Solution Manual For Physical Science 2026 Release Bill W. Tillery

Solution Manual For Physical Science 2026 Release Bill W. Tillery Chapters 1-24 Chapter 1 Contents 1.1 Objects and Properties 1.2 Quantifying Properties 1.3 Measurement Systems 1.4 Standard Units for the Metric System Length Mass Time 1.5 Metric Prefixes 1.6 Understandings from Measurements Data Ratios and Generalizations The Density Ratio Symbols and Equations Symbols Equations Proportionality Statements How to Solve Problems 1.7 The Nature of Science The Scientific Method Explanations and Investigations Testing a Hypothesis Accept Results?

Other Considerations Pseudoscience Science and Society: Basic and Applied Research Laws and Principles Models and Theories Overview Students begin by considering their immediate environment, and then logically proceed to an understanding that science is a simple, clear, and precise reasoning and a way of thinking about their environment in a quantitative way. Within the chapter, understandings about measurement, ratios, proportions, and equations are developed as the student learns the meaning of significant science words such as ―theory,‖ ―law,‖ and ―data.‖ The chapter develops a concept of the nature of scientific inquiry and presents science as a process. It

distinguishes science from nonscientific approaches. It also identifies pseudoscience as a distortion of the scientific process.

Suggestions 1. Ask the class their definition of physical science, accepting all answers, to begin the discussion. Include the natural sciences (the study of matter and energy), applied sciences (engineering), and social sciences in the discussion.

2. When discussing the meaning of concept, point out that different levels of thinking exist.

Lower levels are not necessarily incorrect but are incomplete compared to higher levels.

For example, a young child considers a ―dog‖ to be the short brown furry animal that lives across the street. Later, the child learns that a dog can be any size (within limits) with highly variable colors, and in fact, dogs come in many sizes, colors, and patterns of colors. Still later, a dog (Canis familiaris) is understood to be a domestic mammal closely related to other animals (the common wolf). Each of these generalizations represents a concept, but at different levels of understanding. This discussion of levels of conceptualization will be useful later as a comparison when students argue a concept of something from a lower level of understanding. Many nonscience students have an understanding of acceleration, for example, as a simple straight-line increase in velocity.

This concept is not incorrect (the dog across the street), but it represents an incomplete level of conceptual understanding.

3. To introduce properties and referents, display an unusual rock (not pyrite) or object and ask the class to describe it as if talking to someone on the telephone. Keep track of the descriptive terms, then list them all together and ask the students if they could visualize the object if they heard this description over the telephone. The point about typical, vague everyday communications will be obvious. Ask for a volunteer who is majoring in education (or some other major requiring communications) and who loves coffee to describe the taste of coffee to someone who has never tasted it. The student will have difficulty because of the lack of a referent. The concept of a referent will probably be new to most nonscience students, but it is an important concept that will prove useful to them throughout the course.

4. Many devices are available from scientific equipment companies to demonstrate the metric system of measurement, such as the plastic liter case. It is often useful to call attention to the similarities between the metric prefixes and the monetary system (deciand dime, centi- and cent, and so forth). If students can make change, they can use the metric system.

5. In developing the concept of a ratio, it is useful to have a set of large blocks that you can actually measure to find the surface area to volume ratio. Show all calculations on an overhead transparency or chalkboard.

6. The development of the concepts of a proportionality statement, an equation, and the meaning and uses of symbols is critical if you plan to use a problem-solving approach.

The three classes of equations provide an important mental framework on which future concepts will be hung. A student who does not ―understand‖ density has less of a problem learning that density is a ratio that describes a property of matter. Likewise, a student who does not ―understand‖ an electric field has less of a problem learning that an electric field is a concept that is defined by the relationships of an equation. Identifying equations throughout the course as ―property,‖ ―concept,‖ or ―relationship‖ equations will help students sort out their understandings in a meaningful way.

7. In the discussion of scientific laws, analysis of everyday ―laws‖ can be useful (as well as interesting and humorous). One statement of Murphy’s law, for example, is that ―the bread always lands butter side down.‖ Ask the class what quantities are involved in this law and about the relationship. Humor from the Internet: Another everyday ―law‖ is that a cat always lands on its feet. What would happen if this law conflicts with another law?

For example, what would happen if you strapped a slice of buttered bread on the back of a cat and then dropped it? Would it remain suspended in air? Another everyday law is Bombeck’s law: ―ugly rugs never wear out.‖ You could also make up a law — [your name]’s law: ―the life span of a house plant is inversely proportional to its cost.‖ Analysis?

For Class Discussions 1. An ice cube with a certain weight melts and the resulting weight of water is a. less. b. the same. c. greater.

2. An ice cube with a certain volume melts and the resulting volume of water is a. less. b. the same. c. greater.

3. Compare the density of ice to the density of water. The density of the ice is a. less. b. the same. c. greater.

4. A beverage glass is filled to the brim with ice-cold water and ice cubes floating in the water, some floating above the water level. When the ice melts, the water in the glass will a. spill over the brim. b. stay at the same level.

c. be less than before the ice melted.

5. A homeowner wishes to fence in part of the yard with a roll of wire fencing material. If all the roll of material is used in all situations, which shape of fenced-in yard would enclose the greatest area? a. square b. rectangle c. both would have equal areas.

6. Again considering the homeowner and a fence made with a roll of wire fencing material.

If all the roll of material is used in all situations, which shape of fenced-in yard would enclose the greatest area? a. right-angle triangle b. rectangle c. the answer will vary with the shape used.

7. A 1-cm3 piece is removed from a very large lump of modeling clay with a volume of over 100,000 cm3. Which piece has the greatest density? a. The small piece. b. The large piece. c. The large and the small piece have the same density.

8. A good way to improve communications and understand relationships involved in nature is to a. write a detailed description of everything observed. b. make measurements of objects and events. c. ask a lot of questions as you speak observations aloud several times. d. memorize all the equations in your text.

9. The nature of science is such that a. eventually a scientific law become a scientific theory. b. nature always obeys all the scientific laws. c. scientific laws describe relationships observed in nature. d. scientific theories are statements of absolute truth.

10. Which of the following statements is most correct? a. Science is absolutely always right. b. Nonscientific study has little value. c. Science has all the answers. d. Science seeks to understand nature.

11. When a scientist develops an explanation for patterns or relationships observed among a number of apparently isolated facts a. a new scientific law has been established. b. a new scientific theory has been developed. c. the scientist should announce the explanation in a press conference. d. as a rule the pattern must be published, then verified by others.

12. Scientific method involves each of the following except a. systematic search for information. b. reformulating observations to agree with scientific laws. c. forming and testing possible solutions. d. observation and experimentation.

Answers: 1b, 2a, 3a, 4b (ice floats above the water line because it is less dense; when it melts it occupies the same volume as it displaced while floating), 5a, 6c, 7c, 8b, 9c, 10d, 11d, 12b.

Answers to Questions for Thought 1. A concept is a generalized mental image of an object or idea.

2. A measurement statement always contains a number and the name of the referent unit.

The number tells ―how many,‖ and the unit explains ―of what.‖ 3. The primary advantage of the English system of measurement is that most United States citizens are familiar with the basic units and their sizes. The metric system has the advantage of easily converting the units to a convenient size merely by moving the decimal and using the appropriate prefix with the basic unit.

4. The meter is the metric standard of length and is defined as the distance light travels in a vacuum in 1/299,792,458 seconds. The metric standard of mass is the kilogram, which is defined as the mass of a standard kilogram kept by the International Bureau of Weights and Measures in France. The standard unit of time is the second, which is defined as the time required for a certain number of vibrations to occur in a type of cesium atom.

5. The density of a liquid does not depend upon the shape of its container. Density is a ratio of mass per unit volume. As long as this ratio stays the same, the density does not change.

6. A flattened pancake of clay has the same density as a ball of the same clay. Even though the shape of the material has changed, the volume and the mass of the material have not changed. Since density is a ratio of mass per unit volume, the density is the same.

7. An equation is a mathematical statement that describes a relationship where the quantities on one side of the equal sign are identical to the quantities on the other side.

Equations are used to describe quantities, define concepts, and show how quantities change together.

8. A scientific principle explains a narrow range of observations, while a scientific law describes many general phenomena. Principles can usually be explained in terms of laws.

9. A model is a mental or physical representation of something that cannot be directly observed. A simpler representation of a complex phenomenon is also a model. A model is used as an easily visualized and understood analogy to some behavior or system that is not directly observable or is very complex.

10. Theories do not always enjoy complete acceptance but are rarely rejected completely.

The better a theory explains the results of experiments and correctly predicts the results of new experiments, the greater the degree of acceptance. Theories that do not conform to experiments are usually modified and gain wider acceptance.

For Further Analysis 1.Answering this question requires the critical thinking skills of clarifying values and developing criteria for evaluation. Answers will vary.

2.This question requires students to explore beliefs and evaluate arguments. Answers will vary.

3.This requires the student to evaluate a concept, comparing the concept with the real world. The evaluation should note that density is a mass over volume ratio and larger and larger volumes with the same mass reduces the density.

4.Thinking precisely, the student will realize that doubling a quantity that is squared will result in a four-fold increase.

5.Thinking precisely and evaluating critical vocabulary is required. Answers will vary.

6. Thinking precisely and evaluating critical vocabulary is required. Answers will vary.

7.Exploring arguments and clarifying issues is required. Answers will vary.

Group B Solutions 1. Answers will vary. In general, mass and weight are proportional in a given location, so 1 kg  2.21 lb 1

m 

1 kg 2.21 lb

1 kg 2.21 lb

 weight in pounds 



Kilograms can be converted to grams by the procedure described in the appendix A of the text.

1 kg = 1000 g 1

1 kg 2.21 lb

 m kilograms 

m grams

1000 g 1 kg

2. Since density is given by the relationship  = m/V, then

  

m V 39.5 5.0

 7.9

39.5 g 5.0 cm 3



g cm 3

g cm 3

3. The volume of a sample of copper is given and the problem asks for the mass. From the relationship of  = m/V, solving for the mass (m) tells you that the density () times the volume (V) gives you the mass, m = V. The density of copper, 8.96 g/cm3, is obtained from table 1.3 in the text, and

m V mV Vρ = V m = ρV ρ =

g   =  8.96 10.0 cm 3  3  cm   g = 8.96 ×10.0 × cm 3 3 cm = 89.6 g

4. Solving the relationship  = m/V for volume gives V = m/, and V





5,000 g g 0.92 cm 3 5,000 g cm 3  0.92 1 g

 5, 434.7826 cm 3  5, 400 cm 3

The answer is rounded to provide two significant figures, the least number given in the density of 0.92 g/cm3. This assumes that 5,000 grams of ice means exactly 5,000 grams, so 5,000 has four significant figures.

5. A 50.0 cm3 sample with a mass of 51.5 grams has a density of   

m V 51.5 50.0

 1.03



51.5 g 50.0 cm 3 g cm 3

g cm 3

According to table 1.3, 1.03 g/cm3 is the density of seawater, so the substance must be seawater.

6. The problem asks for a mass, gives the density of gasoline, and gives the volume. Thus, you need the relationship between mass, volume, and density. The volume is given in liter (L), which should first be converted to cm3 because this is the unit in which density is expressed. The relationship of  = m/V solved for mass is V, so the solution is m  m  V V g   m   0.680 94,600 cm 3  3  cm   g  0.680  94,600  cm 3 3 cm  64,328 g  

 64.3 kg

The answer is rounded to three significant figures, the number of significant figures given in the density and volume measurements. The answer of 64,300 g is correct, but usually it is better to express the answer using ―standard‖ conventions being used. Thus 64.3 kg is preferred because the MKS system is (or soon will be) used. Using scientific notation would be better yet because of ease of showing significant figures and the ease of performing mathematical operations.

7. From table 1.3, the density of iron is given as 7.87 g/cm3. Converting 2.00 kg to the same units as the density gives 2,000 g. Solving  = m/V for volume gives V



m 



2,000 7.87



2,000 g g 7.87 cm3 g cm 3  1 g

 254.13 cm 3  254 cm 3

8. The length of one side of the box is 1.00 m. Reasoning: Since the density of water is 1.00 g/cm3, then the volume of 1,000,000 g (1,000 kg) of water is 1,000,000 cm3. A cubic box with a volume of 1,000,000 cm3 is 100 cm (since 100  100  100 = 1,000,000). Converting 100 cm to m units, the cube is 1.00 m on each edge.

9. The relationship between mass, volume, and density is  = m/V. The problem gives a volume, but not a mass. The mass, however, can be assumed to remain constant during the compression of the bun so the mass can be obtained from the original volume and density, or m    m  V V g   m   0.15 240 cm3  3  cm   g  0.15  240  cm 3 cm3  36 g A mass of 36 g and the new volume of 195 cm3 mean that the new density of the crushed bread is m   V 36 g  195 cm 3 

36 195

 0.18

g cm 3 g cm 3

10. According to table 1.3, lead has a density of 11.4 g/cm3. A 1.00 cm3 sample of lead would have a mass of

m  m  V V g   m   11.4 1.00 cm3  3  cm   g  11.4  1.00  cm3 cm3  11.4 g  

Also, according to table 1.3, iron has a density of 7.87 g/cm3. The volume of iron required to balance a mass of 11.4 g of lead is:

m  V  V 11.4 g V  g 7.87 cm3 11.4 g cm3   7.87 1 g  

 1.4485387 cm3  1.45 cm3

m 

2

Motion

Contents 2.1 Describing Motion 2.2 Measuring Motion Speed Velocity Acceleration Science and Society: Transportation and the Environment Forces 2.3 Horizontal Motion on Land 2.4 Falling Objects A Closer Look: A Bicycle Racer’s Edge 2.5 Compound Motion Vertical Projectiles Horizontal Projectiles A Closer Look: Free Fall 2.6 Three Laws of Motion Newton’s First Law of Motion Newton’s Second Law of Motion Weight and Mass Newton’s Third Law of Motion 2.7 Momentum Conservation of Momentum Impulse 2.8 Forces and Circular Motion 2.9 Newton’s Law of Gravitation Earth Satellites A Closer Look: Gravity Problems Weightlessness Overview This chapter primarily contains the patterns of motion developed by Isaac Newton (A.D. 1642–1727). Newton made many contributions to science, but his three laws of motion and his law of gravitation are the most famous. The three laws of motion are concerned with (1) what happens to the motion of a single object when no unbalanced forces are involved, (2) the relationship between the force, the mass of an object, and the resulting change of motion when an unbalanced force is involved, and (3) the relationship between the force experienced by two objects when they interact. The laws of motion are universal, that is, they apply throughout the known universe and describe all motion. Throughout the universe mass is a

measure of inertia, and inertia exists everywhere. A change of motion, acceleration, always results from an unbalanced force everywhere in the known universe. Finally, forces of the universe always come in pairs. Of the two forces one force is always equal in magnitude but opposite in direction to the other. The law of gravitation is also applicable throughout the known universe. All objects in the Solar System — the sun and the planets, the earth and its moon, and all orbiting satellites — obey the law of gravitation. Relativistic considerations should not be mentioned at this time. Concentrate on Newton's laws of motion, not Einstein's modifications of them.

The key to understanding patterns of motion is to understand simultaneously the ideas represented in the three laws of motion. These areas follow: 1. Inertia is the resistance to a change in the state of motion of an object in the absence of an unbalanced force. An object at rest remains at rest and an object moving in a straight line retains its straight-line motion in the absence of an unbalanced force. The analysis of why a ball moving across a smooth floor comes to a stop, as presented in the previous chapter, is an important part of the development of this concept. Newton's first law of motion is also known as the law of inertia.

2. Mass is defined as a measure of inertia, that is, a resistance to a change in the state of motion of an object. Thus the greater the mass the greater the resistance to a change in the state of motion of an object. Acceleration is a change in the state of motion of an object.

According to the definition developed in the previous chapter, an object that speeds up, slows down, or changes its direction of travel is undergoing an acceleration. Students who have difficulty accepting the meanings of mass and acceleration often have less difficulty if they are told these are definitions of the quantities. A force is a push or a pull that is capable of causing a change in the state of motion of an object, that is, capable of producing an acceleration. The resulting acceleration is always in the same direction as the direction of the applied force. Newton's second law of motion is a relationship between mass, acceleration, and an unbalanced force that becomes clear when the conceptual meaning of these terms is understood. The relationship is that the greater the mass (inertia), the greater the force required to bring about a change in the state of motion (acceleration). In symbol form, the relationship is a  F/m, or the more familiar F  ma. Since a newton of force is defined in terms of a certain mass (1 kg) and a certain acceleration (1 m/s2), the units are the same on both sides and the relationship becomes an equation, or F = ma. This is an example of an equation that defines a concept (see chapter 1).

3. A single force never occurs alone; a force is always produced by the interaction of two or more objects. There is always a matched and opposite force that occurs at the same time, and Newton's second law of motion is a statement of this relationship.

Suggestions 1. The need for precision and exact understanding should be emphasized as the various terms such as speed, velocity, rate, distance, acceleration, and others are presented. Stress the reasoning behind each equation, for example, that velocity is a ratio that describes a property of objects in motion. Likewise, acceleration is a time rate of change of velocity, so vf - vi/t not only makes sense but can be reasoned out rather than memorized. Also stress the need to show how units are handled in solving problems. The complete manipulation of units mathematically is stressed throughout this book. Typically, students must be shown how unit work serves as a check on problem-solving steps. Students are sometimes confused by the use of the symbol ―v‖ for both speed and velocity. Explain that speed is the same quantity as velocity but without direction, so the same symbol is used to simplify things. On the point of simplifying things, avoid the temptation to use calculus in any explanation or discussion.

2. Students are generally interested in ―relative to what‖ questions concerning motion. For example, what is the speed of an insect flying at 5 mph from the front to the back of a bus moving at 50 mph? What do you observe happening to an object dropped inside an airplane moving at 600 mph? What would an observer outside the airplane observe happening to the object?

3. The discussion of what happens to a ball rolling across the floor is an important one, and many students who think from an ―Aristotelian framework‖ are surprised by the analysis.

When discussing the role of friction and objects moving on the earth’s surface, it is often interesting to ask why planets do not stop moving around the sun. Spur on the discussion by answering with another question, why should they stop? It might be helpful to review the meaning of vector arrows that represent forces.

4. Another way to consider acceleration is to ask, How fast does ―how fast‖ change? If students have learned the concept of a ratio, then they will better understand the concept of uniform straight-line motion. The acceleration concepts, however, require the use of a ratio within another ratio, that is, a change of velocity (a ratio within) per unit of time (the acceleration ratio). This understanding is necessary (along with some basic math skills) to understand the meaning of such units as m/s2.

5. Demonstrations that illustrate the characteristics of projectile motion are illustrated in several devices found in scientific catalogs. Among the most impressive is the ―monkey and hunter‖ demonstration. Students enjoy this demonstration along with the humor that the instructor can induce while performing it.

6. There are many demonstrations and devices available from scientific suppliers that readily illustrate the laws of motion. However, none seems better than the personal experiences of students who have stood in the aisle of a bus as it starts moving, turns a corner, or comes to a stop. Use the three laws of motion to analyze the inertia, forces, and resulting changes of motion of a student standing in such an aisle of a bus.

7. Stress that weight and mass are two entirely different concepts. You will probably have to emphasize more than once that weight is another name for the gravitational force acting on an object, and that weight varies from place to place while mass does not. Use the second law of motion to show how weight can be used to calculate mass. A large demonstration spring scale calibrated in newtons can be used to show that a 1-kg mass weighs 9.8 N. Other masses can be weighed to show that weight and mass are proportional in a given location.

8. In solving problems involving the third law of motion, it is helpful for students to realize that a change in the state of motion always occurs in the same direction as the direction of an applied force. If you apply an unbalanced force on a ball toward the North, you would expect the ball to move toward the North. Thus if one starts walking toward the North a force must have been applied in the same direction. The foot pushed on the ground in the opposite direction, so it must be that the equal and opposite force of the ground pushing on the foot is what caused the motion toward the North. It seems almost anthropomorphic to state that the ground pushed on a foot, but no other answer is possible with this analysis. The next step, so to speak, is to realize that since the force of the foot on the ground equals the force of the ground on the foot (third law). Then the mass of the earth times the acceleration of the earth (second law) must equal the mass of the person times the acceleration of the person (ma = ma). This means at least two things: (1) that the earth must move when you walk across the surface (earth's acceleration must be greater than zero) and (2) that the earth would move with the same acceleration as the person if both had the same mass. Students are making progress when they can understand or make this kind of analysis.

9. A strong cord attached to a large coffee can half filled with water makes an interesting demonstration of centripetal force and inertia when whirled overhead. Practice this, however, before trying before a class.

10. Additional demonstrations: (a) Show the stroboscopic effect as a means of measuring motion. Use a strobe light or hand stroboscopes, for example, to ―stop‖ the motion of a spinning wheel of an upside-down bicycle. (b) Roll a steel ball down a long ramp and mark the distance at the end of each second. Plot distance vs. time and distance vs. time squared to verify the acceleration equation. (c) Crumple a sheet of paper tightly into a small ball. Drop the crumpled ball and a sheet of uncrumpled paper from the same height. Discuss which is accelerated at 9.8 m/s2 and the roll of air resistance. (d) Use the commercial apparatus that shoots or moves one ball horizontally and drops another ball vertically at the same time. A single ―click‖ means that both balls hit the floor at the same time. This illustrates the independence of velocities. (e) Drop a small steel ball from the highest place practical into a tub of water. Make sure this is done on a day without wind and with no person near the tub. Time the fall with a stopwatch. Measure the vertical distance accurately, then find g from d = 1/2gt2.

(f) Use a spring scale to show that a 1.0-kg mass weighs 9.8 N. Use other masses to show that the weight of an object is always proportional to the mass in a given location. (g) Use an air track to illustrate Newton’s first and second law of motion. If an air track is not available, consider a slab of ice or dry ice on a smooth demonstration tabletop. Wood blocks can be set on the ice to add mass. (h) Will a jet plane backed up to a brick wall take off faster than one out in the open?

Compare the jet plane to a balloon filled with air, that is, a jet of escaping air propels the balloon. Thus, the movement is a consequence of Newton’s third law and the brick wall will make no difference–a jet plane backed up to a brick will take off the same as an identical jet plane out in the open. (i) Seat yourself on a small cart with a CO2 fire extinguisher or a bottle of compressed air from the shop. Hold the device between your feet and legs with the escape valve pointed away from your body. With the way clear behind you, carefully discharge a short burst of gas as you accelerate. This attention-grabber affords an opportunity to review all three of Newton’s Laws of motion. (j) Demonstrate that the acceleration of a freely falling object is independent of weight. Use a commercial ―free-fall tube‖ if one is available. If not, try a large-diameter 1-meter glass or plastic tube with a solid stopper in one end and a one-hole stopper in the other. Place a coil and a feather in the tube, then connect the one-hole stopper to a vacuum pump. Invert the tube to show how the coin and feather fall in air. Pump air from the tube then again invert to show the coin and feather in free fall.

For Class Discussions 1. Neglecting air resistance, a ball in freefall will have a. constant speed and constant acceleration. b. increasing speed and increasing acceleration. c. increasing speed and decreasing acceleration. d. increasing speed and constant acceleration. e. decreasing speed and increasing acceleration.

2. Neglecting air resistance, a ball rolling down the slope of a steep hill will have a. constant speed and constant acceleration. b. increasing speed and increasing acceleration. c. increasing speed and decreasing acceleration. d. increasing speed and constant acceleration. e. decreasing speed and increasing acceleration.

3. Again neglecting air resistance, a ball thrown straight up will come to a momentary stop at the top of the path. What is the acceleration of the ball during this stop?

2 a. 9.8 m/s .

b. zero.

2 c. less than 9.8 m/s .

2 d. more than 9.8 m/s .

4. Again neglecting air resistance, the ball thrown straight up comes to a momentary stop at the top of the path, then falls for 1.0 s. What is speed of the ball after falling 1.0 s? a. 1 m/s b. 4.9 m/s c. 9.8 m/s d. 19.6 m/s 5. Yet again neglecting air resistance, the ball thrown straight up comes to a momentary stop at the top of the path, then falls for 2.0 s. What distance did the ball fall during the 2.0 s? a. 1 m b. 4.9 m c. 9.8 m d. 19.6 m 6. A ball is thrown straight up at the same time a ball is thrown straight down from a bridge, with the same initial speed. Neglecting air resistance, which ball would have a greater speed when it hits the ground? a. The one thrown straight up. b. The one thrown straight down. c. Both balls would have the same speed.

7. After being released, a ball thrown straight down from a bridge would have an acceleration of 2 a. 9.8 m/s . b. zero.

2 c. less than 9.8 m/s .

2 d. more than 9.8 m/s .

8. A gun is aimed at an apple hanging from a tree. The instant the gun is fired the apple falls to the ground, and the bullet a. hits the apple. b. arrives late, missing the apple. c. may or may not hit the apple, depending on how fast it is moving.

9. You are at rest with a grocery cart at the supermarket, when you see an ―opening‖ in a checkout line. You apply a certain force to the cart for a short time and acquire a certain

speed. Neglecting friction, how long would you have to push with half the force to acquire the same final speed? a. one-fourth as long. b. one-half as long. c. for twice as long. d. for four times as long.

10. Once again you are at rest with a grocery cart at the supermarket, when you apply a certain force to the cart for a short time and acquire a certain speed. Suppose you had bought more groceries, enough to double the mass of the groceries and cart. Neglecting friction, doubling the mass would have what effect on the resulting final speed if you used the same force for the same length of time? The new final speed would be a. one-fourth. b. one-half. c. doubled. d. quadrupled.

11. You are moving a grocery cart at a constant speed in a straight line down the aisle of a store. The forces on the cart are a. unbalanced, in the direction of the movement. b. balanced, with a net force of zero. c. equal to the force of gravity acting on the cart. d. greater than the frictional forces opposing the motion of the cart.

12. Considering the gravitational attraction between the Earth and Moon, the a. more massive Earth pulls harder on the less massive Moon. b. less massive Moon pulls harder on the more massive Earth. c. attraction between the Earth and Moon and the Moon and Earth are equal. d. attraction varies with the Moon phase, being greatest at a full moon.

13. You are outside a store, moving a loaded grocery cart down the street on a very steep hill. It is difficult, but you are able to pull back on the handle and keep the cart moving down the street in a straight line and at a constant speed. The forces on the cart are a. unbalanced, in the direction of the movement. b. balanced, with a net force of zero. c. equal to the force of gravity acting on the cart. d. greater than the frictional forces opposing the motion of the cart.

14. Which of the following must be true about a horse pulling a buggy?

a. According to the third law of motion, the horse pulls on the buggy and the buggy pulls on the horse with an equal and opposite force. Therefore, the net force is zero and the buggy cannot move. b. Since they move forward, this means the horse is pulling harder on the buggy than the buggy is pulling on the horse. c. The action force from the horse is quicker than the reaction force from the buggy, so the buggy moves forward. d. The action-reaction force between the horse and buggy are equal, but the resisting frictional force on the buggy is smaller since it is on wheels.

15. Suppose you have a choice of driving your speeding car head on into a massive concrete wall or hitting an identical car head on. Which would produce the greatest change in the momentum of your car? a. The identical car. b. The concrete wall. c. Both would be equal.

16. A small, compact car and a large sports utility vehicle collide head on and stick together. Which vehicle had the larger momentum change? a. The small, compact car. b. The large sports utility vehicle. c. Both would be equal.

17. Again consider the small, compact car and large sports utility vehicle that collided head on and stuck together. Which experienced the larger deceleration during the collision? a. The small, compact car. b. The large sports utility vehicle. c. Both would be equal.

18. Certain professional football players can throw a football so fast that it moves horizontally in a flat trajectory. a. True b. False Answers: 1d, 2c (a = g straight down, but decreases to zero on a level surface), 3a (acceleration is a rate of change of velocity and gravity is acting, F = ma, so a must be occurring), 4b (initial speed was zero, average speed is one-half of final speed), 5d, 6c, 7a (after release only gravity acts on ball), 8a (the apple and bullet accelerate downward together, no matter how fast the bullet is moving), 9c, 10b, 11b, 12c, 13b, 14d, 15c, 16c, 17a, 18b.

Answers to Questions for Thought

1. The speed of the insect relative to the ground is the 50.0 mi/h of the bus plus the 5.0 mi/h of the insect for a total of 55 mi/h. Relative to the bus alone the speed of the insect is 5.0 mi/h.

2. After it leaves the rifle barrel, the force of gravity acting straight down is the only force acting on the bullet.

3. Gravity does not depend upon some medium so it can operate in a vacuum.

4. Yes, the small car would have to be moving with a much higher velocity, but it can have the same momentum since momentum is mass times velocity.

5. A net force of zero is required to maintain a constant velocity. The force from the engine balances the force of friction as a car moves with a constant velocity.

6. The action and reaction forces are between two objects that are interacting. An unbalanced force occurs on a single object as the result of one or more interactions with other objects.

7. Bending your knees as you hit the ground extends the stopping time. This is important since the change of momentum is equal to the impulse, which is force times the time. A greater time therefore means less force when coming to a stop.

8. Your weight can change from place to place because weight is a downward force from gravitational attraction on your mass and the force of gravity can vary from place to place.

9. Nothing! There is no force parallel to the motion to increase or decrease Earth's speed, so the speed remains constant.

10. If you have something to throw, such as car keys or a snowball, you can easily get off the frictionless ice. Since the force you apply to the thrown object results in an equal and opposite force (the third law of motion), you will move in the opposite direction as the object is thrown (the second law of motion). The same result can be achieved by blowing a puff of air in a direction opposite to the way you wish to move.

11. Considering everything else to be equal, the two rockets will have the same acceleration. In both cases, the acceleration results as burning rocket fuel escapes the rocket, exerting an unbalanced force on the rocket (third law) and the rocket accelerates during the applied force (second law). The acceleration has nothing to do with the escaping gases having something to ―push against.‖ 12. The astronaut is traveling with the same speed as the spaceship as he or she leaves. If no net force is applied parallel to the direction of motion of either the astronaut or the spaceship, they will both maintain a constant velocity and will stay together.

For Further Analysis 1.

Similar – both speed and velocity describe a magnitude of motion, that is, how fast something is moving. Differences – velocity must specify a direction; speed does not.

2.

Similar – both velocity and acceleration describe motion. Differences – velocity specifies how fast something is moving in a particular direction; acceleration specified a change of velocity (speed, direction, or both).

3.

This requires a comparison of beliefs and an analysis and comparison with new contexts. Answers will vary, but should show understanding of Newton’s three laws of motion.

4.

This question requires both clarifying beliefs and comparing perspectives. Answers will vary.

5.

Requires refining of understanding. Mass is a measure of inertia, meaning a resistance to a change of motion. Weight is gravitational acceleration acting on a mass. Since gravity can vary from place to place, the weight as a result of gravity will also vary from place to place.

6.

Requires clarifying and analyzing several conceptual understandings. Newton’s first law of motion tells us that motion is unchanged in a straight line without an unbalanced force. An object moving on the end of a string in a circular path is pulled out of a straight line by a centripetal force on the string. The object will move off in a straight line if the string breaks. It would move off in some other direction if other forces were involved.

Group B Solutions 1. The distance and time are known and the problem asked for the average velocity. Listing these quantities with heir symbols, we have

d = 400.0 km t = 4.5 h v = ?

These are the quantities involved in the average speed equation, which is already solved for the unknown average speed:

d t 400.0 km = 4.5 h

v =

= 89

km h

2. Listing the quantities given in this problem, we have

d = 16.0 km t = 45 min v = ?

The problem specifies that the answer should be in km/h. We see that 45 minutes is 45/60, or 3/4, or 0.75 of an hour, and the appropriate units are:

d = 16.0 km t = 0.75 h v = ?

Substituting the known quantities, we have d t 16.0 km = 0.75 h

v =

= 21.3333 = 21

km h

km h

3. Weight is the gravitational force on an object. Newton’s second law of motion is F = ma, and since weight (w) is a force (F), then F = w and the second law can be written as w = ma.

The acceleration (a) is the acceleration due to gravity (g), so the equation for weight is w = mg.

(a)

w = mg m  =  80.0 kg   3.93 2  s   kg × m =  80.0   3.93 s2 = 314.4 N = 314 N (b)

w = mg m  =  80.0 kg  1.64 2  s   kg × m =  80.0  1.64  s2 = 131.2 N = 131 N 4.

Listing the known and unknown quantities,

m = 6000.0 kg a = 2.2

m s2

F = ?

These are the quantities found in Newton’s second law of motion, F = ma, which is already solved for force (F). Thus, F = ma m  =  6000.0 kg   2.2 2  s   kg × m =  6000.0   2.4  s2 = 13200 N = 13000 N

5.

Listing the known and unknown quantities, F  300 N m  3000 kg a  ?

F  ma  a =

F m kg  m s2 3000 kg

300 =

300 kg  m 1  2 3000 s kg m  0.1 2 s 

6.

We see that 30.0 minutes is 1/2 or 0.50 of an hour, and d t 15.0 km  0.50 h

v=

 30.0 km/h

7. We see that the distance units are kilometers, but the velocity units are m/s. We need to convert km to m, then d d v=  t= t v 1.5  1011 m  m 3.0  108 s 11 1.5  10 m s   3.0  108 1 m  5.0 102 s  8.3 min

8. The distance that a sound with this velocity travels in the given time is v =

d t

 d = vt   343m/s  0.500s   172 m 172 m 2  86.0 m

Since the sound traveled from you to the cliff and then back, the cliff must be 172 m/2 = 86.0 m away.

9. Note that the two speeds given (80.0 km/h and 90.0 km/h) are average speeds for two different legs of a trip. They are not the initial and final speeds of an accelerating object, so you cannot add them together and divide by 2. The average speed for the total (entire) trip can be found from definition of average speed, that is, average speed is the total distance covered divided by the total time elapsed. Therefore, we start by finding the distance covered for each of the two legs of the trip:

d  d  vt t km   Leg 1 distance   80.0  1.00 h  h    80.0 km km   Leg 2 distance   90.0   2.00 h  h    180.0 km v 

Total distance (leg 1 plus leg 2) = 260.0 km Total time = 3.00 h v 

d 260.0 km   86.7 km/h t 3.00 h

10.

vf  vi t 15 m/s  5.0 m/s  6.0 s

a 

10.0 m 1  6.0 s s m  1.7 2 s 

11. vf  vi v  vi  t  f t a 22 m/s  8.0 m/s t  m 3.0 2 s 14 m s2   3.0 s m  4.7 s

a 

12. The relationship between average velocity ( v ), distance (d), and time (t) can be solved for time: d v = t vt = d d t = v 380,000,000 m t  m 11,000 s 380,000,000 m s   11,000 1 m  34,545 s  35,000 s (about 9.6 hours)

13. The relationship between average velocity ( v ), distance (d), and time (t) can be solved for distance: d v   d  vt t m    348   4.63 s  s   m  348  4.63 s s  1611.24 m  1610 m

14. ―How many hours...‖ is a question about time and the distance is given. Since the distance is given in km and the speed in m/s, a unit conversion is needed. The easiest thing to do is to convert km to m. There are 1,000 m in a km, and (6.00  109 km)  (1  103 m/km) = 6.00  1012 m The relationship between average velocity ( v ), distance (d), and time (t) can be solved for time: d d v   t  t v 6.00  1012 m t  m 3.00  108 s 6.00 m s   10128  3.00 1 m  2.00  104 s



2.00  104 s s 3,600 h

 5.56 h

15. The initial velocity (vi) is given as 724 m/s, the final velocity (vf) is given as 675 m/s, and the time is given as 5.00 s. Acceleration, including a deceleration or negative acceleration, is found from a change of velocity during a given time. Thus,

a



v f  vi



t  675 m/s    724 m/s  5.00 s



49.0 m/s 5.00 s

m 1  s s m   9.80 2 s (The negative sign means a negative acceleration, or deceleration.)   9.80

16. A rock thrown straight up decelerates to a velocity of zero, and then accelerates back to the surface just as a dropped ball would do from the height reached. Thus the time decelerating upward is the same as the time accelerating downward. The ball returns to the surface with the same velocity with which it was thrown (neglecting friction). Therefore: v  vi a  f t gt  vf  vi vf vf



gt  vi

m m    9.8 2   2.50 s   0 s  s  m  9.8  2.50 2  s s  25 m/s

17. These three questions are easily answered by using the three sets of relationships, or equations that were presented in this chapter: (a)

 at  vi

vf

m m    9.8 2   2.50 s   0 s  s  m  9.8  2.50 2  s s  25 m/s

vf

(b)

v



(c)

v



vf  vi 2



25 m/s  0 2

 13

m s

d  d  vt t  m   13   2.50 s   s m  13  2.50 s s  33 m

d

18. Note that this problem can be solved with a series of three steps as in the previous problem. It can also be solved by the equation that combines all the relationships into one step. Either method is acceptable, but the following example of a one step solution reduces the possibilities of error since fewer calculations are involved: d

    

1 2 gt 2 1 m 2  9.8 2   2.00 s  2 s  1 m 2  9.8 2   4.00 s  2 s  1 m  9.8 4.00  2  s2 2 s 19.6 m

 2.0 101 m

19.

F = ma  a



F m

kg  m s2  3,000 kg 300 kg  m 1   2 3,000 s kg m  0.1 2 s 300

20.

p = mv m    30.0 kg   500  s   kg  m  15,000 s kg  m  20,000 (one significant figure) s

21. Mass of ball: F = ma  m =

F a

kg  m s2  m 9.8 2 s 39.2 kg  m s 2   9.8 s2 m  4.0 kg 39.2

p = mv m    4.0 kg   7.00  s  kg  m  28 s

22. Listing the known and unknown quantities: Shell m = 30.0 kg Cannon m = 2,000 kg Shell v = 500 m/s Cannon v = ? m/s This is a conservation of momentum question, where the shell and cannon can be considered as a system of interacting objects: Shell momentum = Cannon momentum

 mv s =  mv c  mv s   mv c = 0  30.0 kg   500 

m    2, 000 kg  vc  0 s 

m  15, 000 kg     2, 000 kg  vc   0 s   m  15, 000 kg     2, 000 kg  vc  s   m 15,000 kg  s vc  2,000 kg 15,000 kg 1 m   2,000 1 kg s m  7.5 s m 8 s 

23.

