polarization.

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STEMscopedia: CAUSES OF ELECTROSTATIC

FORCES

Polarization is a term used to describe an object that has one side more positively or negatively charged than the other. Since opposites attract, the resulting consequence to this phenomenon is the discharge of the electrical force. Lightning can also be discharged from cloud to cloud, because the tops of the clouds are mostly positively charged. Not only are can you demonstrate polarization at work inside a cloud during an electrical storm, but you can see the effects in everyday objects. Have you ever combed your hair and watched as the hair strands followed your comb? You can also see it at work by rubbing a balloon on your head and watch as the balloon adheres to the wall. Do you really want to show your magical skills at work? Run a comb through your hair and turn on your faucet at home. Watch as the water bends as you move the comb closer to the stream of water.

What Do You Know? In the pictures below draw, positive and negative charges to demonstrate your understanding of electrostatic forces.

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STEMscopedia: CAUSES OF ELECTROSTATIC

FORCES

Connecting With Your Child Talk to your child about the various electrostatic forces that were demonstrated in the text. To make things more concrete for your child, have them test various materials to see which materials transfer electrons the best. Materials • 3 Styrofoam packaging peanuts • Dry and empty water bottle • Various material pieces (fur, faux fur, leather, cotton fabric, polyester fabric, plastic mesh, wool, denim) Procedure 1. Break up the Styrofoam packaging peanuts into one-eighth-inch pieces. 2. Place the Styrofoam pieces into the plastic bottle and place the cap back on. 3. Take one of the material pieces and rub the bottle vigorously, back and forth, on it for one minute. 4. Write down your observations of the Styrofoam pieces inside the bottle. 5. Repeat steps 3 and 4 until you have used each material piece. After completing the activity, create some diagrams to show which materials created the Styrofoam peanuts to adhere to the bottle more. Answer the following follow up questions: 1. Which material created a more electrostatic environment? How do you know? 2. Which materials created the least electrostatic environment? How do you know? Bonus Challenge: If you have more time, use a balloon to test the fabrics and place the Styrofoam peanut pieces on a table. Race your family to see who can pick up the most pieces in a minute.

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8P5B Causes of Electrostatic Forces

Reading Science Name:

Date:

Group:

Measuring Elementary Charge 1

Robert Millikan and Harvey Fletcher performed an experiment to measure the elementary charge in 1909. The diagram to the right shows the experimental setup. Fine oil mist is sprayed into a chamber through a nozzle. Friction in the nozzle makes some droplets become charged. The droplets fall through the chamber into the area between the metal plates. The voltage is turned off initially, and all droplets fall due to gravity. Once the voltage is turned on, the electrical force on charged droplets counteracts the gravitational force, and some drops begin to rise. A single droplet is selected by alternately turning on and off the voltage. The uncharged droplets fall to the bottom.

When the experiment is performed in air, four forces act on each oil droplet. Both buoyancy and the coulomb, or electrostatic, force push the droplet upward. Gravity and friction push the droplet downward. The charge on each droplet can be calculated from the voltage that keeps the droplet stationary. Each droplet should have an integer multiple of the elementary charge. The smallest charge measured is the charge of an electron.

Several important factors influence the success of the experiment. The amount of oil in each droplet cannot change over time. Otherwise, the gravitational force on the droplet changes over time. This would introduce error into the calculation. Intense lights used in this experiment heat the oil. Many types of oil evaporate when heated. Evaporation would decrease the amount of oil in each droplet over time. Therefore, Millikan and Fletcher selected oil that evaporates very little. Another factor is the orientation of the metal plates in the gravitational field. A small difference from perpendicular introduces an error in the calculated charge.

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Reading Science Continued 4

The value Millikan and Fletcher measured for elementary charge is slightly smaller than the currently accepted number. They used an incorrect value for the viscosity of air. This affected their calculation. The number for elementary charge underwent several revisions. Each time the number became a little bigger. Noted physicist Richard Feynman remarked on the way physicists arrived at the currently accepted number. Feynman suggested that physicists calculating a value that was significantly larger than Millikan’s thought they were wrong. They looked for problems in their experiments to explain their “error.” Physicists are subject to bias just as other humans are. Physicists measuring elementary charge trusted the previously published results more than their own calculations. One might call this bias “conformity bias.” Conformity bias can be defined as the belief that previously published findings can’t be very far off. Conformity bias can be both good and bad. It can lead to more thorough experimentation and analysis. It can also ignore truly novel results.

According to theory, all charge has to be a multiple of the elementary charge, the charge of a single electron. More than 100 million additional oil droplets have been measured during the “Search for Isolated Fractionally Charged Particles” performed at Stanford University. An automated apparatus similar to Millikan and Fletcher’s setup was used. No fractionally charged droplet was found. Therefore, while the currently used number for the elementary charge is slightly different from what Millikan and Fletcher measured, the assertion that all charge consists of multiples of the elementary charge is universally accepted.

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8P5B Causes of Electrostatic Forces

Reading Science 1.

Millikan and Harvey set out to measure – A

the diameter of oil droplets under an electric force.

the value of the elementary charge.

the force of gravity on oil.

the viscosity of air at various temperatures.

If the top metal plate is negatively charged, what is the charge of the droplets that will be attracted to it? A

Negative

Neutral or no charge

Positive

Either negative or positive, depends on the droplet size

If a droplet has three extra electrons, what is its measured charge? A

1/3 of an elementary charge

1 elementary charge

2 elementary charges

3 elementary charges

In paragraph 3, evaporation of oil from droplets during the experiment is a potential source of – A

excess charges.

neutral drops.

error.

gravity.

