Next Generation Science Level 6 - Textbook B

Science for the Next Generation

Science Gra d e Si x

Textbook

B

The 5E Model – Guided Inquiry The Next Generation Science series is based on the Biological Sciences Curriculum Study (BSCS) 5E teaching and learning instructional model.

The 5E model is centered on the idea that students understand science concepts best by using prior knowledge to pose questions and find answers through guided inquiry.

This hands-on approach, integrated with engineering and design skills, has students learn science by doing science. Teachers guide the learning process and are able to assess student performance by evaluating student explanations and the application of newly acquired knowledge and skills.

Engage

The Engage phase of the 5E model provides students with the opportunity to demonstrate their prior knowledge and understanding of the topic or concept. Students are presented with an activity or question which serves to motivate and engage students as they begin the lesson. Teachers identify and correct any misconceptions and gather data from students which will guide informed teaching and learning.

Essential to stimulating and engaging students is the use of mixed media such as colorful photos, illustrations and diagrams found throughout the textbooks and activity books. Next Generation Science also includes extensive digital resources such as narrated videos, interactive lessons, virtual labs, slideshows and more.

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Explore

This phase encourages exploration of concepts and skills through handson activities and investigations. Students are encouraged to work together and apply various process skills while gaining concrete, shared learning experiences. These experiences provide a foundation for which students can refer to while building their knowledge of new concepts. This studentcentered phase comes before formal explanations and definitions of the concept are presented by the teacher.

Explain

This phase follows the exploration phase and is more teacher-directed.

Students are initially encouraged to draw on their learning experiences and demonstrate their understanding of the concept through explanations and discussion. After the students have had the opportunity to demonstrate their understanding of the concept, the teacher then introduces formal definitions and scientific explanations. The teacher also clarifies any misconceptions that may have emerged during the Explore phase.

Elaborate

In the Elaborate phase, students refine and consolidate their acquired knowledge and skills. Opportunities are provided for students to further apply their knowledge and skills to new situations in order to broaden and deepen their understanding of the concept. Students may conduct additional investigations, share information and ideas, or apply their knowledge and skills to other disciplines.

Evaluate

This final phase includes both formal and informal assessments. These can include concept maps, physical models, journals as well as more traditional forms of summative assessment such as quizzes or writing assessments.

Students are encouraged to review and reflect on their own learning, and on their newly acquired knowledge, understanding and skills.

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Next Generation Science Next Generation Science is based on the United States Next Generation Science Standards (NGSS). The series consists of full-color textbooks and full-color activity books for Grades K to 6.

Contact Fo

There are many di on the objects arou when objects are t contact forces. Ap examples of conta

Applied Forc

An applied force object applies forc contact with it. You open and close a twist the lid off a ja

Next Generation Science engages students with a highly visual presentation of the disciplinary core ideas in the textbooks and places an emphasis on applying scientific knowledge using NGSS practices through numerous scientific investigations. Next Generation Science sees engineering as an essential element of science education and as such is tightly integrated into both the textbooks and activity books.

You use applied forces when you press the keys on a keyboard as you type.

Try This!

In small groups, discuss examples where applied forces are used to make an object: • • • • • •

The Next Generation Science textbooks include the following features:

Think Deeply

In the Field

Taxonomists Accurately classifying organisms and sharing information on newly discovered species is essential to our understanding of biodiversity. This important job is done by a taxonomist. A taxonomist often works in the field, searching for new organisms and collecting samples that are then taken to a laboratory for closer analysis.

Topic-related questions for group discussion aimed at deepening students’ understanding of the topic.

Goes beyond inquiry by encouraging students to design, model and build to engineer solutions to defined problems.

In the Field Inspirational sciencerelated professions to stir interest in sciencerelated careers.

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What are applied fo How do th they are a

start moving change direction speed up slow down stop moving change shape

The girl uses applied forces when she pulls on the string of the kite.

To ensure that organisms all over the world are classified in the same way, taxonomists name, describe and classify organisms according to the International Code of Nomenclature.

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Taxonomists often specialize in the search for and classification of certain types of organisms.

Some taxonomists specialize in the classification of microorganisms. Others specialize in the classification of specific types of fungi, plants or animals.

If you were a taxonomist, what type of organisms would you specialize in? If you found a new species, what would you name it?

A taxonomist determines which family, genus or species an organism belongs to.

If it has characteristics different from all known organisms, then that’s where the fun starts! If it belongs to a known genus, then a taxonomist can give a newly discovered species its own species name.

If it does not belong to an existing genus, the new organism gets its own two-part scientific name.

Engineer It!

A Closer Look Colonization of Mars

Humans have long been interested in visiting and colonizing another planet. Although we have successfully landed and walked on our moon’s surface, no human has yet to land on another planet.

Many scientists believe that this may soon chang29 e.

Landing on and coloni zing another planet in our solar system presents a number of problems.

Such problems includ e the distance from Earth, composition of the atmos phere, temperature and gravity. In order to find a planet suitable to coloni ze, it would need to be similar to Earth.

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The outer planets are not suitable for coloni zation due to their gaseous comp osition and distance from Earth.

The two rocky planets closest to the Sun, Mercu ry and Venus, may have some suitable features, but the extremes in tempe rature make them largely unsuitable. That leaves just one potentially suitab le planet – Mars.

A Closer Look Invokes enthusiasm in science by presenting interesting topics beyond the syllabus.

The girl is using a and fly the kite. Th which acts again

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Amazing Fact!

Interesting facts to build interest and enthusiasm.

orces

ifferent types of forces acting und you. Some forces occur touching. They are called pplied forces and friction are act forces.

Did You Know?

ce

occurs when a person or an ce to another object when in u use applied forces when you door, push a bike up a hill or am jar.

applied forces to pull on the string he wind applies a force to the kite nst the force of gravity.

e some ways you use orces in daily activities? he forces affect the objects applied to?

AB

Try This!

Optional hands-on activities to be conducted in groups or at home.

Activity 8.4

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Science Words

12.

An organism with a body made up of more than one cell is called a .

13.

An organism with a body made up of just one cell is called a .

Use the words to comp taxonomy species photosynthesis vascular tissue vertebrate

Extra information to build students’ knowledge base of the current topic.

An ice hockey player’s stick is in contact with the puck. The player uses an applied push force on the stick to shoot for goal. The puck accelerates and slides on the ice towards the goal. The goalkeeper uses an applied force in the opposite direction of the motion of the puck.

This causes the puck to stop moving.

The goalkeeper then strikes the puck with his stick. The applied force sets the puck back in motion in the direction of the applied force.

lete the sentences.

invertebrate unicellular organism multicellular organism organelles

cellular respiration tissue organ organ system

1.

A group of tissues that works together to perfor m a specific function forms an .

2.

During , oxygen interacts with glucose which causes chemical changes that give off energy.

3.

The parts of a cell are

4.

An

5.

A

6.

are internal tube-like structures in the roots, leaves of vascular plants stem and .

called

Copy and complete the

table.

Classification of Organ

isms

Kingdom

Characteristics

Archaea

.

is an animal without a

Example

Eubacteria

backbone.

Protists

is an animal with a backb one.

Fungi Plants Animals

7.

is the process by which light, water and carbo used to produce stored n dioxide are chemical energy in the form of glucose.

8. The process of namin g and classifying organ isms is called .

9. A is a group of similar organ isms that are able to reproduce Althou ghof young Mars is the most the same kind. suitable planet for colonization, many challe nges still exist.

These include: 10. A group of similar cells that works function forms • distance from Earth. together to perform the same Using current technology, . it will take about seven month s for a spacecraft to travel 11. Organs thatfrom workEarth toer togeth Mars. to perform a specific function form an .

• surface gravity is just 38 percent of that of the Earth’s.

26 • atmosphere consis ts mostly of carbon dioxid e and very little oxygen.

2.

List two unicellular protist s.

3.

How do fungi get the

4.

List two functions of the

5.

In which cell organelle

energy they need to carry out vascular tissue in the

Discussion

life processes?

stem of plants.

does cellular respiration

take place?

6.

Name two organelles that can be found in plant cells but not in animal cells.

7.

Why is a virus not classif ied as a living organism?

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• very little liquid water.

• toxic soil which is not

Links students to the Next Generation Science Activity Book at the appropriate juncture.

Review 1.

suitable for growing plants

.

• cold temperatures that are comparable to those at the Earth’s poles.

The successful coloni zation of Mars would likely require the establishment of a permanent habitat on the planet’s surface.

Get together with your friends and discuss how such a habitat could overcome the challenges of living on Mars.

Review 17

AB Activity

Topical questions at the end of each chapter for formative assessment.

Topic-related questions and situations for class discussion to build a deeper understanding of topics.

Science Words Lists the essential science vocabulary covered in each chapter.

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Contents

Unit 6 - The Universe What Is the Universe?

Galaxies Stars The Solar System Exploring Space Review

Unit 7 - Matter What Is Matter?

Changes in Matter Mixtures and Solutions Review

Unit 8 - Forces What Is a Force?

Contact Forces Non-contact Forces Laws of Motion Review

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2 4 5 7 10 22 29

32 34 41 47 57

58 60 68 72 79 87

Unit 9 - Work and Simple Machines What Is Work?

Simple Machines Compound Machines Review

90 92 96 107 111

Unit 10 - Electricity and Circuits

112

What Is Electricity?

Electric Circuits Electromagnets Review

114 124 132 136

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Science Skills Scientists ask questions about the world around them. To find the answer to these questions, scientists use special skills to collect, analyze and interpret data. They communicate the things they find out.

Let’s look at how you can use these skills so you can be a scientist too.

Observing You make observations when you gather information about something using your senses. You can observe how something looks, feels, sounds, smells or tastes.

Scientists often use tools and instruments that allow them to observe things closely. Such tools include hand lenses, microscopes and telescopes.

It is important to accurately record your observations in a way that can be easily understood by others. You can make notes, and create charts and tables. You can also draw and label diagrams.

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Comparing and Classifying Scientists compare the things they observe.

To compare means to observe the properties or characteristics of two or more things and identify their similarities and differences.

Classification is the process of placing things into groups based on similarities in their properties or characteristics. Objects around us can be classified by the properties of the materials they are made of. Organisms can be classified by their features, such as the presence or absence of a backbone.

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Measure Measuring is an important science skill. It allows you to quantify your observations.

Distance, time, volume, mass and temperature are some quantities that can be measured.

To measure accurately, you often need to use tools such as rulers, beakers, thermometers and stopwatches.

Make a Model Scientists often construct models to predict, test and observe real-life phenomena.

Models can be physical objects, such a model of a miniature wind turbine to simulate electricity generation or a model of the Earth’s surface to simulate weathering and erosion.

Models can also be in the form of diagrams. A food web diagram is a model that shows the flow of energy in an ecosystem. A map is a diagrammatic model of an area of land or water.

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Infer You infer when you make a guess about something based on what you know or what you observe.

If you see footprints in the snow, you can infer that an animal has passed by after the last snowfall.

If you discover an animal jaw bone with large canine teeth, you can infer that the animal likely ate other animals.

Communicate You communicate when you show or tell other people what you find out.

Communication can be in the form of a written report, visual displays or an oral presentation.

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Scientific Method Scientists ask questions based on observations of the world around them. To find the answers to their questions, they carry out tests and investigations following the scientific method.

Why is it useful for scientists to follow the same scientific method?

The scientific method is a logical set of steps that is followed to help guide an investigation. It also helps to ensure the investigation is carried out fairly and in a manner that can be understood and repeated by other scientists.

Make Observations The scientific method begins by making observations about the world around you.

You may observe that plants in one area grow faster and taller than plants in other areas.

You may notice that you feel hotter in a darker-colored shirt than a lighter-colored shirt.

You may observe that ice melts faster in a cup made of one material than a cup made of another material.

Such observations lead you to ask questions about why these things occur.

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Ask Questions Before a science investigation begins, it’s important to ask questions about what you would like to find out.

Asking questions helps you to define the investigation. Your investigation should be designed to find the answer to your questions.

You can also use prior knowledge and experiences to provide possible answers to your questions.

Why does warm water cool faster in a metal cup than in a foam cup?

Do plants grow taller when fertilizer is added to soil?

Why do amphibians live near water?

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Make a Prediction Once you have asked questions based on your observations, it’s time to make a prediction and form a hypothesis. A hypothesis is a statement about what you think your investigation will show.

A hypothesis is more than just a guess.

It is a statement based on knowledge you already have or things you have observed in the past.

Based on past gardening experience, you may predict that plants will grow faster and taller in humus-rich potting soil than in sandy soil.

Based on a previous investigation, you may already know that metal is a better conductor of heat compared to wood or plastic. These past experiences can help you predict the results of an investigation.

Why is it important to write a procedure that can be easily followed by others?

Plan and Carry Out an Investigation Once you have stated your hypothesis, it’s time to plan and conduct an investigation that will test your prediction. In planning your investigation, you should include all the materials you will need and a procedure that clearly shows the steps you will take to conduct the investigation.

Your materials and procedure should be written in a way that allows the investigation to be easily followed and repeated by others. In your procedure, include the data you will collect and the way it will be recorded.

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Variables An important part in a science investigation are variables. A variable is any factor that can be controlled or changed during the investigation. There are three main variables – the independent variable, the dependent variables and the controlled variables.

The independent variable is the one condition in the investigation that you can change. Usually it is the thing that is being tested. If you were investigating which materials are good conductors of heat, the independent variable would be the type of material.

The dependent variable is the factor that you measure or observe. The dependent variable should change due to changes in the independent variable.

In an investigation on materials that are good conductors of heat, the dependent variable could be temperature of water in a cup. You would expect the temperature of the water to change as you change the independent variable – the type of material the cup is made of.

Imagine conducting an investigation about the growth rates of different seedlings.

What would be the independent variable?

What would be the dependent variable?

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Imagine you were carrying out an investigation into the effect of temperature on plant growth. What would be your controlled variables?

The controlled variables are variables that do not change during the investigation.

Controlled variables could include the type and size of a container, the source and temperature of water and the types of instruments used to take measurements.

The purpose of the controlled variables is to ensure that the only influence on changes in your observations is due to the independent variable.

Collecting and Recording Data Make observations and collect data as stated in your procedure. The data should be recorded in an organized way that can be read and understood by others.