Book momentum  Man momentum

 mv B   mv M  mv B   mv M  0  2.00 kg  10.0 

m    80.0 kg  v M  0 s 

m   20.0 kg     80.0 kg  v M   0 s   vM 

m s 80.0 kg

20.0 kg 

20.0 kg 1 m   80.0 1 kg s m  0.250 s 

24.

(a)

w = mg = (5.00 kg) (9.8

m ) w = mg s2

= 49 N

(b) F = ma  a



F m

kg  m s2  5.00 kg 10.0 kg  m 1   5.00 s2 kg m  2.00 2 s 10.0

25.

F = ma  20.0 kg  10.0

m s2

m  20.0  10.0 kg  2 s kg  m  2.00  102 s2  2.00  102 N

26.

F = ma  60.0 kg  1.00

m s2

m  60.0  1.00 kg  2 s kg  m  60.0 s2  60.0 N

27.

F

 ma and a



vf  vi  F t

 m

vf  vi t

 1,000.0 kg 



 20.0 m/s  10.0 m/s  5.00 s

1,000.0 10.0 

kg 

5.00

s

m 1  2,000 kg   s s 3  2.00  10 N

m s

28.

36.0 km/h  0.2778

m/s  10.0 m/s km/h

F

 ma  m 

F a

a



(a)

and

vf  vi t

 m 

Ft vf  vi

kg  m  5.00 s s2  m m 10.0  0 s s  3,000.0  5.00  kg  m  s  s  10.0 s2 1 m 3  1.50  10 kg 3,000.0

(b)

w = mg

1.50  10 kg    9.8 sm 



3

2

 1.5  104 N

29.

w = mg w

m  60.0 kg  9.8 2 s  588 N  590 N

30.

F  ma and a 

 v2  v2  F  m  r  r  m   5.00  s  1.0000 kg   0.500 m 

1.0000  5.00 

0.500  10.0 N

31.

F  ma and

a

t

3

vf  vi t

 F m

vf  vi t

Contents 3.1 Work Units of Work Power A Closer Look: Simple Machines 3.2 Motion, Position, and Energy Potential Energy Kinetic Energy

kg m 2 1   1 s2 m

 t m

m   0  2.00  s  200.0 kg   kg  m 100.0 2 s kg m s2   200.0  0.0200    1 s kg  m  4.00 s

Energy

2

vf  vi F

3.3 Energy Flow Work and Energy Energy Forms Energy Conversion Energy Conservation Energy Transfer 3.4 Energy Sources Today Science and Society: Grow Your Own Fuel?

Petroleum Coal Moving Water Nuclear Conserving Energy 3.5 Energy Sources Tomorrow ―Solar Power‖ Plants Geothermal Energy Hydrogen Overview Energy is generally a difficult subject for many nonscience students because it is an abstract concept. This chapter begins with the more easily visualized concepts of work and power, develops two general aspects of energy (position and motion) based on concepts learned in previous chapters, and then uses these aspects as a basis for a conceptual scheme for understanding energy. This scheme is then applied in considering the energy sources used today.

Work and energy are closely related concepts. Work is defined in this chapter by using the second class of equations (defining a concept; see chapter 1). Work is defined as the product of a force moving through a distance, or W = Fd. Both metric units and English units are presented because both are in everyday use today. The metric unit of work is the newton-meter, which is called a joule. The English unit of work is the foot-pound, which does not have another name. Along with learning the scientific meaning of work, students will need to become accustomed to using the terms in the sense of work accomplished or the potential for doing work, for example, ―How much work was done on . . .?‖ and ―How much work can the object now do?‖ The energy of position, or potential energy, can be measured by how much work is done on an object to give it energy of position or by how much work it can now do because of its position. Since work involves forces and movement through a distance, the variables involved are the force, the movement (acceleration = change of motion), and the mass of the object (a measure of inertia, or resistance to a change of motion). Thus a non-calculus calculation of potential energy can begin with Newton's second law of motion, or F = ma.

To obtain an expression of work, both sides of this equation are multiplied by distance, h (for

height, which is a vertical distance), which gives Fd = mah. For gravitational potential energy, the acceleration is g and the relationship is W = mgh or PE = mgh. The potential energy unit turns out to be joules, which is the same unit used to do work to create the potential energy to begin with. Thus from this analysis comes the first idea that work = energy = work, or that both are fundamentally the same thing.

The energy of motion, or kinetic energy, can also be measured by how much work is done on an object to give it energy of motion or by how much work it can now do because of its motion. Again, work involves forces and movement through a distance such as is involved in throwing a baseball. The non-calculus relationship again involves the variables in Newton's second law of motion, F = ma. As before, both sides are multiplied by distance to obtain an expression of work, which in this case is the energy of motion, and KE = mad.

Now we need to put the distance quantity (d) in terms of a final velocity (vf) for kinetic energy. This requires the use of the first three equations presented in chapter 2: Step 1. The relationship between the average velocity, distance, and time is v 

d t

 d  vt

Step 2. The average velocity quantity and the time quantity could now be substituted for d in KE = mad, but they are still not in terms of a final velocity. First, a final velocity is substituted for average velocity ( v ) vi  vf v  vf   where vi  0  2 2 Step 3. Next, a final velocity is substituted for time by rearranging the equation for acceleration v  vi v a  f  t  f  where vi  0  t a Now it is a matter of simple substitution of the solutions in step 2 and step 3 into the rearrangement shown in step 1, or v 

d  vt

 from step 1

vf t  from step 2  2  v  v  d   f   f   from step 3  2  a  d 

These terms can now be substituted for the d in KE = mad to put the equation in terms of velocity rather than distance, and

 v  v  KE  ma  f   f   2  a 

The a's now cancel and the equation is rearranged to the more familiar expression of kinetic energy, which is KE 

1 2 mv 2

The kinetic energy unit turns out to be a joule, which is the same unit used to do the work to create the kinetic energy to begin with. Again you can see that work = energy = work, that is, both energy and work are fundamentally the same thing.

The similarities between energy and work are discussed throughout the presentation of the energy flow scheme. Note that many textbooks define heat as a form of energy rather than energy in transit between two forms. Either definition is correct. Considering heat as a form of energy, however, is a conceptual level akin to considering a dog as the animal that lives across the street (see chapter 1 in this manual).

Suggestions 1. An important key to understanding the concepts presented in this chapter is understanding the relationship between the work performed to give an object potential or kinetic energy, the energy that the object has by way of its position or motion, and the work that an object can do as a result of its kinetic or potential energy. Use a demonstration spring scale calibrated in newtons to lift a kilogram mass one meter from the floor to a shelf. Show the weight of the mass is 9.8 N and the work done is 9.8 J in lifting the mass 1 m. Discuss that the work is done against gravity. Now use the equation to show the potential energy of the mass is now 9.8 J as a result of the work done on it. Compare the work done on the mass, the potential energy that the mass has as a result, and the work the mass can now do as a result of its position in the attractive force of earth's gravitational field.

2. Students find it interesting to compare the power ratings in one system of measurement with power ratings in the other. A 1500 W hair dryer, for example, has an English power equivalent of almost 2 hp. A 100 hp car, on the other hand, has a metric power rating of a little less than 75 kW. 3. The expressions of kinetic energy, potential energy, and the law of conservation of energy apply to the conversion of any energy form to another. If the students seem confused by electromagnetic or nuclear interactions, concentrate on mechanical

interactions. They can learn the relationships involved in the mechanical interactions and apply the concepts to more abstract materials in later chapters.

4. A swinging pendulum provides a good demonstration of the conversion of potential to kinetic energy and from kinetic to potential energy. A meter stick can be used to show that the bob rises to about the same height as it speeds up, as it descends, then slows as it moves up the other half of the arc of its swing. Conservation laws can also be shown by the popular line of steel balls supported by wires on a frame. When one ball is released to hit the line of balls, it stops while one swings out the other side. If two are allowed to hit the line of balls, they stop while two swing out the other side. These elastic collisions demonstrate both the law of conservation of energy and the law of conservation of momentum.

5. See the September 1978 issue of the American Journal of Physics for an interesting and important article on exponential growth and doubling time as applied to our energy sources today. The article reveals the ―best-kept secret of the century‖ about our energy supplies, a topic that should be discussed if future energy supplies are considered.

6. Additional demonstrations: (a) Use a pendulum to demonstrate conservation of energy as the bob converts potential energy (top of its swing) to kinetic energy (bottom of swing), then back to potential again. Point out that a book falling from a shelf also converts PE (top of fall) to KE (bottom of fall). (b) Support a long piece of transparent tubing in a long arc, and then roll marbles down one side to see if they roll to the same height at the other side of the tube. Add a loop or several loops and analyze potential energy and kinetic energy at the beginning and end of each loop compared to the overall length of tubing. (c) A line of steel spheres supported by strings can be used to demonstrate conservation of energy in elastic collisions. One mass pulled back and released will result in one mass leaving the row at the other end. If two are pulled back and released two will leave the other end and so on. Try pulling one mass back from one side and two back from the other side, releasing all at the same time. (d) If your classroom is above or below street level, you can ask each student to calculate how much work is done bringing books to (or from) class.

For Class Discussions 1. A spring-loaded paper clamp exerts a force of 2 N on 10 sheets of paper it is holding together. Is the clamp doing work as it holds the papers together? a. Yes! b. No! 2. An iron cannon ball and a bowling ball were dropped at the same time from the top of a building. At the instant before the balls hit the sidewalk, the heavier cannon ball has greater

a. velocity b. acceleration c. kinetic energy d. all of these are the same for the two balls 3. Two students are poised to dive off equal height diving towers to a swimming pool below.

Student B is twice as massive as student A. Which of the following is true? a. Student B will reach the water sooner than student A. b. Both students have the same gravitational potential energy. c. Both students will have the same kinetic energy just before hitting the water. d. Student B did twice as much work climbing the tower.

4. The two students are again poised to dive off equal height diving towers to a swimming pool below. Student B is twice as massive as student A. Just before hitting the water, student B will have a. the same kinetic energy as student A. b. twice as much kinetic energy as student A. c. half as much kinetic energy as student A. d. four times as much kinetic energy as student A. 5. A car is moving straight down a highway under ideal conditions. What factor has the greatest influence on how much work must be done on the car to bring it to a complete stop? a. How fast it is moving. b. The weight of the car. c. The mass of the car. d. The latitude of the location.

6. Two identical cars are moving straight down a highway under identical conditions, except car B is moving three times as fast as car A. How much more work is needed to stop car B? a. Twice as much. b. Three times as much. c. Six times as much. d. Nine times as much.

7. Two identical cars start at rest on a long hill, with car B twice as high as car A. How much more work is needed to stop car B at the bottom of the hill? a. Twice as much. b. Three times as much. c. Six times as much. d. Nine times as much.

8. Suppose your grocery cart is moving at a constant momentum in a straight line down the aisle of a store, without friction. How will the speed change as you drop groceries into the moving cart? a. increase b. decrease c. remain the same 9. Again consider your grocery cart that is moving at a constant momentum in a straight line down the aisle of a store, without friction. How will the kinetic energy of the cart change as you drop groceries into it? a. increase b. decrease c. remain the same 10. A water balloon dropped from a dorm window does not break on the sidewalk. From how much higher would you need to drop the balloon to double the speed of impact? a. Twice as high. b. Three times as high. c. Four times as high. d. Eight times as high.

Answers: 1b, 2c, 3d, 4b, 5a, 6d (W = KE = 1/2mv2 and 32 = 9), 7a (2mgh = 21/2mv2 = 2W), 8b (constant p with increased m in p = mv), 9b, 10c (v = 2gh).

Answers to Questions for Thought 1. Energy is the ability to do work and doing work on something gives it energy.

2. The work done is equal to the increase in gravitational potential energy.

3. Relative to the bus, the person has no kinetic energy because the person is at rest relative to the bus. Relative to the ground, however, the person does have kinetic energy because the person is moving with the same speed as the bus.

4. Because a time factor is in the rating: a watt is a unit of power, and power is work per unit time. A 100 W light bulb uses energy at a rate of 100 J per s.

5. A kWh is a unit of work, and since energy is the ability to do work, it is also a unit of energy. In terms of units, a watt is a joule per second, and an hour, as a second, is a unit of time. The time units cancel, leaving a unit of a joule, which can be used to measure either work or energy.

6. Energy is eventually converted into unrecoverable radiant energy, so new sources of convertible energy must be found in order to continue performing useful work.

7. If the spring clamp does not cause the paper to move, it is not acting through a distance and no work is done.

8. Fossil fuels contain energy from plants or animals that lived millions of years ago.

These plants and animals are known from the fossils they left behind, and the energy in the fuels represents energy stored from these ancient organisms.

9. The machine would not be in accord with the law of conservation of energy.

10. A joule is one newton-meter. A joule of work is from force acting through a distance while a joule of energy is the ability to perform one joule of work. The use of the same unit means that work and energy are fundamentally the same thing.

11. The energy required is less on the moon because the weight of the object (the downward force due to gravity) depends upon the force of gravity, which is less on the moon than on the earth. Less energy is needed to do the work of raising the mass on the moon, and the elevated object on the moon has less potential energy as a consequence of the work done.

12. The energy is converted to heat and sound.

For Further Analysis 1. Analyzing and evaluating the definition of mechanical work shows that work is defined as the product of a force and the distance moved as a result of the force. In other words, movement is part of the definition of work.

2. Similarities – both involve a force moving something through a distance. Difference – power is a time rate of doing work; work by itself does not involve time.

3. This requires analyzing and evaluating an interpretation of work. The correct analysis is that this is a true statement.

4. This requires analyzing, exploring beliefs, and clarifying a conceptual understanding.

Answers will vary, but should clarify that work input always equals work output.

5. Reasoning precisely about the equation shows that K.E. varies directly with the mass, but varies with the square of the velocity. Thus, twice the mass requires twice the work (K.E.) to bring a car to a stop, but twice the speed requires four times the work to bring the car to a stop.

6.

Generating and analyzing this situation will result in answers that vary.

7. Analysis should show mechanical energy (gravitational), chemical (electromagnetic), radiant (electromagnetic), electrical (electromagnetic), and nuclear (nuclear).

8. Evaluating and analyzing should show that this device does not exist.

9. Evaluating and analyzing should show that such contradictions do not exist.

Group B Solutions 1.

W  Fd   800.0 N 1.5 m    800.0 1.5 N  m  1200 J

2.

W  Fd   400.0 N  3.0 m    400.0  3.0  N  m  1200 J

3.

W  Fd  mgh m    5.0 kg   9.8 2   0.300 m  s   kg  m  5.0  9.8  0.300 m s2  14.7 N  m  15 J

4.

W = mgh  h 

W mg



196,000 J  250.0 kg   9.8 m/s2 



196,000  250.0  9.8

kg  m m 1 s2    s2 1 kg m

196,000 m 2450  80 m 

 0.080 km

5.

P



mgh t

1,500.0 kg   9.8 2   360.0 m  m s   60.0 s

 kg  m  m 1,500.0  9.8  360.0   s2    s  60.0  5, 292,000 N  m 60.0 s J  88, 200 s  88, 200 W 

1.00 hp  88, 200 W 746 W 88, 200 hp  W 746 W 118.23 hp 120 hp

6.

(a) 250 W 746 W / hp 250 W hp  746 1 W 0.34 W

(b)

230 hp  746 W/hp 230  746

hp W  1 hp

171,580 W 170,000 W (170 kW)

7.

KE 

1 2 mv 2 2



1 m  0.03kg   200.0  2 s 



 1 m2  0.03kg 40,000.0    2 s2  

1 m2  0.03 40,000.0  kg  2 2 s kg  m  600 2  m s 2  6  10 N  m 

 6  102 J

8. The work done on an object to put it in motion, or the work done by a moving object as a result of its motion is equal to its kinetic energy, so KE 

1 2 mv 2 2



1 m  0.03kg   200.0  2 s 



 1 m2  0.03kg 40,000.0    2 s2  

1 m2  0.03 40,000.0  kg  2 2 s kg  m  600 2  m s 2  6  10 N  m 

 6  102 J

9. (a) W = Fd   50.0 lb 10.0ft   50.0  10.0 lb  ft  500 ft  lb  5.00  102 ft  lb

(b)

PE = mgh    50.0 lb   ft    32  0ft  ft   s2   32 2  s    0

10. (a)

W  Fd  mgd m    50.0 kg   9.8 2  1.5m  s   kg  m  50.0  9.8  1.5 m s2  735 N  m  740 J

(b) PE = mgh m   100 kg   9.8 2  1.5m  s   kg  m  50.0  9.8  1.5 m s2  735 N  m  740 J

(c) Since the PE lost is equal to the KE gained, then KE = 740 J.

11.

KE 

1 2 mv 2

1 m    0.0600 kg   20.0  2 s   

2

 1 m2   0.0600 kg   400 2  2 s  

1 m2  0.0600  400  kg  2 2 s kg  m  12 2  m s  12 N  m 

 12.0 J

12. (a) First, a unit conversion is needed:

m s  72.0 km km h 1.00 h m h km (0.2778)(72.0)   s km h m 20.0 s 0.2778

KE 

1 2 mv 2

1 m   1,500.0 kg   20.0  2 s  

2

 1 m2  1,500.0 kg   400 2  2 s  

1 kg  m 2   1,500.0  400 2 s2 kg  m  300,000 2  m s  300,000 N  m  3.00  105 J

(b) The work done on an object to put it in motion or the work done by a moving object as a result of its motion is equal to its kinetic energy, so 3.00  105 J of work is required to bring it to a stop.

13.

KE 

1 2 mv 2 2



1 m 800.0 kg   20.0  2 s 



 1 m2  800.0 kg 400    2 s2  

1 m2 800.0  400  kg  2 2 s kg  m  160,000 2  m s  160,000 N  m 

 1.60  105 J

KE 

1 2 mv 2

1 m    800.0 kg   40.0  2 s  

2

 1 m2  800.0 kg  1,600 2  2 s  

1 m2   800.0 1,600  kg  2 2 s kg  m  640,000 2  m s  640,000 N  m  6.40  105 J

Thus, doubling the speed quadruples the kinetic energy and 4 times as much work must be done to stop the car.

14.

KE 

1 2 mv 2 2



1 m 800.0 kg   20.0  2 s 



 1 m2  800.0 kg 400    2 s2  

1 m2 800.0  400  kg  2 2 s kg  m  160,000 2  m s  160,000 N  m 

 1.60  105 J

KE 

1 2 mv 2

1 m   1600.0 kg   20.0  2 s   

2

 1 m2  1600.0 kg   400 2  2 s  

1 m2  1600.0  400  kg  2 2 s kg  m  320,000 2  m s  320,000 N  m  3.20  105 J

Thus, doubling the mass results in a doubling of the kinetic energy.

15. (a)

W  Fd  175.0 lb 1,980.0ft   175.0  1,980.0 lb  ft  346,500 ft  lb

(b)

W t 346,500 ft  lb  6,300 s

P=

 55.00

P  55.00

ft  lb s

ft  lb 1.00 hp  ft  lb s 550 s

 0.10 hp

16. (a) P 

Fd t

 t  

Fd P

 2,000 lb  20.0ft 

ft  lb   / hp  10.0 hp   550 s   40,000 ft  lb s hp 1     5,500 1 ft  lb 1 hp  7.3 s

(b)

d t 20.0 ft  7.3 s

v 

 2.8

17. (a)

(b)

ft s

KE = 0 at h = 20.0 ft PE



1 PE0 at h  10.0ft 2

KE



1 KEf at h  10.0ft 2

 PE0

KEf

1 2 mv  mgh 2 v  2gh ft 2  32 2  20.0ft s ft  36 s 

18.

1 2 mv  mgh  v  2

2 KE m 2  1080.0 J m  6.00 60.0 kg s



19.

KE f



PEi

1 2 mv  mgh  v  2

2 gh

m 2  9.8 2  10.0 m s m  14 for both vehicles s 

20. (a) P =

W Fd mgh = = t t t m 70.0 kg  9.8 2  10.0 m s  10.0s  686 W = 690 W = 0.690 kW

(b) P 

4

690W W 746 hp

Heat and Temperature

Contents 4.1 The Kinetic Molecular Theory Molecules Molecules Interact Phases of Matter Molecules Move 4.2 Temperature Thermometers Temperature Scales A Closer Look: Goose Bumps and Shivering 4.3 Heat Heat as Energy Transfer Heat Defined Two Heating Methods Measures of Heat Specific Heat Heat Flow Conduction Science and Society: Require Insulation?

Convection Radiation 4.4 Energy, Heat, and Molecular Theory Phase Change A Closer Look: Passive Solar Design Evaporation and Condensation 4.5 Thermodynamics The First Law of Thermodynamics

 0.92hp

The Second Law of Thermodynamics The Second Law and Natural Processes Overview This chapter presents a short historical development of ideas about heat, and then develops the theoretical basis for the modern understanding of temperature and heat. Concepts of heat and the kinetic molecular theory are closely linked, and observations of heat interactions provide evidence in favor of the kinetic theory. In turn, the particle nature of matter becomes more realistic from the quantitative and qualitative evidence provided by heat. The modern understanding of heat, which is derived from thermodynamics, is that heat is a measure of the amount of internal energy transferred from one object or system to another object or system.

Heat corresponds to work at a molecular level, and they are not considered separate concepts.

Energy, work, and heat are measured in units of joules in science classes for science majors. Calories and Btus are also discussed in this text for nonscience majors because these are the heat measurements in everyday use. A measured amount of heat will affect the temperature of any substance, but the change in temperature will vary with the substance.

Each substance has its own specific heat, which is usually smaller than that of water. Thus, less heat (internal energy) is required to raise the temperatures of these substances and, as they cool, they release less heat, or release less internal energy, than water. Conduction, convection, and radiation are important concepts of heat flow, and understanding them will become more important as present-day lifestyles place more and more demands on the energy supply.

Suggestions 1. A Brownian motion device and a microscope projector (perhaps borrowed from the zoology department) can be used to show the random kinetic energy involved in Brownian motion. A few crystals of potassium permanganate in a tall, graduated cylinder filled with water can be situated so it will remain undisturbed for a week. The resulting diffusion of the purple color can be related to the observed Brownian motion.

2. Linear expansion of heated solids can be demonstrated with a bimetallic strip, which can be compared to the coiled strip in many home thermometers and thermostats. An air thermometer can be demonstrated with an inverted Florence flask with a one-hole stopper and glass tube. An iron ring on a ring stand supports the flask with the glass tube extending into a beaker of colored water. When your hand air warms the flask bubbles come from the tube in the water, providing evidence of expansion of the air inside the flask. As the flask cools water is forced into the tube by atmospheric pressure.

The water level inside the tube is highly sensitive to temperature variations but is not

used as a thermometer because it is also highly sensitive to atmospheric pressure variations.

3. The concept of specific heat can be demonstrated by simultaneously heating a block of iron and an equal mass of water over burner flames. When the water is warm a few drops transferred to the iron will sizzle, indicating the much higher temperature of the iron. The specific heats of water and iron can then be compared and discussed.

4. The concepts of conduction, convection, and radiation may be illustrated with the demonstration conductometer, the convection box, and the radiation outfit, all available from scientific supply houses. Point out that the oven advertised as ―convection oven‖ means forced convection. All ovens heat food through natural convection. A ―convection oven‖ has a fan, which mechanically mixes the air.

5. The latent heat absorbed or released during a change of state is interesting to students.

Ice cubes at 0˚ C placed in a glass of water at 0˚ C absorb latent heat as they melt, and no temperature change is observed during the melting process. Heat obtained from the surroundings is required to melt the ice at 80 cal per gram. When water freezes the same amount of energy (latent heat) is released. Since there is no temperature change, latent heat is not involved in kinetic energy. Since the same amount of heat is released during freezing as is absorbed during melting, the heat must be ―hidden‖ as changes in potential energy. Relate this energy transfer to the energy required to create potential energy in a mechanical system (lift a chair to a tabletop; ice melts). The chair (and the liquid water) has more potential energy as a result of the work done (lifting the chair; separating the molecules from the solid state). When the chair is returned to the floor (the liquid water freezes), the potential energy (latent heat) is released.

6. The concept of relative humidity can be readily demonstrated with a collapsible plastic cup available from most drug stores. Half fill a fully extended cup with water, then ask the class what percent of the cup is filled. The analogy is that air has half the water it can hold at a particular temperature (50 percent relative humidity). Drop the upper ring on the cup, which reduces the capacity about 25 percent (depending on the particular cup used). This is analogous to reducing the air temperature, which reduces the air capacity to hold water. Because of dropping the ring, the cup is now 75 percent full (75 percent relative humidity). Drop the next upper ring and the cup is now 100 percent full, an analogy to saturated air and 100 percent humidity. Drop another ring and water will spill to the floor. Students will probably exclaim ―rain!‖ to which you will ask if rain falls from a clear sky. Point out that the falling water represents condensation, which results in dew or the formation of a cloud. Rain falls from clouds, not clear air.

7. Relationships between heat, boiling, evaporation, condensation, air pressure, and atmospheric pressure can be demonstrated with an ordinary aluminum soda can and a burner. Rinse the can and pour several centimeters of water into the can, asking the class to note how much water you are pouring into the can. Using laboratory tongs, hold the can over a burner flame (with the palm side of your hand up) until the water boils for

a minute. Point out that the visible mist coming from the can is not steam (gases are invisible) but is condensed water vapor just like the droplets in a cloud. Quickly invert the can in a large beaker full of ice water. The can will be immediately crushed with a loud pop. As you raise the can from the beaker of water, it will be obvious that more water is now running from the can than you poured in originally. Ask the students to explain what happened.

8. Additional demonstrations: (a) Measure the temperature of equal amounts of cold and warm water, then mix them together in an empty glass beaker. Take another temperature reading, showing the final temperature is nearly midway between the two initial temperatures. Discuss Q, m, c, T, and why the temperature was not exactly midway. (b) Commercial demonstration devices are available to compare the rates of heat conduction in metals. One such device, for example, has rods of iron, copper, aluminum, nickel, and brass that are set into a metal ring. A thumbtack is attached to the end of each bar with candle wax and the center ring is heated. (c) Commercial demonstration devices are available to show convection in a smoke box. One such device consists of a box with two openings with chimneys. One side is of a transparent material such as glass or plastic. A small, lighted candle (or other heat source) is placed under one chimney and a smoke source is held just over the opening not above the candle. Convection currents can be observed as the smoke moves down one chimney, through the box, and up the other chimney over the heat source.

For Class Discussions 1. A metal lid is stuck on a glass jar. What will help you open the jar? a. Heat it under running water. b. Cool it. c. Heat it under running water, then quickly cool it. d. Nothing; you are stuck.

2. When you add heat to a substance the temperature a. always increases. b. sometimes decreases. c. might stay the same.

3. The cheese on a hot pizza takes a long time to cool because it a. is not elastic. b. low specific heat. c. high specific heat.

d. has a white color.

4. The great cooling effect produced by water evaporating comes from its high a. conductivity. b. specific heat. c. latent heat. d. transparency.

5. Anytime a temperature difference occurs, you can expect a. cold to move where it is warmer, such as cold moving into a warm house during the winter. b. heat movement from cold to warmer regions. c. heat movement from high temperature regions. d. no energy movement unless it is warm enough.

6. The specific heat of copper is roughly three times as great as the specific heat of gold.

Which of the following is true? a. If the same amount of heat is applied to equal masses of gold and copper, the copper will become hotter. b. Copper heats up three times as fast as gold. c. A piece of copper stores three times as much heat as the same mass of gold at the same temperature. d. The melting temperature of copper is roughly three times that of gold.

7. The heat death of the universe is a time in the future when the universe is supposed to a. have the same temperature. b. have a very high temperature everywhere in the universe. c. freeze

Answers: 1a, 2c, 3c, 4c, 5c, 6c, 7a

Answers to Questions for Thought

1. Temperature is a measure of the average kinetic energy of the molecules of a substance.

Heat is the total internal energy of the molecules involved in an energy transfer.

2. As the temperature of a solid increase the vibrations of the individual molecules become larger. When these vibrations become larger, the average distance between the molecules increases to accommodate these larger oscillations, and the solid expands. In a liquid or a gas, the individual molecules move faster as the temperature increases, and the collisions between individual molecules become more violent. Since the molecules are moving faster, they move farther apart as they travel a larger distance in the time between collisions.

3. Tight packing would tend to decrease the insulation value of glass wool because it would squeeze the wool together and give the heat more paths to travel. It is the presence of many small pockets of air, with unattached molecules, that gives glass wool and other similar insulation materials their insulating properties.

4. The vacuum between the walls prevents heat transfer by means of convection or conduction, while the silvered walls reflect radiated energy back into (or away from) the food, preventing energy transfer by radiation.

5. Cooler air is denser than warmer air. This denser air weighs more per volume than the warmer air and pushes the warmer air out of the way as it sinks down to its lowest level.

The warmer, less dense air sits on top of the cooler air because it weighs less per volume.

6. Air is not very dense and conduction is not very efficient at transferring energy because the molecules are much farther apart than they are in solids or liquids.

7. Mechanical energy can be converted to heat as it changes from external mechanical energy to the internal kinetic energy of the molecules. A given quantity of mechanical energy always yields a known amount of heat.

8. When people refer to the ―Calorie content of food,‖ they are referring to the amount of chemical energy available from the food. One way to measure the chemical energy of foodstuff is to find out how much heat is released by complete oxidation. A Calorie (kcal) is a measure of the heat release and thus is a measure of the chemical energy released.

9. The metal is more efficient at conducting heat away from your hand than wood, so it feels cooler because your hand senses heat leaving your body.

10. The latent heats of fusion and vaporization go into or are released from internal energy during a phase transition. There is no temperature change associated with these heat transfers, so they are ―hidden.‖ 11. Condensation occurs when more vapor molecules are returning to the liquid state than are leaving the liquid state. When a water vapor molecule joins a group of liquid water molecules, it has to give up its latent heat of vaporization. This heat is transferred to the surrounding air molecules such as the air in the bathroom.

12. The 10 pounds of ice provide more cooling because as the ice undergoes the phase change into water, it absorbs heat. Ten pounds of ice water simply absorbs heat according to the value of its specific heat until it reaches room temperature and therefore absorbs less heat.

13. Water condenses out of the air onto the cooler surface of a glass because the air near the glass is cooled, lowering its temperature to the dew point. Since the warmer air can hold more water vapor in the summer, it would have more water vapor to condense.

Therefore, you would expect more condensation in the summer.

14. One-hundred-degree Celsius steam contains more energy (540 cal/g) than 100°C water, so the steam burn would be more severe.

15. A heat pump uses energy to move heat from a colder region to a warmer region, which is in the opposite direction of natural heat flow.

16. Entropy is the thermodynamic measure of disorder, which means the lack of patterns and coherent arrangements. Ice is a highly organized crystal framework and water vapor is a randomized, spread out arrangement of water vapor molecules. Liquid water is between this highly organized phase of ice and the dispersed water vapor. Therefore, entropy increases as ice melts to liquid water, then water is evaporated to water vapor.

17. The answer is no. Mechanical energy can be used to do work, but then becomes dispersed as heat through energy form conversions and friction. The resulting heat could be converted to do more work only if there is a sufficient temperature difference.

Temperature differences do not last long, however, as conduction, convection, and radiation quickly disperse the energy even more.

For Further Analysis 1. Table salt takes the shape of a container and has a definite volume. These are the properties of a liquid.

2. Similarities – both heat and temperature involve internal energy, the energy of molecules. Difference – temperature involves an average of the random kinetic energy of the molecules in a body; heat involves the total internal energy, both kinetic and potential. Temperature of a body can be measured anytime; heat can be measured only by adding it or removing it from a body.

3. Clarifying the meaning of these words will show that answers will vary.

4. Analysis will show that copper is more practical and more energy efficient.

5. Developing criteria for evaluation will depend on the local climate.

6. Analysis will show that moving heat without the latent heat of vaporization would restrict the movement to that would take place by conduction, convection, or radiation, which would not be practical.

7. Evaluating and pursuing an alternative concept of the future will result in answers that vary, but should be logical.

Group B Solutions 1.

5 TF  32  9 5   98  32  9 5   66  9  37

TC 

TK = TC + 273 = 37 + 273 = 310 K

2.

Q  mcT  kcal    0.25 kg   0.22  10.0C  kgC    0.55 kcal

3.

1 2 mv 2  1 km m 1.00 h   1,000.0 kg   90.0  1,000   2 h km 3,600 s  

K.E. 

2

m   500.00 kg   25.0  s  2 m  500.00 kg  625 2 s kg  m  312,500 2  m s  313,000 J 1.00 cal Q  313,000 J   74,700 cal  74.7 kcal 4.184 J

4.

Q  KE and KE 

Q  mcT  mcT 2

T



1 m 1.0kg   5.0  1.00 cal  1.00 kcal 2 s    1, 000.0 cal  kcal  1.0 kg   0.11  4.184 J   kgC  

 0.030 C

5.

1 2 1 mv  Q  mv 2 2 2  1 2   1.00 cal    mv    1 2 2   4.184 J   mv  T  2 mc

Q  PE

and PE  n  mgh  where n  number of times up stairs

 Q  n  mgh  and n 

n 

6.

1.00 kcal   4,184 

Q mgh

J   kcal 

m  60.0 kg   9.8 2  10.0 m  s  

 0.71 times

Q  mcT  kcal   5.00 102 kg  0.056  89.0C  20.0C  kgC    0.19 kcal





7.

Q  mcT  m  

Q cΔT 0.19 kcal  kcal  1.0 kg C   0.75 C   

 0.25 kg

8.

W P mcT W  Q  t  P  cal   250.0 g  1.00  100.0C  20.0C  g C   t  J   1.00 cal     300.0   s   4.184 J   P 

W t

 t 

 279 s, and 279 s s 60.0 min



279 60.0

s min  1 s

 4.65 min

9.

Q  mcT  c  

Q mT 2.6 kcal  0.2000 kg  65 C 

 0.20

kcal kgC

10.

Q  mLf  kcal   1.00 kg   80.0 kg    80.0 kcal

11.

Q1  mcT  cal    500.0 g  1.00   80.0 C  g C    4  4.00  10 cal Q2  mLv  cal    500.0 g   540.0  g    2.700  105 cal QTotal  Q1  Q2



 

 4.00  104 cal  2.700  105 cal  3.10  105 cal

12.



Q1  mcT  kcal   1.000 kg   0.48   20.0 C  kg C    9.6 kcal Q2  mLv  kcal   1.000 kg   540.0  kg    540.0 kcal Q3  mcT  kcal   1.000 kg  1.00  10.0 C  kg C    10.0 kcal QTotal  Q1  Q2  Q3

  9.6 kcal    540.0 kcal   10.0 kcal   559.6 kcal

13.

Q1  mcT  kcal    250.0 kg   0.028   308.0 C  kg C    2,156 kcal  2, 200 kcal Q2  mLf  kcal    250.0 kg   5.5  kg    1,375 kcal  1, 400 kcal QTotal  Q1  Q2

  2, 200 kcal   1, 400 kcal   3, 600 kcal

14.

W  J  QH  Q L  J  400.0 kcal  300.0 kcal  kcal J  4184 100.0 kcal  kcal J  kcal  4184  100.0 kcal  418, 400 J  4184

 418.4 kJ

15.

W  J QH  QL  J  60.0 kcal  40.0 kcal  kcal J  4184  20.0 kcal  kcal J  kcal  4184  20.0 kcal  83,680 J  4184

 83.7 kJ

5

Wave Motion and Sound

Contents 5.1 Forces and Elastic Materials Forces and Vibrations Describing Vibrations 5.2 Waves Kinds of Mechanical Waves Waves in Air 5.3 Describing Waves 5.4 Sound Waves Sound Waves in Air and Hearing Medium Required A Closer Look: Hearing Problems Velocity of Sound in Air Refraction and Reflection Refraction Reflection Interference Constructive and Destructive Beats

5.5 Energy of Waves How Loud Is That Sound?

Resonance 5.6 Sources of Sounds Vibrating Strings Science and Society: Laser Bug Sounds from Moving Sources Case Study: Doppler Radar Overview Sound is an ideal way to present velocity, frequency, and wavelength as well as other measurable characteristics of all types of waves. Some attributes of sound are subjective.

The same holds true of electromagnetic waves and others but to a lesser extent. Experience and training provide recognition of the variance present in sound waves, such as pitch, loudness, and quality. With proper demonstrations, you can determine the subjectivity of these measures and ascertain which students are musically inclined or trained.

The chapter begins with vibrations and the characteristics of vibrations, and then logically proceeds to the waves, or disturbances, that are produced by these vibrations.

Characteristic wave terms are introduced, and then used to explore some of the more interesting sound phenomena to which students can relate. Students are familiar with echoes but many have no conception of their cause. It is subjective if a listener hears a reverberation or an echo. There are many methods by which various musical sounds are produced. All sources of musical sounds are represented in the chapter, along with some theory behind some musical notes. The Doppler effect applies to all waves, but it is easier to discuss and to demonstrate with sound. Any constant sound that is in motion relative to the listener will produce the effect. Light also undergoes the Doppler effect, and this application is discussed in other chapters.