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Reading Science 5.

Which of the following may be an example of “conformity bias”? A

Biologists announcing the existence of a new class of mammals.

Chemists using a novel computer program to design cancer drugs.

Stanley Prusiner insisting that prions are a new way to transmit infections.

Physicists dismissing numbers that differ significantly from their previous findings as errors.

The search for fractionally charged particles has – A

measured more than 100 million droplets and found no partially charged droplets.

reanalyzed Millikan and Fletcher’s data and found less than 1% fractionally charged droplets.

been denounced by leading physicists as not necessary.

been discontinued due to numerous errors in the experiment.

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8P5B Series and Parallel Circuits

Math Connections Name:

Date:

Group:

Electricity flows in a closed path to form a series circuit and stops when the circuit is broken. A battery produces the force (measured in volts) that pushes the current through the wires. The force from the battery is shared equally between the bulbs in the circuit. In a series circuit, current can only flow along a single path. In the circuit below, three 9 volt batteries are used to power the circuit.

How many volts run through this light bulb?

As more of the same type of light bulbs are added, the voltage in the circuit is shared equally among them. Fill in the chart below to show the amount of voltage each bulb receives as more bulbs are added to the circuit. Number of Bulbs

Voltage per Bulb 3.

Plot the relationship between the number of bulbs and the voltage of each bulb on the grid below. Provide a title and label the axis with the correct descriptions.

27 24 21

18 15 12 9 6 3 0

What equation describes the relationship between the voltage per bulb, v, and the number of bulbs, n?

Do the bulbs get brighter or dimmer with each additional bulb added?

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8P5B Series and Parallel Circuits

Math Connections In a parallel circuit, current can flow along multiple paths. The total voltage is the same across each path. In the circuit below, four 9 volt batteries are used to power the circuit. 6. How many volts run through each path?

A 7. Will the bulbs in Path A be brighter or dimmer than the bulbs in Path B? Why?

8. How many volts will each bulb in Path A receive?

9. H ow many volts will each bulb in Path B receive? 10. If a bulb from Path A is unscrewed, how many bulbs will continue to stay lit? 11. If a bulb from Path B is unscrewed, how many volts will each bulb in Path A recieve? 12. What is a benefit of using a parallel circuit instead of a series circuit? 13. Draw a parallel circuit using the following clues: • The circuit runs in three paths, each receiving 15 volts of force. • The batteries powering the circuit are 9V batteries. • The light bulbs on Path A each receive 7.5 volts. • The light bulbs on Path C each receive 3 volts. • The light bulbs on Path B each receive 3.75 volts.

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8P5B Causes of Electrostatic Forces

Math Connections Name:

Date:

Group:

Electrostatic force is a result of the electron and proton interactions between different materials. Electrostatic force can be caused between two objects by conduction, induction, and friction. Conduction occurs when a neutral object comes in contact with a charged object. The electrons transfer from one object to another, resulting in a change in charge of both objects. Modeling Conduction with Mathematics Step 1: A negatively charged object and a neutrally charged object are not touching. _

Charge: -4

Charge: 0

Step 2: As the two objects come closer together, the positive and negative charges in the neutral object start to separate. + _ _ _ _

Charge: -4

Charge: 0 = (+2) + (-2)

Step 3: When the two objects touch, some of the negative charge from the negatively charged object will transfer to the neutral object. _

(-2) + (+2) = 0 Step 4: When both objects are separated, the first object is less negatively charged and the second object is left with a negative charge. _

_ _

Charge: -2

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8P5B Causes of Electrostatic Forces

Math Connections 1.

Before the conduction process, how many negative charges did we start with? __________

After the conduction process, how many negative charges resulted? __________________

Did the total overall charge remain constant? _____________________________________

Conduction can also occur when a positively charged object touches a neutrally charged object. The electrons from the neutrally charged object will transfer to the positively charged object. Fill in the blanks using integers to describe the charge of the objects.

Step 1: A positively charged and a neutrally charged object are not touching. - + + - + - + - + +

+ + + + Overall Charge: _______

Overall Charge: ______

Step 2: As the two objects come closer together, the negative charges in the neutrally charged object start to attract toward the positively charged object. - + + + - + +

+ + +

Charge: ___ + ____

Charge: ____ + ____

Step 3: When the two objects touch, some of the negative charges from the neutrally charged object will transfer to the positively charged object. - + +

- + +

+ + +

(___) + (___) = 0

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8P5B Causes of Electrostatic Forces

Math Connections Step 4: When both objects are separated, the first object is less positively charged and the second object is left with a positive charge. + + - + + -

+ + Overall Charge: _________

Overall Charge: _________

Before the conduction process, what is the overall charge between the two objects? ______

After the conduction process, what is the overall charge between the two objects? _______

What law explains why the overall charge remained constant? _______________________

Name two materials that transfer electrons using conduction. __________ and __________

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8P5B Causes Of Electrostatic Forces

Writing Science Name:

Date:

Group:

LOOK

THINK Many people are drawn toward a plasma ball when visiting certain retail stores. People are intrigued by the way the light seems to move; however, many people cannot explain what is occurring in regard to electricity. The outside of a plasma ball is made out of glass. Inside, a mixture of gasses such as neon, krypton, argon, and xenon can be found. At the center of the ball is an electrode that emits a highfrequency, high-voltage current that alternates. When the electrode is powered on and flows through the plasma filaments, strings of light can be seen. Whenever someone touches the glass on the outside of a plasma ball, a string of light appears to be extending from the electrode to their finger or hand. WRITE Explain the process of electrostatic forces at work in a plasma ball. Describe why the string of light changes position and extends to a person’s hand when he or she touches the glass. Be sure to • clearly state your central idea; • organize your thoughts; • develop your essay in detail; • choose your words carefully; and • use correct spelling, capitalization, punctuation, and grammar.