Often, data is recorded in a visual manner, such as charts, graphs and diagrams. Data can also be entered into computer software which can make it easier to analyze and present the data.

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Analyze and Interpret Data Once your observations have been accurately recorded, it’s time to analyze and interpret the data to see if your hypothesis is supported.

You analyze when you look closely at recorded data. You look for patterns to help explain your results. A pattern is when data repeats in a predictable way.

You interpret when you understand and explain what the data means. In interpreting data, you use your prior knowledge, experience, and skills to explain patterns and trends identified in the analysis of the data.

An important part of analyzing and interpreting is to check the accuracy of the data collected. If there are inaccuracies or inconsistencies in the data, you may need to adjust your procedure and repeat the investigation.

Draw a Conclusion By analyzing and interpreting your data, you reach a conclusion. Your conclusion is a summary of the data collected. Your conclusion should indicate the accuracy of your prediction.

Your conclusion should state whether your hypothesis was supported or not supported.

If your hypothesis was not supported, you may decide to form a new hypothesis and plan and conduct a new investigation. If your hypothesis was supported, you may wish to do further investigations to confirm the results or improve the accuracy of the data collected.

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Communicate The final step in a science investigation is to communicate your findings to others.

This allows you to share what you have discovered and also allows others to assess the accuracy of your investigation.

The people you communicate your results with may wish to conduct a similar investigation and compare results. They may also wish to conduct further investigations to find out more.

If they do, they’ll also communicate their results so others can learn from their investigations too.

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Scientific Method Flowchart Make Observations

Ask Questions

Construct Hypothesis Plan and Conduct Investigation Analyze and Interpret Data Form a Conclusion Hypothesis Not Supported

Hypothesis Supported

Communicate Results

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Science Safety In the Laboratory

Follow these safety rules when in your science laboratory or when carrying out any science investigation. o not enter the laboratory without D a teacher. ollow your teacher’s instructions.

F If you have any questions or are unsure of what to do, raise your hand and ask your teacher. o not eat, drink, play or run in D the laboratory. ash your hands with soap when W entering and before leaving the laboratory. Dry your hands properly, especially if you will be working with electrical equipment. If any chemical or hazardous material gets on your hands, inform your teacher immediately. ear appropriate safety gear when W carrying out scientific investigations.

Safety gear includes a lab coat, safety goggles and gloves. Tie long hair back and do not wear open-toed shoes. e careful when handling sharp tools B or working with burners and hot substances.

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o not panic if an accident occurs.

D Be aware of eyewash stations, fire extinguishers, exit doors and other safety equipment and procedures in case of an emergency. eep your workspace clean and K organized. Report any spills or breakages to your teacher. Clean up any spills straight away and dispose of the cleaning products safely. hen cleaning up, ensure all W materials and substances go into the correct bin or container. Do not pour any liquid down the sink unless your teacher has instructed you to do so. ook after the equipment you use and L return it to its proper location in the same condition you received it. Wipe your workstation down after use.

In the Field ake sure you are accompanied by an M adult when on field trips or doing other activities outside of the schoolyard. n long trips, make sure you take O enough water and food. Bring insect repellent if necessary. n sunny days, take Sun protection such O as a long-sleeved shirt, hat and sunscreen.

Try This!

Create a poster of the rules to be followed in your science laboratory or classroom.

Display the poster in a place for everyone to see.

o not touch plants, animals or other D organisms unless instructed to do so by your teacher.

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6

The Universe In this chapter you will ...

• support an argument that the apparent brightness of the Sun and stars is due to their relative distances from the Earth.

• distinguish between solar systems, galaxies and the universe.

• list and describe the general characteristics of the inner and outer planets.

• describe the ways in which humans explore space and list some historic space missions and achievements.

What lies beyond our solar system?

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What are the characteristics of stars?

Go Online!

Access interactive content relating to this topic on the NGScience website. ngscience.com

What objects lie in our solar system?

How can we classify the objects?

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What Is the Universe?

Think about the place where you live. If you zoom out from your town or city, you’ll see that it is located within a country. Zoom out again and you’ll see your country is part of our planet – Earth. Continuing to zoom out reveals that the Earth is one of eight planets that, along with the Sun and its orbiting objects, make up our solar system. The solar system is part of a galaxy – the Milky Way, which consists of billions and billions of stars.

Scientists are uncertain about the number of galaxies in the universe. Some scientists estimate there could be more than a trillion galaxies.

Go Online!

Journey into deep space and discover Earth’s place in the Milky Way in a video on the NGScience website.

QuickCode: R1U2

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What makes up the universe?

Where is Earth located in the universe?

Galaxies

If you observe the night sky on a clear night, you might be lucky enough to see a band of light consisting of many stars. The band of light you see is our galaxy – the Milky Way. A galaxy is an enormous group of stars, planets, dust and gas clouds that are held together by gravity.

The universe is home to billions of galaxies that all contain billions of stars. However, galaxies beyond our own Milky Way are very faint in the night sky.

Despite their extremely large size and the billions of stars contained within them, most galaxies cannot be seen with the naked eye at night. This is because they are such a great distance from the Earth.

Galaxies come in different shapes and sizes. Our own Milky Way is a spiral galaxy. Spiral galaxies are made up of a flat, rotating disk of stars, dust and gas. Most of the matter is concentrated in the center with arms extending out. Our solar system is located on one of the arms of the Milky Way galaxy which contains younger stars than those in the center of the galaxy.

Some galaxies have an egg-like, elliptical shape. Such galaxies usually contain older stars.

Galaxies can also have an irregular shape and contain stars of many different ages.

AB

Try This!

On a clear night, go outside and give your eyes time to adjust to the darkness.

Observe the objects in the night sky. Are you able to see the Milky Way? What other objects are observable to the naked eye?

Activity 6.1

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A Closer Look

The Big Bang About 60 years ago, astronomers observed that objects in space are all moving away from Earth. This observation suggested that the universe was expanding much like a balloon being inflated. This model of the universe suggested that there was a time in the past when all of the objects were much closer together. This was followed by a rapid expansion which scientists named the Big Bang. This event occurred about 13.8 billion years ago.

At the early stages of the Big Bang, matter, space and energy were concentrated in a very small point. Particles were very hot and moved very fast. As the expansion continued, the particles cooled and elements such as hydrogen formed. Eventually the cooling gases became concentrated and formed stars and galaxies. The universe continues to expand and cool today.

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Activity 6.2

Stars Gaze at the night sky on a clear night and you’ll likely see thousands of tiny lights of varying brightness. The lights may appear to be small, but they are actually giant balls of burning hydrogen and helium gases. They are stars.

Our Sun is also a star. During the day it is the largest object in the sky and is our main source of light and heat. So, why is the Sun so much brighter than the stars we see at night? The answer is distance. Compared to other stars, our Sun is about medium-sized. The reason it appears so much larger and brighter than other stars is because it is much closer to Earth than other stars. The stars at night are much further away so they appear smaller and less bright.

Did You Know?

The closest star to our Sun, Alpha Centauri C (also called Proxima Centauri), is about 268,770 astronomical units (AU) away which is 4.25 light years. Alpha Centauri C is part of a the three-star Alpha Centauri star system. The other two stars that make up the system, Alpha Centauri A (Rigil Kentaurus) and Alpha Centauri B (Toliman) are approximately 4.35 light years away.

Why do the stars at night appear much smaller and less bright than our Sun?

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Activity 6.3

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Go Online!

The Sun was born about 4.6 billion years ago when a cloud of dust and gas called a nebula collapsed under its own gravity. In about 5 billion years from now, the hydrogen that powers the nuclear reaction at its core will run out. When this occurs, the Sun will puff up into a huge red star, hundreds of times larger than it is now. At this stage, it is called a red giant. A red giant eventually cools off and collapses into a much smaller star called a white dwarf.

Discover more about star classification in a video on the NGScience website.

QuickCode: A9P9

Did You Know?

Astronomers often refer to the distance of the Earth from the Sun as the ‘Goldilocks Zone’. This is because it is not too hot, like on Venus, and not too cold, like on Mars, but rather ‘just right’ to sustain life.

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The Sun Our Sun is a medium-sized star which lies about 150 million kilometers from Earth. Scientists use this distance as a benchmark unit called an astronomical unit (AU) which is used to measure other distances in the solar system.

Compared to other objects in our solar system, the Sun is by far the largest. It has a diameter of almost 1.4 million kilometers (870,000 mi). The second-largest object in the solar system, the planet Jupiter, has a diameter of just 140,000 kilometers (87,000 mi).

The mass of the Sun makes up more than 99 percent of all mass in the solar system. The Sun’s gravitational force keeps the planets and other objects in the solar system in orbit around it.

The Sun is made up mostly of the gases hydrogen and helium. The light and heat produced by the Sun is caused by nuclear reactions within its core. The Sun is at its hottest at the core where the temperature is about 15,000,000oC (27,000,000oF).

The Sun does not have a solid surface and is made up of a number of layers surrounding the core. The surface temperature of the Sun is about 5,500oC (10,000oF). Fortunately, by the time the Sun’s heat reaches Earth, it is at a more suitable temperature to sustain life.

The Sun formed approximately 4.6 billion years ago and will continue to burn for about another five billion years.

A Closer Look

Structure of the Sun The core is the hottest part of the Sun where the nuclear reactions take place.

Heat moves from the core through the radiative zone to the convection zone.

In the convection zone, heat from the radiative zone is carried up by columns of hot gas.

photosphere convection zone radiative zone core chromosphere corona

The photosphere is the lower part of the Sun’s atmosphere. It is the part of the Sun we see from Earth.

AB

The chromosphere is the middle of the Sun’s atmosphere. It extends from the photosphere to the corona.

The corona represents the Sun’s outer atmosphere. It extends millions of kilometers into space.

Activity 6.4 9

The Solar System In the center of our solar system lies the Sun. Pulled into orbit by the Sun’s gravitational force are objects such as planets and their moons, dwarf planets, asteroids, meteoroids, comets and man-made objects.

The largest objects orbiting the Sun are the eight planets. In order of their distance from the Sun, the four closest planets are Mercury, Venus, Earth and Mars. These planets are called the inner planets or terrestrial planets. They are made up mostly of rock and are similar in size to the Earth. Due to their close distance to the Sun, the inner planets are also much warmer than the planets further from the Sun.

Venus Mercury

Mars

Earth

Jupiter

What similarities do the inner planets share?

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The outer planets are the four furthest planets from the Sun – Jupiter, Saturn, Uranus and Neptune. These planets are much larger than the inner planets. They are not rocky like the inner planets. Jupiter and Saturn are made up mostly of gases such as hydrogen and helium and have dense atmospheres. They are called gas giants.

Uranus and Neptune are made up of heavier substances referred to as ‘ices’ and are classified together as ice giants.

What similarities do the outer planets share?

Saturn

Neptune

Uranus

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The Eight Planets The planets in the solar system have different characteristics. Such characteristics include:

Think Deeply What characteristics of Mercury and Venus make them unsuitable to support life?

• • • • •

composition diameter distance from the Sun rotation speed temperature

Composition is what a planet is made of.

Generally, the inner planets are comprised mostly of rock and metal and have a solid surface. The outer planets are made mostly of gases, such as hydrogen and helium. They do not have a solid surface.

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A planet’s distance from the Sun affects both its orbit and temperature. Usually, the further a planet is from the Sun, the longer it takes to complete a revolution of the Sun and the cooler its temperature.

However, the composition of a planet’s atmosphere can also affect its temperature.

Venus, for example, is further from the Sun than Mercury but its thick atmosphere traps heat, resulting in surface temperatures that can be higher than Mercury which is closer to the Sun.

Go Online!

Discover more about the characteristics of the eight planets in a virtual tour of the solar system.

QuickCode: C8J4

Like Earth, all planets spin about their axis as they revolve around the Sun. It takes the Earth 24 hours to complete one rotation, which we call one Earth day. As we take a closer look at the characteristics of each planet, we will refer to their time to complete a rotation in Earth days.

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Mercury – Quick Facts Composition: metal and rock Distance from Sun: 0.4 AU Diameter: 4,880 km Rotation: 59 days Orbit: 87.97 days Temperature: -180oC to 430oC Moons: none Life: No

Mercury

Mercury is the nearest planet to the Sun. It is also the smallest planet in the solar system with a diameter of 4,880 kilometers (3,032 miles) which is just slightly larger than the Earth’s moon.

Mercury’s orbit around the Sun takes 87.97 Earth days, which is the shortest of all the planets in the solar system. Mercury has a rocky surface and no atmosphere. It has many craters formed by meteorites crashing into its surface.

Venus is the second closest planet to the Sun. It has a diameter of 12,104 kilometers (7,521 miles) and completes an orbit of the Sun in 224.7 Earth days. Venus has a dense atmosphere that traps the heat from the Sun. This makes it the hottest planet in the solar system with temperatures of up to 471°C (880°F) during the day.

Venus

Venus – Quick Facts Composition: metal and rock Distance from Sun: 0.7 AU Diameter: 12,104 km Rotation: 117 days Orbit: 224.7 days Temperature: 471oC Moons: none Life: No

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Earth – Quick Facts Composition: metal and rock Distance from Sun: 1 AU Diameter: 12,742 km Rotation: 24 hours Orbit: 365.25 days Temperature: −89.2oC to 56.7oC Moons: one Life: Yes Earth

Earth is the third planet from the Sun. The Earth’s atmosphere makes the conditions on Earth suitable to support life. Ozone in the atmosphere helps to block harmful ultraviolet (UV) rays from reaching the surface. The Earth’s atmosphere also helps to regulate the temperature on its surface where water exists in three states – as the gas water vapor, liquid water and solid ice. Earth has a diameter of 12,742 kilometers (7,918 miles) making it the largest of the inner planets.

Mars is the fourth planet from the Sun. It is often called the red planet due to its red, rocky surface. Mars has a diameter of 6,779 kilometers (4,212 miles) and completes an orbit of the Sun in 687 Earth days. Mars has a thin atmosphere made up mostly of carbon dioxide. It has two moons – Phobos and Deimos.