Suggestions 1. To illustrate how vibrating matter creates sound, place one end of a ruler, metal strip, or meter stick on the edge of a desk. Hold the end down securely and pluck the opposite end. Practice will enable you to determine proper adjustments. Students should also relate the frequency of the sound produced to the length and rate of the vibrating object.

The vibrations of a struck tuning fork are difficult to observe. They can be illustrated by holding a vibrating tuning fork in one hand and a sheet of paper in the other, lightly touching the vibrating end against the paper. A dramatic (and somewhat humorous) illustration is obtained by plunging a vibrating tuning fork into a beaker of water.

2. Vibrate your arm up and down as you hold a piece of chalk against the chalkboard, walking along the length of the board. Point out that the wave trace obtained is a graph of the vibration and not in itself a wave. Compare the wave traces obtained with more rapid vibration (greater frequency) and more energy (greater amplitude). Ask if anyone hears your vibrating arm, which leads to a discussion of audible waves.

3. A twenty-foot long or so one-inch diameter helical spring is ideal to demonstrate both longitudinal and transverse waves. Shaking the coil from side to side produces a transverse wave, while holding the spring taut and releasing a group of bunched-up coils produces longitudinal waves. The motion of a string tied to the center part clearly shows the characteristic disturbances produced by these two kinds of waves. The coil can also be used later to illustrate standing waves at several different frequencies.

4. A ―trick‖ demonstration involving forced vibrations maintains interest and helps teach the basic wave terms. State that you will illustrate what happens to a sound wave when it is inside a container. Strike a tuning fork and hold it in one hand with the rod end near the tabletop but covered by your hand. Tell the class that you are going to grasp a wave by its crest, and then drops it into a beaker (or some other container). Act as if you are grasping a crest with your thumb and finger near the end of the vibrating tuning fork, then act as if you drop the wave into the container. The trick here is to touch the base of the rod firmly (but quietly) to the tabletop as you ―release the wave‖ over the beaker with your other hand. With a little practice, it will seem as if there is an increase in loudness as you ―drop‖ the wave. You may need to do this several times before someone catches on. You now have the class's undivided attention as you explain the concept of forced vibrations—that the tuning fork touched to the table starts the whole table vibrating. This is an ideal place to reinforce the conservation of energy concept.

Compare the time that the whole table vibrates (with a louder sound) with the time that the tuning fork only vibrates (with a softer sound).

5. A signal generator can be used to illustrate the frequency ranges that students of varying ages are able to hear. Two signal generators can be used to illustrate the beat concept.

Hooking the generators to an oscilloscope provides a visual representation of what they are hearing.

6. Additional demonstrations: (a) Do the classic demonstration showing that the transmission of sound requires a medium. Place an electric bell inside a vacuum pump bell jar, evacuating the jar as the bell rings. Note the bell hammer continues vibrating as the sound level dies out. Stop the pump and restore air to the jar to hear the bell again. (b) Use citizen band radios or mobile telephones to measure the speed of sound over a distance. One student signals the beginning of a sound over the radio or telephone and a student at the other end starts a stopwatch at the signal, stopping it when the sound is heard. The signal used will depend on what is available locally. Measure the distance and make the correction for temperature.

(c) Use a commercial demonstration device that varies the height of a flame with the frequencies of sounds. (d) Demonstrate resonance with commercial resonator boxes fitted with identical frequency sounding bars or tuning forks. (e) Demonstrate beats with commercial resonator boxes fitted with tuning forks that are 1 Hz apart in frequency. (f) Ask the class to close their eyes, and then drop a previously hidden metal drill bit.

Ask the class to open their eyes as you hold up the bit and a board, asking which you dropped. Explain the concept of natural frequency.

For Class Discussions 1. How can astronauts talk to one another on the Moon, where there is no air? a. Air is not needed if one is standing with heavy boots on something solid. b. By radio transmissions. c. By staying inside a pressurized space suit. d. This is impossible; they could not talk.

2. An airplane moves over your location at a speed greater than the speed of sound, so you should hear a. nothing since the plane was moving faster than sound. b. nothing, then a sonic boom, followed by the distant sound of engines. c. a sonic boom only at the instant the plane breaks the sound barrier, then silence. d. two sharp sonic booms, followed by silence.

3. Does a high frequency sound travel faster than a low frequency sound? a. Yes. b. No. c. Sometimes it does, depending on the conditions.

4. What happens if a source is moving toward you at a high rate of speed? a. The sound will be traveling faster than from a stationary source. b. The sound will be moving faster only in the direction of travel. c. A higher frequency will be heard by you only. d. A higher frequency will be heard by all observers in all directions.

5. What happens if you are moving at a high rate of speed with a sound source? You will hear a. a higher frequency than people you are approaching. b. the same frequency as people you are approaching. c. a frequency that is the same as from the source when it is not moving.

6. During a track and field meet, the time difference between seeing the smoke from a starter's gun and hearing the ―bang‖ would be less a. on a warmer day. b. on a cooler day. c. if a more powerful shell is used. d. if a less powerful shell is used.

7. At the same temperature, the gas that would carry a sound with the greatest velocity would be a. oxygen. b. hydrogen. c. carbon dioxide. d. The velocity would be the same in each gas.

8. As you go up a mountain the air becomes less dense, and with everything else constant, the overall velocity of sound a. increases steadily with increasing altitude. b. decreases steadily with increasing altitude. c. increases slowly at first, then rapidly with increasing altitude. d. does not change.

Answers: 1b, 2b, 3b, 4c, 5c, 6a, 7b, 8d.

Answers to Questions for Thought 1. A wave is a disturbance that moves through a medium such as a solid or the air.

2. No, because there is no force acting on the air to return it to its original position after the wave has dislocated it.

3. Loosen. Since the beat frequency depends upon the difference between the two frequencies, you wish to go in the direction of fewer beats per second.

4. There is no medium such as air to transmit sound on the moon.

5. The condition where the frequency of an external force matches the frequency of an object is resonance.

6. Gas molecules have a greater kinetic energy and move faster in warm air than in cold air.

These molecules are able to transfer an impulse from one molecule to the next faster.

7. Longer wavelengths have lower frequencies. Since the velocity of sound is equal to the product of the frequency times the wavelength, the velocity is a constant.

8. The energy of the sound wave is eventually dissipated into heat.

9. The presence and strength of various overtones determine the characteristic sound of a musical note.

10. The sonic boom is from the building up of a pressure wave in front of the moving aircraft. Since this pressure wave is present as long as the plane is moving faster than the speed of sound, the aircraft continually makes a sonic boom.

11. An echo is the return of a sound wave to its source after the wave has been reflected.

12. They all produce standing waves or resonance in whatever is oscillating.

For Further Analysis

1. If the speed of sound decreased with frequency, all the musical notes would become separated with higher frequencies arriving first.

2. Similarities – both longitudinal and transverse waves are mechanical disturbances that move through matter. Differences – In a longitudinal wave the disturbance acts in a

direction parallel to the direction the wave is moving; In a transverse wave the disturbance acts in a direction perpendicular to the direction the wave is moving.

Examples will vary.

3. Possible explanation: The empty room has more echoes that bounce around and garble the sound.

4. Starting with two distinct tones, a fast beat develops, which slows as the frequencies approach each other while tuning the instrument. It slows to a single pitch when tuned.

5. Two identical sounds moving through the air that are 180 degrees out of phase will cancel each other.

6. Vibrations are the sources of all sounds, which is supported by observation as well generalizations.

7. Unlike objects, sounds waves have the ability to pass through one another.

8. If the marching band happens to match the natural frequency of the bridge, resonance could start the bridge swaying and possibly cause damage.

Group B Solutions 1.

1 f 1 = 1 6 s 1  s 6  0.16 s

(a) T =

 0.2 s (b) v  f    6 Hz    3m   18 m/s = 20 m/s

2.

 0.600 m/s  vTP ( m / s )  v0    TP  C   m  0.600 m/s   331     20.0C  s  C  m m  331  12.0 s s m  343 s v vf   f m 343 s  1 20.0 s 343 m s   20.0 s 1  17.15m  17.2 m 3.

f b  f 2  f1

  520 Hz    516 Hz   4 Hz

4. m   0.600 s  vTP (m/s)  v0    TP   C    m  0.600  m  s  20.0C   331    s  C    m m  331  12.0 s s m  343 s

vf  

v f

m s  1 1  106 s 343 m s   1  106 s 1  3.43  104 m 343

 3  104 m

5. Assume room temperature (20.0°C) to obtain the velocity (yes, you can have room temperature outside a room): m   0.600 s  vTP (m/s)  v0    TP   C    m  0.600  m  s  20.0C   331    s  C    m m  331  12.0 s s m  343 s v

d t

d v 400.0 m  m 343 s 400.0 m s   343 1 m  1.166180758s

 t

 1.17s

6. ft    2.00 s  vTP (ft/s)  v0    TP   C    ft   2.00  ft  s  20.0C   1087    s  C    ft ft  1087  40.0 s s ft  1127 s d v=  d = vt t ft     1127  1.00s  s  ft  1127  1.00  s s  1127 ft

The distance to the building is half the distance the sound traveled, so 1127  563.5ft 2  564 ft

7. v=

d  d = vt t m    1530.0   2.250s  s   m  1530.0  2.250 s s  3, 442.5 m  3, 443m

The sonar signal traveled from the submarine to the ship, and then back to the submarine, so the distance to the ship is half of the distance traveled:

3, 443m  1, 722 m 2

8.

vf 1    2.5m   600.0  s  1  2.5  600.0 m  s m  1,500 s

9. m   0.600 s  vTP (m/s)  v0    TP   C     m  0.600   m s  20.0C   331    s  C    m m  331  12.0 s s m  343 s

v=

d t

 d = vt m    343   2.50s  s   m  343  2.50 s s  857.50 m  858 m

10. According to table 5.1, sound moves through water at 25°C with a velocity of 1,497 m/s and through seawater at 25°C with a velocity of 1,530 m/s. Therefore, (a) v =

d  d = vt t m    1, 497   6.00s  s   m  1, 497  6.00 s s  8,982 m  8.98 km

(b) v =

d  d = vt t m    1,530   6.00s  s  m  1,530  6.00 s s  9,180 m  9.18 km

11.

v  f   440.0 Hz    78.0 cm   3.43  104

12.

cm (or 343 m/s) s

v  f f  256.0 Hz

  2   65.23 cm 

1  v   256.0   2  65.23 cm  s   3.340  104 cm/s

13.

 a  T  5.0s b

f 

1 T



1 5.0s

 0.20 Hz

14. v = f   

v f

m s   1 750.0 s 343.0 m s   750.0 s 1  0.4573 m 343.0

15.

v 

f 

v 

 20.0 Hz 17.2 m 

 343 m/s

(b)

v 

 200.0 Hz 1.72 m 

 344 m/s

(c)

v 

 2000.0 Hz  0.172 m 

(d)

v 

 20, 000.0 Hz  0.0172 m 

(a)

 344 m/s  344 m/s

16. (a) d v  t

d  t  v



d

t

ft    2.00 s  and v  v0    Tp  so  C   

ft    2.00 s  v0    Tp   C     5280.0ft  ft   2.00  ft  s  0.0C  1087   s  C     4.9s

(b)

Tp  20.0C  t  4.7s

(c)

Tp  40.0C  t  4.5s

(d)

Tp  80.0C  t  4.2s

17. m   0.600 s  d v   d  vt and v  v0    Tp  so t  C     m   0.600 s  d  v0    Tp  t  C      m  0.600   m  s 10.0C    10.0s    331    s  C         391m 391 m 2  196 m 

18.

TC 

5 TF  32  9

5  90.0  32  9  32C



ft    2.00 s  v  v0    Tp   C     ft   2.00   ft s  32C   1087    s  C    ft ft  1087  64.0 s s ft  1151 s v 

d t

d v 5280 ft  ft 1151 s  4.59 s

 t 

19. v  f   

Air:

v f

ft s  1 600.0 s  1.812 ft 1087.0

Water: ft s   1 600.0 s  8.200 ft 4920.0

6

Electricity

Contents 6.1 Concepts of Electricity Electron Theory of Charge Electric Charge Static Electricity Electrical Conductors and Insulators Measuring Electrical Charges Electrostatic Forces Force Fields Electric Potential 6.2 Electric Current The Electric Circuit The Nature of Current Electrical Resistance Electrical Power and Electrical Work 6.3 Magnetism Magnetic Poles Magnetic Fields The Source of Magnetic Fields Permanent Magnets Earth’s Magnetic Field 6.4 Electric Currents and Magnetism Current Loops Applications of Electromagnets Electric Meters Electromagnetic Switches Telephones and Loudspeakers Electric Motors 6.5 Electromagnetic Induction A Closer Look: Current War Generators Transformers 6.6 Circuit Connections Voltage Sources in Circuits Science and Society: Blackout Reveals Pollution Resistances in Circuits A Closer Look: Solar Cells Household Circuits

Overview This chapter presents the basic concepts of charge and current, and students develop the understanding that electricity is another form of energy perfectly analogous to other forms of energy. It begins by discussing static electricity, which is basic to any study of electrical phenomena, and some very basic atomic theory. Static electric charges are ―at rest‖ but are produced by an excess or deficiency of electrons brought about by friction, generally between unlike insulators.

Electric current is defined as the flow of charge rather than the flow of electrons.

Current in a conductor approaches the velocity of light, a rate of movement not possible for an electron moving from atom to atom under ordinary circumstances. To move an electric charge against the electric field of other electrons requires work, creating electric potential energy that is in every way analogous to gravitational potential energy. In either case work is done against a field to develop the potential energy. The same quantity of work is realized (disregarding losses) when the potential energy is utilized at some place in a circuit. When a joule of work is done on a coulomb of charge to move it against an electric field, the difference in potential between the points is a joule per coulomb. This is called a volt.

Students seem to have two difficulties with this concept, (1) that a coulomb is a quantity of charge and (2) that volt means work per charge. They must be helped over this difficulty and understand that a current of one coulomb per second is called an ampere. Understanding voltage and amperage is necessary before they can be combined to discuss resistance (Ohm's law), work, and power meaningfully. Avoid the temptation to discuss the differences in resistors, voltage, and current in series and parallel circuits unless students are majoring in programs of a technical nature.

Magnetism and its properties are of interest to students, and this chapter presents the major characteristics of magnets and magnetic fields. The fundamental relationship between electric and magnetic fields is discussed and then applied to many common phenomena in the environment and to technological devices. The generation and conditioning of alternating current between its source and its consumption is considered a primary way of transferring energy long distances.

The active cutting of the imaginary lines of force that surround a magnet by a conducting wire causes current to flow in the conductor. If the direction of the moving magnet is reversed, the current flow also reverses. This constant reversal of the moving magnet produces alternating current. Home appliances operate on 60-hertz alternating current. A coil of wire rotating about the poles of a magnet also would produce alternating current. Devices that convert mechanical energy into electrical energy are called generators.

Motors convert electrical energy into mechanical energy. Except for efficiency loss due to resistance and other uncontrollable factors, a combination of the two devices could produce a seemingly endless supply of electricity.

To reduce energy loss from resistance through heating, transformers are used to step up alternating current since the current is inversely proportional to voltage if power is held constant. Alternating current is stepped back down before it enters the home. Direct current cannot be stepped up efficiently without complex circuitry, it cannot be stepped down as easily as alternating current, and it is more costly to generate than alternating current.

Suggestions 1. Demonstrate static electric phenomena with hard rubber rods, cat fur, glass rods, and silk cloth. Use electroscopes and pith balls to show accumulated charges. If you are in an area of high humidity, use an electrophorus in place of the rods, fur, and silk cloth.

Demonstrate how to generate static electric charges, the identity of the charge that accumulates on an electroscope, how like and opposite charges affect each other, and how static electricity accumulates on the surface of a conductor.

2. Bring a negatively charged rod near a small but steady stream of running water and note how the water is attracted. Ask the class what the charge of the water appears to be.

Bring a positively charged rod near the stream of water and note the effect. These observations point out how both electric charges affect the neutral charge of the water.

3. Demonstrate Ohm's law with resistors of known values connected to a large demonstration ammeter and voltmeter. Take readings quickly to avoid heating (and changing the value of the resistors), and let the class do the calculations.

4. The relationships between amperage, voltage, work, and power are popular among students when applied to the cost of using certain electrical appliances. For example, how much does it cost to use a 1,300 watt hair dryer for 15 minutes?

5. The magnetic field of a magnet can be demonstrated to a large class with an overhead projector. Place a clear plastic sheet over a bar magnet. Sprinkle iron filings on the sheet and tap the sheet with your finger. Arrangements that show attraction and repulsion between two magnets can also be dramatically illustrated in this manner.

6. Use a ring stand and clamps to support a length of stiff copper wire vertically through the center of a flat piece of cardboard. Sprinkle iron filings around the wire, then connect the ends to a dry cell or power supply. Tap the cardboard, then disconnect the power supply immediately when the concentric circles form. Use the left-hand rule to determine polarity of the magnetic field.

7. Magnetize a large paper clip (or soft iron nail) by placing it on one end of a strong bar magnet, then tapping it. Remove the clip from the magnet and show that it is magnetic by bringing it near a second, unmagnetized paper clip. Throw the magnetic paper clip (nail) hard against the floor, and then check it again with a different paper clip to show that it has lost most of its magnetism. Explain the entire procedure with the magnetic domain concept.

8. Connect a coil of wire to a large demonstration galvanometer and move the coil toward and away from the magnetic field of a strong magnet (e.g., from a speaker). Show that the needle of the galvanometer moves in one direction when the wire coil moves toward the magnet and in the other direction when the wire coil moves away from the magnet.

Illustrate that the movement is relative by now moving the magnet toward and away from the stationary coil of wire.

9. The operation of an electric motor or generator can be demonstrated with the use of a St. Louis motor, a variable direct current power supply, and a small light bulb. The adjustments of the magnets are critical but easily accomplished. Check to be sure that the bar magnets are installed with the poles of each magnet turned opposite the poles of the other.

10. Additional demonstrations: (a) Demonstrate the nature of static electricity with suspended pith balls, electroscopes, a rubber rod rubbed with cat’s fur, and a glass rod rubbed with silk. Suspend inflated rubber balloons with thread, and then give them a negative charge by rubbing with cat’s fur. (b) Use a small hand-turned generator to demonstrate that work is done to generate electric current. Vary the speed to show that the current generated is directly proportional to the work done. (c) Demonstrate Ohm’s law using a large ammeter and voltmeter with resistors of known values. (d) Show the relationship between a magnetic field and polarity by sprinkling iron filings on a transparent sheet of plastic over a magnet. Ask students to predict shape of fields around horseshoe magnets, bar magnets, and others, then check their predictions. (e) Display rheostats, relays, meters, telephone parts, speakers, and other devices that work with electromagnets. (f) Display a simple St. Louis type motor connected to a dry cell to show how current moving through the motor can do work. Replace the dry cell with a galvanometer, and then give the armature several whirls to show that current can be generated by doing work.

For Class Discussions 1. Three pieces of amber are hung from threads, and then each is charged by rubbing piece A with fur, piece B with silk, and piece C with nylon. It is now observed that piece A and B repel each other and that Piece B and C repel each other. This means a. pieces A and C have opposite sign charges. b. pieces A and C have the same sign charge. c. piece B does not have a charge. d. all three pieces have the same sign charge.

2. If the pieces of amber in the previous question acquired a positive charge, the each of the rubbing materials a. acquired an equal negative charge. b. acquired a positive charge, too. c. acquired a charge, but not equal and opposite to the amber.

3. When a substance acquires a charge from an excess of electrons, would the mutual repulsion repel them uniformly throughout the substance? a. Yes. b. No. 4. Considering the separation of charges, is it possible to have a high voltage without any current? a. Yes. b. No. 5. Which of the following is a measure of electrical work? a. kilowatt b. C c. kWh d. C/s 6. A bird lands on a non-insulated, 80,000 volt high line. Will it receive a shock? a. Yes. b. No. 7. When an object acquires a negative charge it actually a. gains mass. b. loses mass. c. has a constant mass.

8. A positive and a negative charge are initially 2 cm apart. What happens to the force on each as they are moved closer and closer together? It a. increases while moving. b. decreases while moving. c. remains constant.

9. The current in the secondary coil of a transformer is produced by a a. varying magnetic field. b. varying electric field. c. constant magnetic field. d. constant electric field.

10. The nature of the force that enables an electric motor to do its job is a. electric. b. magnetic. c. electromagnetic

Answers: 1d, 2a, 3b (just on the surface), 4a, 5c, 6b (no voltage difference on bird), 7a, 8a, 9a, 10b.

Answers to Questions for Thought 1. The balloon has a net charge as a result of being rubbed. When the balloon is brought near a wall, the net charge on the balloon moves electrons around in the wall. As a result, a small region near the balloon has a net charge of opposite sign than the balloon.

The overall wall is still electrically neutral; there are now small regions that have net charges. The force from the opposite signed charges in the balloon and the wall causes the balloon to stick to the wall. There it will stay until enough charge has leaked away to cancel the charge on the balloon.

2. Excess charge is building up on your body from the carpet as you walk across it. When a metal object is touched, the charge flows out of your body, through the lower resistance of the metal. It finds a path into the ground, which supplied the charge to make up for what you removed from the carpet.

3. An electron carries a negative charge and can be moved to and from objects relatively easy. Since electrons cannot be divided into parts that can move separately, the smallest charge it is possible to have or to move is the charge of one electron. The charge of one electron is referred to as the fundamental charge.

4. The electrons move rapidly inside a wire bouncing against each other like molecules in a gas. Since so many collisions occur, an individual electron cannot move from one end of a wire to another rapidly. The electric field inside the wire, which exerts a force on the electrons, can move rapidly though the wire because it does not require something to carry it. The force from the electric field gives the electrons a drift velocity, which constitutes a current.

5. A kWh is work multiplied by time. Since a watt is energy per time, a kWh is a unit of energy or work.

6. In direct current (dc), the current always flows in a single direction. In alternating current (ac), the flow of current changes direction with a regular frequency.

7. A magnetic pole is a region where the force of magnetic attraction seems to be concentrated. The pole that seeks, or points to a generally north direction, is called a north pole, and the other pole is called a south pole.

8. In an unmagnetized piece of iron, the magnetic domains are pointing in random directions such that the net field is zero. In a magnetized piece of iron, most of the domains are aligned so that their fields add to make a larger field.

9. If the voltage is small, the current is large for a particular amount of power. Increasing the voltage decreases the current. Large currents promote many collisions of electrons inside the wire with other electrons and positive ions. Each collision takes energy from the electric field, diverting it into kinetic energy of the positive ions and heating the wire, so there are fewer power losses with lower currents. Thus a higher voltage means less power loss since the current is lower.

10. The electromagnetic generator uses induction to generate a current in loops of wire moving in a magnetic field. Electrons in the loops of wire are forced toward one end by the magnetic field, which sets up a potential difference.

11. The earth's north magnetic pole is actually a magnetic south pole located near the geographic North Pole.

12. The electron is moving, creating its own magnetic field. The interaction between the magnetic field of the electron and the external magnetic field creates a force on the electron, causing it to move.

For Further Analysis 1. The generation of electricity involve much more than the movement of electrons, including the establishment of electrical potential between two points in a circuit, the creation of an electric field as a result, and the movement of electrons as caused by the field.

2. Similarities – both are electric fields moving through a conductor, which carries energy. Differences – In alternating current the field moves electrons back and forth; in direct current the field moves electrons in one direction.

3. Answers will vary, but it does appear that people should be warned about amps, not volts.

4. Answers will vary, but should be logical and supported by identified insights, beliefs, and arguments.

5. Answers will vary but should show the understanding that solar energy is free, but the bucket to catch it is very expensive.

6. Similarities – both are fields, which is a change of the condition of space around an electrical charge or magnetic field. Differences – an electrical field is found around a charge; a magnetic field is found around a magnet or current carrying wire.

7. Advantage – You can use any one or all devices in a parallel circuit at the same time.

Disadvantage – A short circuit or using too many appliances may overheat the wires and cause a fire.

Group B Solutions

1.

q  ne coulomb    1.00  109 electrons   1.60  1019  electron    1.60  1010 C

2. kq1q2 d2 2  9 Nm  9.00  10 1.6  10 10 C 1.6  10 10 C   2  C    2  0.050 m 

F 

2.304  10 10  0.0025  9.2  108 N

3.

Nm 2 C 2  2 C2 m

V 

W q

 W   q V 

W  100,000C 12.0 V   1.2 106 J  1106 J

4.

I 

q C  2.0 amp  2.0 t s

5. If you wish to limit your lowest current to the minimum charge that can flow by in 1 second, then the smallest current is 1 electron passing by per second.

I 

q 1.60  1019 C  t s

 1.60  1019 amp

6.

V  IR  R  R 

V I

120 V 0.83A

 145   150 

7.

V  IR V  V   3.33A   60.0  A  2  2.00  10 V

8.

(a)

V  IR  I  I 

V R

12.0 V 10.0 

 1.20 A

(b)

P  IV  1.20A 12.0V   14.4 W

9.

V  IR  I  P 

V R

and

V  P  IV , so P   V or R

V2 R

120.0 V  

2

V A 14, 400 J 2 1   2 J 192 C C C s  75.0 W 192

10. cos t  

 60 W  720 h  $0.10 / kWh  1,000 W / kW

 60  720  0.10 

1,000  $4.32 per month

11.

W h $ kW    1 1 kWh W

P  IV  11.5A  240V   2,760 W

12.

2.0 hp 

cos t  

746 W hp

 1, 492 W

1, 492 W 18 h  $0.10 / kWh  1,000 W / kW

1, 492 18 0.10 

W h $ kW    1 1 kWh W

1,000

 $2.69

$2.69/day  30 day/month = $80.70/month 13.

P  IV  I 

P V

J s  J 120.0 C  10.8 A 1,300.0

Since 2 times 10.8 A is 21.6 A, two devices will clearly overload a 15 A circuit.

14. (a) Vp Np



Vs N  Vs  s  Vp Ns Np

1,500  120V 100  1,800 V

Vs 

(b)

Vp I p  Vs I s  I s  Is 

Vs

120 V  15.0 A 1,800 V

 1.0 A 15. (a)

Vp

 Ip

Vp Np



Np 

Vp Vs  Np   Ns Ns Vs 7, 200 V 125 loops 120 V

 7,500 loops

(b)

Vp I p  Vs I s  I p 

Vs  Is Vp

Ip 

120 V  36 A 7, 200 V

 0.60 A (c)

P  VI Pin   7, 200V  0.60A   4,320 W  4,300 W Pout  120V  36A   4,320 W  4,300 W

16. (a) Vp Np



Vs N  Vs  s  Vp Ns Np 1  120V 30 120V  30  4.0 V 

(b) Vp I p  Vs I s  I s  Is 

Vp Vs

 Ip

120 V  90.0 A 4.0 V

 2.7  103 A

(c)

P  VI Pin  120V  90.0A   1.08  104 W  1.1 10 4 W





Pout   4.0V  2.7  103 A  1.08  104 W  1.110 4 W

17. Listing the known and unknown quantities: Resistance (R)

8.0 Ω

Voltage (V)

12 V

Power (P)

?W

Current (I)

?A

Since the three bulbs are connected one after another, the current encounters resistance from each in turn and the total resistance is equal to the sum of the individual resistances, or Rtotal = R1 + R2. Therefore, Rtotal = 8.0 Ω + 8.0 Ω + 8.0 Ω = 24.0 Ω We can now find the current flowing through the entire circuit, which will be the same as the current flowing through each of the resistances:

I

V Rtotal



12 V 24.0 

12 V 24.0 V A V A  0.50  1 V  0.50 A 

The current through each bulb is 0.50 amp. The voltage drop across each lamp can be calculated from Ohm's law, and V = IR = (0.50 A)(8.0 V/A) = 4.0 V.

The power of each glowing bulb can now be calculated from P = IV, and P = (0.50 A)(4.0 V) = 2.0 W.

7

Light

Contents 7.1 Sources of Light Case Study: Bioluminous 7.2 Properties of Light Light Interacts with Matter Reflection Refraction Dispersion and Color A Closer Look: Optics 7.3 Evidence for Waves Interference A Closer Look: The Rainbow Polarization A Closer Look: Lasers A Closer Look: Why Is the Sky Blue?

7.4 Evidence for Particles Photoelectric Effect Quantization of Energy 7.5 The Present Theory A Closer Look: The Compact Disc (CD) 7.6 Relativity Special Relativity General Theory Relativity Theory Applied

Overview Electromagnetic waves have many characteristics of interest, including their methods of production, their properties, and their uses. A review of wavelength, frequency, and wave velocity as they apply to sound relates these concepts to electromagnetic waves. Vibrating matter produces sounds and electromagnetic waves are produced by an accelerated charge.

The energy involved in this acceleration results in the various parts of the electromagnetic spectrum, with visible light making up only a small part of the total spectrum.

After a consideration of the sources of light, the properties of light are considered from a light ray treatment of the laws of reflection and refraction. The early controversy concerning the nature of light is discussed next, leading to evidence for both the particle theory and the wave theory of light. The properties of light that serve as evidence that light is a wave (reflection, refraction, diffraction, interference, and polarization) are considered, followed by the evidence that light is a stream of particles (photoelectric effect and quantization of energy). This leads to the present theory, that light has both wave and particle properties at

the same time. Students enjoy a controversy, and this one is based mostly on their everyday notion that light must be either one or the other since everything else in their everyday world appears to be one or the other. However, there is no reason to identify light as being either waves or particles. The modern model of light (and subatomic particles to be discussed in a future chapter) considers light to have both properties at the same time. The model is just that, a model, and it is used because it seems to explain what is observed. Students historically struggle mightily with the word radiation, and the vague word energy might help students learn this material better.

Suggestions 1. Discussion and demonstrations of light and other electromagnetic radiations that are not visible are suitable to introduce this chapter. A demonstration of infrared can be accomplished by heating a large piece of iron in a burner flame for several minutes, then holding it close to a radiometer. The radiometer vanes spin more rapidly from the infrared radiation emitted by the hot iron. Explain that the radiometer contains some air.

The black sides of the vanes absorb infrared radiation, which shows up as a slight temperature increase on the blackened surface. The silvered sides of the vanes, on the other hand, reflect the radiation without absorbing it. Air particles next to the warm, black surface collide with the surface and rebound with more energy than other particles on the silvered side of the vanes. As a result of the many impulses received from many, many particles on the blackened side the vanes spin in a direction consistent with this explanation.

2. Reflection and refraction can be effectively demonstrated at the same time by filling a small aquarium with water that has been made murky by mixing in some chalk dust. A strong beam of light is aimed downward at a mirror, which reflects the light upward through the aquarium water. A darkened room and chalk dust (or smoke from a smoke source) makes the light beam visible in the air. The same setup can be used to show total internal reflection by directing the beam at increasing angles until it is totally reflected from the inner surface.

3. A prism can be used to cast the spectrum of sunlight on a wall, leading to a discussion of refraction, dispersion, and color.

4. Diffraction can be illustrated with a classroom spectroscope or small squares of plastic replica diffraction gratings. Students should look toward a light source with the grating, either to the right or left of center as they rotate the grating until they see a spectrum. A cloth handkerchief that is stretched tightly in front of a laser beam will show a good diffraction pattern.

5. The mnemonic of ―ROY G. BIV‖ helps students remember the spectrum of major colors, although indigo is not totally accepted as a color by everyone (has anyone seen indigo in a rainbow?).

6. Additional demonstrations: (a) Hold a radiometer near a heated iron block supported on a ring stand to confirm the existence of electromagnetic radiations that are not visible. Discuss how infrared warms the black sides of the vanes, causing air molecules to rebound with more of a ―kick‖ than they do from the silvered side. This ―kick‖ gives the vanes their motion. (b) Show a spectrum produced by a prism. Mount the prism so the spectrum is cast on a wall. (c) Fill a large beaker or aquarium with water and mix in some chalk dust. Aim a narrow beam of light from a slide projector (or laser) at some angle to demonstrate refraction. (d) Cut inexpensive plastic replica grating into 5-cm squares. Instruct students to handle the squares only by the edges to avoid ―oiling the gratings.‖ Tell them to hold the grating close to one eye, viewing a light source through the grating. They should rotate the grating in 90 degree intervals until a spectrum or spectrum lines are seen. These are usually to the left or right of center. Neon, mercury, and sodium lights are good sources for a line spectrum.

For Class Discussions 1. Light from an incandescent source comes from a. glowing atoms with high kinetic energy. b. fast moving electrons, which tend to glow. c. accelerating electrons. d. oxidation at the atomic level.

2. One of the following behaviors of light means it must consist of waves. a. interference. b. photoelectric effect. c. refraction. d. reflection.

3. Diffraction occurs when light passes a. through a pinhole. b. by a sharp edge. c. through a narrow slit. d. all of the above.

4. From a space station on the Moon you would be able to tell planets from the stars because stars twinkle and planets do not. a. Yes. b. No. c. Who knows?

5. If you look straight down and see a fish under the water, it appears to be a. deeper in the water than it really is. b. closer to the surface than it really is. c. where it actually is.

6. If you look at a fish that is some distance from you, it appears to be a. deeper in the water than it really is. b. closer to the surface than it really is. c. where it actually is.

7. A fish under the water always appears to be a. larger than it really is. b. smaller than it really is. c. the size it actually is.

8. Can you can distinguish a mirage of water from real water by using Polaroid sunglasses? a. Yes. b. No.

Answers: 1c, 2a, 3c, 4b (no atmosphere; no twinkling), 5b, 6b, 7a, 8a (light from water is reflected and thus polarized; a mirage is refracted light and is not polarized).

Answers to Questions for Thought 1. The electromagnetic spectrum is made up different types of radiation of various frequencies and wavelengths. The dividing line between adjacent parts is difficult to identify just as the dividing line between red and orange in a rainbow is difficult to pinpoint. Thus, some specific but arbitrary frequency or wavelength is used to identify where one ends and the other begins. In the case of visible light and infrared radiation you could use a frequency of 3.8  1014 Hz as the dividing line.

2. Polarization supports a wave theory of light. Only transverse light waves, vibrating at right angles to the direction of travel will explain how light can be polarized. Polarized, or plane-polarized light vibrates only in one plane.

3. Blue light carries more energy. No, because the energy difference between these two colors is very small. The number of photons determines the intensity of the light.

4. The photoelectric effect supports the particle model, because the effect depended on the frequency and not the intensity of the light. This means that particles of certain energy were creating the effect and not the absorption of a wave.

5. The energy in the light is transferred to the absorbing material.

6. The bluish star is at a higher temperature because higher temperature objects emit more photons of shorter wavelengths (and higher energies) than objects with lower temperatures.

7. Internal reflection occurs when the angle of refraction is equal to or greater than 90°.

This occurs more in the diamond because the critical angle depends upon the ratio of the indices of refraction of the air to the stone. The diamond has a very high index of refraction.

8. The hot air above the surface of the highway has a lower index of refraction than the air above it, so light striking the warmer air is refracted upward. Your brain interprets this refracted light to be reflected light, so you believe you are seeing a reflective surface such as water.

9. Look at the clear sky at an angle of about 90° from the sun. The scattered light from this direction is partially polarized, so if the sky appears to darken as the glasses are turned, the glasses are polarized. If you have a pair of polarizing sunglasses, turn a lens of the unknown pair over a stationary lens of the known, polarizing pair. If the unknown pair is polarizing, light coming through the lens will appear to darken then brighten.

10. Two light beams from a single source striking a card with two small parallel slits in phase with each other are necessary. Light is diffracted through these slits, landing on a screen. Regions where the diffracted light from both of the slits is in phase have a bright line. Regions where the diffracted light from one slit is out of phase with the light from the other slit have a dark line.

11. Reflected light is slightly polarized. When the polarization of the reflected light is parallel with the polarizing sunglasses, it appears brighter. When the polarization of the light is perpendicular with the sunglasses it appears darker.

12. There is no atmosphere to suspend particles above the astronauts to scatter the light from the sun, so they see a black sky. The stars do not twinkle because there is no atmospheric turbulence above them to refract the light in various ways. The earth appears blue because light of that frequency is being scattered the most by the atmosphere below them.

13. Planck’s findings were revolutionary because they meant that vibrating molecules could only have a fixed amount of energy that could only be multiples of a certain amount

called the quanta of energy. All previous experience led everyone to believe that energy could exist in a continuous range of amounts.

14. Neither model totally explains all behavior of light, while a combination of these two models, using each when it is useful, explains all the behaviors of light. There is nothing in conventional experience that behaves as a particle in some situations and a wave in different situations, so the concept is hard to visualize.

For Further Analysis 7. Answers will vary but should describe reflection as light bouncing from a surface and refraction as the bending of light when passing between two different optical media.

8. Answers will vary in this Socratic discussion attempt to clarify the concept of convection.

9. Answers will vary in this attempt to reason dialogically about the nature of light.

10. Answers will vary in the attempt to compare and contrast the used of convex and concave lenses.

11. E is a quantity of energy, which is a particle property, and f is frequency, a wave property. The equation states they are equal, so it equates particle and wave properties.

12. Same – both are electromagnetic radiation that travels at the speed of light. Different – radio waves are longer wavelength.

Group B Solutions c  3.00  108

1. (a)

m s

(b) n 

c c  v  v n 

m s

3.00  108 1.00026

 299,922,020.3  3.00  108

m (from calculator) s

m (significant figures) s

(c) v 



c n m s

3.00  108 1.00029

 299,913,025.2  3.00  108

m (from calculator) s

m (significant figures) s

2.

d d  t  t v 5 3.85  10 km t  km 3.00  105 s  1.28 s

v 

3. d d  t  t t 7 7.83  10 km t  km 3.00  105 s 1 min  261 s   4.35 min 60 s

v 

4. qi  qr  qi  60  qr

5. n 

c v

m s  8 m 2.00  10 s  1.50 3.00  108

This is the index of refraction for glass.