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8P5B Causes Of Electrostatic Forces

Writing Science

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8th Grade Physical Science

8P5C

Strength of Electric and Magnetic Forces

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8P5C Strength of Electric and Magnetic Forces

Student Handout Name:

Date:

Electromagnetic Suction Activity 1. Wrap the copper wire tightly around the straw. The wire-wrapped portion should be about 7.5 cm long and be covered by a couple of layers of wire. 2.

Leave about 45 cm of wire free at either end for later attachment to the battery.

Trim the ends of the straw so it is just a little bit longer than the wire-wrapped portion.

Hold the straw horizontally and put the end of the needle in the straw. Let go of the needle and observe what happens.

Connect the ends of the wire to the battery.

Put the end of the needle in the straw again and let go. Observe what happens.

Disconnect the battery after a few seconds.

Write your observations on the Student Handout.

Post-Activity Questions 9.

Why did the needle get sucked into the straw when the wire was connected to the battery?

10. Is the electromagnet actually creating suction?

11. This technology is called a solenoid. How might solenoids be useful in everyday life?

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8P5C Strength of Electric and Magnetic Forces

Student Journal Name:

Date:

Group:

Answer the following questions using the information that you gathered in the activity. 1.

What was the boundary of the system investigated?

What components were parts of the system?

Was input needed to make this system work?

Did the system investigations produce an output?

What was produced in the coil of wire when the leads were connected and the circuit was completed?

What interactions cause the coil of wire to spin?

What questions could you ask about improving the performance of the simple motor you created?

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STEMscopedia: STRENGTH OF ELECTRIC AND

MAGNETIC FORCES

Reflect

8P5C

Think about all of the electronic objects or appliances that you use every day. Computers, mobile phones, cars, televisions, coffee makers, microwaves, light bulbs, and hair dryers are just a few electronic devices you might use. It may not be so obvious to think of devices that rely on magnetism. However, it turns out that electricity is fundamentally related to magnetism. Many of the electronic devices that you use actually make use of magnetism as well. What exactly are electrical currents and magnetism, and how are the two related? Charged Particles and Electric Current Electricity is not something we can see directly, so it is difficult to understand exactly what it is. We can observe some byproducts of electricity, such as a spark that flashes when an electrical cord is pulled from an electrical outlet. However, these brief flashes of light are not actually electricity. To understand electricity, we must understand the fundamental unit of electricity: a charged particle. A charged particle is a tiny particle (much smaller than an atom) that carries an electric charge. An electric charge can be positive (+1) or negative (-1). A proton is an example of a positively charged particle. An electron is an example of a negatively charged particle. Electrons are the most common charged particles that you will encounter.

Look Out Static electricity and current electricity are different things. Sometimes electric charges build up in a region. For example, they may accumulate on your body as you move across a carpet. This is known as static electricity because the charges remain in one place. However, sometimes the charges will move and discharge onto another surface. When this happens, you may feel an electric shock. The flow of charged particles through a wire is called electric current. In electrical devices, electric current flows through the wires, creating an electrical and magnetic field. Static electricity creates an electrical field but does not create a magnetic field. Electric Force and Electric Fields Charged particles exert forces on one another. The most fundamental rule of electricity is that like charges repel one another and opposite charges attract one another. For example, if an electron were moved into a region near another electron, the electrons would repel, or push away, each other. If the electron were moving near a proton, however, the proton would experience a force pulling it toward the electron. The strength of this force varies at different locations around the electron—closer to an electron, the force is stronger; farther from the electron, the force is weaker—forming an electric field.

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STEMscopedia: STRENGTH OF ELECTRIC AND

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An electric field is a force field surrounding every charged particle. You can think of an electric field as a region of arrows surrounding a charge, with each arrow representing a force. The arrows in the electric field tell you how much force another charge would feel if it were placed at a particular location in the field. The arrows also tell you which direction the force would act. So the arrows representing the electric field of an electron would show the force that a proton would experience if moved into any location near the electron. In general, a charged particle’s electric field decreases as distance from the charge increases. A proton that is close to an electron experiences a very strong attractive force. Conversely, a proton that is far from an electron experiences a much weaker force. Magnets, Magnetic Force, and Magnetic Fields A magnet, or magnetized material, is an object with north and south poles that produce a magnetic field. Certain objects (particularly metals such as iron) that enter the magnetic field are attracted to the magnet. However, magnets also have an important connection to electricity. Magnetism results from the spinning of electrons in a material. All electrons spin; a spinning electron creates a tiny magnetic field with a north and a south pole. In nonmagnetized materials, these electrons spin in different directions and their fields cancel out. However, in magnetized materials, the electrons all spin in the same direction. The magnetic fields of each tiny electron combine to produce a magnetic material. Ferromagnetic materials, such as iron, are materials that are not naturally magnetized, but they can become magnetized easily in the presence of a magnetic field. (The chemical symbol for iron is Fe, from the Latin word ferrum. So the prefix ferro- typically refers to iron.) For example, if you hold a magnet over a pile of iron shavings, the iron shavings will become magnetized. Just as all charged particles are surrounded by electric fields, all magnets are surrounded by magnetic fields. The magnetic field flows out of the north pole of a magnet and into the south pole. Magnetic fields exert forces on other magnets. As a rule, like poles repel each other and opposite poles attract each other. Magnetic fields also exert forces on moving charged particles, as you will see later. Any magnets that are placed in a magnetic field will align with that field. The arrows of the magnetic field lines show how the north pole of a bar magnet would become aligned if it were placed in that field. A compass is a typical example of how a magnetic force acts in a magnetic field. Earth is a giant magnet—recall that our planet’s core contains a lot of iron. As Earth spins, the core generates a magnetic north pole and a magnetic south pole. A compass is made of a small bar magnet. The compass magnet aligns with Earth’s magnetic field. So the south pole of a compass points toward Earth’s magnetic north pole.