Mars

Mars – Quick Facts Composition: metal and rock Distance from Sun: 1.5 AU Diameter: 6,779 km Rotation: 24.6 hours Orbit: 687 days Temperature: −143oC to 35oC Moons: two Life: No

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A Closer Look

Colonization of Mars Humans have long been interested in visiting and colonizing another planet. Although we have successfully landed and walked on our moon’s surface, no human has yet to land on another planet.

Many scientists believe that this may soon change.

Landing on and colonizing another planet in our solar system presents a number of problems.

Such problems include the distance from Earth, composition of the atmosphere, temperature and gravity. In order to find a planet suitable to colonize, it would need to be similar to Earth.

The outer planets are not suitable for colonization due to their gaseous composition and distance from Earth.

The two rocky planets closest to the Sun, Mercury and Venus, may have some suitable features, but the extremes in temperature make them largely unsuitable. That leaves just one potentially suitable planet – Mars.

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Although Mars is the most suitable planet for colonization, many challenges still exist. These include: • distance from Earth. Using current technology, it will take about seven months for a spacecraft to travel from Earth to Mars.

• surface gravity is just 38 percent of that of the Earth’s.

• atmosphere consists mostly of carbon dioxide and very little oxygen.

• very little liquid water.

• toxic soil which is not suitable for growing plants.

• cold temperatures that are comparable to those at the Earth’s poles.

The successful colonization of Mars would likely require the establishment of a permanent habitat on the planet’s surface.

Get together with your friends and discuss how such a habitat could overcome the challenges of living on Mars.

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Jupiter – Quick Facts Composition: hydrogen and helium Distance from Sun: 5.2 AU Diameter: 139,820 km Rotation: About 10 hours Orbit: 11.86 years Temperature: -145oC to 210oC Moons: more than 79 Life: No

Jupiter

Jupiter is the largest planet in the solar system with a diameter of 139,820 kilometers (86,880 miles). Its mass is more than two and a half times that of all the other planets in the solar system combined. It takes Jupiter and its 79 known moons 11.86 Earth years to complete a revolution of the Sun. Like the other outer planets, Jupiter does not have a well-defined solid surface. It is made up mostly of the gases hydrogen and helium.

Saturn is the sixth planet from the Sun. It is often called the ringed planet due to its spectacular ring system. Saturn is the second largest planet in the solar system with a diameter of 116,460 kilometers (72,365 miles). Like Jupiter, Saturn is made up mostly of the gases hydrogen and helium.

It takes Saturn 29.5 Earth years to complete a revolution of the Sun. Saturn

Saturn – Quick Facts Composition: hydrogen and helium Distance from Sun: 9.5 AU Diameter: 116,460 km Rotation: About 11 hours Orbit: 29.5 years Temperature: -175oC Moons: more than 82 Life: No

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Uranus

Uranus – Quick Facts Composition: water, methane and ammonia with a small rocky center Distance from Sun: 19.8 AU Diameter: 50,724 km Rotation: About 17 hours Orbit: 84 years Temperature: -215oC Moons: 27 Life: No

Uranus has a diameter of 50,724 kilometers (31,518 miles). It takes Uranus 84 Earth years to complete a revolution of the Sun. Uranus is made of water, methane and ammonia that surround a small rocky core. The atmosphere of Uranus consists of hydrogen and helium, along with methane which gives the planet its blue color. Uranus has 27 known moons.

Neptune is the furthest planet from the Sun and has a similar atmosphere and composition to Uranus. It has a diameter of 49,244 kilometers (30,599 miles) and orbits the Sun once every 165 years.

Neptune has 14 known moons.

AB

Activity 6.5 Neptune

Neptune – Quick Facts Composition: water, methane and ammonia with a small rocky center Distance from Sun: 30 AU Diameter: 49,244 km Rotation: About 16 hours Orbit: 165 years Temperature: -200oC Moons: 14 Life: No

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Asteroids, Meteoroids and Comets The Sun and the eight planets are amongst the largest objects in our solar system. There are also many smaller objects that, like the planets, orbit the Sun. Asteroids are large, rocky and metallic objects orbiting the Sun. They range in size from just a few meters up to hundreds of kilometers.

Most asteroids orbit the Sun in an asteroid belt between the planets Mars and Jupiter. The largest asteroid observed in the asteroid belt is Ceres, which is also classified as a dwarf planet.

It has a diameter of 940 kilometers (580 miles).

Go Online!

Discover more about comets, asteroids, meteoroids, meteors and meteorites on the NGScience website.

QuickCode: A3A9

If you use a telescope to observe the Earth’s moon on a clear night, you’ll notice the lunar surface is covered with many craters. Similar craters can be found on the surface of each of the inner rocky planets. The craters formed when the planets were struck by meteoroids. A meteoroid is a small, rocky or metallic object orbiting the Sun. Many meteoroids form when asteroids are broken up into smaller pieces.

meteorite

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Meteor Crater, Arizona, USA

Meteoroids have a size ranging from a grain of sand to one meter. If a meteoroid enters Earth’s atmosphere, it becomes known as a meteor.

Most meteors burn up completely before reaching the Earth’s surface. The shooting stars we see at night are most likely meteors burning up in the Earth’s atmosphere.

Occasionally, a meteor doesn’t burn up completely as it enters the atmosphere. A meteor that reaches the Earth’s surface is called a meteorite.

Comets are orbiting bodies comprised of frozen gases, rock, ice and dust. When a comet passes close to the Sun, heat causes some of the ice to change to a gas. The gases form a tail called a coma. The size of most comets ranges from around 700 meters to 20 kilometers. Many comets orbit the Sun in a belt of asteroids and other objects called the Kuiper belt.

The Kuiper belt lies between 30 and 50 AU from the Sun.

AB

Did You Know?

Approximately 50,000 years ago, a metal meteorite with a width of about 50 meters (160 ft) struck the Earth’s surface in the Arizona Desert, USA. The meteorite formed a crater with a diameter of 1,200 meters (3,900 ft) and a depth of 170 meters (560 ft). Today the crater is simply called Meteor Crater and is a popular tourist destination.

Activities 6.6 – 6.7

The Hale-Bopp comet became visible to the naked eye on Earth in 1997 for a record 18 months. It will return to the inner solar system around the year 4385.

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Exploring Space Humans have been exploring space for thousands of years. Space exploration can be as simple as gazing at the night sky with the naked eye and making observations or identifying patterns. To take a closer look at space from the surface of the Earth, a telescope can be used.

radio telescope

Think Deeply Light telescopes used to explore space are often located in places of high altitude such as mountaintops. How does this improve the quality of the images seen through the telescopes?

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The first telescopes used to observe objects in space were light telescopes.

A light telescope reflects or refracts light to magnify distant objects to make them appear closer and in finer detail. When viewing objects in space from Earth, light telescopes are subject to interference from the Earth’s atmosphere.

Radio telescopes are telescopes that detect radio waves given off by distant objects.

Groups of dishes are often used to focus the radio waves. Receivers and computers interpret and produce images from the data. Radio telescopes do not experience interference with the Earth’s atmosphere.

The 10.4 m Gran Telescopio Canarias telescope is the largest reflecting light telescope in the world.

Voyager 1 and Voyager 2 were space probes launched

by NASA in 1977. After successfully collecting a range of data on Jupiter and Saturn, they were sent deeper into space to collect data on Neptune and Uranus. They are currently more than 150 AU from Earth and are heading to deep space.

The best way to get the clearest images of space and collect valuable data is to venture beyond the Earth’s atmosphere using space probes or send people into space aboard spacecrafts.

A space probe is an object launched into space that has specialized instruments on board to study various objects in the solar system. A space probe usually has a mission objective and the instruments it carries are specifically design to achieve the mission objective.

Space probes include space telescopes, robots and unmanned spacecraft. Probes send the data they collect back to Earth for analysis and interpretation by scientists. The National Aeronautics and Space Administration (NASA) has sent probes into space to collect data on all eight planets in the solar system.

AB

Activities 6.8 – 6.9 Go Online!

Learn all about the Hubble Space Telescope and its many discoveries in a video on the NGScience website.

QuickCode: K6S5

The Hubble Space Telescope was launched into low Earth orbit by NASA in 1990. Without any interference from the Earth’s atmosphere, it is able to capture very high quality images of objects in our solar system and far beyond.

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Scientists that travel into space, called astronauts, are highly trained in operating spacecrafts and living in space.

The first man sent into space was Russian cosmonaut, Yuri Gagarin, on board the spacecraft Vostok 1 on April 12, 1961. Vostok 1 completed one orbit around the Earth, lasting about 1 hour and 48 minutes. Since then, almost 600 other people have ventured into space on a range of missions. The timeline below shows some of the greatest achievements in space exploration.

1957 – Sputnik 1

1969 – Moon Landing

1981 – Space Shuttle

Sputnik 1 was the first artificial satellite launched into space (USSR, October 4, 1957).

Astronaut Neil Armstrong became the first man on the moon (USA, July 20, 1969).

First reusable manned spacecraft, the space shuttle launched (USA, April 12, 1981).

1970

1950 1960 1961 – Man in Space Russian cosmonaut, Yuri Gagarin, became the first man in space (USSR, April 12, 1961).

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1980 1977 – Voyager Voyager space probes launched to explore the outer planets (USA, September 5, 1977).

1989 – Galileo

2004 – Rosetta

2021 – Perseverance

Galileo space probe launched to study Jupiter and its moons (USA, October 18, 1989).

Rosetta space probe launched into orbit to study comets (Europe, March 2, 2004).

Mars rover, Perseverance, lands on Mars to collect data on the planet’s surface (USA, February 18, 2021).

1990

2010 2000 1998 – ISS International Space Station launched in low Earth orbit (November 20, 1998).

2020 2015 – Falcon 9 SpaceX lands first reusable rocket, the Falcon 9 (USA, December 21, 2015).

AB Activity 6.10 25

Space Technology – Spin-offs

The technology used to develop scratch-resistant astronaut helmets is now used to make sunglasses and ski goggles.

Exploring space, whether from the ground, using space probes or sending people into space, requires cutting-edge science and often involves the engineering of new technologies. Such advances in science have been invaluable not only to our understanding of space, but also help humans in another important way – spin-offs.

A spin-off is something that is developed from another earlier project. Spin-offs from space technology have led to advances in areas such as health and medicine, transportation, clean energy, safety and computer technology. Let’s take a look at a few of the spin-offs we use today.

In the 1980s, NASA developed new materials for their space helmets that were resistant to scratching and filtered out harmful UV light. Today, these materials are used in sunglasses and ski masks.

Many of the cameras and smartphones we use today have special sensors for capturing light and producing the images we see. These sensors were first created by NASA in order to fit space probes with miniature cameras to capture images of our solar system.

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When astronauts venture beyond the Earth’s atmosphere, monitoring their health from Earth is important. Some of the space technology developed to monitor astronaut health is now used in medical technologies on Earth.

During the 1960s and 1970s, NASA conducted a series of missions to discover more about the Earth’s moon. The missions cost more than US$25 billion and included the development of many new technologies. Many of these technologies are used by people today.

These include freeze-dried food, cooling suits, integrated computer circuits and the development of new, heat-proof materials.

Try This!

In small groups, discuss current technologies used in space exploration and how the technologies may be useful to solve problems on Earth.

The solar panels we use to produce solar electricity uses technology developed to power artificial satellites.

Many spacecrafts, space probes and other artificial satellites use solar cells to produce electricity. The same technology is used in the solar panels we use on Earth to produce clean, renewable energy.

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Science Words Use the words to complete the sentences. galaxy star astronomical unit inner planets 1. The

outer planets asteroid meteoroid

meteor meteorite comet

are the four planets closest to the Sun.

2. The four furthest planets from the Sun are the 3. A

.

is a meteor that strikes the Earth’s surface.

4. A is a small, rocky or metallic object orbiting the Sun. It becomes known as a once it enters the Earth’s atmosphere.

5. The distance from Earth to the Sun is called an

.

6. A is an enormous group of stars, planets, dust and gas clouds that are held together by gravity.

7. A

is a giant ball of burning hydrogen and helium gases.

8. An

is a large, rocky or metallic object orbiting the Sun.

9. A and dust.

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is an orbiting body comprised of frozen gases, rock, ice

Review 1. Copy and complete the table.

Object

Natural Objects in Space Description

Star Solar System Galaxy Universe 2. What is the name of the galaxy in which our solar system lies?

3. Why does the Sun appear much larger and brighter than the stars we see in the sky at night?

4. What characteristics do the inner planets share?

5. What characteristics do the outer planets share?

6. Describe three ways people can explore space.

7. Why is a space telescope able to produce clearer images of space than a light telescope on the Earth’s surface?

8. What is the asteroid belt and where can it be found?

9. In relation to comets, what is a coma and how does it form?

10. What is a spin-off? Provide one example.

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In the Field

Apollo 13 The Apollo project was a NASA space program that ran from 1961 to 1972.

The primary goal of the program was to land humans on the moon. This goal was achieved during Apollo 11, when astronaut Neil Armstrong stepped onto the lunar surface on July 21, 1969.

The following year, Apollo 13 was launched into space with a similar mission.

But this time, things did not go as planned. Two days into the mission, a damaged wire in an oxygen tank caused an explosion which damaged the command module (CM). With insufficient oxygen, the mission was aborted.

Back on Earth, Mission Control faced a large problem – how to move the crew from the damaged CM to its lunar module (LM), then land the LM safely back on Earth. This presented a number of challenges. The LM was only designed to support two astronauts on the lunar surface for two days. To get home, the LM would need to support three astronauts for four days. A key challenge was adapting the CM’s carbon dioxide removal system to fit that of the LM.

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Through a range of simulations, trial and error and improvisation, Mission Control found a solution. Although the crew experienced harsh conditions caused by limited power, little water and cold temperatures, they circled around the moon and landed safely in the South Pacific Ocean on April 17, 1970.

Go Online!

Watch a video about the Apollo 13 mission on the NGScience website.

Discover how quick problem-solving and improvisation resulted in plastic bags, cardboard and tape being used to bring three stranded astronauts back to Earth!

QuickCode: K2Z5

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7

Matter

What are the three states of matter?

How does matter change from one state to another?

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How can matter be mixed? What are some ways we can separate mixtures?

Go Online!