6.   4.60  107 m c  f  E  h

f 

c 

and

E  hf

c 

 8 m  3.00  10  s  E   6.63  1034 Js    4.60  107 m   4.32  1019 J

 E  h

c 

7. red light : f  4.8  1014 Hz maximum E  hf 1    6.63  1034 J  s   4.8  1014  s   3.2  1029 J

This is less than the required photon energy, so no chemical reaction occurs in the paper.

8. (a) f 

c 

m s  6.80  10 7 m 3.00  108

 4.41  1014 Hz

(b) This is in the frequency range of red light.

9.

E  h

1 1  c  E1  E2 hc      1  2 

 m  1 1  E1  E2  6.63  1034 Js  3.00 108     7 7 s   3.00 10 m 5.60 10 m  





E1  E2  3.08  1019 J

10. c  f 

f 

m s f  3 1.00  10 m 3.00  108

 3.00  1011 Hz

c 

11. n=

c c  v= v n 

3.00  108

m s

1.31

 2.29  108

m s

12. cf f 

c 

m s  4.60  107 m 3.00  108



3.00  108 m 1  4.60  107 s m

1 s 14  6.52  10 Hz  6.52  1014

13.

E=hf 1    6.63  1034 J  s   4.30  1014  s    6.63  1034  4.30  1014  J  s  J s s 19  2.85  10 J  2.85  1019

1 s

14. cf f 

c 

m s  3.00  107 m 3.00  108



3.00  108 m 1  3.00  107 s m

1 s 15  1.00  10 Hz  1.00  1015

E=hf 1    6.63  1034 J  s   1.00  1015  s    6.63  1034 1.00  1015  J  s 

1 s

J s s 19  6.63  10 J  6.63  1019

15.

(First step) c   f  f 

c 

m s  7 5.60  10 m 3.00  108



3.00  108 m 1  5.60  107 s m

1 s 14  5.36  10 Hz  5.36  1014

(Second step) E  h f 1    6.63  1034 J  s   5.36  1014  s    6.63  1034  5.36  1014  J  s 

1 s

J s s 19  3.55  10 J  3.55  1019

(Third step) Since one photon carries an energy of 3.55  10-19 J and the overall intensity is 500.0 W for each square meter there must be an average of

500.0 3.55  1019

J s J photon

5.00  102 J photon  3.55  1019 s J photon 1.41  1021 s

8

Atoms and Periodic Properties

Contents 8.1 Atomic Structure Discovered Discovery of the Electron Case Study: Discovery of the Electron The Nucleus Case Study: Oil Drop Experiment 8.2 The Bohr Model The Quantum Concept Atomic Spectra Bohr’s Theory 8.3 Quantum Mechanics Matter Waves Wave Mechanics The Quantum Mechanics Model

Science and Society: Atomic Research 8.4 Electron Configuration 8.5 The Periodic Table 8.6 Metals, Nonmetals, and Semiconductors A Closer Look: The Rare Earths A Closer Look: Semiconductors Overview This chapter is an introduction to the structure of the atom through a historical perspective.

Some of the quantitative aspects of electric and magnetic fields, electromagnetic radiation, and mechanics are used by scientists such as Thomson, Millikan, Rutherford, and Bohr as they identify the parts of an atom and determine how the parts are organized. Thomson's discovery of the electron and Rutherford's discovery of the nucleus are discussed, along with Bohr's development of the planetary model of the atom. How Bohr's model accounted for atomic stability and its ability to produce line spectra is analyzed, along with the weaknesses and shortcomings of the model. The wave nature of particles as suggested by de Broglie is considered next, which leads to the modern quantum mechanics model. Overall, students should be impressed with the symmetry found in nature and understand how scientific models are developed as they learn modern atomic theory.

Symmetry is also found by organizing the experimentally discovered facts about atomic structure into the major concept represented by the periodic table. The periodic table demonstrates the periodic recurrence of physical and chemical properties of elements.

Elements within chemical families are seen to have similar chemical and physical properties because they all have the same number of electrons in their outermost shells. Across a period, elements are seen to have properties of metals with decreasing chemical activity, then properties of semiconductors, then properties of nonmetals with increasing reactivity, and finally the chemically inert noble gases. Metals are recognized as elements with one, two, and sometimes three electrons in the outermost shell. Nonmetals have five, six, or seven outer shell electrons. The inertness of the noble gases is related to the stability of the filled outer shell arrangement. There are many generalizations that can be made from these periodic patterns, making the periodic table an invaluable tool that simplifies the study of matter.

Suggestions 1. The law of definite proportions can be introduced early in this chapter, although the topic is not discussed formally until a later chapter.

2. Illustrate the concepts of Thomson's experiment with Crookes tubes connected to a tesla coil. Demonstrate that the cathode rays travel in straight lines with the Maltese cross,

that they have mass and velocity with the kinetic energy effect tube. Demonstrate that cathode rays have a negative charge with the deflection effect tube, and that they can be deflected by a magnet. These demonstrations should lead to a clear understanding of Thomson's work and the properties of electrons.

3. Spectra of different elements can be shown by using several gas emission tubes and squares of inexpensive plastic replica diffraction gratings. Have the students hold the plastic diffraction gratings by the edges (to keep finger oils off the plastic surfaces) and look through the grating at a glowing gas emission tube (H, Ne, Ar). They should rotate the grating and look to the right or to the left of the center until they see the spectrum.

Radiation from excited atoms is also shown by the popular demonstration of crushing a wintergreen lifesaver between the jaws of a pair of pliers in a dark room. This emission of light is a result of the excitation of sugar molecules by mechanical stress.

4. Apparatuses for demonstrating the photoelectric effect, Thomson's experiment, and Millikan's experiment are available from scientific supply companies. The Millikan apparatus, however, does not lend itself to large-group demonstrations. It is also difficult to use with small groups. Alpha tracks can be shown in a cloud chamber while discussing Rutherford's experiment.

5. Student understanding of the arrangement of electrons in atoms requires that they mentally act on the process of building electron structures as models. If you choose to cover quantum numbers, it may be helpful to use an analogy to an address, such as state, city, street, and street number. Each electron has its own address (set of quantum numbers) just as each student has a particular address.

6. Illustrate metals and nonmetals with samples of gases in tubes; sheets of copper, zinc, lead, and aluminum; and samples of sulfur, carbon, and iodine. Show mixtures of salt and pepper, sand and dirt, or other common mixtures in varying proportions.

7. An electrolysis of water demonstration is an ideal way to begin discussion of compounds and elements. The Brownlee electrolysis apparatus, available from scientific supply houses, is big enough to be viewed by large classes.

8. Illustrate atomic mass units by using a balance to measure the mass of two coins, such as a dime and a quarter. Calculate the ratio of the mass of one coin relative to the other.

Measure the mass of a bag containing equal numbers of both coins, then use the ratio to predict the numbers of each coin in the bag. Define atomic mass units and the abbreviation u.

9. Exhibit a large periodic chart of the elements, referring to the chart often during discussion of chemistry.

10. Illustrate similarities in chemical and physical properties of families and periods of the periodic table. Show the physical properties of Li, Na, and K, then show the chemical reactions with water (Caution: Explosive hydrogen gas), testing the water with litmus.

Compare the reactions of Mg, Al, S, C, and Si with dilute hydrochloric acid. Review the

outer orbital structures or electron dot symbols to show similarities among families and periods for the first twenty elements.

11. Do the classic demonstration showing the change of physical properties when a mixture of sulfur and iron is converted into a compound. First, demonstrate that a magnet will attract iron, but not sulfur, and a magnet can be used to separate iron from a mixture of iron and sulfur. Second, demonstrate that sulfur is soluble in carbon disulfide (Caution: Explosive vapors) by dissolving a little in a one-fourth test tube of carbon disulfide.

Finally, strongly heat a mixture of 4 grams S and 6 grams Fe filings in a test tube until it glows. Break the test tube by immersion in cold water. Compare the appearance and properties of the mixture before and after heating. Discuss if it is still a mixture or a new compound according to the magnet and carbon disulfide tests.

12. Obtain a roll of calculator tape. Draw 100 squares on a length of the tape and write atomic numbers consecutively in the upper left corner of each square. In the center of each square write the chemical symbol for the atomic number. Form a large spiral by taping together, one under the other, the elements of a family that have the similar chemical properties, such as the inert gases. You can hang the spiral in the classroom to make a mobile, then make another one to show how the periodic table is a spread-out spiral. Cut a spiral to the right of the inert gases, then spread and tape the spiral to make a long form of the periodic table. Show how moving two chemical families results in the short form.

For Class Discussions 1. How many electrons in an atom can have a quantum number of n = 2? a. 2 b. 8 c. 18 d. 32 2. When an atom of hydrogen has an electron with a quantum number of n = 2, the atom a. is called ―an ion.‖ b. is now known as an isotope. c. is said to be in an excited state. d. has violated the Heisenberg uncertainty principle.

3. According to the quantum mechanics model of the atom, an electron revolves in an orbit around the nucleus if a. it has no energy.

b. it can make a standing wave. c. its momentum matches the electrical attraction from the nucleus. d. its wavelength describes an elliptical orbit.

4. Hydrogen, with its one electron, can produce a line spectrum with four visible colors because a. an isotope of hydrogen has four electrons. b. electrons occur naturally with four different colors. c. there are multiple energy levels that an electron can occupy. d. electrons are easily scattered.

5. A photon is emitted from the electronic structure of an atom when an electron a. jumps from a higher to a lower energy level. b. jumps from a lower to a lower higher level. c. reverses its spin by 180°. d. is removed from an atom by a high quantum of energy.

6. Two electrons are able to occupy an orbital because a. there is physically not room for more. b. of Newton's laws of motion. c. quantum theory is based on a binary numbering system. d. opposite magnetic poles are attractive.

7. Which of the following electron configurations can not occur? a. 1s22s1 b. 1s22s22p63s2 c. 1s21p62s22p6 d. All of these can occur.

8. Quantum mechanics uses four quantum numbers to describe certain properties of electrons. These properties do not include a. spin. b. what happens in a magnetic field. c. energy. d. mass.

9. According to the Bohr model of the atom, an electron is able to stay in orbit around an atom because of the a. balance between momentum and electrical attraction from the nucleus. b. balance between spin and orbital velocity, which gives the electron high stability.

c. rule that electrons could not move from their allowed orbit. d. fact that moving electrons have mass and velocity, and therefore momentum.

10. Which of the following electron configurations is incorrect? a. Carbon: 1s22s23s2 b. Sodium: 1s22s22p63s1 c. Neon: 1s22s22p6 d. All of these are correct.

11. The quantum mechanics and Bohr models of the atom both agree on a. the significance of the de Broglie wavelength and the circumference of an orbit. b. the importance of momentum in determining the size of an orbit. c. how electrons are able to emit light. d. none of the above.

12. The atomic weight of neon is 20.2. This means a. all atoms of neon have a mass of 20.2 u relative to carbon 12. b. a given atom of neon has a mass of 20.2 g. c. neon occurs as isotopes of different masses and the weighted average is 20.2 u.

13. An atom has 6 protons, 6 electrons, and 6 neutrons so the mass number is a. 18 12 Mg 12 b. 12Mg c. 126 C d. 186 C 14. How many dots would surround the symbol for each alkali metal atom in the electron dot notation for the group IA elements? a. one. b. two. c. six. d. seven.

15. How many dots would surround the symbol for each halogen atom in the electron dot notation for the group VIIA elements? a. one. b. two.

c. six. d. seven.

16. Calcium belongs to which chemical family? a. alkali metals b. alkaline earth metals c. halogens d. noble gases 17. The most important factor in the chemical behavior of an atom is the a. number of neutrons. b. structure of the isotopes. c. ratio of neutrons to protons. d. electron structure

Answers: 1b, 2c, 3b, 4c, 5a, 6d, 7c, 8d, 9a,.10a, 11c, 12c, 13c, 14a, 15d, 16b, 17d.

Answers to Questions for Thought 1. Rutherford was scattering positively charged alpha particles off thin sheets of metal.

Some of the particles were scattered at very large angles, and some particles were indeed scattered back toward the way they came. This behavior could be accounted for only by theorizing that the massive, positively charged alpha particles were being repelled by a massive positive charge concentrated in the center of the metal atoms. Rutherford concluded that the atoms must have a tiny, massive, positively charged nucleus surrounded by the negatively charged electrons.

2. The ―solar system‖ model requires electrons to travel in orbits about the positively charged nucleus and any object moving in a circle is accelerating. Since accelerating electrons emit energy in the form of radiation, this loss of energy would result in the electrons spiraling in to collide with the nucleus. Since atoms are not observed to exhibit this behavior, this model is not adequate.

3. If the size of the nucleus were the same size as the thickness of a dime the atom would be about two football fields wide.

4. The atomic number is 11. The element with an atomic number of 11 is sodium. Its electron configuration is 1s2 2s2 2p6 3s1.

5. The reference level for the potential energy of an electron is zero when the electron is free and removed from an atom. Work must be done on electrons to remove them from an atom, bringing them back up to a potential energy level of zero, so the electrons in an atom have negative energy values.

6. The discrete energy levels, electrons gaining or losing energy by moving from one allowed energy level to another, and the emission and absorption of photons of energy exactly equal to the energy difference of the allowed energy levels are common to both models. Bohr’s model was based on the solar system model, which gives exact radii for the electron orbits. It does not take into account the Heisenberg uncertainty principle as the probabilities contained in the quantum mechanical model do. The Bohr model treats electrons exclusively as particles, whereas the quantum mechanical model accounts for the dual nature of particles.

7. The electron associated with the hydrogen atom in the excited state has more energy than the electron associated with the atom in the ground state. Therefore, the atom in the excited state is said to have more energy than the atom in the ground state.

8. (a) The atomic number is a whole number because it is the number of protons contained in the nucleus of the element. There are no fractions of protons. (b) The isotope mass is the mass of a particular isotope of an element as compared to the mass of the carbon-12 isotope. This ratio does not have to be a whole number. (c) The mass number of an atom is the sum of the protons and neutrons in the nucleus of the atom. This is a whole number since there are no fractional neutrons or protons. (d) The atomic weight is a weighted average of isotope masses. This average is based on the relative abundance of the isotopes and is not required to be a whole number.

9. The carbon-12 isotope is defined to have a mass of 12, and all the other isotope masses are relative masses compared to the assigned mass of the carbon-12 isotope.

10. The noble gasses are all chemically inert, but each has a different atomic number and a different mass.

11. Isotopes of one element are similar because they have the same atomic number and the same chemical characteristics. They are different because individual isotopes have different mass numbers.

12. Elements in the same period have the outermost electrons in the same energy level.

Elements in the same family have the same electron configuration in the outer energy level. Elements in the same family also share many chemical characteristics.

For Further Analysis 10. Answers will vary in this evaluation but will show understanding of Millikan’s technique.

11. Similarities – isotopes of a particular element all have the same atomic number.

Difference – isotopes of a particular element all have different numbers of neutrons in the nucleus, and thus different mass numbers.

12. This requires analyzing and evaluating an interpretation of Thompson’s experiments.

The correct analysis should include a discussion of electrons having mass as shown by response to magnetic field, electrons having a negative change, and the mass to charge ratio being the same for all materials.

13. This requires analyzing, exploring beliefs, and clarifying a conceptual understanding.

Answers will vary but should clarify that atomic weight is a weighted average of the isotopes of an element based on abundance and compared to carbon-12.

14. Answer should include discussion of photons, or quanta of energy that is emitted or absorbed.

15. The Bohr model considered the electron to be a particle and treated it as such with Newtonian mechanics using one quantum number. The Quantum Mechanic model considered the electron to be a wave and solved a wave equation for four quantum numbers that describe the energy of the electrons.

Group B Solutions 1.  

h mv

6.63  1034 J  s  9.11  1031 kg   4.3  106 ms   1.7  1010 m 

2. (a) El n2 13.6 eV  32   1.51 eV

En 

(b)

 1.51 eV  1.60  1019 

J  19    2.42  10 J eV 

3. (a) From figure 8.14: n=1 value is –2.18 10-18J and n=3 value is –2.42 10-19 J

 –2.42 10 J    –2.18 10 J   1.94 10 -19

-18

18

J

(b) E  E  E3  E1   2L    2L  3  1   13.6 eV   13.6 eV      32 12       1.51 eV    13.6 eV   12.1 eV

4. hf  EH  EL 

f   

EH  EL h  5.44  1019 J    2.18  1018 J  6.63  1034 J  s 1.64  1018 J 6.63  1034 J  s

1 s 15  2.48  10 Hz  2.48  1015

5.

El n2 13.6 eV  22   3.40 eV

E2 

6. charge charge/mass

mass  

1.60  1019 C C 9.58  107 kg

 1.67  1027 kg

7.  

h h  v  mv m 

6.63  1034 J  s  9.11  1031 kg 8.33  1011 m 

 8.34  106

m s

8. (a) nitrogen 1s2 2s2 2p3 (b) phosphorus 1s2 2s2 2p6 3s2 3p3 (c) chlorine 1s2 2s2 2p6 3s2 3p5

9. (a) Nitrogen's atomic number is 7, and 2 + 2 + 3 = 7. (b) The atomic number of phosphorus is 15, and 2 + 2 + 6 + 2 + 3 = 15. (c) Chlorine's atomic number is 17, and 2 + 2 + 6 + 2 + 5 = 17.

10. (a) neon 1s2 2s2 2p6 (b) sulfur 1s2 2s2 2p6 3s2 3p4 (c) calcium 1s2 2s2 2p6 3s2 3p6 4s2 11.

Boron-10 10.0129 u  0.1978 = 1.981 u Boron-11 11.00931 u  0.8022 = 8.832 u 1.981 u + 8.832 u = 10.813 u

12.

Protons 7 3 17 20 29 92

(a) (b) (c) (d) (e) (f) 13. (a) (b) (c) (d) (e) (f)

Period 5 4 4 3 4 6

Neutrons 7 4 18 28 34 138

Electrons 7 3 17 20 29 92 Family VIIIA IA VIB VIIIA VIIA IIA

14.

(a) Na: 1 (b) P: 5 (c) Br: 7

(d) I: 7 (e) Te: 6 (f) Sr: 2

15.

16.

17.

18.

(a)

Al

(c)

Mg

(e)

C

(b)

F

(d)

Na

(f)

Cl

(a) Al: 3+

(d) Na: 1+

(b) Cl: 1–

(e) S: 2–

(c) Mg: 2+

(f) H: 1+

(a) Radon: nonmetal

(d) Phosphorus: nonmetal

(b) Francium: metal

(e) Hafnium: metal

(c) Arsenic: semiconductor

(f) Uranium: metal

(a) F1- gained 1: VII A (b) Li1+ lost 1: I A (c) B3+ lost 3: III A (d) O2- gained 2: VI A (e) Be2+ lost 2: II A (f) Si4+ lost 4: IV A

19. (a) 39 19K

(b) 22 10Ne

(c) 184 74W

(d) 127 53I

9

Chemical Bonds

Contents 9.1 Compounds and Chemical Change 9.2 Valence Electrons and Ions 9.3 Chemical Bonds Ionic Bonds Energy and Electrons in Ionic Bonding Ionic Compounds and Formulas Covalent Bonds Covalent Compounds and Formulas Multiple Bonds Case Study: Electronegativity 9.4 Bond Polarity 9.5 Composition of Compounds Ionic Compound Names Ionic Compound Formulas Covalent Compound Names Science and Society: Microwave Ovens and Molecular Bonds Covalent Compound Formulas

Overview This chapter covers the concepts of chemical change, including elements and compounds; chemical bonding (ionic and covalent); electronegativity and types of bonds formed; and polar and nonpolar molecules. Students are led to the conclusion that the tendency of atoms to form positive and negative ions is the result of the difference in the electronegativities of various atoms. An atom with a high electronegativity will gain one or more electrons from an atom with a low electronegativity to produce, respectively, negative and positive ions.

For atoms that have relatively similar electronegativity values, the sharing of electrons to form covalent bonds is illustrated as another way in which atoms react to form compounds.

Some of the more common ions and polyatomic ions are presented, along with the rules for naming the compounds.

Suggestions 1. Illustrate the physical and chemical properties of powdered iron and sulfur before and after heating a mixture in a crucible with a burner to produce an obvious chemical change.

2. Have students make shell diagrams or electron dot symbols for various elements. Then ask them to explain how they could attain the more stable electron structures of the noble gas configurations by loss, gain, or sharing of electrons.

3. To illustrate combustion without the presence of oxygen, heat a piece of steel wool and plunge in into a bottle of chlorine (Caution: Rapid oxidation).

4. Show the polarity of water by deflecting a thin stream from a tap with both a negatively and a positively charged rod. A similar stream of a nonpolar compound, such as mineral oil, is not deflected by either charge.

5. Additional demonstrations: (a) Do the spectacular demonstration of an ammonium dichromate volcano. Place an approximate 5-cm pile of ammonium dichromate on a metal tray. Ignite with a torch or burner flame (or short piece of burning magnesium ribbon). A large volume of green chromic oxide ―cinders‖ will form a conical pile. The burning reaction releases ammonia and oxygen, and the remaining chromic oxide has a weight of about 40 percent less than the original ammonium dichromate. (b) A 110-volt conductivity apparatus with electrodes about 1 cm apart can be used to show that molten NaCl conducts an electric current while solid NaCl does not. Attach the apparatus to a ring stand so the electrodes are in a 2-cm depth of granulated NaCl in a small porcelain crucible. The crucible is in a triangle on a tripod. Show the lamp does not light when the switch is closed. Now melt the NaCl with a Fisher burner under the crucible (requires 3 - 4 minutes), and again close the switch on the conductivity apparatus. Allow the melt to cool and solidify until the lamp goes out. Explain that melted NaCl has mobile ions that can conduct a current. As the rigid lattice structure is established by ionic bonding, the ions are no longer free to move and conduct the current.

For Class Discussions 1. When involved in a chemical reaction with metals, atoms of a nonmetal tend to a. exchange electrons. b. remain neutral. c. gain electrons. d. lose electrons.

2. Potassium is a metal and oxygen is a nonmetal that reacts to form K2O, an ionic compound. How many electrons did an atom lose during the reaction? Each a. potassium atom lost one electron. b. potassium atom lost two electrons. c. oxygen atom lost one electron. d. oxygen atom lost two electrons.

3. A crystal of potassium chloride is made up of a. K and Cl atoms. b. KCl molecules. c. K+ and Cl– ions d. K– and Cl+ ions 4. In a covalent molecule you would find atoms that a. have lost electrons to become ions. b. have gained electrons to become ions. c. are sharing at least one pair of electrons. d. are sharing at least one electron.

5. Which of the following compounds would have the greatest covalent character? a. HCl b. NaCl c. H2O d. H2 6. Which of the following compounds would have the greatest ionic character? a. HCl b. NaCl c. H2O d. H2

7. How many atoms are in a molecule of chalk, which is CaCO3? a. 3 b. 5 c. 6 8. How many atoms of oxygen are in a molecule of Al2(CO3)3? a. 3 b. 6 c. 9 9. If Iron(II) chromate has a formula of FeCrO4, then potassium chromate must have a formula of a. KCrO4 b. K2CrO4 c. K2(CrO4)2 d. K(CrO4)2 10. Should dihydrogen monoxide, which is responsible for substantial damage to the environment each year, be banned? a. Yes. b. No. Answers: 1a, 2a, 3c, 4c, 5d, 6b, 7b, 8c, 9b, 10b (systematic name for water).

Answers to Questions for Thought 1. (a) A sodium atom and a sodium ion both have the same atomic number, and if the two are the same isotope, they have the same mass number. The atom and the ion will have different numbers of electrons, and consequently, different charges. (b) A sodium ion and a neon atom will have the same number of electrons, but they have different atomic numbers and different net charges.

2. In a nonpolar covalent bond, the bonding electrons are shared equally among the bonded atoms. With a polar covalent bond, the electron is located around the atom with the higher electronegativity more often than near the atom with the lower electronegativity.

This creates a negative pole about the first atom and a positive pole about the second.

3. In an ionic bond, one or more electrons are pulled from one atom to fill the outer shell of another atom. The resulting ions that are created are attracted to each other electrostatically. In a covalent bond, electrons are shared between the atoms, and the attraction of each nucleus for the other’s electron binds the atoms together. The atoms

involved in these two bond types both follow the octet rule. This is done either by sharing electrons to have eight in the outer shell as in a covalent bond or by losing or gaining electrons as in the ionic bond.

4. The octet rule states that atoms attempt to acquire an outer orbital with eight electrons.

This rule is a generalization, and not all elements follow this rule.

5. The maximum number of covalent bonds that can be formed by an atom is equal to the number of valence electrons.

6.

H (a) H Cl (b) H O H (c) H C H H 7. Sodium has an electronegativity of 0.9, while that of fluorine is 4.0. The difference in electronegativity is 3.1, which is greater than the 1.7 difference required for ionic compounds, so sodium fluoride is ionic.

8. (a) The formula SnF2 is named tin(II) fluoride. (b) PbS is named lead(II) sulfide.

9. In both ionic and covalent compounds the ―-ide‖ suffix indicates the compound is made up of only two different elements. The only exceptions to this are the ionic compounds know as the metal hydroxides, which involve the hydroxide ion bonded with a metal.

These compounds contain three different elements.

10. Since different compounds can be formed by the same elements, the prefixes are necessary to distinguish different binary compounds.

11. Variable-charge ions are ions of an element that have more than one possibility for their ionic charge. The modern system uses the English name of the metal followed by Roman numerals in parentheses, which indicate the charge number.

12. Polyatomic ions are groups of two or more elements bound tightly together which behave much like a single monatomic ion. The hydroxide ion (formula OH) with a net charge of –1 and the cyanide ion (formula CN) with a net charge of –1 are example polyatomic ions.

13. The formula of magnesium hydroxide is Mg(OH)2. The parentheses indicate that the OH pair is a polyatomic ion that occurs twice in this compound.

14. A double bond is a covalent bond in which two pairs of electrons are shared. Similarly, in a triple bond three pairs of electrons are shared in the bond.

For Further Analysis 8. Similarities – both are recognizable changes in the physical state or chemical composition of matter. Difference – chemical change alters the identity of matter, producing a new substance with different properties; physical change does not alter the identity of matter.

9. Ionic compounds dissolve in water, making a solution of ions that can conduct an electric current. Covalent compounds are molecular, composed of electrically neutral groups of atoms that are tightly bound together.

10. Metal atoms from the left side of the periodic table have a few electrons in outer orbitals that can be transferred to nonmetal atoms that are lacking a few electrons to fill the outer orbitals. This sets up ionic bonding reactions as the octet rule is satisfied.

Nonmetallic elements, on the other hand, can satisfy the octet rule by sharing electrons through covalent bonds.

11. Ionic – state the name of the positive metal ion, then the name of the negative nonmetal ion with an –ide ending. Covalent – The first element in the formula is named with a prefix indicating the number of atoms if the number is greater than one.

The stem name of the second element is named with a prefix if the two elements form more than one compound.

Group B Solutions 1. (a)

(b)

(c)

Li

+

F



– + Li [ F ]

Be

+

S



Be Li

Li + Li

(d)

O

 Li

2+

2–

+

[ O]

[ S]

+ +

–

2. (a) Lead(II) chloride

(c) Chromium(III) oxide

(b) Iron(II) oxide

(d) Lead(II) oxide

(a) Acetate

(d) Nitrate

(b) Hydrogen carbonate

(e) Permanganate

(c) Sulfate

(f) Carbonate

4. (a) Al(OH)3

(d) (NH4)2SO4

(b) Na3PO4

(e) NaHCO3

(c) CuCl2

(f) CoCl2

5. (a) SiO2

(d) H2O2

(b) H2S

(e) CF4

(c) BF3

(f) NH3

3.

6. (a) Dinitrogen monoxide

(d) Phosphorous pentaflouride

(b) Sulfur dioxide

(e) Selenium hexachloride

(c) Silicon carbide

(f) Dinitrogen tetroxide

7. (a)

(b)

(c)

(d)

polar covalent

Cl: 3.0 Cl: 3.0 3.0 – 3.0 = 0.0

covalent

S: 2.5 O: 3.5 3.5 – 2.5 = 1.0

polar covalent

Sr: 1.0 F: 4.0 4.0 – 1.0 = 3.0

(e)

O: 3.5 H: 2.1 3.5 – 2.1 = 1.4

(f)

10

Si: 1.8 C: 2.5 2.5 – 1.8 = 0.7

polar covalent

K: 0.8 F: 4.0 4.0 – 0.8 = 3.2

Chemical Reactions

Contents 10.1 Chemical Formulas Molecular and Formula Weights Percent Composition of Compounds 10.2 Chemical Equations Balancing Equations Case Study: Conservation of Mass Generalizing Equations 10.3 Types of Chemical Reactions Combination Reactions Decomposition Reactions Replacement Reactions Ion Exchange Reactions 10.4 Information from Chemical Equations

ionic

ionic

Units of Measurement Used with Equations Science and Society: The Catalytic Converter Quantitative Uses of Equations

Overview This chapter is concerned with information that can be gained from an understanding of chemical formulas and equations. The concepts include empirical and molecular formulas, percentage composition of a compound, writing formula equations, types of chemical reactions, and an introduction to quantitative information that can be learned from equations.

Each section of this chapter can be presented as is or expanded to include more in-depth subject matter if you so desire. Much information is available to persons who know how to read a chemical equation and how to use the periodic chart.

It is helpful to begin by reviewing the valence electrons and ionic charges on the monatomic ions of elements in groups I, II, VI, and VII and then writing the ionic formulas.

Students should realize that formulas could be easily written by knowing the ion name, symbol, and charge, which can be easily obtained by looking at the group number in the periodic table. Once this is understood, it becomes a matter of following the rules and understanding the basic generalization and models to write balanced chemical equations.

Suggestions 1. Illustrate as many of the types of chemical reactions as possible with demonstrations, explaining the meaning of the generalized form of the reaction in each case. A strip of magnesium can be burned in air, for example, to illustrate a combination reaction. The generalized form of X + Y  XY should be described during the discussion.

2. Decomposition reactions can be illustrated by heating calcium carbonate or soda water, then testing for the production of carbon dioxide with limewater.

3. A variety of metal and salt solution replacement reactions can be demonstrated to illustrate replacement reactions, and the results can be used to establish a relative activity series of metals. Include combinations of metals and salt solutions that result in ―no reaction‖ to help establish the activity series.

4. Ion exchange reactions can be illustrated by looking for the formation of a precipitate, a molecular substance, or a gas. Demonstrate several of these reactions before explaining what happened by way of equations.

5. Depending on the science experience and mathematical background of the students, it may be appropriate to illustrate the quantitative interpretations of the mole relationships in a chemical equation.

6. Additional demonstrations: (a) Burn a strip of Mg (Caution: Use tongs. Do not look directly at burning.) as an example of a combination reaction. (b) As an example of a decomposition reaction, mix concentrated H2SO4 in a small (50 mL or so) beaker half filled with table sugar. The sugar is decomposed to a growing ―tower‖ of carbon. (Caution: Noxious fumes. Use fume hood or perform outside.) (c) As an example for a replacement reaction, place an iron file in copper(II) sulfate solution or Cu wire in silver nitrate solution. (d) As an example of an ion exchange reaction, mix a sodium chloride solution with a solution of silver nitrate. Check for insolubility of products: NaCl + AgNO3  NaNO3 + AgCl.

For Class Discussions 1. The formula weight of glucose, C6H12O6, is a. 24 u. b. 29 u. c. 180 u. d. Weight of sample needed to calculate formula weight.

2. Which of the following represents an empirical formula? a. C6H12O6 b. KCl c. C2H2 d. C8H18 3. What is the mass percentage composition of potassium in saltpeter, KNO3? About a. 16% b. 33% c. 39% d. 48% 4. The coefficients needed to balance the equation Na3PO4 + AgNO3  NaNO3 + Ag3PO4 are a. 1, 1, 1, 1 b. 3, 1, 1, 3 c. 2, 3, 3, 2 d. 1, 3, 3, 1 5. When hydrocarbons and carbohydrates burn with sufficient O2 they a. always give off CO2 and H2O. b. sometimes give off CO2, but never H2O. c. sometimes give off H2O, but never CO2. d. never give off CO2 or H2O. 6. The mass of 6.02  1023 molecules of N2 is a. 14 g. b. 28 g. c. 8.4  1024 d. 1.7  1025

7. One mole of H2O contains a. 3.0  1023 hydrogen atoms b. 1.2  1024 hydrogen atoms c. 6.02  1023 molecules of hydrogen d. 1.2  1024 hydrogen molecules 8. What type of chemical reaction is this: H2O + CO2  H2CO3? a. Combination b. Decomposition c. Replacement d. Ion Exchange

Answers: 1c, 2b, 3c, 4d, 5a, 6b, 7b (2 moles) 8a.

Answers to Questions for Thought 1. An empirical formula identifies the elements present in a compound, as does a molecular formula. Where the empirical formula gives the simplest whole number ratio of atoms of the elements in the compound, a molecular formula gives the exact numbers of atoms in a molecule of the compound.

2. The basic parts of a chemical equation are symbols representing the elements or compounds involved in the reaction, symbols representing the elements or compounds that are products of the reaction, symbols indicating the physical state of the reactants and products, and a symbol indicating if heat is supplied or released. An arrow indicates the direction of the reaction. Gases are indicated by the symbol (g), liquids by (l), solids by (s), and aqueous solutions by (aq).

3. Conservation of mass states that matter is neither created nor destroyed in a chemical reaction. A chemical equation conforms to this law only if each element appears the same number of times on each side of the equation.

4. Beginning with the unbalanced equation, the number of each kind of atom on each side of the equation must be counted. These numbers are used to determine whether to place coefficients in front of the formulas and what the coefficients should be. The equation should be checked to make sure that the number of each type of atom on each side is equal and that the coefficients are in the lowest whole number ratio.

5. A compound made up exclusively of the elements hydrogen and carbon is a hydrocarbon. A carbohydrate is a compound made up of carbon and water. In general, the products of the combustion of hydrocarbons or carbohydrates are carbon dioxide and water.

6. (a) A combination reaction is a synthesis reaction in which two or more substances combine to form a single compound, for example: 2 H + O2  2 H2O. (b) In a decomposition reaction, a compound is broken up into either elements, simpler compounds, or a combination of elements and simpler compounds, for example: 2 HgO  2 Hg + O2. (c) A replacement reaction is when an atom or polyatomic ion is replaced by a different atom or polyatomic ion, for example: Al + 3 CuCl  AlCl3 + 3 Cu. (d) In an ion exchange reaction, the ions of one compound interact with the ions of another compound with the result of either a precipitate, a gas, or water, for example: HCl + NaOH  NaCl + H2O. 7. The formation of a precipitate, a gas, or water must occur for an ion exchange reaction to take place. If this does not occur, no ions have been removed, so no reaction has taken place.

8. (a) The reaction for the combustion of ethyl alcohol is C2H5OH + 3 O2  2 CO2 + 3 H2O. (b) The reaction for the rusting of aluminum is 4 Al + 3 O2  2 Al2O3. (c) There is no reaction between iron and sodium chloride.

9. This formula is molecular because it does not involve the simplest whole number ratio, which is two carbons to five hydrogens.

10. An element higher on the table will replace an element lower on the table in an ionic compound. If the element in the ionic compound is higher on the table than the other element proposed to replace it, no reaction will occur.

11. The gram formula weight is the mass of the compound in grams. This mass is numerically equal to the formula weight, which is the sum of the atomic weights of all the atoms in a chemical formula.

12. Avogadro’s number is the number of C-12 atoms in exactly 12.00 g of C-12, and it has a value of 6.02  1023. A mole is an amount of a substance that contains Avogadro’s number of atoms, ions, molecules, or any other chemical unit of that substance.

For Further Analysis 12. You would know for sure that you have a compound and not an element if it is a pure substance that can be broken down into simpler substances by chemical change.

13. Word equations describe a chemical change in general but say nothing about the quantities of the chemicals involved in the change. The advantage of writing a chemical equation with chemical symbols is that more information is provided about the composition of chemicals as well as the quantities involved. The disadvantage to this is that it requires knowledge and understanding of formulas as well as chemical symbols.

14. Answers will vary but will follow the generalized form of each reaction.

15. (1) write the correct formulas for the reactants and products in a chemical equation.

(2) Inventory the number of each kind of atom on each side of the equation. (3) Place coefficients in front of formulas to balance the equation. (4) Take another inventory to determine if the numbers of atoms on both sides are equal.

Group B Solutions 1.

(a) Empirical (b) Molecular (c) Empirical

(d) ? (e) Molecular (f) Empirical

2.