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MAGNETIC FORCES

Look Out Magnetic fields exert forces in two different ways. First, magnetic fields interact with other magnetic fields. Opposite magnetic poles are attracted to one another, while similar magnetic poles repel one another. Second, magnetic fields exert forces on moving, charged particles. That is, they exert forces on electric current, not stationary charges. As you will see later, motors take advantage of this principle. The Relationship Between Electric Current and Magnetic Fields One of the most important scientific discoveries of the last 200 years was the realization that electricity and magnetism are fundamentally related. This relationship is known as electromagnetism. Moving electric charges (electric current) produce a magnetic field. This means that an electric current produces both an electric field and a magnetic field. For example, a magnetic field will form around a straight wire carrying electric current, as shown below. To determine the direction of the magnetic field around a straight wire, use the righthand rule. Point the thumb of your right hand in the direction of the current. If the wire is connected to a battery, current moves from the negative (-) terminal to the positive (+) terminal. Then curl your fingers around the wire. Your fingers point in the direction of the magnetic field. This principle can be used to create an electromagnet. An electromagnet is a temporary magnet created by an electric current. An electromagnet typically has a ferromagnetic core, such as iron. A simple electromagnet can be made by wrapping wire around an iron nail. When the wire is connected to a voltage source, current flows through the wire, producing a magnetic field. This magnetic field causes the iron nail to become an electromagnet. The greater the current flowing through the wire, the stronger the magnetic field produced. You can also increase the strength of the electromagnet by increasing the number of windings of wire around the iron nail. Increasing the length of the wire, however, would decrease the strength of the magnetic field. Some electromagnets are so strong they can lift entire cars. You can see these electromagnets on cranes at a junkyard. Just as moving charges produce magnetic fields, a moving magnet produces an electric field. In other words, a changing magnetic field will produce an electric field. This is known as electromagnetic induction because a moving magnet can induce current in a wire, even if no battery or other voltage source exists. The induced voltage in a circuit can be measured with a voltmeter (voltage is measured in volts). The induced current, or amperage, in a circuit can be measured with an ammeter (current is measured in amperes). As you will see in the next section, electromagnetic induction plays an important role in the generation of electricity around us.

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MAGNETIC FORCES

What Do You Think? A student designs an electromagnet by wrapping an insulated copper wire around an iron nail, and then connecting the wire to a battery to supply an electric current. Which of these factors could increase the strength of the magnetic field produced by the electromagnet? • Increase the number of windings • Decrease the voltage of the battery • Increase the electric current through the wire • Increase the length of the wire Motors, Generators, and Transformers The interactions between electricity and magnetism are applied in many common devices. One application is a motor. Motors are devices that cause objects to move when electricity is applied. For example, a motor causes the blades of a fan to spin and the wheels of a car to rotate. Motors transform electrical energy into mechanical energy. In fact, more electricity is used by motors than by any other technology on Earth. A basic motor consists of a rotating loop of wire and a magnet. The loop of wire is placed between the poles of a magnet so that it is inside of a magnetic field. Recall that the magnetic field will exert a force on moving charged particles. So when electric current begins to flow through the loop of wire, the magnetic field exerts a force on the loop. This magnetic force causes the loop to rotate. In this way, electrical energy is transformed into mechanical energy when the loop begins to rotate. While a motor converts electrical energy into mechanical energy, a generator is a device that performs the opposite task: it transforms mechanical energy into electrical energy. In other words, it generates electricity from a moving source of energy. Like a motor, a basic generator consists of a loop of wire and a magnet. However, the assembly is different for a generator. This time, the magnet is placed in the center of the loop of wire and it can rotate freely. As the magnet rotates, the changing magnetic field induces an electric current in the loop of wire. Thus, the rotating mechanical energy of the magnet is transformed into electric energy. A number of forces can cause the magnet in a generator to rotate. In most cases, the magnet is attached to a larger, spinning apparatus called a turbine. For example, wind turbines are large, pinwheel-shaped devices that spin when the wind strikes them. The spinning arms of the wind turbine spin a magnet inside of the structure. This generates electricity in the wire around the magnet.

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MAGNETIC FORCES

Similarly, hydroelectric energy is produced in a dam when flowing water spins the arms of a turbine. The turbine spins a strong magnet, and electricity is generated in electrical wire around the magnet. At nuclear power plants, nuclear energy heats water, and the water evaporates into steam. At other power plants, the energy for heating water into steam comes from burning fossil fuels such as coal or oil. In each case, the pressure from the steam spins a turbine and electricity is produced. A transformer is a device that transfers the electrical energy in the form of alternating current (AC) from one circuit to another. (In contrast to DC, or direct current, which flows in one direction only, AC constantly changes direction.) A transformer consists of at least two sets of coiled wire around a ferromagnetic material, such as an iron core. When AC flows through the first set of coiled wire, known as the primary coil, it produces a magnetic field that magnetizes the iron core. Because AC constantly changes direction, the magnetic field induced in the iron core constantly changes directions. The changing magnetic field in the iron core then induces an electric current in the second coil of wire, known as the secondary coil. Transformers are also used to change the amount of voltage or current in a circuit. For example, a household electrical outlet delivers 120 volts of electricity. However, some devices, such as a mobile phone, require only five volts. So you may need to plug a five-volt adaptor into a wall socket to change the voltage delivered to your device. The small box attached to the plug of the adapter is a transformer. Whenever a transformer increases the voltage in a circuit, it is known as a step-up transformer. Similarly, whenever a transformer decreases the voltage in a circuit, it is a step-down transformer. The following list describes items or places that make use of electric and magnetic forces in the world around us. Identify which of the following items are examples of motors, generators, and transformers, and then sort them into the table on the next page.