Access interactive content relating to this topic on the NGScience website. ngscience.com

In this chapter you will ...

• develop a model to describe that matter is made up of particles too small to be seen.

• describe the properties of the three states of matter and provide examples of each.

• describe and provide examples of physical and chemical changes.

• explain and provide examples of heterogeneous and homogeneous mixtures.

• demonstrate the different ways in which the components of mixtures can be separated.

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What Is Matter?

Fill a graduated cylinder with 100 milliliters of water. Place a ball of modeling clay into the cylinder and observe what happens to the level of the water. What does this tell you about the modeling clay?

The graduated cylinder, water and the modeling clay are all matter. The air around you is matter.

Even you are matter. Matter is anything that has mass and volume.

The rise in the level of the water shows that the ball of modeling clay has volume.

Mass is the amount of matter an object has.

Mass is measured using a scale or balance and is commonly measured in kilograms, grams, ounces or pounds. If you place a marble on one side of a pan balance and a ping pong ball on the other, you’ll observe that the marble has more mass than the ping pong ball.

Volume is how much space matter takes up.

When a ball of modeling clay is placed in a graduated cylinder containing water, the level of the water rises. This shows that the ball of modeling clay takes up space.

The banana has a greater mass than the apple.

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Matter is made up of tiny particles, called atoms.

They are the basic unit of all matter. Atoms are so small they can only be seen with high-powered microscopes.

Matter typically exists in three states – solids, liquids or gases. The state matter is in depends on the arrangement and behavior of the atoms.

Let’s take a look at the properties of each state of matter along with the arrangement and behavior of the atoms in each state.

Try This!

Blow air into a balloon. Take note of how the balloon changes. Let the air out of the balloon. Discuss what happens to the air. Use your observations to provide evidence that matter is made up of particles too small to be seen.

States of Matter When you take some ice cubes and place them into a cup, no change takes place. The ice cubes may have moved from the ice cube tray to the cup, but their shape and volume do not change.

Ice is water in a solid state. Matter in a solid state has a fixed shape and volume.

The particles that make up solid matter are tightly packed in an organized pattern.

The particles that make up solid matter are tightly packed together in an organized pattern.

They do not move past each other but vibrate back and forth in fixed positions. This gives solid matter its rigid shape. The tightly packed particles also means solid matter cannot be compressed.

Your desk, chair, books, pens and pencils are all examples of solid matter.

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The particles in a liquid are free to slide past each other.

Pour some water from a cup into a rectangular container. What change takes place?

Try This!

In small groups, use a variety of liquids, containers and a balance to demonstrate that liquids can change in shape, but not volume.

Water is matter in a liquid state. When you pour water from one container to another, the shape of the liquid changes – it spreads out to take the shape of the container it is in. Compared to a solid, the particles that make up a liquid are less tightly packed together. They are free to slide past each other. This property allows liquids to flow and change shape.

If you pour the water in the container back into the cup, you will notice that the amount of water is unchanged. Like solids, liquids have a fixed volume. This means the amount of space taken up by a liquid remains the same even when moved from one container to another. Like solids, liquids cannot be compressed.

Water, fruit juice and cooking oil are examples of matter in a liquid state.

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The particles that make up a gas are able to move about freely.

If you take a balloon filled with air and squeeze it gently you will notice that the shape of the balloon changes. When you let the air out of a balloon, the air spreads out in all directions. Air is a gas. It is matter in a gaseous state. The particles that make up a gas are able to move about freely. This property allows gases to change in both shape and volume. When a gas is heated, the particles move about more rapidly. When a gas is cooled, the particles slow down.

Gases can be compressed. When a gas is compressed, its volume decreases. We compress air to fill a scuba tank. Inside the scuba tank, the compressed air has a volume similar to a few breaths. When the air in a scuba tank is released, its volume increases, providing a scuba diver with enough air for hundreds of breaths, allowing the diver to remain underwater for a long time.

Discuss, compare and contrast the properties of each state of matter.

AB

Activities 7.1 – 7.2

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The Changing States of Water Inside a freezer, the temperature is below 0oC. When solid ice is placed in a freezer, it remains in a solid state. When you remove ice from a freezer, it gains heat and the particles that make up the ice begin to move more rapidly.

Eventually, the particles break away from each other and begin to flow freely. The ice is melting.

It is changing from a solid state to a liquid state.

If liquid water is heated, it will also change state. It will evaporate into the gas water vapor.

Matter changes state when it is heated or cooled. Some matter require large increases or decreases in temperature before they change state. Gold is a solid at room temperature. It needs to be heated to over 1,000oC (1,832oF) before it begins to melt. Other matter can change state more easily.

At 0oC, water changes from a liquid to a solid.

On Earth, water exists in three states – as solid ice, liquid water and as the gas water vapor. Let’s take a look at how water changes states when it is heated and cooled and the temperatures at which these changes take place.

At room temperature, water is in a liquid state. When water is cooled to 0oC (32oF), it begins to change into solid ice. This process is called freezing and the temperature at which this occurs is called its freezing point. So, the freezing point of water is 0oC.

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At temperatures above 0oC, ice melts and changes from a solid to a liquid.

At temperatures below 0oC, ice will remain in its solid state. When ice is heated, it will change from a solid to a liquid. The process in which matter changes from a solid to a liquid is called melting. The temperature at which this begins to occur is called the melting point. The melting point of matter is the same as its freezing point.

So ice has a melting point of 0oC (32oF).

At 100oC, water boils and changes into a gaseous state.

When water is heated, it changes from a liquid into the gas water vapor. This process, called evaporation, occurs more rapidly the more water is heated. At 100oC (212oF), water begins to boil. Boiling is the process by which a liquid rapidly changes into a gas. When water boils, it changes into an invisible gas called steam. The temperature of a boiling liquid does not increase, even when more heat is added.

Discuss the processes and changes in state that take place when ice is heated in a beaker.

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Have you ever noticed water droplets forming on the side of a cold can of soda? The droplets of water form when water vapor in the air cools as it comes in contact with the cold can. This process of changing from a gas to a liquid is called condensation. Condensation can occur at any temperature.

AB

Activities 7.3 – 7.4

A Closer Look

Freezing, Melting, Boiling and Condensation At 0oC, liquid water freezes and becomes solid ice. freezing

melting

At 0oC, solid ice melts and becomes liquid water.

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When water vapor cools, it condenses into liquid water. condensation

evaporation/boiling

At 100oC, liquid water boils and becomes gaseous steam.

Changes in Matter Physical Changes A potter takes a ball of clay and spins it on a pottery wheel. The clay changes shape as it is pulled, pinched, pressed and molded. Once complete, the ball of clay has changed into the shape of a vase.

Although the appearance of the matter changed, its composition remained the same. Such a change, in which the composition of matter does not change and no new matter is made, is a physical change.

You make physical changes to matter when you tear a sheet of paper, or cut the ingredients to a fresh garden salad. In each example, no new matter is made.

What are some physical changes to matter that take place in everyday life?

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When a physical change is made to matter, the amount of matter does not change. If you take a block of butter and cut it into pieces, the butter will have a different shape and appearance, but the amount of butter and its composition does not change.

Physical change can also take place when matter is heated or cooled. If you heat the pieces of butter in a saucepan, they will melt into a liquid. If you turn off the heat and allow the butter to cool, it will form a solid again.

When butter changes from a solid to a liquid and back to a solid again, the amount and composition of the matter remain unchanged.

Cutting butter into smaller pieces is a physical change.

Many physical changes, including those that involve a change in state, are reversible. This means the matter can be changed back to its state or condition before the physical change occurred.

Melting butter is a reversible physical change.

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Dissolving one substance into another to form a solution is also a physical change. When a solution is made, the substance that dissolves is called the solute. The substance into which it dissolves is called the solvent.

When you add a sugar cube to a glass of warm water and stir it, the sugar dissolves. As it dissolves, the sugar molecules disperse throughout the warm water.

However, no new matter is made as the individual sugar molecules remain unchanged.

Is dissolving sugar in water a reversible change? What could you do to find out?

Dissolving sugar in water is a reversible physical change. If you heat the solution, the water will evaporate leaving only the sugar in the glass.

AB

Activity 7.5

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Chemical Changes Chopping wood is a physical change.

To make firewood, an axe is used to split a log of wood into smaller pieces. In doing so, a physical change has been made. Although the wood has changed appearance, the composition of the matter is unchanged and no new matter is produced. When the wood is burned, a chemical reaction occurs whereby the carbon in the wood reacts with oxygen in the air. As it burns, smoke is produced and light and heat are given off. The smoke is a new type of matter. It consists mostly of carbon dioxide.

Burning wood is an example of a chemical change. A chemical change occurs when two or more substances combine and new substances are formed.

Chemical changes are usually not reversible unless further chemical changes are made.

A change that is not reversible is called an irreversible change.

Explain why burning wood is an irreversible chemical change.

Burning wood is a chemical change.

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Consider an iron nail that is left outside.

Over time, the oxygen from air combines and reacts with the iron to form a new substance – rust (iron oxide). Rusting is a chemical change.

A similar chemical change occurs on the copper exterior of the Statue of Liberty in the United States. Today, the statue has a distinct green color. When first constructed, it was light brown and had a much more shiny appearance. Over time, a slow chemical reaction has been taking place between the copper, water, and the oxygen and carbon dioxide in the air. The reaction forms a new substance on the statue’s surface, called patina. The patina gives the statue its green color.

The formation of iron oxide on the surface of the nails is a chemical change.

Chemical changes occur at different rates.

Some changes can occur very rapidly, like the explosion of fireworks. Others occur at slower rates, like the slow burning of a wooden log.

Chemical changes like the weathering of rocks can occur over millions of years.

The Statue of Liberty’s green color is due to a chemical reaction between its copper exterior, water, oxygen and carbon dioxide.

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We can identify when a chemical change is taking place or has taken place in the past by looking for evidence of a chemical change. Such evidence can include a change in color like the presence of rust on iron or a patina on a copper statue.

The production of light, heat or sound also often indicates that a chemical change is taking place. We can observe this when fireworks explode in the air.

Chemical changes can also be accompanied by a change in scent. When you walk past a bakery, the scent of freshly baked bread is evidence of a chemical change.

The production of gases which can cause bubbling or fizzing can indicate a chemical change is taking place. Placing aluminum foil in a strong acid will cause it to fizz, bubble and become warmer as hydrogen gas is created. Placing an antacid tablet in water, and mixing baking soda and vinegar are both chemical reactions that produce gases.

AB

Activities 7.6 – 7.7

Discuss some other examples where evidence lets you know a chemical change is taking place.

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Mixtures and Solutions What Is a Mixture?

A mixture is two or more kinds of matter that are mixed together. The different kinds of matter in a mixture retain their individual chemical properties, but the mixture may have new properties. It may be different in color, taste or have different melting and boiling points.

A salad is a simple example of a mixture.

It is a mixture of lettuce leaves and various types of fruits and vegetables. The different components of a mixture can be easily separated. Once separated, each component retains its original properties.

Mixtures can be classified into two broad groups based on how the components are mixed. In a heterogeneous mixture, the components that make up the mixture are not mixed evenly. A salad is a heterogeneous mixture. It contains different amounts of fruits and vegetables.

A trail mix and a salad are examples of heterogeneous mixtures.

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water

soil In a suspension, the substances that make up the mixture will separate if allowed to settle.

In some heterogeneous mixtures, the different components will separate themselves if allowed to settle. Such a mixture is called a suspension. Cooking oil mixed with water is a suspension. If allowed to settle for a few seconds, the oil will float on top of the water.

Some suspensions take longer to settle than others. A mixture of soil and water for example, will settle in about an hour. Sand and rock particles will sink and the organic matter that makes up the humus will float.

Take a teaspoon of table salt and stir it into a glass of warm water.

After a while, you will not be able to see the salt in the water. The salt dissolves in the water forming a solution of salt water.

A mixture in which the substances mix completely and are evenly distributed is called a homogeneous mixture. All solutions are homogeneous mixtures.

Think Deeply When you make a solution of sugar and water, the sugar seems to disappear.

What can you do to find out if the sugar is still present in the water? How does this provide evidence that matter is made up of particles too small to be seen?

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salt water solution In a homogeneous solution, the substances that make up the mixture are indistinguishable.

salt

Solutions can be in gases, liquids and solids. Air is a solution. It is a mixture of nitrogen, oxygen, carbon dioxide and other gases.

Many metals are solutions. People often mix different kinds of metals together or with other substances to produce a new metal with specific properties. They may be made to be lighter or stronger. These mixtures of metals are a type of solution called alloys.

Aluminum alloys contain mostly aluminum along with other metals, such as steel.

They are often used when an object needs to be lightweight. Stainless steel is a metal solution made of iron and other metals to make it more resistant to the chemical change of rusting.

Gold is often used to make jewelry. As pure gold is soft, it is often mixed with other metals to make the jewelry stronger and more durable.

Discuss some other examples of solutions in gases, liquids and solids.

AB

Think Deeply What changes in states of matter take place when an alloy is made? How are the changes in state achieved?

Activity 7.8

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Separating Mixtures Mixtures can be separated into their individual components. Generally, heterogeneous mixtures are easier to separate than homogeneous mixtures.

The ways in which a mixture can be separated depends on the properties of the matter that make up the mixture. Such properties include particle size, density, magnetism, evaporation and boiling point.

A sieve can be used to separate fine soil particles from rocks and organic matter.

Sifting is a process that can be used to separate a mixture of solids made up of large and small particles. To separate a mixture by sifting, we use a sieve. A sieve is a tool with a meshed bottom. By sifting a mixture of solids through the mesh, the larger solids remain in the sieve and the smaller solids pass through the holes in the mesh thereby separating the solids.

sieve

pebbles sand mixture of sand and pebbles

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Sifting can be used to separate pebbles from sand whereby a sieve allows the sand particles to pass through, leaving the pebbles in the sieve.

A mixture of magnetic and non-magnetic solids can be separated using a magnet. When a magnet is passed over a mixture of sand and iron filings, only the magnetic iron filings are attracted to the magnet. As magnetic force acts at a distance, the magnet does not need to be in contact with the iron filings.

Engineer It! Use a battery, iron nail, electric wires and art and craft supplies to design and build a device that can separate magnetic materials from non-magnetic materials in a mixture.