(a) N2O: 2(14.0 u) + 16.0 u = 44.0 u (b) PbS: 207.2 u + 32.1 u = 239.3 u (c) MgSO4: 24.3 u + 32.1 u + 4(16.0 u) = 120.4 u (d) HgCl2: 200.6 u + 2(35.5 u) = 271.5 u

3. (a) K2CO3 K: C: O:

(b) CaSO4 Ca: S: O:

(c) KNO3 K: N:

2(39.1 u) + 12.0 u + 3(16.0 u) = 138.2 u 2  39.1u   100%  56.6% 138.2 u 12.0 u  100%  8.7% 138.2 u 3 16.0 u   100%  34.7% 138.2 u

40.1 u + 32.1 u + 4(16.0 u) = 136.2 u 40.1u  100%  29.4% 136.2 u 32.1u  100%  23.6% 136.2 u 4 16.0 u   100%  47.0% 136.2 u

39.1 u + 14.0 u = 3(16.0 u) = 101.1 u 39.1u  100%  38.7% 101.1u 14.0 u  100%  13.8% 101.1u

O:

3 16.0 u   100%  47.5% 101.1u

(d) C8H10N4O2

8(12.0 u) + 10(1.0 u) + 4(14.0 u) + 2(16.0 u) = 194.0 u

C:

8 12.0 u   100%  49.5% 194.0 u

H:

10 1.0 u   100%  5.2% 194.0 u

N:

4 14.0 u   100%  28.9% 194.0 u

O:

2 16.0 u   100%  16.5% 194.0 u

4. (a) 2 NO + O2  2 NO2 (b) 2 KClO3  2 KCl + 3 O2 (c) 2 NH4Cl + Ca(OH)2  CaCl2 + 2 NH3 + 2 H2O (d) 2 NaNO3 + H2SO4  Na2SO4 + 2 HNO3 (e) PbS + 4 H2O2  PbSO4 + 4 H2O (f) Al2(SO4)3 + 3 BaCl2  2 AlCl3 + 3 BaSO4 5. (a) Decomposition (b) Replacement (c) Combination

(d) Ion exchange (e) Ion exchange (f) Replacement

6. (a) 2 C3H6(g) + 9 O2(g)  6 CO2(g) + 6 H2O(g) (b)H2SO4(aq) + 2 KOH(aq)  K2SO4(aq) + 2 H2O(l) (c) C6H12O6(s) + 6 O2(g)  6 CO2(g) + 6 H2O(l) (d)Na3PO4(aq) + 3 AgNO3(aq)  3 NaNO3((aq) + Ag3PO4(aq) (e) 3 NaOH(aq) + Al(NO3)3(aq)  3 NaNO3(aq) + Al(OH)3(aq) (f) 3 Mg(OH)2(aq) + 2 H3PO4(aq)  Mg3(PO4)2(aq) + 6 H2O(l)  7. (a) ZnCO3(s)  ZnO(s)+ CO2  (b)2 H2O2(l)  2 H2O(l) + O2(g) (c) NH4NO2(s)  2 H2O(l) + N2(g)

8. (a) Zn(s) + FeCl2(aq)  Fe(s) + ZnCl2(aq) (b)Zn(s) + AlCl3(aq) No reaction (c) Cu(s) + HgCl2(aq) Hg(s) + CuCl2(aq) (d)2 Al(s) + 6 HCl(aq) 2 AlCl3(aq) + 3 H2(g) 9. (a) Ca(OH)2(aq) + H2SO4(aq)  CaSO4(aq) + 2 H2O(l) (b) NaCl(aq) + AgNO3(aq)  NaNO3 + AgCl(s) (c) no reaction, both potential products are soluble (d) Na3PO4(aq) + 3 AgNO3(aq)  3 NaNO3(aq) + Ag3PO4 10. Iron(III) oxide yields two moles of iron for every mole of ore, magnetite yields three moles, and siderite yields one mole; therefore, magnetite gives the highest yield.

11

Water and Solutions

Contents 11.1 Household Water 11.2 Properties of Water Science and Society: Who Has the Right?

Structure of Water Molecules The Dissolving Process Concentration of Solutions A Closer Look: Decompression Sickness Solubility A Closer Look: What is BPA? 11.3 Properties of Water Solutions Electrolytes Boiling Point Freezing Point 11.4 Acids, Bases, and Salts Properties of Acids and Bases Explaining Acid-Base Properties Strong and Weak Acids and Bases The pH Scale Properties of Salts Hard and Soft Water A Closer Look: Acid Rain

Overview This chapter provides opportunities for the application of many fundamental chemical principles that were introduced in previous chapters. These principles are centered on solutions—what they are, how they are measured, and how they are used in many everyday activities. The concepts of mixtures, formula weights, ionic and polar compounds, and chemical equilibrium are used to explore many concepts. These include solubility and insolubility, the physical properties of water, the dissolving process, the properties of acids, bases, and salts, the pH concept, water hardness, and buffer solutions. The chapter materials can be presented at practically any depth to match the interest and abilities of the class.

Student interest in the materials of this chapter is generally high because of the many apparent applications to and explanations of everyday activities.

Suggestions 1. A variety of everyday solutions that relate concentrations can be displayed, such as bleaches, vinegar, hydrogen peroxide, beverages, and so forth. Recent news articles that report concentrations of minerals or pollutants in water or in the atmosphere can be analyzed and compared to other concentrations to bring relevancy to the lesson.

2. The concept of a solution is illustrated by mixing 100 mL of absolute alcohol with 100 mL of water. The resulting solution has a volume less than 200 mL, which raises the question of what happened to the missing solution. Use 100 mL of salt mixed with 100 mL of B-Bs for a model to show how smaller particles can get between the spaces of the larger particles. This makes less total volume (a bushel of peas mixed with a bushel of potatoes does not make two bushels of peas and potatoes). Relate the model to the alcohol and water mixture.

3. Stir small amounts of a soluble salt, such as potassium nitrate, in water in ever increasing amounts. Have the class identify when the solution is dilute, when it is concentrated, and when it is saturated. Students soon understand the vagueness of the terms ―dilute‖ and ―concentrated,‖ opening the way for a discussion of different ways to express concentration measurements.

4. Demonstrate how much the boiling point is elevated by adding a pinch of salt to a liter of water. Then relate the findings to the habit of some cooks adding a pinch of salt to water when cooking. See how much salt you must add to cause a meaningful change in the boiling point. Relate findings to text materials.

5. Test the electrical conductivity of various compounds and solutions with a flashlight bulb and battery. Complete the circuit by plunging the two ends of the exposed wires

into pure acetic acid placed in a beaker. Then add water to produce ions and test again.

Try the same arrangement with powdered sodium hydroxide, then add water and repeat.

6. If a pH meter is available, add equal amounts of hydrochloric acid and acetic acid to two beakers containing 100 mL of water. To give a color variation add several drops of universal indicator to each beaker. With the pH meter, check the pH of bleach and of vinegar. Pour the two substances together very slowly and check the pH to show neutrality. The amounts to produce neutrality should be determined in advance.

Demonstrate the pH of distilled water and tap water.

7. Additional demonstrations: Set up the apparatus as illustrated in Figure 11.1 for the classic ammonia fountain demonstration. The long glass tube has a tapered end that reaches about two-thirds of the way into a one-liter Florence flask. The medicine dropper contains a small amount of water. The beaker contains about 2-L water with about 6 drops of phenolphthalein. Charge the fountain by filling the Florence flask with relatively dry NH3. In a hood, use a gas generator with concentrated NH4OH dropped into solid NaOH pellets. Fill the Florence flask with the dry NH3 by downward displacement of air.

(Caution: Use a fume hood. Do not inhale ammonia.) Fit the stopper assembly into the flask, then invert over the beaker with phenolphthalein solution. Start the fountain by squeezing the water from the medicine dropper.

For Class Discussions 1. Substances that are ionic crystals are made up of a. isotopes. b. ions. c. atoms. d. molecules.

2. The intermolecular force of attraction known as a hydrogen bond comes from a. uneven distribution of charges around a molecule. b. electrons being transferred from one molecule to another. c. the symmetry of even charge distribution in a molecule. d. electrons being shared and re-shared in a symmetrical molecule.

3. A solution with a pH of 7 is a. slightly acidic. b. slightly basic. c. neutral.

4. Water is able to dissolve certain ionic compounds because water is made up of a. separated positive and negative ions. b. symmetrical covalent molecules. c. strongly polar molecules. d. slightly acidic molecules.

5. Suppose it is late during a very cold winter and there is a very deep lake that has a thick layer of ice on top. The temperature of the water at the bottom of this lake should be a. 0°C b. 4°C c. 10°C d. unknown 6. Adding a solute, such as salt, will have what effect on the freezing point of water? It a. is lowered. b. is raised. c. remains the same.

7. A strong acid is strong because it is a. completely ionized in water.

b. free of dissolved materials. c. mostly insoluble in water. d. made up of nonpolar molecules.

8. During a reaction that involves chemical equilibrium a. the forward and reverse reactions are stalled. b. a forward reaction occurs at the same time as a reverse reaction. c. the forward reaction has stopped and the reverse reaction is beginning. d. the reverse reaction has stopped and the forward reaction is beginning.

9. Will a solute that raises the boiling point of water also raise the freezing point? a. Yes. b. No. Answers: 1b, 2a, 3c, 4c, 5b, 6a, 7a, 8b, 9b.

Answers to Questions for Thought 1. A solution is a homogeneous mixture of ions or molecules of two or more substances.

Not all mixtures are homogeneous and not all are mixtures of ions or molecules.

2. If the attraction between the ions is greater than the hydration energy the ionic compound is insoluble in water. Ionic compounds whose attraction to the polarized water molecules is greater than those between ions are soluble.

3. The presence of the dissolved salt decreases the number of water molecules at the surface. This occurs since the sodium ions and chlorine ions are taking up some of the space near the surface. Since there are fewer water molecules near the surface to escape, the vapor pressure is lowered. This increases the temperature necessary to obtain the vapor pressure required to boil the water and salt solution.

4. The greatest density of water occurs at a temperature of 4º C. A lake covered with ice (0º C) would probably have the greatest density water—with a temperature of 4º C—at the bottom of the lake.

5. Water at very close to freezing has hydrogen bonds present between many of the molecules. These bonds spread out the water molecules. As the temperature of the water increases above the freezing point (from 0º to 4º C), the bonds break and allow the molecules to collapse together.

6. A solution of Ca2+ or Mg2+ ions in water is called hard water. Removing the calcium and magnesium ions softens the water.

7. NaCl does not donate protons to form hydronium ions, and it does not accept protons to form hydroxide ions when it is dissolved in water. Since the pH scale is a measure of the hydronium ion concentration, the pH does not change because the hydronium ion concentration does not change.

8. A hydrogen bond is a weak to moderate strength bond between the hydrogen end (+) of a polar molecule and the negative end (–) of a second polar molecule. The bond forms when the positively charged end of a polar molecule, which is usually a hydrogen atom, is attracted to the negative end of another polar molecule. This negative end is usually an oxygen, fluorine, or nitrogen atom. If the two ends come close enough together, this electrical force of attraction forms a bond.

9. A soap molecule has two parts, a part that is polar, which allows the soap to be soluble in water, and a nonpolar part, which is absorbed into oil. Soap molecules attach onto oil molecules and carry the oil away with rinse water.

10. (a) Acids are associated with the presence of hydronium ions in a water solution. (b) Bases are associated with the presence of hydroxide ions in a water solution.

11. The pH scale is based upon the reciprocal of the hydronium ion concentration in water.

Pure water has a hydronium ion concentration of 1  10-7, the reciprocal of which is 1   107. The pH is the exponent of the ten, so 7 is defined as neutral. If any other number were used, the scale would make no sense and would have to be redefined.

For Further Analysis 9. Similarities – both are measures of concentration. Differences –salinity is the mass of salt in 1,000 g of solution; a comparable percent by weight is the weight of salt in 100 weight units of solution.

10. Answer will vary, but should recognize the ratios of 1/1,000,000 (ppm), 1/1,000,000,000 (ppb), 1/100 (percent), and g salt/kg solution (salinity).

11. Possible explanation should involve a discussion of water as a polar molecule and hydrogen bonding.

12. A salt that will dissolve does so because the attraction between the polar water molecules and a charged ion is greater than the attraction between the ions. A salt that will not dissolve has greater attractions between the ions than between the polar water molecules and the ions.

13. The boiling point is defined as occurring in pure water at sea level pressure.

14. Similarities – Acids and bases are chemical opposites dissolved in water and a salt is produced by a neutralization reaction between and acid and a base. Differences – An acid is a proton donor in a water solution; a base is a proton acceptor in a water solution; a salt is an ionic compound produced when acids and bases react.

15. Answers will vary, but should include the basic idea that pH is a power of ten notation that expresses the hydronium ion concentration. The scale ranges from 1 (most acidic) to 14 (most basic), with 7.0 as the pH of a neutral solution.

16. (1) If the hard water is caused by magnesium or calcium bicarbonates, heat the water.

(2) If caused by calcium sulfate, add washing soda, TSP, or borax. (3) Use ion exchanger to remove magnesium or calcium ions. (4) Distill the water.

Group B Solutions 1. msolute  100.0%  % solute msolution

2.19 g  100.0%  2.9% NaCl by weight 75 g

2.

10 g  100.0%  9% NaCl by weight 100 g  10 g 

3.

part  100% whole 0.5 g  100%  5  195 % SO2 by weight 1,000,000 g % 

4. % by volume =

 Vsolute



Vsolute  100.0% and Vsolution Vsolution

% by volume  Vsolution 100.0%

Finally : Vsolvent

 Vsolutiont  Vsolute

% by volume   1   100.0%   70%   1    150 mL  100.0% 

 Vsolutiont

 500 mL

Vsolvent

and Vsolvent

 Vsolvent  Vsolute

5.

Vsolute  100.0%  Vsolute Vsolution

% by volume =

Vsolute





% by volume  Vsolution 100.0%

0.05%  6300 mL  3.2 mL of alcohol 100.0%

6.

Vsolute  100.0%  Vsolute Vsolution

% by volume =

Vsolute





% by volume  Vsolution 100.0%

5.0%  355 mL  18 mL of alcohol 100.0%

7. (a)

0.25 ppm ppm 1  104 %

 2.5  105 %

mass of part  100% of whole = % of part mass of whole

(b) mass of part  100% of whole = % of part mass of whole mass of whole  mass of part =  % of part 100% of whole 80,000 g mass of part =   2.5  10 5%  100% of whole  0.02 g

(c)

0.80 ppm  8.0  105% ppm 1  104 %

8. (a) donor: H3PO4 acid: H3PO4

acceptor: H2O base: H2O

(b)donor: H2O acid: H2O

acceptor: N2H4 base: N2H4

(c) donor: HNO3 acid: HNO3

acceptor: HC2H3O2 base: HC2H3O2

(d)donor: NH4 acid: NH4

acceptor: Mg base: Mg

12

Organic Chemistry

Contents 12.1 Organic Compounds 12.2 Hydrocarbons Alkenes and Alkynes Cycloalkanes and Aromatic Hydrocarbons 12.3 Petroleum 12.4 Hydrocarbon Derivatives Alcohols Ethers, Aldehydes, and Ketones Organic Acids and Esters Science and Society: Aspirin, a Common Organic Compound 12.5 Organic Compounds of Life Proteins Connections: Protein structure and Sickle-Cell Anemia Carbohydrates Fats and Oils Synthetic Polymers

Overview The ubiquitousness of organic compounds should be stressed to students in introducing organic chemistry. It should be pointed out, for example, that the gas, coal, and oil used by our society are all organic compounds. The trees and plants of the forested lands of the earth are also made of organic compounds. Indeed, all animals (including humans) are made up of organic compounds. A very strong case can be made for oil and coal not being used as fuel because they are such marvelous sources of the types of organic compounds needed in our technological society.

Various organic compounds of special interest to students have been included in this chapter. These compounds are used as examples of the classes of hydrocarbon derivatives — alcohols, ethers, aldehydes, ketones, organic acids, and esters. The particular structures are included in the various classes of derivatives to act as attention-getting subjects that will give students greater reason to familiarize themselves with that particular group of organic compounds. For instance, considerable interest can be generated in the classroom by considering the various kinds and types of alcohols and what happens when a bottle of wine ―goes bad.‖ There can be interest in the organic compounds of insect stings and why they hurt. Many are usually interested in the esters responsible for the aroma and flavor of fruit and for the aroma of roses and lilacs. Synthetic polymers, the many types of plastics, and synthetic fibers in use in our society today are also topics of special interest to students, including the environmental problems created by the plastics.

The importance of bond orientation in chemical compounds can be stressed by pointing out the relatively small difference in the way that the glucose molecules of starch and cellulose are linked. Also, to be stressed is the tremendous difference in the chemical and physical properties of starch and cellulose because of the different way in which the glucose units are chemically bound together.

Suggestions 1. Ask students to list and/or collect various organic compounds available in today’s home.

Remind students that organic compounds are present in many places in the home rather than just in the kitchen.

2. The distinguishing characteristics of organic acids, alcohols, and esters can be contrasted with those of inorganic acids, bases, and salts.

3. The distillates from crude oil and their physical differences make an interesting display for students to observe. You can obtain a sample of crude oil by writing public relations officers of the major oil companies if there is not a local source. The distillates should be sealed in airtight containers to retard evaporation.

4. To illustrate the carbon content in an organic compound, add a sufficient amount of concentrated sulfuric acid to cover the surface of about 100 g of granular sugar that is poured into a beaker. Stir the mixture with a glass rod until a color change appears, then watch the black column of carbon rise above the beaker. Obnoxious odors are produced by this reaction, so use a fume hood, perform the demonstration outside, or display only the result of the reaction to the class.

5. Additional demonstrations: (a) Generate ethylene gas by cautiously boiling 25 mL C2H5OH with 80 mL concentrated H2SO4. Boil the mixture with boiling chips in a Florence flask on a ring stand that is fitted with a thistle tube and gas collection tube in a two-hole stopper.

Collect the gas by water displacement, gradually adding all the acid to the thistle tube as you gently boil the mixture. Add an inverted bottle of ethylene to a plastic bag with unripe fruit. (b) Show a few of the esters produced when an alcohol reacts with an acid. (1) In a test, heat 2 mL butyric acid, 2 mL ethyl alcohol, and 1 mL concentrated H2SO4 (dehydrating agent). Ethyl buterate should form, which has the odor of pineapples. (2) To produce amyl acetate, heat 5-mL acetic acid, 3-mL amyl alcohol, and 1-mL concentrated H2SO4.

Amyl acetate has the odor of bananas.

For Class Discussions 1. Carbon atoms can form so many different organic compounds because they a. can combine with up to four other carbon atoms as well as other kinds of atoms. b. form covalent bonds by sharing electrons. c. are easily decomposed by heat. d. have a tetrahedral molecular shape.

2. Compounds with the same molecular formulas but different structures are known as a. polymers. b. isotopes. c. isomers. d. polytopes.

3. One of the following is an incorrect alkane formula. a. CH4 b. C2H8 c. C4H10 d. C8H18 4. Of the following, the most stable is a. C2H6 b. C2H4 c. C2H2 d. none of the above 5. Of the following, which is most likely to be found in gasoline? a. CH4 b. C7H16 c. C14H30

d. C16H34 6. Jet fuel, kerosene, coal oil, and lamp oil are names for the same group of hydrocarbons. a. Yes. b. No.

7. All of the different kinds of alcohols a. have either one, two, or three OH functional groups. b. are safe to drink. c. are denatured. d. have one OH functional group.

8. The building blocks of all proteins are a. monosaccharides. b. esters. c. alpha-amino acids. d. triglycerides.

9. Polyunsaturated oils are oils that a. have room for more cholesterol. b. have a higher number of units with double bonds. c. are dry oils, containing no water. d. are used in the manufacture of polymers.

10. Synthetic polymers that are variations of ethylene-derived monomers are manufactured from a. fruit extracts, such as citrus fruit skins. b. fermentation reactions. c. fossil fuels. d. formaldehyde Answers: 1a, 2c, 3b, 4a (ethane is saturated), 5b, 6a, 7d, 8c, 9b, 10c.

Answers to Questions for Thought

1. A compound with carbon as its principal element is defined as an organic compound.

2. Organic compounds are more numerous because carbon atoms can link with other carbon atoms as well as with atoms of other elements. This ability is unique to carbon and allows it to form a wide variety of compounds. In addition, carbon’s valence of four allows it to link up with four other carbon atoms, or a wide range of other kinds of atoms, allowing for an almost limitless range of combinations.

3. The process by which straight-chained hydrocarbon molecules are converted into branched molecules is called cracking and reforming. Cracking is accomplished by heating the straight-chained molecules in the absence of oxygen, which causes the longer chains to break into smaller carbon-chain units. Passing the smaller hydrocarbons through a catalyst promotes the reformation reaction, inducing reforming of the smaller chains into branched-chain molecules.

4. Ethane has only one structure because it has so few atoms, so it does not have any isomers.

5. Ethylene has a double carbon bond that can be broken to provide sites for single covalent bonds to join the ethylene units. Ethane is an alkane, so it does not have a double carbon bond to break to allow it to form long chains.

6. (a) Natural gas is a mixture of hydrocarbon gases, mostly methane. (b) LPG is liquefied propane or butane. (c) Hydrocarbons with five to seven carbon atoms per molecule are called petroleum ethers.

7. The octane number scale describes the burning rate of gasoline. The scale is based on pure n-heptane, straight-chain molecules that are assigned an octane number of 0, and a multiple branched isomer of octane, 2,2,4-trimethylpentane, which is assigned an octane number of 100.

8. A functional group is the atom or groups of atoms in an organic molecule that is the site of a chemical reaction. Functional groups are chemically active because they have multiple bonds that can be broken in order to have chemical reactions, or because they have lone pairs of electrons that can participate in reactions.

9. The structural formula for alcohol is ROH. Alcohols are named according to the hydrocarbon group (R) in the ROH formula. For example, ethyl alcohol (ethanol, or C2H5OH) is

H

H

H

C

C

H

H

OH

10. Fats and oils are esters formed from glycerol and three long-chain carboxylic acids.

Unsaturated fats and oils do not contain the maximum number of hydrogen atoms;

instead, multiple bonds are present. Saturated fats and oils contain the maximum number of hydrogen atoms possible for their molecules.

11. A polymer is a long chain of repeating molecular units. Cellulose is a polymer formed naturally in plants. Polyethylene is a synthetically produced polymer.

12. A bottle of ―bad‖ wine has been oxidized, converting the ethyl alcohol of the wine into acetic acid. Acetic acid is the acid of vinegar, and an oxidized bottle of wine is indeed now a bottle of vinegar. Since people usually do not like to drink vinegar, the person who ordered the wine customarily tastes a small portion first. This person also breaks the bottle cork to make sure it is dry, since the cork is supposed to seal the wine from oxygen in the atmosphere. If moist, the cork is sometimes sniffed to check for the odor of vinegar.

For Further Analysis 1. Many people feel that by using a higher-octane gasoline in their vehicles that they will get ―better performance.‖ What is the difference between high octane and regular gasoline? The amount of octane will vary depending on the gasoline investigated. Does scientific evidence bear this out? The octane rating of an engine depends on the manufacturer’s recommendation. In certain situations, the answer is yes. What octane gasoline is recommended for your vehicle? Answer will vary depending on the engine.

2. There have been some concerns about the ―additives‖ used in gasoline. What are these additives? Most gasoline contains alcohol. What purpose does it serve? What are the negative impacts of adding alcohol to gasoline?

3. The so-called ―birth control pill,‖ or ―the pill,‖ has been around since the early 1960s.

This medication is composed of a variety of organic molecules. What is the nature of these compounds? The ―pill‖ contains hormones that are members of the lipid group known as steroids. How do they work to control conception since they do not control birth? These hormones at the proper concentration prevent ovulation. What are some of the negative ―side effects‖ and what are some of the related benefits of taking ―the pill?‖ Increased risk of blood clots, stroke and heart attack.

4. Many communities throughout the world are involved in recycling. One of the most important classes of materials recycled is ―plastic.‖ There has been concern that the cost recycling plastics is higher than the cost of making new plastic products. Go to the Internet and a. Identify the kinds of plastics that are commonly recycled. b. Explain how a plastic such as HDPE is recycled. c. Present an argument for 1. Eliminating the recycling of HDPE 2. Expanding the recycling of HDPE.

Answers will vary.

Group B Solutions

1.



V = 20.0 L Ρ = 0.85 g/mL M=?

m  m  V V g     0.85   20, 000mL  mL   g  0.85  20, 000  mL mL =17,000 g =17 kg

2.

F4C2 = 4(19.0) + 2(12.0) = 100 3.

Propyl alcohol has a single OH and there are two possibilities:

4.

Alcohol is a hydrocarbon radical joined by one or more OH. Methyl alcohol is a methyl radical and one OH,

5.

An ether molecule is two hydrocarbon radicals joined by an oxygen atom, or R-O-R. In methylethyl ether a methyl and an ethyl group are linked to an oxygen,

6.

A ketone molecule is two hydrocarbon radicals joined by a carbon atom with an oxygen. In methyl ethyl ketone methyl and ethyl group are linked to a carbon and oxygen,

7.

The OH functional group is alcohol.

8.

Hexane contains the maximum number of hydrogen atoms, so it is saturated.

13

Nuclear Reactions

Contents 13.1 Natural Radioactivity Nuclear Equations The Nature of the Nucleus Types of Radioactive Decay Radioactive Decay Series 13.2 Measurement of Radiation Measurement Methods A Closer Look: How Is Half-Life Determined?

Radiation Units A Closer Look: Carbon Dating Radiation Exposure 13.3 Nuclear Energy A Closer Look: Radiation and Food Preservation A Closer Look: Nuclear Medicine Nuclear Fission Nuclear Power Plants A Closer Look: Three Mile Island and Chernobyl Nuclear Fusion A Closer Look: Nuclear Waste Science and Society: High-Level Nuclear Waste The Source of Nuclear Energy Overview The general public often needlessly fears all sorts of radioactivity because people generally do not understand radioactivity. It seems to be something invisible that can move through the air and kill. Just as people are afraid of the dark because they do not know what is there,

radioactivity is feared because of a lack of knowledge. This does not mean that radioactivity is safe, but rather that erroneous and distorted information should not be used as a basis for decisions about nuclear energy. The purpose of this chapter is to develop a more accurate understanding of radioactivity and the issues involved in its uses.

As often happens in science, many great discoveries in this area were the result of seemingly unimportant incidents. The accidental exposure of photographic film to a uranium ore led to Becquerel’s discovery of radioactivity. His continued research, along with that of Rutherford and the Curies, opened a new frontier for scientists of all specialties to explore.

The nature of the nucleus, the types of radioactive decay, the resulting radioactivity emitted, and the methods of measuring radiation set the stage for the discussion of the uses of nuclear energy. Few students know the identity of alpha and beta particles, nor do they often understand their origins. The similarities of gamma rays, X rays, radio waves, light, and so forth should be discussed. Only energy and origin separate one from the other since the electromagnetic spectrum is continuous. The binding energy and mass defect are meaningful applications of the relationship of matter to energy, E = mc2. It is generally a surprise for students to learn that it is a physical impossibility for a nuclear power plant to explode as a nuclear bomb. Once this is understood, it is natural then to discuss the consequences of exposure to radioactivity and the controversy surrounding this topic. Finally, the concerns about nuclear wastes are explored.

Suggestions 1. The scientific area encompassing radioactivity and its properties is one in which most students are almost completely lacking in knowledge. Their impressions have developed from misconceptions, so as the instructor you should develop their understanding carefully and thoroughly, without bias one way or the other.

2. Hospitals may release to you various X ray photographs that might prove of interest to students. The negatives can be projected with an overhead projector.

3. Most states have a department of disaster or emergency services that have a supply of portable GM counters and other survey meters. You may find that these units are already available within the school, and they are excellent for demonstrations. Check with your radiation safety officer or health physicist.

4. Alpha particles can be detected with certain GM counters, for example, Pancake GM Tube Survey Meter Model #3 from Ludlum Measurements, Inc., Sweetwater TX. Other tubes are also available that can detect the alpha particle with some efficiency.

5. A portable GM counter, along with beta and gamma sources, is most useful in illustrating the properties of the two particles, including their activity, energy, and charge. The counter can also be used to check rocks, watches, pottery, dinnerware, and other substances for radioactivity. The lantern mantle used in unleaded gasoline and

propane lanterns contains thorium oxide and provides an excellent source of radioactivity for demonstrations and laboratory measurements.

6. Additional demonstrations: (a) A cloud chamber can be used to show the tracks produced by emissions from radioactive materials. (b) A Geiger-Muller tube and counter can be used to show background radiation and test everyday materials for radioactivity. Test old, orange-colored pottery since uranium salts were formerly used as a color pigment. (c) Place a metal key on high-speed photographic film, then cover the key and film with cutup lantern mantles. Develop the film in about a week or so. The black area around the white key image is a result of exposure to radiation. The lantern mantle contains radioactive thorium oxide.

For Class Discussions 1. The property of radioactivity in materials is caused by a. the pull of electrons on and the repulsion of protons in the nucleus. b. instability from struggles between electromagnetic and nuclear forces. c. nuclear instability from an accumulation of isotopes. d. nuclear forces, which squeeze particles out of the nucleus.

2. Radiation from a radioactive material can be any of the following except a (an) a. helium nucleus. b. electron. c. proton. d. gamma ray.

3. A beta particle, sometimes called a beta ray, is a (an) a. electron from the nucleus. b. photon from the nucleus. c. proton from the nucleus. d. photon from the second energy level.

4. Which of the following is most likely to happen to an alpha particle after it is emitted? a. It escapes to space, where it is known as a cosmic ray. b. After being absorbed by matter it is dissipated as radiant energy. c. After joining with subatomic particles it finds itself in a child’s balloon. d. It joins others of its kind to make lightning and thunder.

5. Which of the following is most likely to happen to a beta particle after it is emitted?

a. It escapes to space, where it is known as a cosmic ray. b. After being absorbed by matter it is dissipated as radiant energy. c. After joining with subatomic particles it finds itself in a child’s balloon. d. It joins others of its kind to make lightning and thunder.

6. A nucleus emits a beta particle so the number of nucleons it contains is now a. more. b. less. c. the same.

7. A nucleus emits an alpha particle so the number of nucleons it contains is now a. more. b. less. c. the same.

8. The mass of an atomic nucleus compared to the mass of the individual nucleons making up the nucleus is always a. less b. more c. the same.

9. Enriched uranium has more a. energy. b. radioactivity. c. deuterium d. uranium-235.

10. The maximum binding energy per nucleon occurs in nuclei of a. low mass number. b. high mass number. c. intermediate mass number

Answers: 1b, 2c, 3a, 4c, 5d, 6c, 7b, 8a, 9d, 10c.

Answers to Questions for Thought 1. Radioactive materials emit invisible radiation. A radioactive material contains atoms that spontaneously emit particles or energy from their nuclei. This often results in the change of identity of these atoms, so radioactive materials often decompose into different materials. Nonradioactive materials exhibit none of this behavior.

2. Radioactive decay is the natural spontaneous disintegration or decomposition of a nucleus. Changing the decay rate is not possible.

3. The three kinds of radiation emitted by radioactive materials are as follows: alpha particles, which are helium nuclei; beta particles, which are electrons ejected at high speed; and gamma radiation, which is a high-energy burst of electromagnetic radiation.

Alpha particles eventually acquire electrons and become ordinary helium atoms. Beta particles either remain free electrons or join an ion to become part of an atom. Gamma radiation is absorbed by materials, giving its energy to the material absorbing it.

4. The force known as the strong nuclear force binds protons and neutrons together in a nucleus. This force, over very short distances, is much stronger than the electromagnetic force and overcomes it.

5. A half-life is the time it takes half of the unstable nuclei in a radioactive substance to undergo radioactive decay. Iodine 131 has a half-life of eight days; after forty days, five half-lives have elapsed, and only 1/32 of the original material remains.

6. Isotopes with a longer half-life are less active than isotopes with shorter half-lives because the activity rate determines the half-life of a material. High activity gives short half-lives and more radioactivity.

7. (a) A curie is a unit of activity of a radioactive source and is defined to be 3.70  1010 nuclear disintegrations per second. (b) A rad is a measure of radiation received by a material. One rad releases 1  10-2 joules per kg. (c) A rem measures the possible biological damage produced by different types of radiation. Since it depends upon the location as well as the type of source, the definition of a rem is very complex.

8. Background radiation is radiation from natural sources that are part of the environment.

The normal dose of background radiation is between 100 and 500 millirem per year.

9. Lack of knowledge, as well as the difficulty in obtaining reliable results not due to extraneous factors, fuels the controversy over long-term, low-level radiation exposure.

Since cancer can arise from many factors, including a combination of seemingly unrelated actors, it is difficult to say that low-level radiation is responsible for any increased incidence of cancer.

10. The difference between the actual mass of a nucleus and the sum of the masses of individual nucleons making up the nucleus is the mass defect of the nucleus. This difference in mass has been converted to energy, which was released as the more stable nucleus was formed. This energy is equivalent to the binding energy of the nucleus, and it can be calculated by using the mass defect as the mass in Einstein’s equation E = mc2.

11. Nuclear fusion is the process in which two nuclei with low mass numbers collide at very high speeds and ―stick together‖ to form a heavier, more stable nucleus. Nuclear fission is the nuclear reaction of splitting a massive nucleus into more stable, less massive nuclei. Both processes release energy because in both cases more stable nuclei are the result. More stable nuclei have larger binding energies, so energy must be released by less stable nuclei to gain stability.

For Further Analysis 8. A radioactive isotope has an unstable nucleus that will disintegrate into a simpler nucleus, giving off alpha, beta, or gamma radiation. An isotope that is not radioactive has a stable nucleus that will not disintegrate.

9. All types of radioactive decay are ionizing radiation, and this ionization can produce free polyatomic ions that can interfere with cell functions or disrupt chemical bonds in essential organic molecules such as DNA. 10. Answers will vary but address that some nuclear arrangements are less stable than others are.

11. Answers will vary but should illustrate the basic differences between the two models.

12. Figure 13.13 shows that the maximum binding energy per nucleon occurs around mass number 56, and then decreases in both directions. As a result, fission of massive nuclei and fusion of less massive nuclei both release energy.

13. Answers will vary but should point out that waste fuel rods contain an appreciable amount of usable uranium and plutonium.

14. Similarities – both supply energy through nuclear reactions. Differences – a fission power plant slowly provides energy through fission processes; a fusion power plant provides much energy through fusion processes; a fission reaction can be contained in a nuclear reactor, but a fusion reaction requires confining hot plasma in a magnetic field.

Group B Solutions

1. (a) Al: 13 protons; 12 neutrons

(c) Sn: 50 protons; 70 neutrons

(b) Tc: 43 protons; 52 neutrons

(d) Hg: 80 protons; 120 neutrons

2. (a)

25 12

(b)

95 43

Al Tc

(c)

120 50

(d)

200 80

Sn Hg

3. (a) Unstable, because isotopes with an atomic number less than 83 are stable when the ratio of protons to neutrons in the nucleus is 1:1, which is not the case here. (b) There are odd numbers of both protons and neutrons, and the ratio of protons to neutrons is not 1:1, therefore it is unstable. (c) Stable, because there are even numbers of protons and neutrons. In addition, 50 is a particularly stable number of nucleons. (d) Stable, because there are even numbers of protons and neutrons, allowing them to pair up.

4. (a)

14 6

C 

(b)

60 27

Co 

60 28

Ni 

(c)

24 11

Na 

24 12

Mg 

(d)

241 94

Pu 

241 95

(e)

131 53

I 

(f)

210 82

Pb 

210 83

5. (a)

241 95

Am 

237 93

(b)

232 90

Th 

228 88

Ra 

4 2

He

(c)

223 88

Ra 

219 86

Rn 

4 2

He

(d)

243 92

U 

239 90

(e)

242 96

Cm 

238 94

(f)

237 93

Np 

233 91

14 7

N 

131 54

0 1

e 0 1

e

0 1

Am 

Xe 

0 1

0 1

Bi 

e

e 0 1

Np 

Th 

e

e

4 2

4 2

He

He

Pu 

4 2

Pa 

4 2

He

He

6.

The fraction remaining is

We wish

1.0g 1.0 1  or 3 3 1.0  10 kg 1.0  10 1,000

1 1 to equal or 2 n  1,000; 210  1,024, therefore n 2 1,000

ten half-lives have passed, for a total time of: 10  30 years = 300 years.

14

The Universe

Contents 14.1 The Night Sky 14.2 Stars Origin of Stars Brightness of Stars Star Temperature Star Types The Life of a Star Protostar Stage Main Sequence Stage Red Giant Stage Back Toward Main Sequence Beginning of the End for Less Massive Stars A Closer Look: Observing with New Technology Science and Society: Light Pollution Beginning of the End for Massive Stars 14.3 Galaxies A Closer Look: Extraterrestrials?

The Milky Way Galaxy Other Galaxies 14.4 The Universe The Life of a Galaxy A Closer Look: Dark Matter

Overview

It is usually news to some students that our Sun is a star much like the other stars in the universe. You should point out that we know as much about stars as we do because we have a star, our Sun, relatively nearby to study. We are able to make photographs and measurements and obtain instrument readings of the Sun by telescopic observations and flyby space probes. The position of our star in the Hertzsprung-Russell diagram will help students realize that our Sun is but an average star in terms of size, surface temperature, and luminosity. The section on the life of a star can be made more personal to students by discussing the birth, evolution, and death of our Sun and the consequences of these events on Earth.

Our galaxy, with its hundreds of billions of stars, also contains many immense patches of gas and dust particles known as nebulas. All nebulas are essentially alike, but bright nebulas are bright because they are close to hot, bright stars, so the nebulas shine by reflections and fluorescence. Dark nebulas are so far from hot, bright stars that they appear dark. Most nebulas have been formed from the debris of exploding stars. New stars are still forming in the regions of many nebulas. This chapter also discusses our galaxy, the Milky Way. Invariably, a few students will confuse our galaxy with our solar system; consequently, you should point out the difference each time either is discussed. Invariably, a few students will confuse our galaxy with our solar system; consequently, you should point out the difference each time either is discussed.

Suggestions 1. Compare life among the ancients with our lives today. Why might they have noticed more about the night skies than we do?

2. Point out the ancients’ need for accurate information about the positions of the stars, the Moon, and the Sun compared to our need for such information.

3. You might have available crude models of the simple instruments the ancients used to make accurate measurements of the positions of the Sun, the stars, and other astronomical objects. To illustrate stellar parallax, draw a spot on the board. Have the students close one eye, hold a finger of an extended arm on the spot, and move their heads in a circular motion to simulate the revolution of Earth about the Sun. 4. Have an art major illustrate his or her interpretation of the birth of stars. Others may give their renditions of the various star classifications.