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STEMscopedia: STRENGTH OF ELECTRIC AND What Do You Know?

MAGNETIC FORCES

Laptop charger: Converts 120 volts of electricity from a wall outlet into 16.5 volts for a computer to use. Desk fan: Electricity ﬂows through a coil of wire surrounding a magnet. The coil spins turning the blades of a fan. Wind farm collector substation: Electricity from many wind turbines is collected at the substation. The voltage of the electricity is increased so that it can be transmitted along high-voltage power lines. Geothermal power plant: A pump pulls steam from a reservoir of hot water under Earth’s surface. The steam turns a magnet. Electricity begins to ﬂow in wire surrounding the magnet. Bicycle light bulb assembly: The pedals of a bicycle are connected to a magnet, wire, and light bulb assembly. When a cyclist pedals, the magnet spins and the light bulb lights up. Electric toothbrush: Batteries supply electricity to a coil of wire surrounding a magnet. The coil rotates quickly and turns the head of the toothbrush.

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STEMscopedia: STRENGTH OF ELECTRIC AND

MAGNETIC FORCES

Connecting With Your Child Designing an Electromagnet One example of the interaction between electricity and magnetism is a simple electromagnet. An electromagnet is a magnet produced when an electric current flows and produces a magnetic field. For example, this can happen when electric current flows around a ferromagnetic material, such as an iron nail. This causes the nail to become magnetized. To construct an electromagnet, provide your child with the following materials: • Iron nail • Copper wire, 20 centimeters long • D-cell battery • Tape • Paper clips • Rubber gloves Have your child think about the relationship between electric current and magnetic fields. How could your child arrange the wire so that the iron nail becomes magnetized? If your child needs more directed instruction, follow this procedure: 1. Wrap the copper wire around the nail many times. 2. Connect the free ends of the wire to the terminals of the D-cell battery. You can attach the free ends to the battery with tape. (Sometimes the tape does not provide a good connection between the wire and terminals. If this is the case, you should wear rubber gloves and press the wire against the terminals to ensure a better connection.) 3. To observe the properties of the electromagnet, move the electromagnet over a pile of paper clips. If the setup is assembled correctly, the paper clips will be attracted to the iron nail. Your child can modify aspects of the design to observe how the strength of the magnetic field changes. (The strength of the magnetic field is related to the number of paper clips that the electromagnet can pick up.) There are numerous factors that affect the strength of the magnetic field. Some of these factors include the number of windings of wire around the nail, the voltage of the battery, and the type of nail used. Here are some questions to discuss with your child: 1. What happens around the iron nail when the wire is connected to the battery? 2. How might increasing the current through the wire affect the number of paper clips that the nail picks up? 3. What other factors might affect the strength of the iron magnet? How could you investigate this question?

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8P5C Stength of Electric and Magnetic Forces

Reading Science Name:

Date:

Group:

The World’s Strongest Superconducting Magnet 1

Ever since the first natural magnet called a lodestone was found to attract pieces of iron, humans have been inspired to make bigger, more powerful magnets. In 1820, Danish scientist Hans Christian Ørsted discovered magnetic fields were created by electric currents. Soon after, British scientist William Sturgeon used this knowledge to invent the first electromagnet by wrapping copper wire around a horseshoe-shaped iron core powered by a single battery. His electromagnet could lift about 4 kg.

Electromagnets are created when a current from a battery or another source flows through a coiled wire, creating a magnetic field as though it were a permanent magnet. Electromagnets are useful because the magnet can be turned on and off by switching the current on and off. Adding more coils of wire and/or increasing current produces a stronger magnetic field, which can also generate heat.

Today, scientists have advanced the use of the simple electromagnet by inventing enormous industrial strength superconducting electromagnets. This new generation of electromagnets uses coils of superconducting wire cooled to cryogenic temperatures to sidestep the issue of heat. A superconducting wire conducts huge electric currents without heat, which ordinary wire cannot do. A superconducting magnet creates intense magnetic fields without the expense or heat of traditional electromagnets. Superconducting electromagnets are typically used in MRI machines and in scientific equipment such as spectrometers and particle accelerators.

To measure the strength of industrial size magnetic fields (magnetic flux density), scientists use the tesla unit (T), which is equivalent to 1 kilogram per second squared per ampere (kg · s -2 · A -1 ). The tesla was named for Nikola Tesla who provided the basis for modern electrical power systems. Everyday electromagnets use a smaller unit called the gauss (G). It takes 10,000 gauss to equal the magnetic strength of 1 tesla.