Challenge your friends to see who can separate the components the fastest.

A magnet can be used to separate magnetic objects from non-magnetic objects.

We can separate mixtures of liquids and solids by allowing the mixture to settle, then decanting the mixture. Decanting can be used to separate mixtures of matter that have different densities.

In a mixture of sand and water, the sand is denser than water. When allowed to settle, the sand will sink to the bottom. The water can then by poured out, leaving only the sand.

Go Online!

Observe different separation techniques in action in a series of videos on the NGScience website.

QuickCode: L8L2

Decanting can be used to separate mixtures that contain matter of different densities.

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Engineer It! In small groups, use common kitchen ingredients to make a heterogeneous mixture.

Give you mixture to another group and challenge them to separate the components.

When fine-grained solids are mixed with a liquid, we can separate the mixture using filtration. Take a mixture of water and flour. To separate the mixture, we can pour it into a funnel containing filter paper. The filter paper allows the water to pass through, but not the flour. The flour left in the filter paper is called the residue. The water that passed through the filter paper is called the filtrate.

mixture of water and flour.

When a mixture of water and flour is filtered, the water passes through, leaving the flour in the filter paper.

Think Deeply

flour particles (residue)

Why is filtration not a suitable separation technique for a solution of salt and water?

water (filtrate)

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funnel and filter paper

Separation methods, such as filtration and sifting, are not effective in separating solutions. One way we can separate the matter in a solution is by evaporation.

Take a solution of sugar and water. By heating the solution in a beaker, the water evaporates into the gas water vapor, leaving the sugar in the beaker.

The composition of the sugar is the same as before it was made into a solution.

When separating a solution using evaporation, the liquid part of the solution is lost unless the separating technique includes the condensation and collection of the water.

Evaporation is how salt is separated from water during the water cycle. The water vapor rises as it evaporates and condenses in clouds before falling back to Earth as precipitation. water vapor

water and sugar solution

Sea salt can be harvested by using the heat from the Sun to separate the salt from water.

Think Deeply How could you separate the sugar from a mixture of sand, sugar and fresh water?

Evaporation can be used to separate the sugar from a solution of sugar and water.

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One way that matter in a solution can be separated is through the process of distillation.

Distillation separates the matter in a solution using boiling and condensation. Let’s look at how distillation can separate a solution of salt water.

Salt water is a solution of water and salt. The boiling point of water is lower than that of salt.

When a salt water solution is heated in a flask, the water will boil, change into a gas and leave the flask through a tube. The salt, which has not reached its boiling point, remains in the flask.

The water vapor then cools and condenses in a condenser and changes back to liquid water.

thermometer

AB

distilling flask

Activity 7.9

condenser water vapor

salt water solution water out cool water in

Bunsen burner

distillate of fresh water The water and salt that make up a salt water solution can be separated by boiling the solution and condensing and collecting the water vapor.

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A Closer Look

Desalination Clean, fresh water is important to people all over the world. In areas with high precipitation, such as near the equator, fresh water is readily available all year round. In parts of the world with low precipitation, fresh water may not be available at all times. In many places where the supply of fresh water is inadequate, desalination is used to obtain clean, fresh water from sea water. Desalination is a separation technique in which salts are removed from water, leaving fresh water that is suitable for use by people.

One way that sea water can be desalinized is using solar distillation.

Solar distillation is very similar to the movement of water between the hydrosphere and the atmosphere during the water cycle. Large amounts of sea water are heated, either by the Sun’s heat directly, or using solar electricity. The heat causes the sea water to evaporate into water vapor, leaving the salt behind. The water vapor is then cooled and condensed into fresh water.

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Science Words Use the words to complete the sentences. mass volume atoms freezing point

melting point steam physical change chemical change

heterogeneous mixture homogeneous mixture distillation

1. A occurs when two or more substances combine and new substances are formed.

2. A change in which the composition of matter does not change and no new matter is made is a .

3.

is the temperature at which solid ice begins to melt.

4. When water boils, it changes into an invisible gas called 5.

is how much space matter takes up.

6.

is the amount of matter an object has.

7. Matter is made up of tiny particles, called basic unit of all matter.

8. solid ice.

. They are the

is the temperature at which liquid water changes to

9. A mixture in which the substances mix completely and are evenly distributed is called a .

10.

separates the matter in a solution using boiling and condensation.

11. In a mixed evenly.

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, the components that make up the mixture are not

.

Review 1. List and describe each state of matter. Draw simple diagrams to show the arrangement of the particles.

2. Describe what happens to the particles in matter when it is heated and cooled.

3. What is the difference between a physical change and a chemical change?

4. List three examples of evidence that can let you know a chemical change has taken place.

5. Label each change as a physical change or chemical change. (a)

(b)

paper is shredded (d)

(c)

an egg is fried

(e)

hair is cut

an ice cream melts (f)

bread is toasted

a motorcycle rusts

6. Describe how the components in each mixture can be separated.

(a) (b) (c) (d)

a solution of sugar and water a mixture of steel ball bearings and sawdust a mixture of water, salt and sand a mixture of talc power and water

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8

Forces

In this chapter you will ...

• describe forces and the ways they affect motion.

• use a model to demonstrate the effect of balanced and unbalanced forces acting on an object.

• list and describe different contact and non-contact forces.

• support an argument that the gravitational force exerted by Earth on objects is directed downwards.

• describe Newton’s three laws of motion.

How can forces affect the motion of objects?

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What types of forces occur when objects are touching? What are some forces that can act at a distance?

Go Online!

Access interactive content relating to this topic on the NGScience website. ngscience.com

How can our knowledge of forces allow us to predict motion?

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A pull force applied to the cart sets it in motion.

What Is a Force?

You use a push when you press the modeling clay on the table causing it to change shape.

An object’s motion changes when unbalanced forces act upon it. When there are no forces acting on an object, or the forces are balanced, an object’s state of motion remains the same. If the object is at rest, it will remain at rest. If the object is moving at a constant speed, it will continue moving at a constant speed.

Put simply, a force is a push or a pull.

Forces can set things in motion. They can change the speed or direction of an object in motion. Forces can also cause things to change shape.

A push is when you press something away from you. You use a push force when you throw a paper plane in the air.

You use a push when you throw a paper plane into the air. The push sets the plane in motion.

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A pull is when you tug something closer to you.

You pull on a fishing rod when you wind in a fish.

The gravitational force of the Earth pulls everything to its surface.

A force has magnitude and direction.

Magnitude is the strength or size of a force. A large, strong force will move an object further and faster than a smaller, softer force.

How a force affects the motion of an object also depends on the object’s mass. Larger, stronger forces are required to move objects of greater mass. The magnitude of the force required to lift a bowling ball is greater than that required to lift a soccer ball.

The magnitude of force required to raise an object to a higher position under gravity directly relates to the object’s mass. A bowling ball has a mass approximately 10 times that of a soccer ball. Therefore, a force of magnitude 10 times greater is required to raise the bowling ball the same height as the soccer ball.

How does the magnitude of a force acting on an object affect its motion?

AB

Activities 8.1 – 8.2

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Think Deeply During a game of tug-of-war, both teams are pulling on the rope with the same amount of force. What will happen to the motion of the team members if the rope was cut in the center?

Why will this occur?

Balanced and Unbalanced Forces

In a game of tug-of-war, one team pulls the rope in one direction and the other team pulls the rope in the opposite direction. What happens if both teams pull with the same force? What happens when one team pulls with a stronger force than the other team?

What must a team do in order to win a game of tug-of-war?

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When both teams use the same amount of force in opposite directions, the forces cancel each other out. They are balanced forces.

When the forces acting on an object are balanced, there is no change in motion.

To win a game of tug-of-war, one team must pull with greater force. When this occurs, the forces acting on the rope are no longer balanced. Forces that are not equal and do not cancel each other out are unbalanced forces.

When there are unbalanced forces acting on an object, there is always a change in motion.

Think Deeply A weightlifter attempts to lift a barbell off the ground. He pulls with all his might, but cannot move the barbell.

What was the net force acting on the barbell?

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Consider a computer mouse at rest on a desk.

The force of gravity is pulling the mouse towards the ground. The table exerts a push force upwards in the opposite direction of the force of gravity. The forces are of equal magnitude and cancel each other out – they are balanced.

When you apply a force to the mouse and push it away from you or pull it towards you, the forces acting on the mouse become unbalanced and the mouse moves.

Try This!

Use an object in your classroom to demonstrate the effect of unbalanced and balanced forces on the motion of the object.

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However, if you apply a push force directly down on the mouse, its motion does not change. This is because the desk applies an equal force in the opposite direction to balance the forces acting on the mouse.

Forces that do not sum up to zero can cause changes in an object’s speed or direction. When the boy shoots a basketball, he applies a force greater than the force of gravity. This creates an unbalanced force and sets the ball in motion.

When there are unbalanced forces acting on an object, a change in motion occurs. Unbalanced forces can cause an object to start moving, speed up, slow down, change direction or stop moving.

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In a game of baseball, the pitcher applies a force to the ball and sets it in motion towards the batter.

The batter swings the bat which makes contact with the ball. This applies a force to the ball which increases its speed and changes its direction.

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A fielder dives and applies a push force to stop the ball moving.

A fielder throws the ball to first base by applying a push force. The ball speeds up and flies in the direction of first base.

AB

Activity 8.3 67

Contact Forces There are many different types of forces acting on the objects around you. Some forces occur when objects are touching. They are called contact forces. Applied forces and friction are examples of contact forces.

Applied Force An applied force occurs when a person or an object applies force to another object when in contact with it. You use applied forces when you open and close a door, push a bike up a hill or twist the lid off a jam jar.

You use applied forces when you press the keys on a keyboard as you type.

Try This!

In small groups, discuss examples where applied forces are used to make an object: • • • • • •

start moving change direction speed up slow down stop moving change shape

The girl is using applied forces to pull on the string and fly the kite. The wind applies a force to the kite which acts against the force of gravity.

What are some ways you use applied forces in daily activities?

How do the forces affect the objects they are applied to?

The girl uses applied forces when she pulls on the string of the kite.

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An ice hockey player’s stick is in contact with the puck. The player uses an applied push force on the stick to shoot for goal. The puck accelerates and slides on the ice towards the goal. The goalkeeper uses an applied force in the opposite direction of the motion of the puck.

This causes the puck to stop moving.

The goalkeeper then strikes the puck with his stick. The applied force sets the puck back in motion in the direction of the applied force.

AB

Activity 8.4

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Friction Take a book and gently give it a push across your desk. The book will start moving and then come to rest. Objects remain at rest or constant speed unless an unbalanced force acts on them. What caused the book to come to rest on the desk?

The book slows down and comes to a stop due to a contact force called friction.

Friction is a force that opposes motion. It occurs when the surfaces of objects rub together.

The force of friction between two objects is dependent on how hard the objects are pushing together and the roughness of their surfaces.

Go Online!

What are static friction, sliding friction and rolling friction? Find out on the NGScience website.

QuickCode: N1M8

Rough surfaces produce more friction than smooth surfaces. The book will slide across a smooth desk easier than a concrete floor as it experiences less friction.

Friction is also greater when surfaces press harder together. In the case of our book and the desk, the magnitude of the force pressing the surfaces together is determined by the mass of the book. If more books were stacked on top, the increase in mass would create a greater pressing force and result in greater friction.

Friction between the surface of the book and the surface of the table opposes motion.

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Sometimes it is useful to reduce friction. A playground slide has a smooth surface to reduce friction. Bowling lanes are made of smooth wood with a coating of oil to reduce friction on the bowling ball. This prevents the bowling ball from slowing down and allows the ball to slide as well as roll on the surface.

As a force that opposes motion, we can increase friction to help things to slow down or stop.

Rubber tread on hiking boots increases friction to prevent slipping.

Brake pads on a bicycle increase friction when they press against the wheel rim. This allows the cyclist to slow down or stop moving.

The smooth surfaces of the bowling ball and the lane reduces the friction between them as the ball rolls towards the pins.

In what ways can friction be helpful? In what ways can it be a hindrance?

AB

Activity 8.5

Rough soles on hiking boots increases the friction between the hiker and the terrain.

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Non-contact Forces Some forces can act on objects without direct contact. They are able to act at a distance and are called non-contact forces. Magnetic force, electric force and gravitational force are noncontact forces.

Magnetic Force A compass needle is a magnet.

Engineer It! When allowed to turn freely, a magnet will come to rest with the north pole pointing in the direction of north. Use this property of magnets to create a compass using a bar magnet.

Place a magnetic compass on a table and observe the compass needle. What do you notice?

A magnet is an object with magnetic force.

Magnetic force occurs in an object due to the motion of electrically-charged particles. The compass needle is a magnet. When allowed to spin freely, a magnet will align with the Earth’s natural magnetic field. The north pole of the magnet will come to rest pointing in the direction of north.

Magnetic force is a non-contact force. It can act through solids, liquids and gases at a distance.

Magnetic force can attract objects made of certain metals such as iron and nickel.

Magnetic force cannot attract objects made of non-magnetic materials such as plastic, wood, rubber or glass.

Why is magnetic force a type of non-contact force?

A magnet can attract magnetic materials.

The attraction force is strongest at the poles of the magnet.

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A magnet has two poles – a North pole and a South pole. It is at each pole that the magnetic force is the strongest.

When the like poles of two magnets are brought together, they push or repel each other. When unlike poles are brought together, they pull or attract each other.

Try This!

Walk around your home and make a list of the different ways magnets are used. What property of magnets makes them suited to their use?

Unlike poles attract each other.

Like poles repel each other.

How can the properties of magnets be useful to people?

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Many objects make use of magnetic force.

Some doors use magnets to keep them closed.

Magnets are used to stick notes and photographs to refrigerators. They are used in electric motors, loudspeakers and for storing data on computer disks.

Magnetic force can also be created when current flows through a conductor such as a wire. These types of magnets are called electromagnets and can generate a magnetic force much greater than ordinary magnets.

Electromagnet attached to a crane can be used to sort magnetic materials from non-magnetic materials.

These powerful magnets are used in a variety of applications. Recycling plants use electromagnets to collect scrap metal.