5. Pulsars can be related to the flashing lights of lighthouses, ambulances, or police vehicles. Recordings of sounds made by various pulsars can be obtained from radiotelescope observations.

6. Plastic balls of various sizes and colors can be prepared to represent the different classifications of stars. The sequence involved in the life of a star can be illustrated very vividly with the models.

7. Have students observe the Milky Way if you are in a location where it can be seen at night. Point out that they will be looking along the long axis of our galaxy.

8. Have students determine the length of a light year and then the dimensions of our galaxy in miles and kilometers.

9. The big bang theory of the expanding universe is well illustrated by a balloon with spots painted on it. An ant on the balloon’s surface would see all spots recede as the balloon expands.

For Class Discussions 1. The radius of Earth’s orbit around the Sun is a. a pair of seconds. b. a light year. c. an astronomical unit. d. an arc second.

2. More massive stars generate a. higher temperatures. b. lower temperatures. c. average temperatures. d. temperatures that are neither higher nor lower than less massive stars.

3. More massive stars on the main sequence tend to be a. brighter and bluish. b. white, with an average brightness. c. yellow, with an average brightness. d. fainter, with an reddish color.

4. Where a star is on the main sequence and what happens to it next depends on its a. composition. b. radius. c. temperature. d. mass.

5. Comparing the following list of star types, the oldest star is probably a(n)

a. main sequence star. b. red giant. c. white dwarf. d. blue giant.

6. Only a more massive main sequence star will have an opportunity to become a(n) a. white dwarf. b. supernova. c. red giant. d. red dwarf.

7. The star known as the Cepheid variable is important because they a. are very bright and easily identified. b. can be used as cosmic distance mileposts. c. help determine where a main sequence star is in the H-R diagram. d. serve as lighthouses, warning of cosmic hazards.

8. Our Milky Wag galaxy a. is about 33,000 light years across. b. has a radius of approximately 1 or 2 light years. c. contains about 95% of all the know stars in the universe. d. has a diameter of about 100,000 light years.

9. According to the accepted model of the life cycle of a star, the Sun will next become a a. red giant b. white dwarf c. supernova d. black hole 10. A black hole might form when a. a white dwarf cools, no longer emitting light. b. the core of a super-massive star collapses. c. a neutron star begins to spin, creating an extremely powerful magnetic field. d. a supernova implodes.

Answers: 1c, 2a, 3a, 4d, 5c, 6b, 7b, 8d, 9a, 10b.

Answers to Questions for Thought 1. The celestial meridian is an imaginary line passing through the point on the celestial sphere directly above your head, through the north celestial pole, continuing around to pass through the south celestial pole back to the point above your head. Since this line runs north south, and the Sun appears to move from east to west, the Sun never moves along the celestial meridian.

2. A light year is a unit of distance defined as the distance light travels during one year.

This distance is about 9.5  1012 km.

3. Astronomical distances are so large that measuring them in units of miles or kilometers would result in huge numbers. In addition, the large distances cause the standard units of length to have little meaning because there are no referent points of comparison. So light-years are used to measure distances in terms of time, and parsecs measure distances in terms of angles.

4. As the gas forming the protostar falls together, the gravitational potential energy of the gas is decreased. This energy is converted first to kinetic energy of the gas molecules.

This kinetic energy is then converted to heat when the gas molecules collide as the gases grow denser.

5. Located at the center of a star and extending about one quarter of the distance to the surface of the star is the core. This region contains about half the mass of the star at a density of about twelve times that of solid lead and at a pressure of about 300 billion atmospheres. The temperature is about 15 million degrees Celsius. Above the core extending to about nine-tenths the way to the surface is the radiation zone. It has about the density of water and absorbs and re-radiates energy from the core. The convection zone is in the final tenth of the way to the star’s surface and is not very dense—only about 1 percent the density of water. Gases at the boundary between this zone and the radiation zone are heated, rise to the surface, and radiate away the energy that was originally released in the core of the star. The cooler gases then contract and fall to begin the process again. The temperature at the surface is about 5500°C. 6. The more massive a star, the higher the pressure at the core, and the faster the fusion reactions take place. Therefore, in general, even though more massive stars have more fuel, they use it at such a rapid rate that the massive stars ―burn out‖ more quickly than less massive stars. A star that has a mass of one twenty-fifth that of the Sun would last longer than both the Sun and a star sixty times as massive as the Sun. 7. Apparent magnitude is a measure of how bright a star appears in the sky. Since different stars of the same size might be at different distances from Earth, they might have different apparent magnitudes. To be able to compare the brightness of stars to one another directly, the absolute magnitude scale is used. This scale gives the brightness of a star if it were located 10 parsecs away from Earth.

8. The color and temperature of an incandescent object have long been understood to be closely related. This relationship is due to the electrons surrounding an atom being excited by higher temperatures to higher energy levels. When the electrons return to the ground state energy level, they emit light. The more energy that the electron has to lose to return to the ground state, the higher energy light it has to emit. Higher energy light is shorter frequency light, or ―bluer‖ light. So hotter objects glow closer to the blue end of the spectrum and cooler objects emit light that is closer to the red end of the spectrum.

Comparing the intensities of blue light and red light emitted by a star gives a good measure of the temperature. The spectral classification scheme is based upon the temperature of the star. Originally it was based upon the intensities of the hydrogen lines in the star’s spectra. The current system has a set of temperature ranges assigned to each classification. Type O is 30,000 to 80,000 K and is bluish. These stars are shortlived. Type B is 10,000 to 30,000 K and again is bluish. The range of 7,500 to 10,000 K is type A, which is still bluish. The white type F has a range of 6,000 to 7,500 K, and the yellow stars like our type G Sun has a temperature of 5,000 to 6,000 K. The relatively cool type K stars are 3,500 to 5,000 K and are orange-red in color. The type M stars have a temperature of 2,000 to 3,500 K and are reddish.

9. The Hertzsprung-Russell diagram is a plot of the temperatures of stars indicated by spectral type versus the brightness of the stars indicated by absolute magnitude. The diagram shows that most stars fall close to a narrow diagonal band called the main sequence. The position of a star on this diagram suggests the star’s mass and age.

10. The main sequence on the H-R diagram is the narrow diagonal band that runs from the bright blue stars down to the dimmer red stars. Most stars fall on or near this diagonal band. The mass of a main sequence star is the prime factor in determining if a star is hot and blue, cooler and yellow, or cold and red.

11. A star begins as a large cloud of gas that is gradually attracted together by gravity into a protostar. The protostar collapses down until the temperature and pressure at the center become high enough to sustain nuclear fusion. This fusion heats the core even more and the pressure at the core increases. Eventually equilibrium between the outward force of the pressure and the inward force of gravity is established after about fifty million years.

The star is now a part of the main sequence and burns its fuel steadily. Eventually, the hydrogen in the center of the star begins to run out. The fusion reaction slows down and the equilibrium between the pressure and gravity is upset. The star again begins to collapse until the hydrogen remaining outside the core begins to fuse. This causes the outer layers of the star to expand, and the star becomes a red giant. The star is no longer on the main sequence because its properties have changed. The helium core is heated by the fusing hydrogen surrounding it and eventually, after its temperature has risen enough, begins to fuse as well. The star moves back toward the main sequence when this stage is reached. After millions of years of helium fusion in the core and hydrogen fusion in the outer layers, the star heats up and again expands to a red giant. After this

expansion, the center may cool enough so that the atoms in the core become neutral rather than part of an ionized plasma. These neutral atoms absorb heat from the surrounding star and the star expands and cools. As it cools it begins to collapse back, heating the star again. This occurs several times and eventually blows the outer layers of the star away, forming a planetary nebula. The carbon core and helium fusion layer surrounding it gravitationally collapses to form a white dwarf.

12. A violent flare up of a star for a short time is called a nova. Many novas occur because they are part of a binary star system. An old white dwarf star can pull matter off a younger companion star until enough matter builds up on the surface of the white dwarf for a fusion explosion to ignite. A supernova is the rebound explosion from the catastrophic collapse of a massive star that has run out of fuel. The collapse is caused by the loss of the supporting pressure from the fusion in the interior of the star as the fuel runs out.

13. (a) A white dwarf is formed if the star is about the mass of the Sun or less. The low mass of the star allows its center to convert from hot plasma to neutral matter. This absorbs heat from the surrounding star until the surrounding material undergoes an expansion-cooling and contraction-heating process. Eventually the matter surrounding the core is blown away in a violent explosion. (b) A red giant star forms as the hydrogen in the core runs out and the star begins to collapse. When the hydrogen in the outer layers gets hot enough to fuse, the star expands to a red giant. A star can become a red giant twice in its life if helium in the core begins to fuse after it collapses from its initial red giant stage. The heat from this new energy source again expands the star. (c) When a star has used up all of its energy sources, it collapses in a catastrophic explosion called a supernova. If the remains of the compressed core after the supernova are between about 1.4 and 3 solar masses, the remaining matter is compressed so much that the nuclei of all the atoms collapse, forcing protons and electrons together into neutrons and forming the core of a small, superdense neutron star. Such a neutron star has a center core of pure neutrons. (d) A black hole is the final stage of a supermassive star (with a mass greater than 3 solar masses) when all the fuel in the center has been used up. The core undergoes a gravitational collapse that has nothing to stop it. The force of gravity overwhelms all other forces and even prevents light from escaping. (e) A supernova is the result of the collapse of a star more massive than the Sun when all its fuel has been exhausted. The energy released in this collapse causes the outer layers of material to rebound outward in a violent explosion.

14. The pressure from the high temperatures at the center of a star trying to expand the core balances the force of gravity attempting to collapse the star. This equilibrium can last millions of years because the pressure is a result of the high temperatures from the

fusion process. Since there is so much matter in a star, it takes millions of years to fuse together.

15. Massive stars can fuse elements to create heavier elements up to iron. If the stars are sufficiently massive to undergo a supernova, the energy released in the supernova explosion can fuse atoms to make even heavier elements.

16. Helium nuclei are more massive than hydrogen nuclei, and therefore when traveling at the same speed as hydrogen atoms they have a higher kinetic energy. Since temperature is a measure of the energy of the atoms, the temperature is higher. In addition, a helium nucleus has a higher positive charge than a hydrogen nucleus. This higher positive charge creates a larger repulsive force between helium nuclei than hydrogen nuclei, requiring even higher speeds for the nuclei to collide and fuse. These higher speeds mean higher kinetic energies of the atoms, which mean higher temperatures.

17. A protostar becomes a star when the fusion process is started in the core. If this does not happen, the protostar could result in a cold gas giant such as Jupiter or Saturn.

18. A red giant star is a bright, low-temperature star that is very large. A red giant star forms as the hydrogen in the core runs out and the star begins to collapse. When the hydrogen in the outer layers gets hot enough to fuse, the star expands to a red giant. A star can become a red giant twice in its life if helium in the core begins to fuse after it collapses from its initial red giant stage. The heat from this new energy source again expands the star. A red giant can be brighter than it was as a main sequence star because even though it has a lower surface temperature and is not as luminous, it has much more surface area radiating light, making the star very bright.

19. Since there is not enough mass to create the high pressures and temperatures required to fuse the heavier elements, the fusion process stops at helium fusion.

20. The expansion of the universe is the expansion of space itself. The galaxies are not growing larger, they are moving with space as it expands.

21. The big bang theory is supported by the presence of present-day microwave background radiation from outer space, the current data on the expansion of the universe, the relative abundance of hydrogen and the products of fusion reactions, and measurements of background microwave radiation by satellites.

For Further Analysis 8. If this year is 2011, light leaving the star 519 years ago would have left in 1492 which is about when Columbus sailed the ocean blue.

9. In general, a massive star is brighter, hotter, and has shorter a live than average-sized stars such as the Sun. This means the massive star will go through the various stages of its life in a shorter period.

10. Answers will vary but should include the understanding that absolute magnitude compensates for distance, while apparent magnitude represents what you see.

11. The Hertzsprung-Russell diagram is a temperature-brightness graph that shows groups of stars. These groups represent stars in various stages of their lives.

12. Answers will vary.

Group B Solutions

6.

M = 3MSun T =?

T T

1 M

2.5

1 3

2.5

T  0.064 solar lifetimes

7.

Part 1 M = 2MSun T =?

T T

1 M

2.5

1 2.5

2 T  0.177 solar lifetimes

Part 2 M = 1/3MSun T =?

T T

1 M

2.5

1 2.5

.333 T  15.6 solar lifetimes

8.

 = 1 x 103 atoms/cm3 V = 4.19 x 1057 cm3 M = 1 x 1057 atoms/star Star = 0.5MSun

(1 x 103 atoms/cm3) (4.19 x 1057 cm3) (0.5) (1 x 1057 atoms/star) (1 x 103 atoms/cm3) (4.19 x 1057 cm3) (0.5) (1 x 1057 atoms/star) (1 x 103 atoms) (4.19 x 1057) (0.5) (1 x 1057 atoms/star) = 8380 stars

9.

Blue stars have a peak wave wavelength on about the 10,000 K curve, although stars hotter than this will also appear mostly blue.

15

The Solar System

Contents

15.1 Planets Near the Sun Mercury Venus Mars Case Study: Worth the Cost?

15.2 Planets Far from the Sun Jupiter Saturn Uranus and Neptune 15.3 Small Bodies of the Solar System Comets Asteroids Meteors and Meteorites 15.4 Origin of the Solar System Stage A Stage B Stage C 15.5 Ideas About the Solar System The Geocentric Model The Heliocentric Model

Overview You might use the technique of ―zooming down‖ to the solar system as if aboard a galactic visitor’s spaceship. By asking students what a galactic visitor would see upon approaching our solar system, you can discuss the relative dimension of the system, the counterclockwise movement of the planets around the Sun as viewed from the direction of the North Star, and the relative sizes of the planets.

Depending on the time of year and the night viewing conditions at your location, students may be able to observe meteor showers at night. Usually, the local paper carries information on potentially spectacular showers, and observation of these can be made as a homework assignment. Also, a trip to a planetarium (if within a reasonable distance) would be helpful. Most planetariums have one or more meteorites on display, and some have displays and exhibits of light phenomena, telescopes, and other related topics.

Theories about the origin of the solar system are discussed in some detail, which leads naturally to the consideration of the planets as divided into two groups. The inner, or earthlike, planets are discussed as a group because of their similarities in terms of density, size, temperature, and chemical make-up. The outer planets are discussed as a group for the same reason. In turn, each planet is discussed individually. You will be able to supplement materials in this section as more information is gained by flyby missions and planetary probes.

Suggestions 1. For students who persist in the ancient belief of astrology and the influence of the Sun, Moon, and planets, ask what is so special about the influence at time of birth, that is, the time when they moved through the birth canal. Even if a rational person believed that the position of the Sun, Moon, and planets could influence a person, it would seem more reasonable to assume that this influence would take place at the time of conception, about nine months earlier.

2. Have the students assist in collecting items that represent the Sun, the Moon, and various planets measured to scale. Use these objects to point out how measurements such as relative size and distance were first performed by the ancients.

3. If available, compare models of the geocentric theory of the solar system with that of the heliocentric theory. Show how epicycles helped answer questions about discrepancies noted in the early geocentric theory with its perfectly circular orbits.

4. Establish the relationship between a planet’s distance from the Sun and its temperature, orbital period, and orbital velocity. Consider other variables that may be related to planetary distance, such as rate of rotation, atmospheric composition, mass, and number of moons.

5. Models of the solar system are available from various scientific companies. Plastic balls of various sizes can be glued onto bases to make useful models. The balls representing the smaller planets can be mounted on pins; the other end of each pin can be secured into a wooden base.

6. To illustrate the effect of rotational rate on the shape of planets and stars, attach a centrifugal hoop to a hand rotator and vary the rate of rotation.

For Class Discussions 1. The first and necessary event in the formation of the solar system was a. formation of an accretion disk. b. formation of protoplanets. c. initial flare-up of Sun, igniting fusion processes. d. supernovas of massive stars.

2. The motion of a planet as it moves around the Sun is a(an) a. rotation. b. orbit. c. orbit. d. ellipse.

3. Which of the following planets does not belong with the other three? a. Mars b. Venus c. Earth d. Neptune 4. The planet with a very hot surface from a greenhouse effect is a. Mercury b. Venus c. Mars d. Earth 5. The smallest planet is a. Mercury b. Venus c. Mars d. Neptune 6. The largest planet is a. Jupiter b. Saturn c. Neptune d. Uranus 7. Leftovers from the formation of the early protoplanets might become a. asteroids. b. comets. c. meteors. d. meteorites.

8. The rings of Saturn are made up of a. dust and particles. b. clouds of frozen gases. c. thin layers of rocks. d. sheets of refractive liquids.

9. The planet with the longest day is a. Jupiter. b. Saturn. c. Venus. d. Earth.

10. Craters on the planets and moons of the solar system is the result of meteoroid bombardment that took place a. throughout the history of the solar system. b. about 4 billion years ago. c. 70 million years ago. d. about 6,000 years ago.

Answers: 1d, 2b, 3d, 4b, 5d, 6a, 7b, 8a, 9c, 10b.

Answers to Questions for Thought 1. The protoplanet nebular model is easiest to describe in stages: Stage A involves the creation of a large, slowly rotating cloud of dust and gases from the supernovas of earlier stars. These supernovas created the material of which the planets are made.

In stage B the cloud begins to undergo gravity-induced collapse. The nebulous cloud begins to rotate faster as it contracts. Most of the mass is pulled into the center, forming the protostar that will become the Sun. The remaining gas and dust forms into an enormous accretion disk. The matter in the disk begins to clump together from numerous collisions.

Stage C begins with the protosun becoming established as a star, perhaps undergoing an initial flare-up that may have blasted away most of the hydrogen and helium surrounding the inner planets. The planets underwent heating sometime early in their formation, allowing the heavier elements to be pulled to the center. Gases from the interiors of the planets gave them their early atmospheres. Comets were left over in the outer regions of the condensed cloud. Some people see different problems with this model. There are various parts of the model that may not seem credible, such as why did the planets form, why the accretion disk did not remain a disk, and why are the inner planets rocky when the outer planets are gaseous.

2. The terrestrial planets are mainly rock and iron, while the giant planets are primarily hydrogen and helium with some methane. In addition, some of the giant planets radiate away more energy than they receive from the Sun, which is not characteristic of the terrestrial planets. The protoplanet nebular model attempts to explain these differences

by claiming that the inner planets lost most of their hydrogen and helium atmospheres in the flare-up during the ignition of the Sun. According to some astronomers, Jupiter is a ―failed star.‖ It could have become a star, but it did not have enough mass to create the pressure and temperature necessary for the ignition of fusion in its core.

3. Mars has inactive volcanic regions, huge systems of canyons, terraced plateaus near the poles, and flat regions pitted with craters. The atmosphere is tenuous and is about 95 percent carbon dioxide. The temperature is cold, about –53 degrees Celsius, and the water present is frozen in layered sheets.

4. The canyons and channels that appear to be riverbeds indicate that liquid water may have existed on Mars at one time. The atmosphere may have been denser, with the abundant carbon dioxide creating a greenhouse effect, causing the temperature to rise to the level where liquid water could exist. As carbonate rocks formed and volcanic activity abated, the planet lost its source of water vapor and carbon dioxide in the atmosphere, so the greenhouse effect declined. As the planet cooled, the water froze.

5. Jupiter and Saturn are less dense than Earth. Saturn is less dense than water, and if an ocean large enough could be found, the planet could float! These low densities indicate that the planets are made up mainly of light elements, such as hydrogen and helium.

Measurements indicate that the planets both contain some heavier rocky substances. In both planets a thick layer of metallic hydrogen surrounds rocky cores. Above this layer is ordinary liquid hydrogen, and above this is the outer atmospheric layer of hydrogen, helium, water ice, ammonia gas, and ammonia clouds. The banded appearance of both planets, more noticeably Jupiter, is from a mixture of sulfur and organic compounds in the uppermost ammonia clouds.

6. Saturn’s rings are made up of particles of various sizes, ranging from minute dust particles to rocks and ices meters across.

7. Jupiter’s moon Io has the only volcanic activity known outside Earth and resembles a pizza in certain photographs. Europa is covered with smooth water ice networked with long, straight, dark ridges. Ganymede has the appearance of an active geologic history, and Callisto is the most heavily cratered object in the solar system.

8. The Sun and Jupiter are the two most massive bodies in the solar system, and both radiate more heat than they absorb. Jupiter, however, does not have the mass necessary to create the conditions required for the fusion reactions occurring in the Sun. 9. One of the theories attempting to explain why the Great Red Spot exists states that the spot is an upwelling of gas deflected from an island or some other surface feature below the atmosphere. The existence of a similar spots on Saturn would not really support or disprove this theory, because a similar structure could exist on Saturn as well. Since both planets are similar in make-up, the same types of storms could arise in both of their atmospheres.

10. Venus and Uranus exhibit retrograde rotation, opposite to the rotations experienced by the other planets.

11. Craters exist on most of the moons in the solar system as well as on the planets Mercury, Earth, and Mars. This indicates that earlier in the history of the solar system there were more rocks moving around.

12. Mercury is very unlikely to support life. The wide variations of temperature and the lack of an atmosphere make conditions too harsh for life to evolve. Venus, on the other hand, has too much atmosphere. The high pressures and temperatures on the surface, as well as the lack of water or free oxygen, make life as we know it improbable. Mars may have at one time supported life and is the most viable candidate for extraterrestrial life. This life will probably be microbial survivors from the earlier ages when Mars was warmer and had flowing water on its surface. The controversial findings of the Viking lander missions to Mars have not given much promise of finding life. The giant planets are very unlikely to have life evolve on them. Even if the planets do have surfaces, the pressures at the surfaces would be so great that anything present not made out of rock would be crushed. Speculation about life in the atmospheres of these planets has no evidence to support it.

13. A shooting star is a meteor burning in Earth’s atmosphere from atmospheric friction.

Most meteors are small particles left by a comet in its orbit. The vast majority of meteors burn away before they can reach the surface of Earth; however, some do fall to the surface, and many museums have meteorites on display.

14. Asteroids are small, rocky or iron bodies thought to be left over from a planet that never made it to the final stage before being pulled apart. The orbits of the asteroids mainly lie in a belt between Mars and Jupiter, leading to speculation that they are the remains of a planet that was somehow broken apart. Spectral composition studies, analyses of orbits, and studies of meteorites all indicate that the asteroids are not the remains of a planet.

They are believed to have formed in the original solar nebula, but their close proximity to massive Jupiter prevented the clumping process that forms a planet.

15. Comets are estimated to originate some 30 AU to a light-year or more from the Sun. They are believed to be dirty ice balls left over from the formation of the solar system.

For this reason, they are studied for information about the early conditions of the solar system.

16. A meteor is an object falling into Earth’s atmosphere leaving behind a streak of smoke and light. Most meteors are probably rocks and boulders left over from the collision of asteroids, or they are small particles left by a comet in its orbit.

17. Meteorites are meteors that have made it to the surface of Earth. Most meteorites are the remnants of asteroid collisions.

18. A meteorite is defined as an object that has struck the surface of Earth, not the Moon: Meteor-ology is the study of Earth’s atmosphere. An object that strikes the Moon or any other planet is probably an asteroid, but rocks from Mars and the Moon have been found on Earth.

19. The Kuiper Belt is a region of objects just beyond Neptune’s orbit, around 50 AU from the Sun. Most of these objects are orbiting in the same plane as the planets. In contrast, the Oort cloud is a spherical region of comets at 50,000 AU, completely surrounding the solar system. The two regions differ greatly in shape and in distance from the Sun.

For Further Analysis 13. Similarities – both the terrestrial and giant planets are believed to have rocky materials and iron as a core. Differences – the rocky materials of the giant planets are surrounded by tremendous amounts of hydrogen, helium, and methane. Speculations vary but could include the idea that all planets at one time had hydrogen, helium, and methane atmospheres, but it was blown away from the terrestrial planets with the Sun’s initial startup.

14. The four Galilean moons listed in increasing distance from Jupiter are: Io, Europa, Ganymede, and Callisto. As with the system of planets orbiting our Sun, the smallest moons are closest to Jupiter with the largest ones orbiting at greater distances.

Similarly, the inner moons have very young and active surfaces, as does Earth, whereas the outer moons have ancient surfaces that don’t change much over time.

Finally, the inner planets orbit Jupiter at a much greater velocity than the outer planets, as do the planets orbiting our own Sun.

15. The mass, size, and density of Venus is very similar to Earth. Other than that, Venus is very hot, very high atmospheric pressure, and hostile.

16. Answers vary, but the probability of life as we know it on each of the other planets is near zero.

17. Answers will vary.

18. The vast majority of comets exist in the very distant spherical Oort cloud surrounding Earth. Comets are quite small, perhaps averaging 10 km (6 mi) in size and emit no light of their own. At a distance of 50,000 AU, they are nearly impossible to observe, so no one knows how many there are as we can only observe them when they are close to the Sun, about 360 per year are observed.

Group B Solutions

2. d = 380,000 km V = 1,000 kph t =?

v

d t



t

d v

= 380,000kmkm 1,000 /hr = 380 hours

4. tUranus = 0.71833 Earth-days 1 Earth-day = 24 hrs SpinsUranus = ?

PeriodUranus = 24 hrs x 0.71833 Earth-days/spin = 17.2 Earth-hours per spin Number of spins = 24 hrs  17.2 Earth-hours per spin = 1.4 spins

7.

TF = 462F TC = ?

TC = 5/9 (TF - 32) = 5/9 (462F - 32) = 239C

14. gMoon = 1.62 m/s2 h = 30 m vf = ?

vf = (2gh)1/2 = ( 2 x 1.62 m/s2 x 30 m ) 1/2 = 9.86 m/s

16

Earth in Space

Contents 16.1 Shape and Size of Earth 16.2 Motions of Earth Orbit Rotation Precession 16.3 Place and Time Identifying Place Measuring Time Science and Society: Saving Time?

Yearly Time Monthly Time 16.4 The Moon Composition and Features History of the Moon 16.5 The Earth-Moon System Phases of the Moon Eclipses of the Sun and Moon Tides

Overview This chapter considers the motions of Earth and Moon as an astronaut returning from some other planet might view them. It then considers how people on Earth identify places and measure time using these motions. The overall approach starts with the universe, galaxies, and the stars (chapter 14), then moves to the solar system (chapter 15), then to the motions of Earth and its Moon. This approach is intended to impress upon students the observation that Earth is just one of the eight planets of our solar system, which is located in one of billions of galaxies. The next chapters take a closer look at this planet that happens to be—as far as we know so far—the only home of humanity.

The Foucault pendulum provides evidence of a rotating Earth and you can demonstrate the principle rather easily as a classroom demonstration. Tie a heavy object on the end of a string, and then start the object swinging back and forth in the directions of the students.

Now slowly turn the direction you are facing, and the students will be able to see that the swing of the pendulum remains in the same plane as the person holding the string moves. If you now swing the pendulum while standing over a spinning globe, students should be able to see that a person on the globe looking up would see what appears to be a pendulum that appears to turn once on its axis during a day.

In the section covering seasons the definition and location of the tropic of Cancer, the tropic of Capricorn, the Arctic Circle, and the Antarctic Circle are discussed. Most students are aware that the Arctic Circle experiences long periods of darkness and long periods of daylight during a year’s time. You can use this knowledge to help explain why the Arctic Circle and the Antarctic Circle are located at certain latitudes.

During the discussion of the precession of Earth you can point out that during the time of Jesus and for a considerable time before and after, sailors of the world had no North Star by which to navigate. Sailors during this period used either the Big Dipper or the Little Dipper as navigational guides.

Most students will enjoy viewing some of the many beautiful color images of the Moon that are available via the Internet. Since some will have telescopes or binoculars at their disposal point out that surface features of the Moon are also visible when it is not in its full phases.

Suggestions 1. The principle by which the Foucault pendulum illustrates the rotation of Earth can be illustrated with a yo-yo or with a heavy mass attached to a string. Start the object swinging; then turn on your heels without touching the swinging object. Point out how the direction of the swinging object remains unchanged. A Foucault pendulum for use with a hand rotator is available from many commercial scientific suppliers.

2. A rotating stool and two masses of 2 kg each are ideal to illustrate concentration of mass and its effect on rotation. Ask a student of small stature to sit on the stool with arms extended. Place a 2-kg mass in each of the student’s hands, and then rotate the stool slowly. While rotating, have the student move the weight toward his or her chest.

Observe the change in rate of rotation.

3. Earth photographed from the Moon appears to the eye to be a sphere. Have students make measurements of the polar diameter and the equatorial diameter of Jupiter to illustrate that the spin of a planet produces an oblate spheroid rather than a perfect sphere.

4. To illustrate procession of a rotating object in a gravitational field, use a toy top and spin it at various rates.

5. To illustrate a lunar and a solar eclipse, use two plastic balls of significantly different sizes. Darken the room and hold the two balls in the light from an overhead projector, slide projector, or filmstrip projector. Move one ball relative to the other to demonstrate both eclipses.

6. The seasons of Earth and the effect of its rotation can be well illustrated in a darkened room with a low-intensity light bulb (25-40 watt incandescent bulb mounted vertically) and a world globe. Maintain Earth’s 23.5˚ tilted axis away from the perpendicular as

you rotate the globe, then move it in a slightly elliptical path about the light bulb. Point out the winter and summer seasons at both the North and South Poles as well as the Northern Hemisphere seasons at Earth’s perihelion and aphelion.

7. As a creative activity that requires understanding of the concepts presented in this chapter, students could write a creative essay about how life on Earth would be different if the axis were somehow shifted from its present inclined position to an upright position.

For Class Discussions 1. Earth’s axis of rotation a. is parallel to the ecliptic. b. is perpendicular to the ecliptic. c. is inclined to the ecliptic. d. varies over the course of a year from perpendicular to parallel.

2. Earth’s seasons are a result of a. changes in orbital velocity during a yearly orbit around the Sun. b. variations in the Sun’s output and direction of output. c. the elliptical nature of Earth’s orbit around the Sun. d. the constant orientation of Earth’s axis of rotation.

3. In the Northern Hemisphere the Sun at noon reaches its lowest altitude above the horizon at the a. winter solstice. b. summer solstice. c. spring equinox. d. fall equinox.

4. The length of daylight and night are the same everywhere on Earth during a. a solstice. b. New Year day on a leap year. c. an equinox. d. no time since this does not happen.

5. Earth’s axis always has and always will point to the North Star, Polaris. a. Yes. b. No.

6. The most convincing evidence that Earth rotates comes from a. the fact that Earth has seasons. b. the observation that nighttime is always followed by daylight. c. watching a pendulum swing back and forth at different locations. d. measuring sunlight falling into a deep well.

7. You can identify where you are on Earth relative to the equator by using an identifying position based on a. the angle between the North Star and the ecliptic. b. the number of km from the Greenwich Observatory. c. Earth’s rotational axis. d. Earth’s position in its elliptical orbit around the Sun. 8. A sundial and a clock show the same time how many times a year? a. Once b. Twice c. Four times. d. All the time.

9. Leap years are needed to correct the calendar because a. Earth does not complete an exact number of turns during one complete orbit. b. Earth completes a slightly greater number of turns during one complete orbit. c. Earth turns faster around the equator than it does at the poles.

10. A solar eclipse can only occur with a a. full moon. b. new moon. c. any moon phase.

Answers: 1c, 2d, 3a, 4c, 5b, 6c, 7c, 8c, 9a, 10b.

Answers to Questions for Thought 1. Earth undergoes three basic motions, a yearly orbit around the Sun, a daily rotation about its axis, and a slow wobble of its axis called precession. Both the precession and the orbit are influenced by the Sun, only rotation is unaffected by the outside sources of the Sun and the galaxy.

2. (a) Evidence that Earth is a spherical shape was recognized even back in ancient times.

The different length of shadows at the same time of day at different latitudes is one indication of this shape. Another is the disappearance of objects below the horizon. (b) The movement of a Foucault pendulum indicates that Earth undergoes some type of rotational motion. The Coriolis effect is another indication of rotational motion.

3. The pendulum maintains its plane of movement in space from inertia while Earth rotates under it. This rotation causes the pendulum to appear to change its plane of movement, giving evidence for the rotation of Earth.

4. On the equator, an almost nonexistent shadow would be observed at noon on the day of the autumnal equinox. (a) In the Northern Hemisphere shadows point northward at noon on the day of the autumnal equinox. (b) A southward-pointing shadow would be seen in the Southern Hemisphere at noon on the day of the autumnal equinox.

5. ―Solstice‖ means, ―Sun stands still‖ in Latin. The solstices occur when the Sun has the highest altitude in the sky of either the Northern or Southern Hemisphere. This occurs when the axis of Earth is pointing as close to the Sun as possible, or when the Sun is as far north or south as it will travel on the celestial sphere. The solstices occur on about June 22 and December 22.

6. ―Equinox‖ is from the Latin meaning ―equal nights.‖ On the equinoxes, both day and night are of the same length. On the equinox, the Sun crosses the celestial equator when viewed on the celestial sphere. The approximate dates for the equinoxes are March 21 and September 23.

7. Precession is the slow wobble of Earth’s axis.

8. Earth’s axis is used to define the north-south position or latitude of a point on the surface. The North Pole is defined as +90° latitude, while the equator is 0° latitude and the South Pole is –90°. North south lines run through the poles to identify how far east or west an object is to a reference line. These lines are referred to as meridians of longitude.

9. Answers will vary.

10. The tropic of Cancer and the tropic of Capricorn identify the limits toward the poles where the Sun appears directly overhead during the year. They are located at 23.5° N and 23.5° S latitude respectively. The Arctic and Antarctic circles identify the limits toward the equator where the Sun appears on the horizon all day for at least once during the summer. They are located at 66.5° N and 66.5° S latitude respectively.

11. (a) The movement of the Sun across the celestial meridian is noon. (b) A.M. stands for ante meridiem, or the time before the Sun crosses the celestial meridian. (c) P.M. stands for post meridiem, or the time after the Sun has crossed the celestial meridian.

12. Standard time zones were established to avoid the confusion of having clocks set to local mean solar time. Each time zone is 15° wide in terms of longitude. This was chosen so that there are twenty-four time zones, one for each hour in the day. In this way, the variation in clock time between the time zones is in units of whole hours.

13. Texas is in the Central Time zone. (a) The Eastern Time zone, where Jacksonville, Florida, is located, is one hour later than in the Central Time zone, so 12:00 noon in Texas is 1:00 P.M. in Jacksonville. (b) Bakersfield, California is located in the Pacific Time zone, where it is two hours earlier than in the Central Time zone. At 12:00 noon in Texas, it is 10:00 A.M. in Bakersfield. (c) At the North Pole, the time is defined to be Greenwich Mean Time, or 7:00 P.M. when it is 12:00 noon in Texas.

14. Since the orbit of the Moon is inclined to Earth’s orbit, the Moon is usually above or below the shadow of Earth when it passes behind.

15. A total eclipse of the Sun is observed when the Moon’s shadow passes over the surface of Earth. The eclipse is observed to be total where the complete shadow or umbra falls on the surface. The umbra must reach Earth’s surface for a total eclipse, otherwise the eclipse is annular, or a ring of Sun is seen around the Moon.

16. During a new moon, the Moon is located between Earth and the Sun (but not usually directly between). First quarter is when the Moon has passed new moon and is still on the Sun side of Earth. A half-moon occurs when the Moon has moved beside Earth, while three-quarters is when the Moon begins to move behind Earth. A full moon is when the Moon is farthest from the Sun, and behind Earth. The phases go in reverse order after the full moon to reach another new moon.

17. A ―new earth‖ or dark disc would be observed from a full moon.

18. The smooth, dark areas on the Moon’s surface are maria or ―seas.‖ Ancient floods of lava poured across the surface and solidified to form these dark areas.

19. The craters on the Moon are believed to have been caused by collisions with asteroids and other debris left over from the formation of the solar system. Most of the craters were formed from 4.2 to 3.9 billion years ago as the crust of the Moon cooled.

20. The Moon would be full because if it were in an earlier phase it would rise earlier, while a later phase would rise later. Only when the Moon is on the opposite side of Earth from the Sun will it rise as the Sun sets.

21. The tilt of the orbit of the Moon relative to Earth’s orbit causes the shadow of the Moon usually to fall above or below.

22. The time is not the same because Earth is orbiting the Sun at the same time the Moon is orbiting Earth. The position of the Sun in the sky changes and the Moon has to travel more than a full circle to ―catch up‖ and complete the cycle of phases.

23. An annular eclipse is when the umbra shadow cone of the Moon does not reach Earth’s surface during a solar eclipse. Annular eclipses are more common than total solar eclipses. This is because the Moon must be closer to Earth for a total eclipse to occur.

The combination of proximity of the orbit to Earth with the alignment of the orbit so that the Moon passes between Earth and the Sun is not as likely to occur as just the passage of the Moon between Earth and the Sun. 24. An eclipse of the Sun can only occur during a new moon. During other phases, the Moon is not positioned between Earth and the Sun. 25. (a) Spring tides occur during full and new moons. The alignment of the Sun, Moon, and Earth allows the gravitational effects of the Sun and Moon to combine to make larger tides. (b) Neap tides occur during the half phases when the Sun and Moon are at right angles when measured from Earth.

26. The Julian calendar is longer than the tropical year by about 0.0078 days per year. Over a long time this error becomes noticeable. The Gregorian calendar corrected for this error by dropping the additional leap year day included in the Julian calendar three century years out of every four. Therefore, the year 2000 was a leap year, but 2100, 2200, and 2300 will not be leap years.