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8P5C Strength of Electric and Magnetic Forces

Reading Science 5

Small refrigerator magnets have the strength of a tiny fraction of a tesla, while the largest superconducting magnet has 27 teslas of magnetic flux density. • • • • • •

mT – refrigerator magnet .25 T – neodymium magnet 2.4 T – loudspeaker magnet 3 T – medical MRI 27 T – most superconducting electromagnets at cryogenic temperatures 32 T – National High Magnetic Field Laboratory superconducting electromagnet

The superconducting electromagnet at the National High Magnetic Field Laboratory (NHMFL) in Tallahassee, Florida is made of two giant magnets working together to create a magnetic strength of 32 tesla. The outer layer is a super-cooled, superconducting magnet chilled to nearly absolute zero with a superfluid helium cryogenic system. In the center is a massive resistive magnet. Even though the NHMFL system is large, the test area is small at about the size of a pencil. Subatomic particles do strange things in the presence of extremely high magnetic forces. Electrons can dance in their orbit and materials may morph.

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8P5C Strength of Electric and Magnetic Forces

Reading Science 1.

What discovery by Ørsted led to the development of electromagnets? A.

Electric currents produce magnetic fields.

Magnetic fields produce electric currents.

Magnets produce electricity.

Magnets produce heat.

What change to an electromagnet produces a stronger magnetic field? A.

Decreasing the number of wire coils

Increasing the amount of aluminum in the coil

Increasing the number of wire coils or current

Decreasing the current

Why are superconducting magnets cooled to cryogenic temperatures? A.

To eliminate friction

To eliminate the buildup of heat from strong current

To eliminate the buildup of heat from the magnetic field

To eliminate the magnetic flux

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8P5C Strength of Electric and Magnetic Forces

Reading Science 4.

Superconducting electromagnets are best suited for which of the following? A.

MRI and particle accelerators

Metal scrap yards

Audio speakers

Credit cards

One kilogram per second squared per ampere is equal to ___________. A.

10,000 tesla

10,000 gauss

10,000 watts

10,000 amperes

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8P5C Strength of Electric and Magnetic Forces

Math Connections Name:

Date:

Group:

Electromagnetism manifests as both electric fields and magnetic fields: a changing electric field generates a magnetic field, and a changing magnetic field generates an electric field. This effect, called electromagnetic induction, is the basis of operation for electrical generators, induction motors, and transformers. A solenoid is a current-carrying coil that produces a magnetic field. MRI machines use solenoids to produce the magnetic field needed to scan the body. Three variables can effect the magnetic strength of a solenoid: (a) the amount of current in the coil, (b) the number of coils in the wire, and (c) the magnetic permeability of the core. The strength of a magnetic field within the solenoid can be calculated using the formula: Bsolenoid = μonI, where: • B=magnetic field strength in Tesla • μo=4π×10–7 N/A2 • n=ratio of the number of loops per unit length (meters) of the solenoid=N/L • I=current in amps 1.

A long solenoid has 2,000 turns on its 50 cm length. The diameter of the solenoid is 2 cm. The solenoid carries a current of 400 mA. What is the magnetic field strength of the solenoid? (1000 mA=1 amp).

A short solenoid has 20 turns on its 1 m length. The diameter of the solenoid is 3 cm. The solenoid carries a current of 40 mA. What is the magnetic field strength of the solenoid?

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8P5C Strength of Electric and Magnetic Forces

Math Connections Let’s investigate the effect the number of coils has on the strength of a solenoid’s magnetic field. 3.

Calculate the magnetic field strengths, relative to the number of coils, for a solenoid with a current of 6 volts and a wire length of 2 m. No. of coils

Process

Magnetic Strength, T

10 20 30 40 4.

Plot the relationship between the number of coils and the magnetic strength of the solenoid on the graph below. 0.00016

Magnetic strength, T

0.00014 0.00012 0.00010 0.00008 0.00006 0.00004 0.00002 0

Number of coils 5.

What would the magnetic strength be with 0 coils?

What is the rate of increase in the magnetic strength per 1 coil (slope)?

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8P5C Strength of Electric and Magnetic Forces

Math Connections 7.

Create an equation to describe the magnetic strength of this solenoid in terms of the number of coils.

Is this relationship proportional? How do you know?

Describe the relationship of the magnetic fields and the number of coils on a solenoid.

10. If the number of coils doubled, how would that affect the strength of the magnetic field?

Let’s investigate the effect that current has on the strength of a solenoid’s magnetic field. 11. Calculate the magnetic field strengths, relative to the level of current in amps, for a solenoid with a wire length of 2 m and 200 coils. The current varies based on the chart below. Current, amps

Process

Magnetic Strength, T

100 200 300 400

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8P5C Strength of Electric and Magnetic Forces

Math Connections 12. Plot the relationship between the number of coils and the magnetic strength of the solenoid on the graph below. 0.08

Magnetic strength, T

0.07 0.06 0.05

0.04 0.03 0.02 0.01 0 0

100

200

300

400

500

Current, amps 13. What would the magnetic strength be with a current of 0 amps?

14. What is the rate of increase in the magnetic strength per amp (slope)? Create an equation to calculate the magnetic strength of this solenoid in terms of current available in amps.

15. Is this relationship proportional? How do you know?

16. Describe the relationship of the magnetic fields and the amount of current exerted on the solenoid.

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8P5C Strength of Electric and Magnetic Forces

Writing Science Name:

Date:

Group:

LOOK

THINK Think about electric currents and magnets.

WRITE Explain how electric currents and magnets can exert force on each other.

Be sure to clearly state your central idea; organize your thoughts; develop your essay in detail; choose your words carefully; and use correct spelling, capitalization, punctuation, and grammar.