Magnetic Resonance Imaging (MRI) machines use electromagnets to generate very strong magnetic forces that interact with tissues in our bodies. Computers collect data on the interactions and create images of the internal structures of our bodies without the need for surgery.

MRI machines use powerful electromagnets that allow doctors to see tissues and organs without the need for surgery.

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Electric Force All matter is made up of tiny particles which can have a positive charge or a negative charge.

Electric forces are created when there are unbalanced electrical charges inside an object.

An object that has more positive particles is positively charged. An object that has more negative particles is negatively charged.

When two objects with the same charge are close to one another, they repel each other.

When two objects with different charges are close to one another, they attract each other.

Objects with opposite charges attract each other. Objects with like charges repel each other.

When an object has a balance of positive and negative charges, we say the object has neutral charge. Neutral objects are attracted to both positively and negatively-charged objects.

Neutral objects are attracted to charged objects.

AB

Activity 8.6 75

Under the right conditions, charges can move between objects that are rubbing against each other. This can create an imbalance of charge between objects.

Neutrally charged water is attracted to a free-hanging charged balloon.

A girl slides down a slide at the playground. She notices that her hair is standing on its end. What caused this to happen? As she moved down the slide, charges moved between her body and the slide. This resulted in her body having an imbalance of like charges. The like charges in her hair repelled each other and caused her hair to stand on end.

Rubbing a balloon through your hair creates an imbalance of charge too. When the charged balloon is placed near a stream of water, they attract each other. The water has a neutral charge and is attracted to the charged balloon.

An imbalance of charges causes the girl’s hair to stand on end.

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Gravitational Force Consider a pencil at rest on a table. What forces are acting on the pencil? The weight of the pencil presses down on the table and the table pushes against the pencil in the opposite direction. The force that gives the pencil its weight is called gravitational force, or gravity.

Gravity is a non-contact force that acts on all objects on Earth. Imagine the pencil is pushed. It rolls off the edge of the table and falls to the floor. While the pencil was in contact with the table, the table was applying a reaction force to the pencil. When the pencil rolls off the table, there is no longer a reaction force against gravity and the pencil’s motion changes as it falls to the floor. The force of gravity continues to act on the pencil the whole time it is in motion. The pencil eventually comes to rest again when the floor provides a reaction force to balance the force of gravity.

Think Deeply What energy conversions take place when you jump on a trampoline? What force pulls you back down to the trampoline mat?

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The force of gravity is always attractive – any two objects with mass will attract one another.

The strength of the gravitational force is dependent on the mass of the objects. Objects with more mass have more gravity.

Just as the gravity of Earth pulls down on an apple, the apple also has its own gravitational force that pulls up on the Earth. However, the apple’s gravitational force is too weak to be observed as its mass is tiny compared to the mass of the entire Earth.

The gravity of Earth pulls down on the apple.

The Sun’s gravity attracts the Earth and other planets in the solar system. It keeps the planets and other objects in the solar system in orbit around the Sun. Gravitational force also depends on distance.

The closer objects are to each other, the greater the gravitational force.

AB

Activity 8.7

The Earth is pulled up by the gravity of the apple.

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Laws of Motion Sir Isaac Newton is considered one of the most important scientists in history. He made many discoveries and provided detailed explanations for the many scientific theories he proposed.

Newton’s work provided explanations about the force of gravity and the movement of the moon around the Earth and the planets around the Sun.

Go Online!

Learn more about Sir Isaac Newton and his many theories and discoveries on the NGScience website.

QuickCode: X5X2

Think Deeply The unit of measurement for forces is newtons (N), named after Sir Isaac Newton.

On Earth, a one-kilogram mass exerts a force of 9.8 newtons. Use this to calculate your weight in newtons.

Sir Isaac Newton

Much of our understanding of force and motion comes from Newton’s laws of motion – three laws that describe the relationship between the motion of objects and the forces acting on them.

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First Law of Motion

Think Deeply How do the seat belts, anti-lock braking system and airbags in a car help to keep you safe in an accident or when the car needs to stop quickly?

When a moving car stops quickly, the inertia of the passengers causes them to continue moving forward.

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Newton’s first law of motion says that an object at rest will remain at rest until an unbalanced force acts upon it. Similarly, an object that is already moving will continue moving until an unbalanced force acts upon it. The tendency of objects to resist change in their velocity is called inertia.

Consider sitting in a car at a red light. Both you and the car are at rest. The light turns green and the car jolts forward as it takes off. Your body’s inertia resists the change in motion and you may feel the seat push you forward. Once the car reaches a cruising speed, both you and the car are in constant motion and you don’t experience any external forces.

Imagine a cat jumps out in front of the car and the driver quickly applies the brakes. The inertia of your body continues to move forward and resists the change in motion. Your seat belt applies a force to stop your forward motion.

An object’s resistance to change in motion is related to its mass. The more mass an object has, the greater its inertia. It is much harder to push a full shopping trolley than an empty one.

The combined mass of the items in the trolley resists the change in motion when it is pushed.

In space, objects that overcome the gravity of the planets and the Sun keep moving and will continue to do so unless an unbalanced force acts on them. The NASA space probe Voyager 1 was launched into space in 1977 and has been in motion ever since. It is currently more than 2.2 billion kilometers (1.36 billion miles) from Earth and is moving at a speed of about 56,000 kilometers (35,000 mi) per hour.

Voyager 1 will continue to move at this speed unless an outside force changes its velocity.

More force is required to move a full shopping trolley than an empty one.

An artist’s impression of Voyager 1 as it passes close to Saturn.

Try This!

Place a piece of cardboard or playing card over a cup. Place a coin on the cardboard.

Use your finger and thumb to quickly flick away the card. Use your knowledge of Newton’s first law of motion to describe what you observed.

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Engineer It! In small groups, design and build a toy car that is powered by a balloon filled with air. Change the amount of air in the balloon and predict the motion of the car. How will changing the mass of the toy car affect its motion?

Second Law of Motion Newton’s second law describes how objects change velocity when unbalanced forces act upon them. It allows us to predict the motion of objects. It states that when an unbalanced force acts on an object, its change in velocity, or acceleration, depends on its mass and the magnitude and direction of the unbalanced force acting upon it.

Imagine you are sitting in a box car. Your father gives the box car a push and you accelerate forward. The amount you accelerate depends on the masses of the car and your body. It also depends on the magnitude of your father’s push.

Your sister arrives to join in on the fun. She starts by helping push the box car. If the car is pushed with twice the original force, it will accelerate twice as much.

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Now your sister hops into the car to ride with you. Your father is left to push the car.

What do you think will happen in terms of force and acceleration?

The car now has more mass. It requires more force to accelerate the same amount. The car will accelerate less if pushed with the same original force.

How does Newton’s second law allow us to predict the motion of objects?

Sports cars are designed for high speed and acceleration. To achieve this, the mass of the vehicle must be as low as possible. Sports cars are usually small and made with lightweight materials such as carbon fiber to reduce the mass. Their engines must also turn the wheels with as much force as possible.

How does reducing the mass of a sports car affect its motion?

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Third Law of Motion Newton’s third law of motion states that for every action, there is an equal and opposite reaction.

This means forces always act in equal but opposite pairs.

Let’s look at Newton’s third law using the example of a rocket launching into space. While sitting on the launch pad, the force of gravity pushes down on the rocket. The launch pad pushes up on the rocket in the opposite direction.

The forces are of equal magnitude and in opposite directions – they are balanced and no motion results. When the engine is ignited, very hot and fast-moving gases exit the rocket and push down on the launch pad. The force is greater than the force of gravity and the rocket is pushed upwards as it makes its journey into outer space.

Use Newton’s third law of motion to explain how a boat moves through water.

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In athletics, sprinters use special blocks to secure their feet before the race begins. When the race begins, the sprinters exert an action force onto the blocks behind them. The blocks exert a reaction force in the forward direction and propel the sprinter forward.

Similar to a rocket, octopuses move about by squirting jets of water behind them. The force of the water jet creates an unbalanced force on the octopus which results in forward motion.

AB

Think Deeply Use Newton’s third law to explain why a cannon moves backwards as it fires a cannon ball.

Activity 8.8

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Science Words Use the words to complete the sentences. force magnitude balanced forces unbalanced forces

contact force applied force friction non-contact forces

electric forces gravitational force inertia

1. The tendency of objects to resist change in their velocity is called .

2. An occurs when a person or an object applies force to another object when in contact with it.

3. is a force that opposes motion. It occurs when the surfaces of objects rub together.

4.

are forces that can act at a distance.

5. A force that occurs when objects are touching is called a 6. When there are change in motion.

7. When in motion.

8. A 9.

.

acting on an object, there is always a are acting on an object, there is no change

is a push or a pull. is the strength or size of a force.

10. are created when there are unbalanced electrical charges inside an object.

11. The Earth’s its surface.

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is an invisible force that pulls objects to

Review 1. How does the magnitude of a force acting on an object affect the motion of the object?

2. How does the mass of an object affect its motion when a force is applied to it?

3. How does the direction of a force applied to an object affect its motion?

4. Consider a football at rest on the ground.

(a) What can you infer about the forces acting on the football? (b) What must occur to set the football in motion?

5. Provide examples whereby a force can:

(a) (b) (c) (d) (e)

set an object in motion. slow down a moving object. speed up an object in motion. change the direction of an object in motion. stop an object in motion.

6. What is an electromagnet? List two ways they are used by people.

7. Describe how the mass of an object and its distance from another object affect its gravitational force.

8. What causes an object to become charged?

9. Describe the interaction that takes place when: (a) objects of like charges are close together. (b) objects of opposite charges are close together. (c) an object of neutral charge is close to a charged object.

10. Describe Newton’s second law of motion.

11. Use Newton’s third law of motion to describe why an inflated balloon flies around a room when it is let go and the air is released.

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In the Field

Sir Isaac Newton Sir Isaac Newton was an English mathematician, physicist and astronomer who was born in 1643.

He was fascinated with the natural world and made a number of discoveries in mathematics and science.

He discovered that white light can be separated into the colors of the rainbow by passing it through a prism.

His experiments with light, lenses and mirrors led him to invent the reflecting telescope. Reflecting telescopes were an improvement on existing refracting telescopes as they were more powerful and more compact.

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Newton’s reflecting telescope

Newton observed the world around him and posed questions to develop his theories and discoveries. Through observations and experiments, Newton formed the three laws of motion.

While observing an apple fall to the ground, he questioned why the apple fell straight down and not sideways.

He concluded that gravity was a force of attraction between two objects. He inferred that the force of gravity that pulled objects to the Earth’s surface was the same force that kept the moon orbiting the Earth and the planets orbiting the Sun. This led Newton to form a mathematical explanation of gravity which allows us to predict the motion of bodies on Earth and in space.

Sir Isaac Newton was a scientist ahead of his time. In fact, the modern meaning of the words ‘scientist’ and ‘physicist’ were not invented until the 1800s. In Newton’s time, people that studied nature and the physical universe were called ‘natural philosophers’.

Many great discoveries in science are the result of building on Newton’s theories, laws and discoveries.

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9

Work and Simple Machines

In this chapter you will ...

• list and describe the functions of the main simple machines.

• describe how each simple machine functions to make work easier.

• define and provide examples of compound machines.

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What are simple machines?

How are they used?

Go Online!

Access interactive content relating to this topic on the NGScience website. ngscience.com

How do simple machines make work easier?

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What Is Work?

We use the word ‘work’ to describe many activities in everyday life. You might help your family to do work in the garden, or help out with housework. In science, the word ‘work’ has a different and very specific meaning.

Put simply, work is defined as force moving an object a certain distance. Work has been done when a force (effort) is applied to an object (load) and it moves a given distance.

Consider a box of toys on your bedroom floor. The force of gravity is acting on the box but it is not in motion so no distance is being covered. No work is being done on the box. Now consider bending down, picking up the box and raising it above your head. You apply a force to the box as you lift it against the force of gravity to a higher position. A force has been applied and the box has moved a distance – work has been done.

The amount of work done relates to the magnitude of the force and the distance moved.

A heavier box would require more force to move the same distance. More work would be done. Similarly, moving the same box to a higher position on the shelf would result in more work done as the distance covered is greater.

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Let’s look at some more examples of work in everyday life.

A weightlifter does work on a barbel as they lift it a distance from the ground to above their head. When they release the barbel, the force of gravity pulls the barbel back to the floor and more work is done.

The force of gravity acts on a coconut in a tree. The forces acting on the coconut are balanced and no work is being done. The stalk of the coconut breaks and the coconut falls to the ground under the force of gravity. The force of gravity pulled the coconut through a distance equal to the height of the tree – work was done.

When doing work, the force acting on the object can be contact or non-contact.

What two things must happen for work to occur?

AB

Activities 9.1 – 9.2

Work is done when a coconut is pulled by the Earth’s gravity covering a distance from the top of the tree to the ground.

Think Deeply Imagine trying to lift a heavy weight into the air. You try with all your might, but are unable to move the weight.

Has work occurred? Explain your answer.

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A Closer Look

Calculating Work Imagine going shopping with your parents. To help out, you offer to push the shopping trolley. In doing so, you apply a push force to the trolley and it moves in the direction of the applied force. You are doing work. The magnitude of a force is measured in units called Newtons – named after the famous scientist Sir Isaac Newton. The distance an object moves can be measured in meters. To calculate work, we multiply the magnitude of the force by the distance the object moved. work = force x distance The standard units for measuring work are Newton meters (N • m), which can also be expressed in joules (J).

Suppose you push the shopping trolley with a force of 100 N for a distance of 10 meters. How much work has been done? work = 100 N x 10 m = 1,000 N • m = 1,000 J

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If work is calculated by multiplying force by distance, what factors will increase or decrease the amount of work done?

Let’s look at the work done when a bucket of water attached to a rope is pulled from the ground to a tree house.

If the weight of the bucket of water is 50 N, then it will need to be pulled with an upward force of 50 N in order to be raised. If the distance from the ground to the tree house is four meters, we can calculate the work needed to move the bucket of water to the tree house by multiplying the required force by the distance. work = 50 N x 4 m = 200 N • m = 200 J So when the bucket moves from the ground to the tree house, 200 J of work will be done.

If your weight is 400 N, how much work will be done if you climb the ladder to the tree house?