27. The dust is a result of millions of years of bombardment by micrometeorites.

28. The Moon began in the origin stage from the impact of Earth with a very large object, perhaps as large as Mars. The Moon formed from ejected material produced by this collision. The molten surface stage followed, in which heating from impacts of rock fragments melted the outer surface. The craters were formed near the end of this stage as the surface cooled and solidified. The molten interior stage followed. Radioactive decay created this heat source and drove the eruptions that created the maria. The cold and quiet stage is the present stage of the Moon, in which the interior and exterior are cold.

29. A lunar eclipse can be seen from wherever the Moon is visible since it involves a phenomenon occurring on the Moon caused by Earth. A solar eclipse can only be seen in the narrow path that the shadow of the Moon follows as it passes over Earth.

30. The Moon’s gravity pulls Earth away from the ocean on the opposite side. This forms a tidal bulge on the outside of Earth’s path of orbit on the opposite side from the Moon.

The bulge on the same side as the Moon is caused by the Moon’s gravity pulling the water toward the Moon.

For Further Analysis 19. The tropic of Cancer is the limit toward the pole (23.5°N) where the Sun appears directly overhead during a year. The Arctic Circle identifies the limit toward the equator (66.5°N) where the Sun appears above the horizon all day during the summer.

20. Similarities – both are the beginnings of seasons recognized from the altitude of the Sun in the sky at noon. Differences – an equinox marks the beginning of summer or winter and occurs when the Sun reaches its highest or lowest altitude in the sky at noon; a solstice marks the beginning of spring or fall and occurs when the Sun is halfway between summer and winter, so daylight and night are of equal length.

21. Earth is closest to the Sun in January. The orientation of Earth’s axis to incoming sunlight is more important than distance in determining seasons.

22. The plane of the Moon’s orbit is inclined to Earth’s orbit about 5° so the shadow from the Moon or the shadow from Earth usually falls above or below the other body, too high or too low to make an eclipse.

23. The difference is a result of the shape of Earth’s orbit, and the fact that the angle between the plane of the ecliptic and the plane of the equator are different.

24. Answers will vary, but the reason is as follows: The period of twelve hours and twenty-five minutes is half the average time interval required for the Moon the pass directly overhead, and the tidal bulge follows the Moon. The daily rotation of Earth on its axis is 24 hours, which is different from the time required for the Moon to pass directly overhead.

Group B Solutions

11.

TFullMoon = 29.5 days Age = 33 years

First, determine how many days in 33 years:

33 years x 365.25 days/year = 12, 053 days Second, determine how many Full Moons:

= 1 FullMoon / 29.5 days x 12,053 days = 408 Full Moons

.

15. t = 2.70 s v = 3 x 108 m/s d=?

v

d t

 d  vt

= (3 x 108 m/s) (2.70 s) = 21 x 108 m

17

Rocks and Minerals

Contents 17.1 Solid Earth Materials 17.2 Minerals Crystal Structures Silicates and Nonsilicates Physical Properties of Minerals 17.3 Mineral-Forming Processes 17.4 Rocks Igneous Rocks Science and Society: Using Mineral Resources A Closer Look: Asbestos Sedimentary Rocks Metamorphic Rocks Science and Society: Using Mineral Resources

17.5 The Rock Cycle

Overview This chapter is an introduction to an Earth science section about the dynamic, ever-changing Earth and how geology seeks to understand the natural processes behind these changes. It begins with an account of the materials that make up Earth, including the chemical composition of various Earth materials and the overall structure of Earth.

The solid Earth materials include minerals and rocks. A mineral occurs naturally, it is inorganic in composition, and it has a definite internal structure. The composition of a mineral can vary only between well-defined limits, a feature that accounts for the thousands that geologists have identified. Most minerals are composed of oxygen, silicon, aluminum, and either sodium or potassium. Most of the other elements appear in such small quantities as to be considered impurities. If iron-bearing minerals did not concentrate while in the molten state, iron, along with metals in other ore minerals, could not be mined profitably.

Minerals are classified and identified according to various properties, the most useful of which are streak, hardness, and cleavage. These properties can be determined readily by geologists at a deposition site.

Rocks are composed of at least two minerals. One or more minerals act as the cementing agent or, in the case of igneous rocks, form a crystalline melt into which other minerals are embedded. Although rocks sometimes yield various valuable minerals, their greatest importance to geologists lies in the way their physical properties and compositions offer mute evidence about conditions on Earth during their formation. The research of N. L. Bowen led to considerable understanding of igneous rocks. In a laboratory he duplicated the conditions under which some of the major igneous rocks were formed. The Bowen reaction series reveals the relationship of various igneous rocks to others.

Sedimentary rocks may include organic matter along with naturally occurring minerals.

This category of rock is the product of erosional processes. The study of sedimentary rocks has made scientists aware of changes in living organisms and conditions on Earth when the sediment was laid down. Further correlation of fossil life and layers of sediment, as well as the geologic processes that occur at mid-ocean ridges, have left little doubt that our continents have drifted apart from the gigantic landmass they formed at least twice in the past.

Metamorphic rocks are formed from sedimentary, igneous, or other metamorphic rocks.

Most metamorphic rocks were typically formed as a result of exposure to great pressure and high temperatures. They did not re-melt under these conditions, however. Other metamorphic rocks were formed as hot fluids circulated through them.

Suggestions 1. Specimens can be placed in a display cabinet for students to view. See that each specimen is labeled in terms that the nonscience students can readily understand.

2. A set of color slides can be used to show rock types, formations, and illustrations of the geologic processes that shape the surface of Earth. Choose selections from the many available from supply houses that are most beneficial for the presentation of this and other geology-oriented chapters. Supply houses can also supplement the types of rocks and features that are not present in your location.

3. The petrology collection of rocks and minerals available from supply houses is an excellent way to teach geology concepts for smaller classes. Many specimens from these collections have features that can be distinguished by students in larger classes. A video camcorder is useful to display close-ups of specimens on the screen for all students to view.

For Class Discussions 1. One of these minerals does not belong with the other three. a. quartz b. gypsum c. mica d. orthoclase 2. A mineral property that is controlled by the internal crystal structure is a. cleavage. b. color. c. streak.

3. Of the following minerals, the one most difficult to scratch is a. quartz. b. gypsum. c. calcite.

4. One of these rocks does not belong with the other three. a. gypsum b. limestone c. schist d. sandstone

5. One of these rocks does not belong with the other three. a. granite b. marble c. basalt d. rhyolite 6. The rock cycle concept states that all rocks a. are endlessly changing from one type to another. b. will eventually be sedimentary rocks. c. will eventually be metamorphic rocks. d. will eventually be igneous rocks.

Answers: 1b, 2a, 3a, 4c, 5b, 6a.

Answers to Questions for Thought 1. A mineral is a naturally occurring, inorganic solid element or compound with a crystalline structure. Ice can be called a mineral because it is naturally occurring, it is not an organic compound, and it has the regular, repeating pattern of atoms in a crystal structure.

2. Silicates all have the basic silicon-oxygen tetrahedral unit either isolated or joined in a crystal structure. The silicates are mainly made up of silicon and oxygen, but they can contain other elements as well.

3. Each mineral has its own defined chemical composition or range of chemical compositions. These chemical compositions, as well as the arrangement of the atoms in their own crystal structures, give different minerals different physical properties.

4. Color, streak (the color of the finely powdered mineral), hardness, crystal form, cleavage, fracture, luster, and density can all be used to identify a mineral. The most useful are crystal form and streak, because they are the most consistent. Color and luster are probably the least useful because color is inconsistent and luster is subjective.

5. Tests are used to eliminate all minerals that do not exhibit the characteristic revealed by the test. A mineral chart is used, and a property is tested. Then, after the initial elimination, other properties are tested to eliminate more minerals until eventually, you have a good idea of what the sample is.

6. A rock is an aggregation of one or more minerals and perhaps mineral materials that have been brought together into a cohesive solid.

7. The rock cycle is a concept that an igneous, sedimentary, or metamorphic rock is a temporary stage in the ongoing transformation of rocks to new types.

8. Igneous rocks formed as hot, molten magma cooled and crystallized to firm, hard rocks.

Slowly cooling magma forms coarse-grained intrusive igneous rocks, and quickly cooled magma produces fine-grained extrusive igneous rocks. Sedimentary rocks are formed from sediments. Conglomerate rocks are made up of large sediments, sandstone contains intermediate-sized sediments, and shale is made up of fine sediments. These rocks are formed through compaction and cementation of the sediments. Metamorphic rocks are previously existing rocks that have been changed by heat, pressure, or hot solution into a different kind of rock without melting. Sedimentary rock can be changed from shale to slate and then to schist, and finally gneiss. Each stage has a characteristic crystal size and alignment known as foliation.

9. On the surface sedimentary rock would be the most expected, because the forces of erosion are continually working to provide new source material for this type of rock.

Deeper into the crust, metamorphic rock would prevail in the higher pressures and temperatures. Even deeper and on the ocean floors, igneous rock would be found in quantity, close to the hot magma from which it forms.

10. Lava is magma that is forced out to the surface.

11. Coarse-grained texture means that mineral crystals can be seen with the naked eye, while if a lens or microscope is needed to see the crystals, it is fine-grained. Coarse-grained rock cooled slowly enough for large crystals to form, while fine-grained rock cooled so quickly that no large crystals could form.

12. Basalt is dark and fine-grained, whereas granite is light-colored and coarse-grained.

Basalt makes up much of the ocean basins. Seafloor spreading allows the hot magma to contact the seawater and cool rapidly to form basalts. Granite is common on the continents because the air is not able to cool magma as quickly.

13. If the magma were hot enough, the heavier iron would sink to the bottom of the fluid, causing the bottom layers to be richer in iron than the top.

14. If a rock has basalt’s chemical composition but it is not fine-grained, it is gabbro and not basalt.

15. Clastic sediments are weathered rock fragments. They are classified according to size, the largest being boulders and gravel, then sand, and then silt and clay being the finest.

16. As sediments are deposited, the overlying sediments cause an increasing pressure on the sediments below. This process squeezes the grains together, reducing the pore spaces.

This compaction of the grains reduces the thickness of the sediment deposit and squeezes out the water. Cementation by chemical deposits between the sediment particles binds the particles together into a rigid, cohesive mass of sedimentary rock.

17. Metamorphic rocks are previously existing rocks that have been changed by heat, pressure, or hot solutions into a distinctly different kind of rock. The temperatures involved must be less than the melting point of the rock, because if the rock melts and re-solidifies, it is an igneous rock and not a metamorphic rock.

18. Slate is formed from shale as the microscopic crystals line up due to heat added to the rock. Greater heat and pressure can cause more metamorphic change, resulting in lager crystals and increased foliation or parallel sheets of aligned crystals. This new rock produced from slate by further metamorphism is schist. The mica crystals can be broken down by further metamorphism, which produces alternating light and dark bands of minerals. This is the metamorphic rock gneiss. Even if the rock does not stay in these forms, the slate and schist sequence must be followed. This is true because the changes in the rock that can occur depend upon the initial structure of the rock.

19. The rock cycle is a concept that all rocks are eventually cycled from igneous, to sedimentary, to metamorphic, and back to igneous. There are several pathways available, but given enough time all the rocks could start and end as igneous rocks. This appears to be unique to the planet Earth because no great igneous rock activity or movement of plates has ever been observed on other planets.

For Further Analysis 25. Similarities – all rocks are made up of one or more minerals and perhaps other materials. Differences – igneous rocks formed as a hot, molten mass of rock materials cooled and solidified; sedimentary rocks formed from particles or dissolved materials from previously existing rocks; metamorphic rocks formed from igneous or sedimentary rocks that were deformed or recrystallized by high temperatures and pressures.

26. Answers will vary, but ice seems to fit the definition of a mineral.

27. Answers will vary.

28. Weathering and erosion produce sedimentary rocks, and this is what is occurring on Earth’s surface.

Group B Solutions

18

Plate Tectonics

Contents 18.1 History of Earth’s Interior 18.2 Earth’s Internal Structure Body Waves Surface Waves The Crust The Mantle The Core A More Detailed Structure A Closer Look: Seismic Tomography 18.3 Theory of Plate Tectonics Evidence from Earth’s Magnetic Field Evidence from the Ocean Lithosphere Plates and Boundaries Divergent Boundaries Convergent Boundaries A Closer Look: Measuring Plate Movement Transform Boundaries Present-Day Understandings Science and Society: Geothermal Energy

Overview The structure of Earth is considered from two viewpoints (1) considering Earth to have the three main parts of a crust, mantle, and a core, and (2) considering Earth to have a lithosphere (rocky layer), asthenosphere (weak, plastic layer), mantle, outer core, and inner core. Both structural considerations are adequate models, with the second proving more detail that the three-part model.

The concept of plate tectonics is introduced after a discussion of the asthenosphere and sea-floor spreading. As a model, plate tectonics explains volcanic activity, earthquakes, and the diversity of features of relief found on the surface of Earth.

Suggestions 1. Relief globes that provide a view of Earth’s interior (crust, mantle, and core) and plastic globes with raised relief are available from scientific supply companies.

2. Cut out the various landmasses from a world map and try to assemble them so the masses fit together as pieces of a jigsaw puzzle. Explain how erosion and other geologic processes might account for areas from which landmasses are missing. Also point out to the students that the best fit between continents is not between shorelines but between continental shelves.

3. The model of Earth’s interior has changed since the early 1960s. Students could investigate how the model has changed by reviewing journal articles before and after that time.

4. If Los Angeles, California, is on a plate moving at a rate of 10 cm per year, calculate how long it would take for Los Angeles to move the distance to where San Francisco, California, is presently located.

For Class Discussions 1. Volcanoes are least likely to be as frequent on which type of plate convergence? a. ocean-continent b. ocean-ocean c. continent-continent d. all are the same 2. A deep oceanic trench is most likely to be associated with which type of plate boundary? a. divergent b. convergent c. transform d. any of the above 3. Evidence that Earth has a liquid outer core and a solid inner core comes from a. drilling samples. b. volcanoes. c. earthquakes. d. laboratory simulations.

4. About how far would a plate, such as the North American plate, be expected to move in a century? About a. 1 m b. 3 m c. 10 m d. 25 m

5. Convincing evidence for the support of the plate tectonics theory came from studies of a. paleomagnetics. b. meteorites. c. earthquakes. d. shapes of continents.

Answers: 1c, 2b, 3c, 4b, 5a.

Answers to Questions for Thought 1. The second melting of Earth due to the presence of radioactive materials allowed the heavier elements to accumulate toward the center of the planet. Since iron is the most abundant of the heavier elements in Earth, the core would be predominantly formed of this element. Information about the core is obtained from seismological data, or earthquake waves that pass through the core; the nature of meteorites, which give information as to the relative abundance of materials in the nebula that condensed to form the planet; and geological data at the surface of Earth.

2. (a) Earth’s core is mostly iron, and the innermost part to a radius of 1,200 km is solid. A layer above this center is liquid layer out to a radius of 3,470 km. (b) Above this is the mantle composed mainly of silicate minerals less dense than the metallic core. At a depth of 400 and 700 km the mantle changes character. In the upper 400 km the dominant olivine mineral structure is that of a typical silicate, but below 400 km the silicate collapses into a denser molecular arrangement. Below 700 km, the silicon atom now has six oxygen atoms surrounding it as opposed to the normal four, and the atoms are compressed into an even more compact arrangement. Since it is also observed that earthquakes always occur above 700-km depth, this depth is identified as the boundary between the upper and lower mantle. (c) The crust is the outer shell of Earth. It varies in thickness and is thinner under the oceans than under the continents. In general, continental crust is less dense, granite-type rock. Oceanic crust is primarily basalt.

3. The asthenosphere is the layer of plastic, mobile, yielding rock located from 130 km to 160 km in depth. The asthenosphere is believed to be one of the important sources of magma that reaches Earth’s surface.

4. (a) The lithosphere includes the entire crust, the Mohorovicic discontinuity, or Moho, which is a region of crust that has a different composition from the surrounding layers, and the upper part of the mantle.

(b) The asthenosphere is a part of the mantle below the lithosphere and is a very thin, plastic layer. (c) The crust is the outer layer of Earth and includes the Moho. (d) The mantle contains part of the lithosphere, all the asthenosphere, and the mesosphere, which is the solid, dense, lower part of the mantle.

5. Continental drift is the idea that individual continents can shift positions on Earth’s surface. Plate tectonics gives the underlying reason for continental drift, which did not offer any explanation as to why or how the continents drift around on a solid Earth.

6. Sediments become thinner as you near an oceanic ridge. This is because the older layers farther away from the spreading center would have more time to accumulate the sediments.

7. The magnetic bands are a result of the ―flipping‖ of the magnetic field of Earth several times in the last 150 million years. When the iron minerals in the forming basalt are exposed to this field, they become magnetized and freeze in a record of the field direction as they solidify.

8. The seafloor is new crust that is created in the ridges. Older seafloor is plowed under at the edges of continents in subduction zones to re-melt and possibly migrate back to the spreading ridge. Therefore, all the ancient rock has already been pushed into a subduction zone in this recycling process.

9. Divergent boundaries occur between two plates moving away from each other. New crust is formed at these boundaries. Convergent boundaries occur between two plates moving toward one another. This is where crust is destroyed to make room for the newly created crust at the divergent boundaries. Transform boundaries occur between plates sliding by each other. Crust is not created or destroyed in these regions; however, many earthquakes are caused by sudden jerks at these boundaries.

10. An island arc is a curving chain of volcanic islands that occur near an ocean-ocean plate boundary. Islands form where subducted material rises up through the overriding plate above sea level. These occur near convergent boundaries because the subducted material is the source of magma, which forms the islands.

11. The melting of the outer layer of Earth occurred due to meteoric bombardment and the melting of the interior occurred due to heat from radioactive decay. Both meltings allowed Earth to undergo a differentiation process where the heavier elements and compounds sank to the center of Earth. As the outer layer cooled, it formed the crust, and different densities of materials formed the different layers above the solid iron core.

Changes in pressure at different levels also encouraged the formation of layers.

12. According to plate tectonics the lithosphere is broken up into a number of fairly rigid plates that move on the asthenosphere. Some plates contain continents and part of an ocean basin and others contain only ocean basins. The motion of the plates and the interaction at the boundaries explain a number of geographic features. Volcanoes are explained by the subduction of one plate below another, plates colliding or sliding past

each other form mountain ranges, and new crust is created in suboceanic divergence boundaries.

13. An oceanic trench is a region of great depth that marks a subduction zone of an oceancontinent plate convergence. The trench is formed as the ocean plate is forced beneath the continental plate.

14. The most probable source of earthquakes in southern California is the San Andreas Fault, which is a transform boundary between the Pacific Plate and the North American Plate. If the plates stick together for a time, then violently break apart, an earthquake occurs.

15. This part of the North American Plate is near the plate boundary. This boundary is probably an ocean-continent plate convergence. A deep trench would probably be caused off the coast on the seafloor by the subduction of the oceanic plate.

16. The crust is being created at the mid-oceanic ridges as plates spread apart and new crust forms from the upwelling mantle. This crust replaces that which is forced down into the interior of Earth at subduction zones. The material forced into the subduction zones may cause volcanoes, creating new continental crust, or it may be recycled back to the spreading center to form new crust.

For Further Analysis 29. Volcanoes form where plate boundary convergence is taking place. The eastern United States and Canada are near the center of the North American Place, not a boundary, so you would not expect volcanoes to occur there.

30. Atmospheric gases and vapors, water of the surface, and flowing interior rock materials all cycle. Other planets lack the atmospheric gasses, liquid water, or internal molten rock materials necessary for cycling.

31. Answers will vary.

32. Answers will vary, but should include evidence of an interior with molten or plasticlike materials.

Group B Solutions

3. d = 5 x 106 m v = 3.25 x10-2 m/yr t=?

v

d t

 t

=

d v 5 x 106 m 3.25 x10-2 m/yr

= 1.53 x 108 yrs

19

Building Earth’s Surface

Contents 19.1 Interpreting Earth’s Surface 19.2 Earth’s Changing Features Stress and Strain Folding Joints and Faults 19.3 Earthquakes Causes of Earthquakes Locating and Measuring Earthquakes Measuring Earthquake Strength A Closer Look: Earthquake Safety 19.4 Origin of Mountains Folded and Faulted Mountains Volcanic Mountains A Closer Look: Volcanoes Change the World

Overview This chapter is about the dynamic, ever-changing Earth and how geology seeks to understand the natural processes behind these changes. This chapter is concerned with the processes that build up land and how an understanding of these processes makes possible an interpretation of the present-day landscape for meaning about the past. Maximum landscape relief occurs in long mountain ranges, which are elevated by folding, faulting, and other responses to the stresses created by the movement of Earth’s plates. Plate tectonics has changed the accepted way of thinking about the solid, stationary nature of Earth’s surface and ideas about the permanence of the surface as well. The surface of Earth is no longer viewed as having a permanent nature, but is understood to be involved in an ongoing cycle of destruction and renewal. Old crust is destroyed as it is plowed back into the mantle through subduction, melts, and becomes mixed with the mantle. New crust is created as molten materials move from the mantle through sea-floor spreading and volcanoes. Over time, much of the crust must cycle into and out of the mantle.

The mantle-crust cycle is but one of many cycles involving Earth materials. Crust exposed to the atmosphere is involved in another kind of cycle that was introduced in the previous chapter as the rock cycle. The atmosphere and rocks of the crust interact and rocks are weathered to sediments, which are buried and formed into sedimentary rock.

Metamorphosis or melting may take place as forces from the movement of plates deform and

elevate rocks into mountains. Here, they are again weathered to sediments and the rock cycling process begins again.

The movement of plates, the crust-mantle cycle, and the igneous-sedimentarymetamorphic rock cycle all combine to produce a constantly changing surface. There are basically two types of surface changes: (1) changes that originate within Earth, resulting in a building up of the surface, and (2) changes that result from rocks being exposed to the atmosphere and water, resulting in a sculpturing and tearing down of the surface. This chapter is about the building up of the land. The concepts of this chapter will provide you with something far more interesting about Earth’s surface than the scenic aspect. The existence of different features (such as mountains, folded hills, islands) and the occurrence of certain events (such as earthquakes, volcanoes, faulting) are all related. The related features and events also have a story to tell about Earth’s past, a story about the here and now, and yet another story about the future.

Suggestions 1. Physiographic relief globes that provide a view of Earth’s interior (crust, mantle, and core) and plastic relief globes with a raised relief are available from scientific supply companies.

2. A set of color images can be used to show rock types, formations, and illustrations of the geologic processes that shape Earth’s surface. Choose selections from the many available from supply houses that are most beneficial for the presentation of this and other geology-oriented chapters and that supplement the types of rocks and features that are not present in your location.

3. Models of rock layers are available from supply houses. These models are helpful in illustrating several of the concepts discussed. A deck of cards spread out on a desk can be used to illustrate the relative age of rock layers. Cards toward the bottom of the deck must have been laid down before the upper ones if the deck has not been disturbed.

4. Assign students the task of finding and reporting on six different examples of mass movement they can find on or near the campus.

5. If a road cut is nearby, ask students to figure out the local Earth history by studying the road cut.

For Class Discussions 1. The volcanoes along the Washington and Oregon coastline originated from a. ocean-continent convergence. b. ocean-ocean convergence. c. a divergent boundary.

d. a transform boundary.

2. The Appalachian Mountains were a result of erosion after an origin of a. folding. b. faulting. c. volcanic.

3. The Sierra Nevadas of California were formed by a. folding. b. faulting. c. volcanic activity.

4. One of the following formed as fault block mountains: a. Black Hills of South Dakota. b. Adirondack Mountains of New York. c. Teton Mountains of Wyoming. d. Mauna Loa in Hawaii.

5. One of the following was formed by volcanic activity: a. Black Hills of South Dakota. b. Adirodack Mountains of New York. c. Teton Mountains of Wyoming. d. Mauna Loa in Hawaii.

6. Each higher number on the Richter scale means how much more ground movement than the preceding number? a. 2 times more. b. 5 times more. c. 7 times more. d. 10 times more.

Answers: 1a, 2a, 3b, 4c, 5d, 6d.

Answers to Questions for Thought 1. The principle of uniformity is the frame of reference that the same geologic processes that change rocks seen today are the same processes that changed them in the past. It is based on the assumption that Earth’s history can be interpreted by tracing it backward

from the present to the past. This tracing requires a frame of reference of slow, uniform change.

2. (a) A slow increase of pressure on deeply buried warm layers of rock would create an elastic deformation and then an elastic flow. (b) A slow increase of pressure in cold rock layers would result in a plastic deformation. (c) A quick increase in pressure on cold rock or warm rock would result in a break.

3. An anticline is an arch-shaped fold in rock layers, while a syncline is a trough-shaped fold.

4. The presence of folded sedimentary rock indicates that the region has undergone geologic stress in the time since the sedimentary rock was formed.

5. Faulting is generally caused by sudden stress on the cooler, more brittle rock near the surface. A fault is directly caused by movement between the rocks on either side of a fracture. Folding occurs in deeper rock, which has stress applied more slowly.

6. Normal faulting results from pulling apart stresses such as those associated with diverging plates. Reverse faulting results from compressional stresses that may be from converging plates.

7. The sudden movement of blocks of rock produces vibrations that move out as waves throughout Earth. These vibrations are known as earthquakes. Generally, the motion at plate boundaries creates the stress conditions necessary for the sudden movements of the blocks of rock.

8. The theory of plate tectonics would predict that earthquakes would occur at any plate boundary, since stresses on rock always occur in these regions.

9. The time lag between the S-waves and P-waves gives the distance to the earthquake source. The direction to the source is calculated by drawing a circle on a map using the calculated distance as the radius. The point where the circles of three recording stations cross identifies the earthquake source.

10. Folded mountains form where the crust has been thickened as compressional forces produced tight, almost upright folds. This folding could be caused by colliding plates or the intrusion of magma or from the motion of a plate over a hot spot, so they can occur almost anywhere. Fault block mountains are the result of compression and relaxation of compressional forces on a regional scale. Since they are the result of faults in the rock formed from compressional forces, they are generally located near plate boundaries.

11. Each higher number of the Richter Scale indicates an increase of ten times in the ground movement and an increase of about thirty times more energy.

12. The primary region of volcanic activity in the United States is in the Northwest, where an ocean-continent subduction zone exists, and in Alaska, where there is another subduction zone.

13. The most basic source of energy behind the earthquakes in southern California is the radioactive decay of rocks within Earth. It is the heat from this decay that drives the convective motion that moves the crustal plates.

14. Some volcanic eruptions blast huge amounts of volcanic dust, ash, and gas high into the atmosphere. Some of the dust particles and sulfur dioxide gas can be pushed high into the stratosphere, where the gas reacts with water to form sulfuric acid. Droplets of the acid and the dust can form a layer around the entire Earth, reflecting and scattering sunlight. This tends to produce cooler weather patterns, which can last for years.

15. Most magma that forms volcanoes is produced within the outer 100 km or so of Earth’s surface from a partial melting of the rocks within the crust or the uppermost part of the mantle. Some volcanoes, such as those in Hawaii, are formed from magma that rises from deep within Earth’s mantle.

16. Shield volcanoes are formed from thin, low viscosity lava. Cinder cone volcanoes are formed from frothy blobs of lava that cooled as they were thrown into the air.

Composite volcanoes are formed from thick, mud like lava and mixtures of this lava with ash and cinders.

17. Mountains are elevated landforms that tend to develop along the edges of plates that are converging. Mountains are built in long, thin belts along the boundary as the crust thickens through the process of folding, faulting, and associated earthquakes and volcanic activity.

For Further Analysis 33. Answers will vary but should include evidence of observable geologic events and an understanding of geologic time.

34. Answers will vary, but should describe geologic events associated with plate tectonics, and evidence from geologic history about the past.

35. Similarities – both elastic and plastic deformation are changes brought about by the application of forces. Differences – elastic deformation is temporary and the material returns to its original shape; plastic deformation permanently alters the shape of a material.

36. Variables: A ductile condition from confining pressure and deep burial; relatively slow application of compressive stress.

Group B Solutions

12. m

a = 9.8 m/s2

First, convert kph to /s

vf = 1.4 x 103 km/hr

= 1.4 x 103 km/hr x 1000 m / 1 km x 1 hr / 3600 s

d=?

= 389 m/s Then,

v f  2ad  d  (388 m ) 2 s  m 2(9.8 2 ) s  7.7  103 m

s

v 2f 2a

20

Shaping Earth’s Surface

Contents 20.1 Changing Rocks into Soil Mechanical Weathering Chemical Weathering Soils 20.2 Erosion Mass Movement Running Water Glaciers Wind Science and Society: Acid Rain 20.3 Development of Landscapes Rock Structure Weathering and Erosion Processes Stage of Development

Overview This chapter is concerned with the processes that tear down the land, and how an understanding of these processes makes possible an interpretation of the present-day landscape for meaning about the past. Elevated landscape features are exposed to the elements and undergo weathering and erosion processes that have sculptured them into today’s landscapes. The sculpturing, cutting, and transportation actions of running water, wind erosion, and glacial effects are covered after first considering the preparation of the surface through physical and chemical weathering. There are many examples of the results of chemical and mechanical weathering that can be observed by students during their travels.

Many road cuts from the building of highways afford opportunities for students to observe how the relatively smooth faces of these road cuts are slowly disintegrating, with the resulting buildup of talus deposits at the bottom.

Sculpturing of Earth’s surface takes place so gradually that humans are usually not aware it is happening. Some events such as a landslide or the movement of a big part of the beach by a storm are noticed. The continual, slow downhill drift of all the soil on a slope or the constant shift of grains of sand along a beach is outside the awareness of most people.

People do notice the muddy water moving rapidly downstream in the swollen river after a storm. Few, however, are conscious of the slow, steady solution of limestone by acid rain percolating through it. Yet, it is the processes of slow movement, shifting grains and bits of

rocks, and slow dissolving that will wear down the mountains, removing all the features of the landscape that you can see.

This chapter is about the sculpturing and tearing down of the land. The sculpturing begins with the decomposition of rocks, physical and chemical reactions that decay solid rock into fragments and soluble components. The tearing down, or degradation, of the surface continues with the removal of the fragments and solutions. The process continues further with the depositing of fragments and sediments elsewhere. What are the agents of all the movement and re-deposition of Earth’s surface? The work is accomplished by gravity, moving water, glaciers, and the wind. This rate of removal is continual and slow and would require about 20 million years or so to level the continents to sea level. However, the destructive forces have never won in the past. The constructive forces of diastrophism and vulcanism seem to balance the continual and slow degradation. The look of the landscape has changed, and the shapes and sizes of continents have changed. You would expect such changes as the forces of upheaval build up the land and the forces of degradation tear it down. So far, the records indicate that the forces must be balanced since the continents have persisted about the same average elevation above sea level for billions of years.

Suggestions 1. Ask the students to list the types of weathering and agents of erosion according to their order of importance in the immediate geographic region. Does the order vary from their respective home areas?

2. A stream table is extremely useful to illustrate the erosive features produced by running water. The device uses a mixture of sand of various colors or of sand and several different soils. The stream table should be set in operation and placed on display to permit students to observe changing conditions over time.

3. To illustrate physical weathering, a handful of sharp-edged pieces of limestone can be placed in a jar with a lid and shaken several hundred times. Changes in the sharpness of the rock edges and changes in the composition of the water will show the effects. To illustrate chemical weathering, compare what happens to a sample of limestone in a beaker of water to one in a beaker of water with dilute hydrochloric acid. The chemical action releases bubbles of carbon dioxide.

4. Assign students the task of finding and reporting on six different examples of weathering and any examples of erosion they can find on or near the campus.

For Class Discussions 1. Which of the following is the most important agent of erosion? a. glaciers b. wind c. ocean waves d. streams 2. Which one of the following does not belong with the other three? a. floodplain b. U-shaped valley c. delta d. meanders 3. Glaciation might leave a deposit called a a. moraine. b. delta. c. dune. d. oxbow.

4. A slowly flowing stream with wide meanders in a wide floodplain is in what stage of development? a. youth b. maturity c. old age d. rejuvenation 5. Is it possible to have erosion without weathering? a. Yes. b. No.

Answers: 1d, 2b, 3a, 4c, 5b.

Answers to Questions for Thought 1. Mechanical weathering is the physical breaking up of rocks without any changes in the chemical composition of the rock. Chemical weathering is the breakdown of minerals by chemical reactions with water, gases of the atmosphere, or solutions. Both act to break down rocks, but mechanical weathering breaks the rocks into smaller and smaller pieces of the original rock. Chemical weathering dissolves or breaks down the minerals of the rock into new compounds.

2. Quartz sand, clay minerals, metal oxides, and soluble salts are the end products of granite weathering. The clay minerals and soluble salts are washed away in the weathering process. The quartz sand and metal oxides are generally removed through erosion.

3. Landslides move material rapidly to lower levels, where they can be eroded by streams.

Glaciers can move large amounts of materials and create their own valleys. Wind is less efficient at eroding.

4. Rainfall carries the products of weathering to a stream through sheet erosion as well as carrying the soluble products of weathering. The small stream moves to larger channels and transports the materials as dissolved rock minerals carried in solutions, as clay minerals and small grains carried in suspension, and as sand and larger rock fragments that are rolled, bounced, and slid along the streambed.

5. A floodplain is the wide, level floor of a valley built by a stream. It gets its name because this is where the stream floods when it spills out of its channel.

6. Youth is characterized by a steep gradient, a V-shaped valley without a floodplain, and the presence of features that interrupt its smooth flow such as boulders in the streambed, rapids, and waterfalls. Erosion eventually brings the onset of the mature stage. The boulders, rapids, and waterfalls are eroded away, the valley smoothed, and the gradient reduced. Meanders begin to form over the wide floodplain, and the higher elevations are now sloping hills rather than steep channel sides. Old age is marked by a very low gradient in extremely broad, gently sloping valleys. The meanders have become broad sweeps across the wide floodplain. The flow is sluggish, and floods are more common.

7. A glacier is a mass of ice on land that moves under its own weight. This motion erodes by bulldozing rocks and soil, by abrading the rocks on the valley sides and floors, and by plucking as water seeps into cracked rocks and freezes, becoming a part of the solid glacial mass.

8. Abrasion from the erosion process of glaciers pulverizes rock into ever-finer fragments, eventually producing powdery, silt-sized sediment called rock flour.

9. If the stream had an outlet lower than sea level, such as the Dead Sea, the erosion could continue as far down as the stream could flow. Otherwise, at sea level, if the stream lets out into the sea, the flow rate would be very slow and very little erosion would occur.

10. Glacial erosion occurs by pulling rocks up and along with the glacier as well as by abrasion. There is very little erosion above the glacier, however, causing the valley to be U-shaped. A stream fed by rainfall allows the land above it to be eroded rapidly because it provides an outlet for the rainwater to carry away its sediments. In addition, the stream erosion occurs much faster than that of a glacier, cutting deeply into the land, creating a V-shaped valley.

11. Answers will vary.

12. A soil that has balanced amounts of sand, silt, and clay mixed with an abundance of humus is usually thought of as a good soil. It is good since it is fertile and well drained yet holds enough moisture for sustained plant growth. The sand grains help keep the soil loose and aerated, allowing good water drainage. Clay minerals help hold water in the soil. The balanced mixture of clay minerals and sand provide plants with both the air and water that plants need for optimum root growth.

13. Gravity acts directly on individual rock fragments, and it acts directly on large amounts of surface materials as a mass, pulling all to a lower elevation. The movement to a lower elevation is called mass wasting, which occurs whenever anything happens to reduce the cohesiveness or to reduce friction.

14. Stream erosion: A stream develops a valley on a widening floodplain. The development of a steam channel into a widening floodplain seems to follow a general, idealized aging pattern. When the stream is on a recently uplifted land mass, it has a steep gradient, a V-shaped valley without a floodplain, and the presence of features that interrupt its smooth flow such as boulders in the streambed, rapids, and waterfalls.

During maturity meanders form over a wide floodplain that now occupies the valley floor. During old age the stream has a very low gradient in extremely broad, gently sloping valleys. The stream now flows slowly in broad meanders over the wide floodplain. Floods are more common in old age since the stream is carrying a full load of sediments and flows sluggishly.

Wind erosion: Two major processes of wind erosion are called abrasion, and deflation.

Wind abrasion is a natural sand-blasting process that occurs when the particles carried along by the wind break off small particles and polish what they strike. Deflation, named after the Latin meaning, ―to blow away,‖ is the widespread picking up of loose materials from the surface. Deflation is naturally most active where winds are unobstructed, and the materials are exposed and not protected by vegetation.

Glacial erosion: Deposits of bulldozed rocks and other materials that remain after the ice melts are called moraines. Plucking occurs as water seeps into cracked rocks and freezes, becoming a part of the solid glacial mass. As the glacier moves on, it pulls the fractured rock apart and plucks away chunks of it. The process is accelerated by the frost wedging action of the freezing water. Plucking at the upper-most level of an alpine glacier, combined with weathering of the surrounding rocks, produces a rounded or bowl-like depression known as a cirque.

15. Stream deposits: When a stream flows into the ocean or a lake it loses all of its sediment-carrying ability. It drops the sediments, forming a deposit at the mouth called a delta.

Wind deposits: The most common wind-blown deposits are dunes and loess. A dune is a low mound or ridge of sand or other sediments.

Glacier deposits: Glaciers produce a wide variety of materials from rocks, soil, and sediments by the leading edge of an advancing glacier. Deposits of bulldozed rocks and other materials that remain after the ice melts are called moraines. The pulverizing of rock into ever-finer fragments eventually produces powdery, silt-sized sediment called rock flour.

16. There is more pollution in city areas, leading to more chemical weathering than occurs in rural areas.

17. Chemical weathering occurs more in a humid climate where sufficient moisture is available. Not as much chemical weathering occurs in a dry climate because water is necessary in the scheme of things.