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8P5C Strength of Electric and Magnetic Forces

Writing Science

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absorption

GLOSSARY OF TERMS

balanced forces

atom – the smallest particle absorption – when a part or the whole amount of light is lost of an element that maintains the chemical identity of that inside of an object element; made of electrons, acceleration – change of an protons, and neutrons object’s speed or direction atomic mass – the mass of acceleration – the rate of an atom, approximately equal change in velocity, such as to the number of protons and speeding up, slowing down, or neutrons in the atom changing direction balanced chemical equation amplitude – the height of a – a symbolic representation of wave measured from midway a chemical reaction in which between the highest and lowest both sides of the equation points contain equivalent numbers of atoms of each element; the at rest – the state of an object mass and the charge must be when it is not in motion balanced on both sides of the reaction atom – the smallest unit of an element that has all of the balanced forces – separate properties of that element and forces on an object that contains a nucleus within an together do not change the electron cloud motion of the object

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battery

GLOSSARY OF TERMS

battery – something with one or more cells, which converts chemical energy into electricity and is used as a source of power

coefficient

chemical formula – a shorthand notation that uses chemical symbols and numbers as subscripts to represent the type and number of atoms that are present in the smallest unit of a substance

boiling point – the temperature at which a substance changes states from chemical property – characteristics of a substance a liquid to a gas that become apparent only bond – any of several forms of during a chemical reaction electrostatic attraction between chemical property – atoms that holds the atoms characteristics that can only be together observed or measured when charged object – matter with atoms of matter rearrange a surplus or deficiency of during a chemical change electrons closed circuit – a pathway chemical change – a change that allows an electric current to that alters the identity of a flow freely substance, resulting in a new coefficient – a number placed substance or substances with in front of a chemical symbol or different properties formula in order to balance the chemical equation – chemical equation formulas and symbols written to represent a reaction 454

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collision of atoms

GLOSSARY OF TERMS

density

collision of atoms – the result of two or more atoms striking each other and the release or absorption of energy

conservation of energy – energy cannot be created or destroyed, it is simply converted into different forms

combustivity – a measure of how easily a substance will set on fire, through fire or combustion

convection – transfer of thermal energy through circular motion caused by heating and cooling in fluids (liquids and gases)

compound – pure substance made of two or more kinds of atoms bound together

convex lens – a lens with a surface that curves outward like the outer surface of a sphere

concave lens – a lens having at least one surface curved like current – a directional flow of electrical charge through an the inner surface of a sphere object or medium conduction – transfer of density – the amount of matter thermal energy that occurs in solids, liquids, and gases when in a given space or volume; it is a relationship between mass two substances of different and volume. Less dense matter temperatures touch will form layers above denser conductor – materials that matter. allow electrons to flow freely density – the amount of matter from particle to particle in a given space or volume © Accelerate Learning Inc. - All Rights Reserved

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diffraction

GLOSSARY OF TERMS electromagnetic spectrum

diffraction – occurs when a wave encounters an object in its path and bends around it echo – sound caused by the reflection of sound waves off a surface travelling back to the listener electric – producing, transmitting, or operating by electric currents

electricity – the presence and flow of an electrical charge electromagnetic – related to the combination of electricity and magnetism electromagnetic force – force resulting from interaction between electrically charged particles

electromagnetic radiation – electric circuit – the pathway the type of energy released by through which electrical current stars consisting of electric and magnetic waves that travel at flows the speed of light. electric current – the flow of electromagnetic spectrum – a electricity through a circuit grouping of all possible energy electrical energy – a form of levels of electromagnetic energy made available by the radiation, from radio waves to flow of electric charge through gamma radiation and includes a conductor. visible light

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GLOSSARY OF TERMS electromagnetic wave

gamma rays

energy transformation – the electromagnetic wave – oscillations of electromagnetic change of energy from one fields that carry energy through form to another a medium or through a vacuum force – a push or pull that can change the motion of an object; electron – a negativelymeasured with a spring scale in charged subatomic particle of Newton (N) units the electron cloud; involved in the formation of chemical frame of reference – a system bonds that uses coordinates or background objects to establish element – a pure substance position or to measure that cannot be separated into simpler substances by physical movement of a point in space or chemical means frequency – the number of wave cycles that pass a given element – a pure substance composed of the same type of point per unit of time atom throughout friction – a force that resists energy – the ability of a system the motion of two surfaces sliding across one another to do work; energy is required for changes to happen within a gamma rays – electromagnetic system waves with the highest energy; produced by supernovas, or energy transformation – the the destruction of atoms or the change of energy from one decay of radioactive material form to another © Accelerate Learning Inc. - All Rights Reserved

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gas

GLOSSARY OF TERMS

gas – one of the four states of matter in which the molecules are moving at high rates of energy

insulator

warmer site to cooler site until all sites have reached the same temperature

heat transfer – thermal energy gravity – attraction between being moved from one object two objects with a strength that to another via conduction, is proportional to the masses of convection, or radiation the objects; a force that causes objects with mass to attract one inertia – an objects tendency another to resist changes in its motion groups – the columns on a periodic table that arrange the elements by the number of electrons there are in the outermost shell; also called a family hand lens – device with a handle and a piece of glass or plastic that is used to make objects appear larger

infrared rays – electromagnetic waves with longer wavelengths than visible light, but shorter than radio waves infrared waves – electromagnetic waves with longer wavelengths than visible light, but shorter than radio waves

heat – energy transferred between two objects of different temperatures, energy will continue to move in a predictable pattern from

insulator – a material that does not conduct heat or electrical current

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interactions

GLOSSARY OF TERMS

interactions – action that occurs as two or more objects have an effect upon one another kinetic energy – the energy of the object due to its motion

mechanical waves

magnet – an object that is surrounded by a magnetic field and that has the property, either natural or induced, of attracting iron or steel magnetic – material or object that produces a magnetic field

lens – a clear piece of curved magnetic force – attraction or glass or plastic that bends passing light to focus or spread repulsion that arises between the electrically charged the light rays particles because of their motion light energy – a form of energy which exhibits wavemass – a measure of how like behavior as it travels much matter is present in a through space; part of the substance electromagnetic spectrum light wave – electromagnetic waves with a shorter wavelength than visible light but longer than X-rays

mechanical energy – a form of energy that organisms use in muscular activity and to do work

liquid – one of four states of matter; has a definite volume but no fixed shape

mechanical waves – a wave that is created by the vibrating of matter and therefore transfers energy through a medium