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Simple Machines Imagine hammering a nail into a piece of wood. As you hit the nail, it bends and needs to be replaced. How could you remove the nail? You probably would not be able to apply enough force using only your fingers and hands.

If you use the claw of the hammer, much less force is required and the nail can be removed easily.

A hammer is an example of a simple machine. Simple machines are devices, usually with one moving part, that make work easier. They make work easier by performing one or more of the following: • multiplying the applied force by increasing the distance of the effort.

• multiplying speed.

• changing the direction of the applied force.

The main types of simple machines are shown below.

inclined plane

wheel and axle

lever

pulley

gears

wedge

AB 96

Activity 9.3

Inclined Plane An inclined plane, commonly called a ramp, is a flat surface that is tilted at an angle so that one end is higher than the other. An inclined plane makes work easier when we need to move a load to a higher or lower position. It does this by reducing the effort required, but increasing the distance the load moves.

Inclined planes are used in many ways in everyday life, particularly when we need to move heavy loads over vertical distances.

Common examples include a ramp used to load a truck or wheelchair, pedestrian ramps, and the ramps in a multistory car park.

Although not a single, flat surface, staircases are examples of inclined planes. They allow us to move to higher or lower positions using much less effort.

Did You Know?

A screw is an object that consists of a cylinder with an inclined plane wrapped around it. This helps the screw sink into wood and other surfaces when it is turned.

How does an inclined plane function to make work easier?

AB

Activities 9.4 – 9.5

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Levers A lever is a simple machine that includes a bar that is free to move about a fixed point called a fulcrum. Levers make work easier by reducing the effort required to move the load, but increasing the distance moved by the effort. This can be achieved by moving the fulcrum closer to the load or applying the effort further from the fulcrum.

There are three types of levers – first-class levers, second-class levers and third-class levers. Each type of lever makes work easier in different ways.

A seesaw is a first-class lever.

Try This!

Create a first-class lever using a ruler and a piece of modeling clay as the fulcrum. Place a smaller piece of modeling clay on one end of the ruler. Launch it into the air by applying a push force to the other end. How does moving the fulcrum closer to the load affect the force applied to the load?

In a first-class lever, the fulcrum is between the load and the place on the bar where the effort is applied. This changes the direction of the effort. Work is the easiest when the effort is applied to the bar as far from the fulcrum as possible. The distance the effort moves is increased but the force applied to the load is multiplied.

How does a first-class lever function to make work easier? effort

load fulcrum

first-class lever

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Moving the fulcrum closer to the load increases the distance the effort moves and increases the force applied to the load.

effort

load fulcrum

You use a first-class lever when you use a screwdriver to open a tin of paint. The rim of the paint tin is the fulcrum. The fulcrum is close to the load which increases the distance the effort moves and multiplies the force applied to the lid.

The back of a claw hammer, crowbars, seesaws and scissors are objects we use that function as first-class levers.

Think Deeply Look at the crowbar in the photograph below. Identify the fulcrum, load and effort.

99

In second-class levers, the load is between the effort and the fulcrum. The effort moves over a larger distance to raise the load a smaller distance but with greater force. The closer the load is to the fulcrum, the larger the distance the effort moves and the greater the force applied to the load. Notice that in second-class levers, the effort applied is in the same direction as the force applied to the load.

fulcrum

load effort second-class lever

Wheelbarrows, nutcrackers and bottle-openers are objects we use that function as second-class levers.

How do first-class and second-class levers function to make work easier?

100

In both first-class and second-class levers, work is made easier by decreasing the effort required but applying the effort over a greater distance. In a third-class lever, the effort is between the fulcrum and the load.

Greater effort is required to move the load, but the speed at which the load moves is multiplied. As in second-class levers, the direction of the effort and the force applied to the load is in the same direction.

How does a third-class lever function to make work easier? effort

A fishing rod is an example of a third-class lever.

fulcrum load third-class lever

Fishing rods, baseball bats and brooms are objects that function as third-class levers.

AB

Activities 9.6 – 9.7

1 01

Pulleys A pulley is a simple machine that is often used to raise or lower an object. A pulley consists of a wheel that rotates freely with a rope or chain that runs through and winds around the wheel.

The load is usually attached to one end of the rope and the effort applied to the other.

There are two main types of pulleys – fixed pulleys and movable pulleys. In some cases, multiple pulleys can be used to create a pulley system.

In a fixed pulley, the wheel is attached to a support in a fixed position. A fixed pulley does not change the magnitude of the effort or force applied to the load. It makes work easier by changing the direction of the effort. Fixed pulleys are often used when we need to raise an object.

This is achieved by pulling down on the rope in order to raise the load. Work is made easier as the effort is in the same direction as the Earth’s gravitational force. When a fixed pulley is used to raise an object, the effort and the load move the same distance.

load

effort fixed pulley

1 02

A movable pulley is not attached to a fixed support. The pulley is often attached to the load and moves as the load moves. Unlike a fixed pulley, the effort and movement of the load is in the same direction.

A movable pulley makes work easier by reducing the effort required, but increasing the distance over which it is applied.

How are fixed and movable pulleys different in terms of the effort required to move a load of the same mass?

A pulley system uses a combination of pulleys that function together. Pulley systems often contain both fixed and movable pulleys. They make work easier by changing the direction of the effort and also reducing the effort required by increasing the distance over which it is applied.

effort

load

movable pulley

effort load

pulley system fixed pulley

movable pulley

Think Deeply How would adding another movable pulley to the pulley system above affect the amount of force needed to raise the load?

Compare and contrast fixed pulleys, movable pulleys and pulley systems in terms of how they make work easier.

AB

Activity 9.8 103

Wheel and Axle When you turn on a tap, you are using a simple machine called a wheel and axle. As its name suggests, a wheel and axle consists of a wheel which is attached to a rod called the axle. The radius of the wheel is greater than the radius of the axle.

When the wheel is turned, the axle also turns.

The effort applied to the wheel results in less effort required to turn the axle as the effort to turn the wheel is applied over a greater distance.

When effort is applied to a doorknob, the force applied to the axle is multiplied.

wheel axle

Try This!

In small groups, discuss some other objects that make use of a wheel and axle. For each object, identify which part is the wheel and which part is the axle. How does each object function to make work easier?

AB

104

Activity 9.9

Generally, the function of a wheel and axle is to multiply the force on the axle. Steering wheels, cranks, hand drills and doorknobs all make use of this function of a wheel and axle to make work easier.

In some cases, such as the wheel and axle in a rolling pin, the effort is applied to the axle in order to multiply the distance the wheel moves.

Gears Gears are simple machines that consist of two or more wheels that fit together with interlocking teeth. When one gear is turned, the other interlocked gear turns in the opposite direction.

Think Deeply Many bicycles have a rear wheel fitted with gears of different sizes which are attached to a front gear by a chain. How does using larger and smaller rear gears affect the effort required and the distance the wheel moves?

Connected gears turn in opposite directions.

Gears function in different ways. They can change the direction of the applied force. They can multiply the applied force when the effort applied to a smaller gear moves over a greater distance than a connected larger gear. They can also multiply speed when a larger gear turns a smaller gear.

Bicycles, fishing reels, analog watches and can openers are objects that make use of gears.

AB

Activity 9.10

gears inside an analog watch

can opener with gears

105

Wedge A wedge is a simple machine that is triangular in shape, much like an inclined plane or, in some cases, two inclined planes joined back-to-back.

A wedge makes work easier by changing the direction of the applied force.

The head of an axe is a wedge. To split a piece of wood, a downward force is applied to an axe. As the wedge enters the wood, it presses sideways, pushing the wood apart.

A wedge changes the direction of the applied force.

Knives, needles, saws, scissors and doorstops are examples of objects that make use of wedges.

Wedges are useful in many ways. They can be used to cut and slice, separate objects or hold them in place.

How does a wedge function to make work easier?

AB

1 06

Activity 9.11

Compound Machines Many objects we use from day to day consist of two or more simple machines that work together to achieve a common function. An object that consists of two or more simple machines is called a compound machine.

Scissors are an example of a compound machine.

Scissors consist of two levers held together by a pivot which is the fulcrum. Each blade of the scissors is a wedge. The levers and wedges function together to make the work easier when you cut an object.

A bicycle is a compound machine. The handle bars and pedals are wheel and axle machines.

A chain connects gears on the bicycle frame to gears on the rear wheel. The brakes and brake handles are levers. All of the simple machines that make up a bicycle function together to form a compound machine.

AB

Scissors consist of two types of simple machines – levers and wedges.

Think Deeply You have learned that a wheelbarrow is an example of a second-class lever. Why is a wheelbarrow an example of a compound machine?

Activity 9.12

107

A Closer Look

Fighter Jets – The Ultimate Machines One of the most complex compound machines invented are fighter jets. A fighter jet consists of hundreds of thousands of parts that work together and enable it to fly faster than the speed of sound!

Let’s take a look at some of the main parts of this amazing compound machine.

Wings are designed to make air move faster over the top of the wings which produces an upward force called lift.

Flaps on the wings help the jet to take off and land in short distances.

Wheels allow the plane to take off and land. Tires provide traction by creating friction between the tires and the ground.

108

The tails are horizontal rudders called stabilizers. They provide stability to the aircraft and assist the pilot in maintaining a steady and straight flight.

Inside the cockpit are a variety of controls and instruments that enable the pilot to accurately fly the aircraft at high speeds.

Computers and sensors provide the pilot with information about the state of the aircraft’s interconnected systems.

Jet engines are specialized components that continually suck air in at the front with a fan.

A compressor within the engine raises the air pressure which is then sprayed with fuel and ignited. The ignited gas pushes out of the rear of the engine causing the aircraft to be thrust forward.

109

Science Words Use the words to complete the sentences. work simple machine inclined plane lever 1. A the axle.

fulcrum pulley wheel and axle

gears wedge compound machine

consists of a wheel which is attached to rod a called

2. A is triangular in shape, much like an inclined plane or, in some cases, two inclined planes joined back-to-back.

3. A is a simple machine that includes a bar that is free to move about a fixed point called a .

4. An is a flat surface that is tilted at an angle so that one end is higher than the other.

5. A is a device, usually with one moving part, that functions to make work easier.

6.

is defined as force moving an object a certain distance.

7. A consists of a wheel that rotates freely, with a rope or chain that runs through and winds around the wheel.

8. An object that consists of two or more simple machines is called a .

9. are simple machines that consist of two or more wheels that fit together with interlocking teeth.

110

Review 1. List the three ways in which simple machines can make work easier.

2. Label the simple machines. (a)

(b)

(c)

(d)

(e)

(f)

3. Draw simple labeled diagrams to show the positions of the effort, fulcrum and load in: (a) first-class levers. (b) second-levers. (c) third-class levers.

4. What simple machine is used to achieve the following tasks?

(a) (b) (c) (d)

splitting a piece of wood. turning on a tap. loading a motorcycle into a small truck. raising and lowering an engine into a car.

5. Draw a simple diagram of a compound machine. Label the simple machines it is comprised of.

111

10 Electricity and Circuits In this chapter you will ...

• define and distinguish between electric charge, electric discharge and electric current.

• list the ways in which people use electricity.

• assemble electric circuits with components arranged in series and parallel.

• draw and interpret circuit diagrams.

What is electricity and what makes it so useful to people?

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How can components be assembled to create an electric circuit?

Go Online!

Access interactive content relating to this topic on the NGScience website. ngscience.com

How does arranging circuit components in series and parallel affect the devices in a circuit?

113

What Is Electricity?

Think Deeply What are the different ways people produce electricity?

What are the advantages and disadvantages of each type of electricity production?

All matter is made up of tiny particles called atoms. An atom is made up of much smaller particles called protons and electrons. Protons have a positive charge and electrons have a negative charge.

Most objects contain a balanced number of positive and negative charges. The charges cancel each other out.

Sometimes electrons can move from one atom to another. When this occurs, the atom that lost the electron becomes positively charged and the atom that gained the electron becomes negatively charged. The energy associated with these exchanges and movement of charge is called electricity.

Understanding how charge moves between and within materials allows us to generate and control electricity in different ways.

What happens to an atom when it loses an electron?

Electricity is produced at power stations and travels through an interconnected grid to our home and cities.

114

Electricity powers our homes and cities.

Electricity can be easily converted into other forms of energy, such as mechanical energy, light, heat and sound. Electricity is used by people in many ways. It is used to power lights, electric motors and many household appliances.

Devices such as phones, flashlights and electric cars use electricity that is stored as chemical energy in batteries.

Why is electricity useful to people?

What are some ways we use electricity?

AB

Amazing Fact!

Electric cars are gaining popularity all over the world as they do not produce any of the harmful emissions that fuel-powered cars do.

Scientists and engineers are continually improving electric car designs and developing new technologies that allow electric cars to travel further and faster than many fuel-powered cars.

Activity 10.1

Electric cars use batteries that convert stored chemical energy into electricity.

115

Electric Charge When an electron separates from an atom, the atom becomes positively charged. When the electron joins a new atom, that atom will become negatively charged. This movement of charge occurs constantly within matter. If the movement of charge is within the same object, the overall charge of the object remains the same as the charges cancel each other out.

Unlike charges between the balloons and the boy’s hair cause them to attract each other.

Sometimes electrons from atoms in one object are transferred to the atoms of another object. When this occurs, the object that loses electrons will become positively charged and the object that gained electrons will become negatively charged. As unlike charges attract, the two objects experience a force of attraction. This property of particles that causes them to attract or repel one another is called electric charge.

Have you ever opened the clothes dryer and discovered that some of the clothes are stuck together? This happens because some clothes gain or lose charge as they tumble in the dryer.

The clothes stick together when the positively-charged clothes are attracted to the negatively-charged clothes.

AB Unlike charges between the balloon and the cat causes them to attract each other.

116

Activities 10.2 – 10.3

static dischargers

Electric Discharge Have you ever received an electric shock when touching a metal doorknob? An electric shock is an example of an electric discharge. Electric discharge is the movement of the buildup of electric charge from one place to another.

When you walk on a surface such as carpet, you gain negatively-charged particles – your body becomes slightly negatively charged. As you reach for the doorknob, the negative charges in your hand attract the positive charges in the metal. At a close enough distance, the buildup of charge can cause the air between your hand and the doorknob to become electrically charged. This creates a path for the charges to move from your hand to the doorknob.

The electric shock you experience is the movement of electrons from your hand, through the air and into the doorknob. This electric discharge occurs rapidly and excites the air around it – creating a flash of light.

Did You Know?

On an airplane, electric discharge can be dangerous as it can interfere with the plane’s electronics and communication equipment.

To prevent the build up of electric charge, airplane wings are fitted with static dischargers. These conducting rods gradually release charge from within the plane into the air.

Electric discharge occurs as electrons rapidly move from your hand to the metal doorknob.

117

Lightning is an example of an electric discharge. During a storm, small bits of ice and raindrops bump into each other as they move around within a cloud.

This creates an electric charge within the cloud. Normally the top of the cloud becomes positively charged and the bottom of the cloud becomes negatively charged.

As opposite charges attract each other, the negative charge at the bottom of a cloud causes the ground beneath it to become positively charged. Eventually the buildup of charge is so great that the negative charges race to the positivelycharged ground. When the electric charge discharges, we see a bright flash in the sky – lightning.

118

The electric discharge happens very quickly. As the negative charges race towards the ground, they excite the air around them – causing it to light up. The charges also cause the air around them to heat up very quickly and create a pressure wave. We hear this pressure wave as thunder when the air rapidly contracts as it cools.

We see lightning before we hear thunder as the speed of light is much faster than the speed of sound.

When lightning strikes the surface of the Earth, it can cause damage to property and can injure or kill people.

It is very important to stay indoors during a thunderstorm.

What causes the thunder we hear during a thunderstorm?

Did You Know?

The roofs of tall buildings are often fitted with lightning rods. These metal rods are connected to the ground by wire. Lightning prefers to strike the rod as it creates an easier path for the electric discharge to flow. This protects the building from fire, damage and electrocution.

Think Deeply Sound travels a distance of one kilometer in just over three seconds. If you hear thunder 10 seconds after you see a lightning strike, how far away was the lightning strike?

119

Copper wires are electrical conductors. The plastic that surrounds them are electrical insulators.

Electric Current Electric charge is the buildup of charged particles within matter. Electric current is the continuous flow of electric charge.

Think Deeply Why do electrical appliances use a combination of electrical insulators and conductors?

Did You Know?

Water contains dissolved substances that make it a good conductor of electricity.

You should never use electrical appliances near water or with wet hands.

120

Some materials allow charges to move more easily than others. Metals such as copper are usually good electrical conductors. The atoms that make up these metals have electrons that are not bound to a single atom. The electrons are free to move from atom to atom within the metal. Materials that allow charges to move freely are called electrical conductors.

Plastics, such as those used to wrap electrical wires, do not allow charges to move freely.

Materials that restrict the flow of charges are called electrical insulators. Wood, glass and rubber are also good insulators.

Electricity is the flow of charges in one direction through a material. Electricity is very useful for transferring and transforming energy into other different forms of energy.

When you turn on a light, electricity flows through the wires to the light bulb. In the light bulb, the electrical energy is transformed into light and heat energy.

Try This!

In small groups, observe the different parts of a light bulb. Draw a simple labeled diagram to show which parts are electrical conductors and which are electrical insulators.

When you turn on a hair dryer, electricity flows into an electric motor and heats a metal element. In doing so, the hair dryer transforms electrical energy into kinetic energy and heat.

Discuss some of the other energy conversions that take place when electrical appliances are switched on.

AB

Activity 10.4

121

Using Electricity Electricity is very useful to people as it can be easily converted into other forms of energy.

Many devices like flashlights, mobile phones and watches use electrical energy from batteries.

The devices convert the stored chemical energy in the batteries into electrical energy. The electrical energy is then converted into other forms of energy such as light, sound and heat.

Most homes are powered by electrical energy that is generated at power stations.

The electrical energy travels along power lines in an interconnected grid. Homes are fitted with an electrical meter that records the amount of electricity used.

Homes can be fitted with solar panels which provide them with a supply of electricity.

In homes, electrical appliances convert electrical energy into light, heat, sound and mechanical kinetic energy. Lights convert electrical energy into light and heat. Washing machines and many kitchen appliances convert electrical energy into mechanical kinetic energy. Electric ovens and clothes dryers use electricity to produce heat.

How do you use electricity at home and at school?

122

Saving Electricity The electricity we use in our homes is measured by an electrical meter. We pay for the amount of electricity we use. Reducing the amount of electricity we use can help save money. Many power stations produce electricity by burning fossil fuels. The burning of fossil fuels produces pollutants that are released into the air.

By reducing the amount of electricity we use, we can help protect the environment too.

Here are some things you can do to reduce electricity around the home and at school: • Wear warm clothes on cold days rather than using heaters. Open a window on warm days rather than using an air conditioner.

• Instead of using a clothes dryer, use the natural light and heat from the Sun to dry clothes.

• Use energy-saving lights, appliances and devices. Some appliances are given a rating based on the amount of electricity they use.

Choose appliances with good ratings.

Did You Know?

LED lights are very efficient compared to incandescent light bulbs. Although LED lights are more expensive, they use far less electricity to produce the same amount of light as an incandescent light bulb.

This results in less electricity consumption which will save money over time.

• Turn off lights and appliances when they are not being used.

AB

Activity 10.5

123

Electric Circuits Simple Circuits Think Deeply Does the location of a switch and output device in a simple electric circuit affect the way electricity flows?

Explain your answer.

Use insulated copper wires to connect a light bulb, battery and switch in a closed loop. Close the switch and the light bulb lights up. Open the switch and the light bulb turns off. What causes these changes to occur?

Assembling the circuit components in a closed loop creates an electric circuit. An electric circuit is a path around which electricity flows.

In an electric circuit, electrical energy flows from an energy source, through conducting wires, to an output device that changes the electrical energy into other forms of energy. A light bulb, for example, changes electrical energy into light energy and heat energy. A fan can change the electrical energy into kinetic energy, sound energy and heat energy.

A simple circuit consists of a battery, wires and a bulb.

A switch can be used to control the flow of electricity.

124

For electric current to flow through a circuit, there must be a complete path along which the electrical energy can flow. A switch is often used to control the flow of electrical energy by opening and closing the path.

When a switch is in the ‘on’ position, there is a complete path for electrical energy to flow. The circuit is closed. When the switch is in the ‘off’ position, the circuit is open and electric current cannot flow. An electric circuit may also be open if the circuit components are not connected properly or are broken in some way.

What is the function of a switch in an electric circuit? What effect does opening and closing a switch have on the output devices?

AB

Think Deeply Over time, lights and other electrical appliances get worn and eventually burn out or break down. How does a switch help to prolong the life of lights and electrical appliances?

Activity 10.6

Closing a switch in a simple circuit creates a complete path along which electricity can flow.

125

Series and Parallel Circuits

Engineer It! In small groups, design, build and test a device that makes use of a simple circuit to solve a simple given problem. Demonstrate how your device solves the given problem to other groups.

Evaluate the effectiveness of your design and those of other groups.

There are two main types of electric circuits – series circuits and parallel circuits. The circuits are different in the arrangement of the circuit components.

In a series circuit, the components are assembled in a way that there is only a single path along which electric current can flow.

In the series circuit below, the bulbs have been arranged in series. When output devices are arranged in series, the electric current is equally distributed among the output devices. When two bulbs are arranged in series, the bulbs will be less bright than if there was only one bulb.

How will adding a third bulb in series affect the brightness of the bulbs?

When bulbs are added in series, the electric current is distributed equally between the bulbs.

1 26

In the series circuit below, two batteries are arranged in series. When batteries are arranged in series, more electric current flows through the circuit and the output devices. In the case of a bulb, arranging two batteries in series will result in the bulb glowing brighter compared to a bulb in a circuit with a single battery.

How does arranging batteries in series affect the brightness of the bulbs?

Did You Know?

If too much electric current flows through a circuit, it can become overheated. A fuse is a circuit component that contains a piece of metal that melts when overheated. This opens the circuit and helps to prevent damage to the circuit components and potential fire.

When batteries are added in series, more electric current flows through the circuit and the bulb glows brighter.

A bulb produces light and heat when electric current flows through a coiled wire inside the bulb called the filament. If too much current flows through the filament, it can overheat and break. If one of the output devices arranged in series breaks, the circuit is open and none of the output devices will function.

AB

Activities 10.7 – 10.8 127

In a parallel circuit, the components are assembled in a way that there is more than one path along which electric current can flow.

In the parallel circuit below, the bulbs are arranged in parallel. Use your finger to trace along the wires and you will see that there are two paths along which the electric current can flow. Two bulbs arranged in parallel will glow brighter than if they were arranged in series.

Bulbs in a circuit glow brighter when arranged in parallel than when arranged in series.

Think Deeply Most houses have lights, appliances and electrical outlets arranged in parallel.

What is the advantage of this arrangement as opposed to arranging them in series?

An advantage of arranging output devices in parallel is that if one device was to break, there still remains a complete path for electric current to flow. As such, the output devices along the complete path will continue to function. In the parallel circuit above, if one bulb was to break, the other bulb will continue to light up.

What happens to the other bulbs in a parallel circuit if one bulb breaks?

128

Multiple batteries can also be connected in parallel. When batteries are arranged in parallel, such as those in the circuit below, the current flowing through the circuit and output devices is the same as if there was just a singe battery.

Therefore, a bulb in a circuit with two batteries arranged in parallel is equally as bright as when connected to one battery.

What effect does arranging batteries in parallel have on the brightness of a bulb?

Go Online!

Learn more about series and parallel circuits in a video on the NGScience website.

QuickCode: Q9H7

Think Deeply Rechargeable batteries can be charged and reused hundreds of times. What are the advantages and disadvantages of choosing rechargeable batteries to power devices such as phones and toys?

Batteries arranged in parallel will last longer than batteries arranged in series.

An advantage of arranging batteries in parallel is that they will last proportionally longer. This means two batteries in parallel will last twice as long as a single battery.

AB

Activity 10.9

129

A Closer Look

Circuit Diagrams Each of the components in a circuit can be represented by simple symbols. The symbols for some common circuit components are shown below.

Circuit Component

Circuit Symbol

battery

two batteries

wire

open switch

bulb

motor

buzzer

1 30

closed

To show the components in a circuit and how they are arranged, a circuit diagram can be used.

Circuit with a closed switch, two bulbs and two batteries in series.

circuit diagram

circuit diagram

Circuit with a buzzer, fan and two batteries in series.

What is a circuit diagram?

How are circuit diagrams useful?

AB

Activities 10.10 – 10.11

Try This!

With a classmate, take turns in drawing circuit diagrams.

Predict how the output devices will operate then build and test each circuit.

131

Electromagnets Engineer It! In small groups, design, build and test a device that makes use of an electromagnet to solve a simple given problem. Demonstrate how your device solves the given problem to other groups.

Evaluate the effectiveness of your design and those of other groups.

What Are Electromagnets?

When electric current flows through a wire, it produces a magnetic field. We can use this knowledge to create electromagnets.

An electromagnet is a magnet that attracts magnetic materials due the electric current flowing through it.

Electromagnets are usually made by coiling a wire around a magnetic material such as iron or steel. Each coil around the magnetic object increases the strength of the magnetic field.

Electric current flowing through the coiled wire produces a magnetic field.

Electromagnets are particularly useful as the magnetic property can be easily switched on and off by controlling the flow of the electric current. Many appliances and devices we use contain electromagnets. They can be found in speakers, electric bells, electric motors, computer hard disks and MRI machines.

What produces the magnetic field in an electromagnet?

AB 1 32

Activities 10.12 – 10.13

Strength of Electromagnets What factors can affect the strength of an electromagnet?

A number of factors can affect the strength of the magnetic field produced by an electromagnet. One way to increase the strength of an electromagnet is to increase the number of coils of wire. The more coils of wire, the stronger the electromagnet.

Increasing the number of coils will increase the strength of the electromagnet.

A coiled wire alone will still create an electromagnet. However, coiling the wire around a magnetic material increases the strength of the electromagnet.

Coiling a wire around a magnetic material such as iron or steel increases the strength of the electromagnet.

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We can also increase the strength of an electromagnet by adding more batteries in series. An electromagnet with two batteries in series will have a stronger magnetic field than an electromagnet with a single battery.

Adding batteries in series increases the strength of an electromagnet.

Did You Know?

The pickups on an electric guitar make use of electromagnets. The electromagnet detects the vibrations of guitar strings and converts them into electrical energy.

Using Electromagnets Electromagnets are used in many appliances and devices. Devices with electric motors make use of electromagnets. Such devices include fans, vacuum cleaners and blenders.

A magnetic crane uses a powerful electromagnet to sort magnetic materials from non-magnetic materials.

magnetic crane

Loudspeakers, guitar pickups and electric bells also use electromagnets. electromagnet

electromagnet

134

speaker

Science Words Use the words to complete the sentences. electricity electric charge electric discharge

electric current electric circuit series circuit

parallel circuit circuit diagram electromagnet

1. In a , the components are assembled in a way that there is more than one path along which electric current can flow.

2. In a , the components are assembled in a way that there is only a single path along which electric current can flow.

3. The energy associated with the exchanges and movement of charge is called .

4. The property of particles that causes them to attract or repel one another is called .

5. is the movement of the buildup of electric charge from one place to another.

6. An is a magnet that attracts magnetic materials due to the electric current flowing through it.

7. A is a diagram that shows the components and their arrangement in a circuit.

8. An 9.

is a path around which electricity flows. is the continuous flow of electric charge.

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Review 1. What occurs when an object becomes charged?

2. What causes an object to become negatively charged?

3, What causes lightning and thunder?

4. List two electrical conductors and two electrical insulators.

5. What energy conversions take place when a battery-powered flashlight is switched on?

6. List two advantages of reducing electricity consumption.

7. In a simple circuit, what effect does adding a battery in series have on the brightness of the bulb?

8. A circuit contains two bulbs in series. The filament in one bulb overheats and breaks. How does this affect the circuit?

9. Describe one advantage of arranging bulbs in parallel in a circuit.

10. Draw a circuit diagram to represent the circuit below.

11. List two objects that make use of an electromagnet.

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