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medium

GLOSSARY OF TERMS Newton’s law of inertia

medium – the material through neutron – a subatomic particle of the nucleus of an atom which a wave travels that is without charge and contributes to the mass of an melting point – the atom temperature at which a substance changes states from Newton’s law of action/ a solid to a liquid reaction – Newton’s law that microscope – a scientific tool states that for every action there is an equal and opposite used to greatly enlarge the reaction; often referred to as image of small objects Newton’s third law of motion mixture – a combination of two or more substances that do not Newton’s law of force and chemically combine and can be acceleration – acceleration of an object depends on the separated object’s mass and magnitude of molecule – the simplest unit of the force acting upon it; (F=ma) a chemical compound that can is often referred to as Newton’s exist; formed when two or more second law of motion atoms join together chemically Newton’s law of inertia – an object at rest stays at rest or an motion – a change in an object’s position with respect to object in motion stays in motion until unbalanced forces act time and in comparison to the upon it; this is often referred to position of other objects used as Newton’s first law of motion as reference points

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open circuit

GLOSSARY OF TERMS

open circuit – a pathway that prevents electric current from flowing freely or stops the flow periodic table – a table in which all the known elements are arranged by properties and are represented by one or two letters, referred to as chemical symbols periods – the rows in a periodic table that classify the elements by the number of electron shells

products

polarity – a separation of electric charge between atoms in a molecule resulting from the unequal sharing of electrons in a covalent bond potential energy – the energy stored in an object that is not moving precipitate – an insoluble solid formed from a chemical reaction

prism – a transparent piece of glass, usually with triangular ends, used for separating white physical change – a change to a substance without forming light passed through it into a spectrum or for reflecting a new substance, such as changing size or state of matter beams of light physical property – properties products – a substance that describe matter, including produced during a chemical reaction color, texture, smell, boiling point, melting point, and density plasma – an ionized state of matter similar to a gas © Accelerate Learning Inc. - All Rights Reserved

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proton

GLOSSARY OF TERMS

proton – a positively-charged subatomic particle of the nucleus of an atom which contributes to the mass of the atom pure substance – a single substance, either an element or compound, with definite composition and properties

solution

reactivity – the rate at which a chemical substance tends to undergo a chemical reaction reflection– energy waves bouncing off the surface of an object refraction – a change in the direction of a wave as it passes through different objects at different speeds

radiation – the transfer of energy through matter or refraction – change in the space as electromagnetic waves, such as visible light and direction of a wave as it passes through different objects at infrared waves different speeds radio astronomy – the study relative position – where an of celestial objects that emit object is located in relation to radio waves another object radio waves – electromagnetic solid – one of four states of waves with long wavelengths matter that does not change its and low frequencies shape or volume reactants – a substance that solution – a liquid mixture with takes part in and undergoes a uniform composition change during a reaction

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sound energy

GLOSSARY OF TERMS

sound energy – a form of energy that is made by vibrations and requires a medium (air, water, or solids) in order to travel. Sound waves travel slower than light waves sound wave – the pattern of disturbance caused by the movement of energy traveling through a medium (such as air, water, or any other liquid or solid matter) speed – the measurement of the rate of change of position with respect to time states of matter – distinct forms of matter known in everyday experience: solid, liquid, and gas; also referred to as phases subscript – a number written below and to the right of a chemical symbol that shows the number of a specific type of atom present © Accelerate Learning Inc. - All Rights Reserved

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ultraviolet waves

system – a group of interacting or interdependent elements forming a complex whole, as in all the factors or variables in an environment, or all the variables that might affect a science experiment telescope – an optical instrument used to view distant objects thermal energy – the total amount of kinetic energy from the moving particles inside a piece of matter; the faster the particles move, the warmer the matter can get ultraviolet light – a portion of the electromagnetic spectrum emitted by the Sun; can cause tanning, sun burning, and skin cancers ultraviolet waves – electromagnetic waves with a shorter wavelength than visible light, but longer than x-rays 463

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unbalanced force

GLOSSARY OF TERMS

X rays

unbalanced force – a force on wavelength – the distance an object that causes change in between the same two points on a wave (i.e. crest to crest) the motion of the object valence electron – the electrons in the outermost energy level of an atom that influence how an element will react with other substances

X-rays – electromagnetic waves that are the second highest in energy and are used in medical and astronomical applications

velocity – measurement of speed and direction of an object visible light – electromagnetic waves with wavelengths within the range that can be detected by the eye wave – a rhythmic disturbance or oscillation that travels through matter or space, transferring energy wavelength – the distance between any two corresponding points that are adjacent on a wave, such as from peak to peak 464

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8 STEMscopes Georgia Student Notebook

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a part of STEMscopes NGSS Georgia_8th_Book.indd 1

8th grade

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developed by Accelerate Learning, Inc. & Rice University

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