18. Answers will vary but could include local effects—as the rain forest is cleared away and burned for new fields of tropical agriculture, the thin humus layer is soon exhausted and subjected to leaching without replenishment. The remaining laterite is incapable of sustaining agricultural efforts, sometimes baking into a hard, brick-like layer that is impossible to plow. Other reasons include the destruction of oxygen-producing vegetation, the worldwide increase in carbon dioxide levels, and the destruction of the plant gene pool.

For Further Analysis 37. Similarities – both are changes in the destruction of solid rock. Differences – weathering is the slow breaking up, crumbling and destruction of solid rock; erosion is the physical removal of weathered rock materials.

38. Answers will vary.

39. No, sea level is the limit of erosion. Observation of a delta will show that materials are deposited, not eroded at sea level.

Group B Solutions

21

Geologic Time

Contents 21.1 Fossils Early Ideas About Fossils Types of Fossilization 21.2 Reading Rocks Arranging Events in Order Correlation 21.3 Geologic Time Early Attempts at Earth Dating Modern Techniques The Geologic Time Scale Geologic Periods and Typical Fossils Mass Extinctions Interpreting Geologic History—A Summary

Overview Geology, as is typical of other natural sciences, is based on well-established laws. A geologist learns to rely on each law to describe events that transpired in Earth’s past. The laws are used to determine the age of rock formations and to describe the changes Earth has undergone. The application of the laws also helps a geologist locate valuable mineral deposits, oil, natural gas, and other natural resources. The laws, such as the law of superposition and the law of faunal succession, are supplemented with data obtained, for example, by the determination of the age of a particular stratum by analysis or the radioactive elements present in those strata. Altogether, the laws and dating methods have resulted in a standard time scale used by all geologists. Major changes in the surface of Earth as well as major changes in the life forms living on Earth are used to mark this geologic time scale.

Historical geology is a branch of geology concerned with the development of Earth and the organisms on it over time. Physical and historical geology together provide a basis for understanding much about Earth and how it has developed.

One reason to study geology is to satisfy an intellectual curiosity about how Earth works. Piecing together the history of how a mountain range formed or inferring the history of an individual rock can be exciting as well as satisfying. As a result, you appreciate the beauty of our Earth from a different perspective.

Suggestions 1. Many models of fossil life from Earth’s past are available from various scientific supply companies. The proper selection can illustrate many of the concepts discussed in this chapter.

2. Assign students the task of finding and reporting on examples of the law of superposition and the law of crosscutting relationships on the campus. An example of superposition would be objects that are stacked on top of each other. An example of crosscutting relationships would be cracks or cuts in a sidewalk.

3. If a road cut is nearby, ask students to figure out the local Earth history by studying the road cut.

4. Use a series of regularly repeated events that happen on your campus to make a relative time scale for your school. A list of historical events for your school could also be used to make a local time scale.

For Class Discussions 1. To be useful as an index fossil, the plant or animal in question should a. widely distributed and live a short period of time. b. widely distributed and live a long period of time. c. have a restricted distribution and live a short period of time. d. have a restricted distribution and live a long period of time.

2. One of the logical structures used to guide thinking states ―the present is the key to the past.‖ This logic is also known as the principle of a. superposition. b. original horizontality. c. uniformity. d. crosscutting relationships.

3. How old is Earth? About a. 6,000 years. b. 2 million years. c. 4.6 billion years. d. 18 billion years.

4. The major blocks of time in Earth’s history are based on changes in life forms. a. True b. False

5. Abundant marine fossils first appeared, but no land fossils, in the time period known as the a. Cambrian. b. Carboniferous. c. Triassic. d. Tertiary.

6. The first reptiles and insects appeared on land in the time period known as the a. Cambrian. b. Carboniferous. c. Triassic. d. Tertiary.

7. The first dinosaurs appeared in the time period known as the a. Cambrian. b. Carboniferous. c. Triassic. d. Tertiary.

8. The dinosaurs were extinct and mammals became the dominate life form in the time period known as the a. Cambrian. b. Carboniferous. c. Triassic. d. Tertiary.

Answers: 1a, 2c, 3c, 4a, 5a, 6b, 7c, 8d.

Answers to Questions for Thought 1. The principle of uniformity is the frame of reference that the same geologic processes that change rocks today are the same processes that changed them in the past. This leads to the assumption that Earth’s history can be interpreted by tracing it backward from the present to the past. The frame of reference also requires slow, uniform change over very long time periods.

2. The geological time scale is a method of keeping track of events that have occurred in Earth’s geologic history. The appearance and disappearance of particular fossils in the sedimentary rock record identify the eras.

3. Rocks older than this have not yet been found. Any rocks that were formed that long ago have probably succumbed to the process of weathering and no longer exist. The rock record for eras earlier than 3.8 billion years ago would probably show that the atmosphere was primarily carbon dioxide and that water was beginning to condense out to form the oceans.

4. Sedimentary rocks provide much information both about the life present and about the conditions of Earth during the time of their formation.

5. The Paleozoic and Mesozoic eras both ended with mass extinctions. It has been proposed that bombardment by meteors could have changed the climate enough to cause these extinctions.

6. The principle of uniformity states that the same geologic processes have been operating throughout the history of Earth. The principle of original horizontality states that any layer of rock that is not horizontal has been subjected to forces that have deformed Earth’s surface. The principle of superposition states that for undeformed rocks, newer rock is layered on top of older rock. The principle of crosscutting relationships states that any geologic feature that cuts across or is intruded into a rock mass must be younger than the rock mass. The principle of erosion states that there may be breaks in the record because erosion does not always occur at the same rate. Finally, the principle of faunal succession implies that the same types of fossil organisms lived only briefly and should occur only in rocks that are the same age.

7. In an angular unconformity, the oldest sediments were deposited and formed into rock.

Then some type of tilting or folding occurred followed by a significant period of erosion.

After the erosion, there was another period of deposition, at an angle to the first, forming rock layers at an angle to the first layers.

8. Superposition is used to determine the relative age of a layer as being younger than the layers below it and older than the layers above it. If the layers are not horizontal, the principle of horizontality states that they were originally horizontal and that the principle of superposition can be used on the layers. Faunal succession is used to correlate the dates at one site with the dates at another site.

9. The numbers of the ages of eras and other divisions of the geological time scale are determined from geological clocks such as (a) those that find the radiometric age of rocks in years by measuring the radioactive decay of unstable elements within the crystals of certain minerals and (b) those that find the age on a geomagnetic time scale that is based on the number and duration of magnetic field reversals that have occurred during the past six million years.

10. Fossilization methods include actual preservation of remains, alteration or replacement of remains, preservation of the shape of an organism, and preservation of signs of activity.

11. Correlation–one of the most important uses of fossils is correlating rocks in one location with those in another. Paleoenvironments–the kinds of fossils found at a particular locality can help in determining the former environment of a region. Paleoecology– detail studies of fossil changes and studies of changes in the type of sediment in which the fossil was found can lead to deductions about how the animal adapted to the environment, its relationship to other organisms, and how ancient communities were structured. Paleogeography –the geographic distribution of fossils also aids in paleogeography studies. From these studies, it is possible to determine the distribution of land and sea areas, paleolatitudes, ancient shorelines, and land connections.

Paleoclimates–geologists can also determine the paleoclimate or climates for a given region by studying fossil types and fossil. Evidence for evolution –the vertical distribution of fossils provides much support for the idea that living organisms have gradually changed or evolved into their present forms. Evidence for plate tectonics– the distribution of fossils found on continents that are today separated by an ocean provides evidence that the continents were connected at one time.

For Further Analysis 1. A pot is something made by humans and a piece of a pot – a shard – might be studied to learn about past human life. A fossil, on the other hand, is any evidence of ancient organisms in the history of life.

2. One would expect most fossils to be preservation or alteration of hard parts because these are more difficult to destroy than signs of activity such as footprints, or preservation of shape.

3. The discussion should represent the viewpoints that Earth is unchanging, with catastrophically formed landscapes, vs. a frame of reference of slow, uniform change over a very long period of time.

4. The geologic time scale is based on radiometric age, a process that has been operating since Earth was formed. The yearly time scale is based on movements of Earth and the Moon.

5. The different blocks of time are based on events of evolution and extinctions in the history of life.

6. Such changes take place slowly, so it is difficult to see significant changes in the brief span of a lifetime. It is a mental framework that is based on a lack of appreciation of the many changes that have occurred slowly over time.

Group B Solutions

22

The Atmosphere of Earth

Contents

22.1 The Atmosphere Composition of the Atmosphere Atmospheric Pressure Warming the Atmosphere A Closer Look: Hole in the Ozone Layer?

Structure of the Atmosphere 22.2 The Winds Local Wind Patterns A Closer Look: The Windchill Factor Science and Society: Use Wind Energy?

Global Wind Patterns 22.3 Water and the Atmosphere Evaporation and Condensation Humidity The Condensation Process Fog and Clouds

Overview Even if we do not consider the multitude of different chemicals present as the result of pollution, the atmosphere of our planet contains a considerable variety of elements and compounds. The atmosphere is a remarkably pure gaseous solution of nitrogen, oxygen, carbon dioxide, and argon with traces of neon, helium, methane, krypton, hydrogen, xenon, ozone, radon, and so forth. Only two of these gases (nitrogen and oxygen) make up about 99 percent of the total composition. The composition of gases in the atmosphere is the same percent everywhere around Earth up to an altitude of 25 km (about 15 mi), except for small variations of carbon dioxide.

About half of the radiant energy from the Sun makes it through the atmosphere. Most of the wavelengths shorter than those of visible light are absorbed by ozone in the upper atmosphere. About 30 percent of this energy is reflected back into space. The energy that reaches the surface is mainly in the form of visible light and longer wavelengths.

The Sun’s energy that does reach Earth’s surface is absorbed, increasing the temperature of materials on the surface. These materials re-emit the absorbed energy with longer wavelengths of infrared light. The longer wavelengths are absorbed in the atmosphere by molecules of water vapor and carbon dioxide, increasing the temperature. The lower atmosphere is heated from the bottom up and the process is called the greenhouse effect.

Based on changes in temperature with increasing altitude, the atmosphere is divided into five main layers, each with its own lapse rate pattern. The layer closest to Earth is called the troposphere, within which the temperature decreases with increasing altitude. The troposphere is that part of the atmosphere where practically all weather occurs. The layer

above the troposphere is the stratosphere, within which the temperature rises with increasing altitude. Within the stratosphere is the ozone layer that absorbs most of the energy at ultraviolet wavelengths from the Sun. Above the stratosphere is the mesosphere, where the temperature decreases with increasing altitude. The layer above the mesosphere is the thermosphere, where the temperature again increases with altitude. The thermosphere includes an ionic layer that reflects most radio waves and allows planet-wide radio communication. Above the thermosphere is the exosphere, which literally fades into space.

Earth eventually re-emits all the energy back into space that Earth initially receives from the Sun. Because Earth spins on its axis, winds that blow toward the North (in the Northern Hemisphere) and toward the South (in the Southern Hemisphere) are deflected to the right.

The deflection is called the Coriolis effect, and this effect, along with convection currents, accounts for worldwide wind patterns.

Evaporation, condensation, and the movement of water vapor in the atmosphere are discussed, as are relative humidity, dew, fog, and precipitation. The main types of clouds are presented along with photographs of typical examples. This sets the stage for a discussion of weather and weather patterns, the topics of chapter 25.

Suggestions 1. Students will be interested in various phenomena of the atmosphere such as why the sky appears blue, northern lights, why sunsets are red, and why airplanes fly in the stratosphere.

2. If possible, borrow an instrument package used with weather balloons and explain how the instruments provide information about the atmosphere.

3. On a calm, sunlit day, have students measure air temperatures just above the grass in a field and just above the asphalt or concrete of an adjacent parking lot. Use this information as the basis for a prediction about which way the air is moving near the surface between the grass and parking lot. Use soap bubbles to indicate the direction of air movement and test the prediction.

4. Watch for newspaper reports of Santa Ana and Chinook winds (compressional winds).

Sometimes the results of these warm winds can be very dramatic, melting as much as ten inches of snow or more in a single day.

5. Have students do a literature search to determine how the doldrums, trade winds, and horse latitudes got their names. They could also find how the global wind belts have affected history, for example, what discoveries were a result of the wind belts and how the wind belts affected trade.

6. The requirements for the condensation process can be demonstrated with a large, smallmouth jug. Add a small amount of water to the jug and shake it thoroughly to saturate the air. Place your mouth against the clean opening, then blow into the jug to increase

the air pressure inside. Quickly release the pressure, explaining that the expansion will cool the air and result in condensation. Nothing happens when this is done. Now add a smoking match to the jug. When the process is repeated, a fog forms in the jug. Explain the necessary conditions of saturated air, cooling, and the presence of condensation nuclei (provided by the match) in order for condensation to form.

For Class Discussions 1. An airplane flying at an altitude of 10 km (about 6 mi) is above about how much of Earth’s atmosphere? About a. 90% b. 70% c. 50% d. 30% 2. The lower part of Earth’s atmosphere is mostly heated by a. the Sun b. Earth c. exhaust from combustion engines.

3. Ozone is a. O b. O2 c. O3 4. Without adding or removing any water vapor, a sample of cooling air will have a relative humidity that is a. increasing. b. decreasing. c. the same.

5. The dew point temperature occurs when a. the relative humidity is 100%. b. condensation begins to form. c. the air becomes saturated. d. any of the above.

6. When air that is saturated is cooled, a. some of the water vapor condenses. b. the relative humidity decreases. c. the capacity of air to hold moisture increases. d. the relative humidity increases to greater than 100%.

Answers: 1b, 2b, 3c, 4a, 5d, 6a.

Answers to Questions for Thought 1. The average value of atmospheric pressure at sea level has been defined as the standard atmospheric pressure. This is sometimes referred to as the normal pressure and is measured at 1,013.25 millibars or 760.0 mm of mercury.

2. The greenhouse effect is caused by certain gases in the atmosphere referred to as greenhouse gases. These gases absorb infrared energy emitted by the ground and reemit this energy in all directions. Some of this re-emitted energy is again absorbed by the ground, starting the process over, some is absorbed by other molecules in the atmosphere, increasing the temperature, and some is radiated to outer space. This results in a slowdown of the rate that energy from the Sun escapes into space. Since some of the energy is redirected to the surface, the surface temperature is increased over what it would have been if this effect were not present. As an analogy for this behavior, a greenhouse is misleading. The glass in a greenhouse allows the short wavelength light energy in but does not allow the heat to escape by convection. The greenhouse gases do not trap the infrared light but are involved in a dynamic absorption and emission process. The more greenhouse gases, the more the temperature is increased, but adding more glass layers does not increase the temperature in the greenhouse significantly.

3. If an inversion is not present, the temperature decreases with height above the surface until an average altitude of 11 km. Then the temperature becomes relatively constant.

The layer up to where the temperature becomes constant is called the troposphere. The region where the temperature remains constant is called the tropopause. Above the tropopause is the layer called the stratosphere. The temperature increases with height in this region. The stratopause is the upper boundary of the stratosphere where the temperature reaches a maximum of about 10°C. Above the stratopause, the temperature decreases again and then begins to increase with altitude. These layers are the mesosphere and the thermosphere. The exosphere is the outermost layer, where the molecules merge with the diffuse medium of outer space.

4. The ozone shield protects living things on the surface of Earth by absorbing damaging ultraviolet light. Chemical reactions that occur in this layer of the atmosphere require

ultraviolet light. Much of the ultraviolet light passing through this layer is absorbed in these chemical reactions. Chemicals used on the surface of Earth have reached this layer of the atmosphere. They combine with oxygen to form stable compounds; thus, the amount of oxygen available for ozone-forming chemical reactions, which absorb ultraviolet light, is decreasing. The resulting increase in ultraviolet light at Earth’s surface could have serious health consequences and decrease the output of farms.

5. A horizontal movement of air is called wind. Uneven heating of the atmosphere causes warmer, less dense parts of the atmosphere to be pushed up by cooler, denser parts of the atmosphere. Thus the Sun provides the energy to drive the wind.

6. In warmer air, the individual molecules have more kinetic energy and are therefore moving faster. These faster-moving molecules collide more violently until their higher speed drives them apart. Since the molecules are farther apart, there are fewer molecules in a unit volume and so the density is less.

7. Heated air is less dense than cooler air. The cooler, denser air pushes the less dense, more buoyant warm air up as the cooler air sinks.

8. There are strong winds in the top of the troposphere called the jet stream. The winds generally blow from the west and can slow an airplane flying west and speed the journey flying east.

9. Since the process of water going from the gaseous state to the liquid state releases energy, the temperature of the surroundings should increase, because this energy is absorbed by the surroundings.

10. Warm air molecules have higher kinetic energies. Water molecules in warm air also have higher kinetic energies. These higher kinetic energies help stop the water from clumping together and forming droplets. Cooler air has lower kinetic energy and can allow the attractive forces between water molecules to pull them together to form water droplets that fall out. Cooler air cannot hold as much water vapor as warmer air, so when the temperature decreases, the denominator in the relative humidity ratio decreases. As the denominator in a fraction gets smaller the value of the fraction increases. Thus the decrease in the amount of water vapor needed to saturate the air increases the relative humidity for the same amount of water vapor present in the air.

11. High humidity prevents the addition of water vapor from the evaporation of perspiration to the air. Since the evaporation of perspiration carries heat away, when this evaporation does not take place, individuals feel hotter.

12. The dew point temperature is the temperature at which the water vapor presently in the air will begin to condense out of the air.

13. Clear nights allow a greater loss of energy at infrared wavelengths by objects than cloudy nights. The air must be cold and calm to allow the water vapor to condense directly onto objects and freeze.

For Further Analysis 40. Fill a long garden hose with water and cap one end. Place the open end in a bucket of water and support the hose vertically. Standard pressure should support (29.92 inches Hg)  13.6 (density of Hg) = 406.912 inches of water. Divide 406.912 inches of water by 12 inches/foot = 33.9 ft of water.

41. Air expands and cools as it rises.

42. Answers will vary.

43. It is convection that moves air, and differential heating is needed for convection.

44. First, find the current condition of temperature and absolute humidity (found from relative humidity at the current temperature). Place pencil point on the temperature and absolute humidity data point. Move pencil to left until it touches saturation line.

Follow this point straight down to the x-axis to read the dew point temperature.

Group B Solutions

23

Weather and Climate

Contents

23.1 Clouds and Precipitation Cloud-Forming Processes Origin of Precipitation 23.2 Weather Producers Air Masses Weather Fronts Science and Society: Urban Heat Islands Waves and Cyclones Major Storms Thunderstorms Tornadoes Hurricanes 23.3 Weather Forecasting Climate Major Climate Groups Regional Climatic Influence Describing Climates Major Climate Zones Local Climates 23.4 Climate Change Causes of Global Climate Change Case Study: El Niño Global Warming Overview If a mass of air is over a particular location for a sufficient amount of time, from several days to a week or so, it begins to acquire nearly homogeneous temperature and moisture conditions from the surface it is over. These horizontally uniform temperature and moisture conditions identify the physical properties of different air masses, which are named from these properties. Thus, tropical air masses are hot, and polar air masses are cold; maritime air masses are moist, and continental air masses are dry. Pressure differences and prevailing wind belts cause massive air masses to break loose from their source regions. This sends a huge mass of polar air southward or a huge mass of tropical air northward. These masses are shifted eastward by the prevailing westerlies. Thus, most of the United States can have weather influenced by continental polar air for a few days. Then weather can be influenced by a mass of maritime tropical air, and an occasional weather pattern produced by a mass of maritime polar air. In general, continental polar air drifts farther south in the winter and maritime tropical air moves farther north in the summer.

Moving air masses bring rapid weather changes along the leading edge of the mass (frontal weather), and slow changes occur after the air mass arrives (air mass weather). Cold air is denser than warm air and wedges under the warm air. A front is usually convex in the direction of movement, acting much as the surface of a huge bubble moving across the land.

Since warm air is less dense than cold air, a moving warm air mass overrides as it pushes a colder air mass. The overriding air mass produces a series of cloud changes that foretell the coming of a warm air mass. Cirrus clouds and then cirrostratus clouds, which can produce a halo around the Sun or Moon, may appear some 12 hours before a warm front arrives.

Weather forecasting is based on information about air masses, high- and low-pressure systems, and the movement of fronts. Information is gathered from satellite photographs, radar, and other sources of observations and used to construct a weather map, which is analyzed and interpreted for coming changes in different locations.

Climate is the average weather that occurs over a period of years at a given location.

There are a number of different climatic factors that can be used to distinguish one climate from another, but any scheme used is going to be artificial. Boundaries between general climatic patterns are not sharp but are wide zones of transition. Climate regions actually blend into one another gradually.

Suggestions 1. Have students record daily temperature, barometric pressure, wind direction, and wind velocity in the morning, at noon, and in the evening. Also have them note cloud cover and amount of precipitation every day. At the end of a week, have a class discussion of correlations between the various factors measured and the type of weather that prevailed during the week of study.

2. Use a series of daily weather maps to identify kinds of air masses and track their movement over time. Look for correlations between the different kinds of air masses and the weather that each brings to your location. Have someone obtain hourly temperature readings for the day before an air mass arrives and for a day after it arrives.

Graph the temperature readings and determine when the air mass arrived.

3. Elementary school teachers sometimes claim they can predict a coming storm (lowpressure area) from the noise and activity level of their classes. Some students might be interested in investigating if there is any basis for such claims of changes in the social behavior related to atmospheric pressure changes.

4. The effect of sunlight at different latitudes can be demonstrated with a strip of paper with equally spaced drops of wax from a candle. The paper strip is taped to a globe, running from pole to pole, with the wax drops on the outside surface. A strong spotlight directed toward the equator will melt the wax drops on the equator first, then poleward.

5. Many new buildings are now constructed with a window overhang or awning so that sunlight shines in a south-facing window in the winter but not during the summer. The size of the overhang or awning can be calculated for your location from a simple threestep procedure. First, determine the time of year that the window should receive full noontime sunlight (e.g., December 21) and the time of year it should receive no

noontime sunlight (e.g., March 21). Second, determine the solar altitude at noon for these two dates. Finally, calculate the overhang or awning length and the height of the overhang or awning above the window. The overhang length is found by dividing the height of the window by the tangent of the solar altitude at noon on the selected summer date, minus the tangent of the solar altitude at noon on the selected winter date. The answer for this part is the length, or how far the overhang or awning should ―stick out‖ from the building. The height of the overhang or awning above the window can be found by multiplying the overhang length by the tangent of the solar altitude at noon on the selected winter date.

6. Understandings of how climates are influenced can be demonstrated by predicting what the climates of North America would be like if there were no mountains in the West and if there were a mountain range running from New Mexico and across Texas to north Florida.

7. Some students may be interested in investigating microclimates on your campus. A map of the microclimates can be prepared by investigating plant growth and taking measurements. The influence of a large city on the climate can be investigated by comparing the temperature, precipitation, and humidity of a city with the surrounding countryside.

For Class Discussions 1. An air from over the Gulf of Mexico makes which type of air mass? a. continental polar b. maritime polar c. continental tropical d. maritime tropical 2. Which one of the following has more associated stormy weather? a. cold front b. occluded front c. warm front d. stationary front

3. A thunderstorm that occurs at 3 AM is more than likely caused by a. moving air that has cooled. b. a cold front. c. convection. d. a warm front.

4. A hurricane is a tropical cyclone with a wind speed of at least a. 75 km/h (46 mi/h) b. 100 km/h (62mi/h) c. 120 km/h (75 mi/h) d. 100 km/h (15 mi/h) 5. The most violent weather disturbance is a a. tornado. b. thunderstorm. c. hurricane. d. cyclone.

6. Clear, fair weather is usually associated with a(n) a. warm front b. cold front c. cyclone d. anticyclone 7. Is it possible for water vapor to condense in clean, cool air? a. Yes. b. No. 8. Which of the following climatic influences would probably make the temperatures of a city more even? a. high altitude b. low altitude c. large body of water nearby d. surrounded by large areas of land

Answers: 1d, 2b, 3b, 4c, 5a, 6d, 7b, 8c.

Answers to Questions for Thought 1. A cloud is a collection of water droplets high in the air. A cloud forms when air containing water vapor is cooled and the water vapor condenses onto dust and other small particles in the air.

2. Atmospheric stability is a measure of how air moved up in the atmosphere will react. In stable air, any air moved upward will tend to return to its former level. This behavior discourages the formation of clouds, and any clouds that do develop are usually arranged in the horizontal layers of stratus-type clouds. In unstable air, any air moved upward will tend to continue rising. Cumulus clouds usually develop in these types of conditions.

3. Coalescence of cloud droplets involves larger, slower-moving cloud droplets colliding and merging with smaller droplets as they fall. This merging process forms raindrops after many collisions. In the ice crystal process, ice crystals capture water molecules and grow to larger sizes while neighboring water droplets are evaporating. As they grow larger and begin to drift toward the surface, they may coalesce with other ice crystals or water droplets. If they fall during the summer, the warm air below melts the crystals to form raindrops. In winter, they reach the ground as snow.

4. An air mass is a large, uniform body of air with nearly the same temperature and moisture conditions throughout. Ordinary air does not necessarily have the same temperature and moisture conditions throughout it.

5. (a) The passage of a warm front has clouds forming far in advance of the ground-level base of the front. These high-level clouds are usually followed by thicker and lower stratus clouds as the front advances. A broad band of drizzle, fog, and continuous light rain usually accompanies these clouds. (b) Towering cumulus clouds accompany a cold front, with intense thunderstorms and a rapid temperature drop occurring as the front passes. A rapid shift in wind direction and a rapid increase in the barometric pressure also mark the passage of a cold front.

6. (a) Clouds and cyclonic storms are associated with low-pressure centers. Obviously, low atmospheric pressure is associated with low-pressure centers as well. In the Northern Hemisphere, inward flowing winds wind around counterclockwise to a low-pressure center. (b) A high-pressure center has outward moving winds that wind around clockwise in the Northern Hemisphere. Higher atmospheric pressures and clear weather are associated with high-pressure centers.

7. A maritime tropical air mass would probably have afternoon thunderstorms. As the land below the mass warms up during the day, the warmer air near the ground would create thermals in which cumulus clouds could develop from the moist air. These clouds could be the source of the afternoon thundershowers.

8. The first stage begins as convection, mountains, or a dense air mass slightly lifts a mass of warm, moist air in an unstable atmosphere. The lifted air mass expands and cools and

cumulus clouds form. An updraft is created as the released latent heat of vaporization warms the air. Soon the upward moving saturated air reaches the freezing level and ice crystals and snowflakes begin to form. When they become too large to be supported by the updraft, they begin to fall to the surface, melting into raindrops. The mature stage begins when these drops reach the surface. As the raindrops fall through the air, friction between the falling drops and the cool air produces a downdraft. This mass of air spreads out when it reaches the surface, and the leading edge has the appearance of a miniature cold front. This air mass may play a role in creating new cells in front of the thunderstorm. This stage in the life of a thunderstorm has the most intense rainfall, winds, and possibly hail. As the downdraft spreads throughout the cloud, the supply of new moisture is cut off and the thunderstorm enters the final, dissipating stage.

9. A tornado is the smallest, most violent weather disturbance that occurs on Earth. A tornado forms with intense thunderstorms mainly in the spring and early summer afternoons. The states of Texas, Oklahoma, Kansas, and Iowa have the highest incidence of tornadoes.

10. A hurricane is a large, violent circular storm that is born over the warm, tropical ocean near the equator. As a hurricane approaches the air seems unusually calm as a few clouds appear, then thicken as the wind begins to gust. Over the next six hours or so the overall wind speed increases as strong gusts and intense rain showers occur.

Thunderstorms, perhaps with tornadoes, and the strongest winds occur just before the winds suddenly die down as the sky clears with the arrival of the eye of the hurricane. It takes the eye about an hour to cross then the thunderstorms and high winds begin again, this time blowing in the opposite direction.

11. Weather is the current condition of the atmosphere. Climate is the larger pattern these weather changes create. ―Climate is what you expect, weather is what you get.‖ 12. The tropical climate zone occupies the low latitudes and overall is hot. The polar climate zone occupies the regions near the poles and is generally extremely cold. The temperate climate zone is located between the tropical and polar climate zones and has high and low temperatures that range between their two extremes.

13. Altitude, mountains, large bodies of water, and ocean currents all affect a regional climate. Average air temperature decreases with altitude. Mountains affect the conditions of passing air masses. Generally, the eastern slopes of mountain ranges in the Northern Hemisphere are dryer than the western slopes because water precipitated out of the air as it crossed the mountains. Large bodies of water tend to moderate the temperature of a region. Ocean currents can influence the temperature of air masses that move from the water to the land, influencing the temperature on the land.

14. As heated air rises, the lower pressure at higher altitudes allows the air to expand. The work required to accomplish this expansion reduces the energy of the molecules of the air, lowering the air temperature. Since the temperature is now lower than at ground level, snow can exist at higher elevations when it has melted at lower elevations.

For Further Analysis 45. Dew (or frost) forms directly on objects and the ground. It does not fall, and this is a requirement to be precipitation.

46. Similarities – Both are changes in the weather conditions. Differences – air mass weather conditions undergo slow, gradual changes; frontal weather conditions undergo rapid, intense changes.

47. A tornado is the smallest most violent weather disturbance on Earth, but a hurricane covers significantly more area. In addition, hurricanes can sometimes spawn tornadoes in addition to the damage done by sustained hurricane winds.

48. Answers will vary, but could include regional changes caused by altitude, mountains, large bodies of water, or ocean currents.

Group B Solutions

Carbon dioxide concentration in the atmosphere since 1860, in parts per million (ppm).

24

Earth’s Water

Contents 24.1 Water on Earth Freshwater Science and Society: Water Quality Surface Water Groundwater Freshwater as a Resource A Closer Look: Water Quality and Wastewater Treatment 24.2 Seawater

Oceans and Seas The Nature of Seawater Movement of Seawater A Closer Look: Estuary Pollution A Closer Look: Rogue Waves Ocean Currents 24.3 The Ocean Floor

Overview Unlike other planets, Earth has so much water on the surface that it appears blue when viewed from space. Most of this water, however, is salty ocean water that covers about 70 percent of the surface. Available water that is not salty, called fresh water, makes up less than 1 percent of all the water on Earth. Precipitation is the source of almost all the fresh water found in streams, in lakes, and underground. Each year, about one meter of water falls to the surface when averaged over the whole Earth. About a meter of water is also evaporated into the atmosphere from the surface each year. Fresh water is available because the amounts precipitated and evaporated differ over land and the oceans. The amount evaporated and precipitated varies from location to location, but on the average, more water is precipitated over land than is evaporated from it. This excess of ocean-derived precipitation eventually returns to the ocean to complete the water cycle.

Demand for fresh water will increase in the future, which may cause shortages in some areas with limited water supplies. The surface and groundwater supplies of fresh water are moving, so they cannot be conserved by nonuse. What is needed is a balance between use and recharge. Building storage reservoirs, manipulation of the weather, recycling water, and conversion of salt water to fresh water can increase supplies of fresh water.

Many people point to the ocean, the prevalent environment of Earth’s surface, as the answer to water, food, and other needs of our growing population. If the population continues to increase, and if resources of the land continue to become depleted, it seems reasonable to expect that the ocean will be used to provide more and more of humanity’s needs. Much remains to be learned about the ocean and the circulation of ocean water, however, and there is concern that the present practice of using the ocean as a convenient place for dumping wastes may cause serious problems on a long-term basis.

Suggestions 1. Demonstrate the distribution of Earth’s water by showing a 40-liter aquarium filled with water to represent all the water of Earth. Remove 968 mL to a l liter container to represent all the fresh water on Earth. The water remaining in the aquarium represents

all the salt water of the oceans. To illustrate how the fresh water is distributed, place three 250-mL containers and a medicine dropper in front of the 1-liter container. Pour 760 mL from the ―fresh water‖ container into one of the small containers to represent the amount of fresh water locked up in ice. Pour 200 mL into a second container to represent the amount of fresh water that is underground. Pour the remaining 8 mL into the third container to represent the water in all the rivers, streams, and lakes of the world. A medicine dropper with about three-quarters of a drop from the third container will represent how much water is in the atmosphere at a given time.

2. Use a 250-mL beaker full of marbles to illustrate the concept of porosity. The porosity of the container of marbles is the measured amount of water that you can pour into the beaker divided by the volume of marbles multiplied by 100. Show the porosity of a brick by measuring the mass of a dry brick, then measuring it again after the brick has soaked in a container of water for some time.

3. In addition to problems of pollution and the cost of cleaning water supplies, the study of fresh water provides many opportunities for discussion of difficult social issues. For example, a new reservoir constructed on a river can provide economic benefits, an increased water supply, new recreational areas, and electric power. On the other hand, construction of the reservoir can displace people and wildlife, destroy areas of scenic beauty by covering them with water, and change the environment. Other social issues concerning water include the question of who should have the right to existing water supplies—farmers, who need water to grow food; industries, which need water for jobs, producing energy and products that people need; or cities, which need water for domestic use by people for cooking, cleaning, washing, and everyday consumption.

4. Using a map showing the major ocean currents, students could predict where a bottle with a message inside might be expected to be found after a week, a month, and a year.

5. Watch for news reports that illustrate how humans are changing the oceans. Examples are ocean waste dumping, oil-well drilling, oil-tanker accidents, coastal city waste disposal, and landfills for development.

For Class Discussions 1. Generally, most of the freshwater supply is obtained from a. streams or lakes. b. groundwater. c. the ocean.

2. If water is in short supply, who should have first priority for use? a. agriculture b. city domestic use c. industries

d. The answer is controversial.

3. How many separate, independent oceans are found on Earth? a. 1 b. 5 c. 7 d. 10 4. What is the origin of all the seawater on Earth? a. Accumulated rainwater over the years. b. It formed soon after Earth. c. Outer space, by way of comets. d. Volcanoes.

5. How has the composition of seawater changes after millions of years of rainfall, evaporation, and more rainfall? a. Fresh in the beginning, increasing in salinity throughout history. b. It has changed very little. c. The salinity has decreased ever since the last ice age. d. The salinity of seawater varies for ocean to ocean, depending on the location.

6. The flow rate of all of the ocean currents in the world must be equal? a. Yes. b. No. 7. Which one of the following does not belong with the others? a. Gulf Stream. b. California Current. c. Labrador Current.

8. Where does the ocean basin begin? a. At the beach. b. End of continental shelf. c. Beyond continental slope. d. Bottom of submarine canyon.

Answers: 1a, 2d, 3a, 4b, 5b, 6a (sea level does not change), 7a (warm other cold; also called a stream), 8c.

Answers to Questions for Thought 1. On average, about 98 percent of Earth’s water exists as liquid, about 2 percent as ice, and a fraction of a percent as water vapor. Over 97 percent of the water is stored in the oceans as salt water, and about two-thirds of the fresh water is locked up in the ice caps of Greenland and the Antarctic and in glaciers. Less than 1 percent of all water on Earth is available as liquid fresh water.

2. The four main events of evaporation of water from the ocean, the transport of water vapor through the atmosphere, the condensation and precipitation of water on the lands, and the return of water to the ocean make up the hydrologic cycle. Evaporation from the ocean is an important part of the hydrologic cycle because the water vapor leaves the dissolved salts behind, forming precipitation that is fresh water. It is a cycle because the water evaporated from the ocean eventually returns to the ocean.

3. Water that falls on land either evaporates, flows downhill to a lower place, or soaks into the ground.

4. The flow of a stream comes from the groundwater that has seeped into the channel.

5. The water table is the boundary between the zone of saturation and the zone above it. A hole that is drilled to the water table is a well. Holes not drilled this far are not wells and do not have groundwater collect in them. Water only accumulates in the portion of the well below the water table.

6. (a) Surface water contains more sediments, bacteria, and possible pollutants than groundwater because it is more active and is directly exposed to the atmosphere. Its higher treatment cost is offset because it is more readily available, but it can be very sensitive to precipitation amounts. (b) Groundwater is naturally filtered as it moves through the pore spaces of an aquifer, so it usually does not need to be filtered. It must be pumped up to the surface, and the energy required for this pumping can be expensive. Dissolved minerals that are usually present in groundwater also may require treatment.

7. Arguments may vary. (a) Agricultural interests claim that they should have priority because they produce the food and fibers that people must have. (b) Industries maintain that they need priority because they create jobs and products that people must have. (c) Cities claim that domestic consumption is most important because people cannot survive without water.

8. Possible ways of extending the freshwater supply include recycling wastewater or desalinating water from the ocean. One of the more radical ideas is to tow icebergs from the polar regions to regions that need water. Conservation is an easily applied method to stretch existing water supplies.

9. Natural processes remove dissolved materials as quickly as the rivers add them.

Calcium and silicon are removed by plants and animals to make solid shell, bones, and other hard parts. Other dissolved minerals form solid deposits directly and also make

sediments that settle to the ocean floor. These solid deposits and the hard parts of animals and plants are recycled into Earth’s interior along with the solid sediments deposited by rivers.

10. Regular groups of low profile, long-wavelength waves are called swell. They form initially in a storm as a chaotic, superimposed mixture of waves. As the waves travel away from the storm area, the longer wavelengths travel faster and last longer than the shorter wavelengths. The longer wavelengths eventually travel alone as a swell.

11. Refraction caused by the shallow water near the shore causes the waves to approach the shore head-on. The part of the wave in the shallower portion refracts because it is traveling slower than the rest of the wave. The circular motion of the water particles reaches the bottom when the depth is about half a wavelength, and friction with the bottom is what slows the shallower end of the wave. This slowdown allows the part of the wave farther from shore to catch up and forces the wave to become parallel to the shore.

12. Wind speed, the length of time the wind blows, and the fetch, or the distance over which the wind blows, all affect the formation of waves. Larger waves are produced by strong winds that blow for a long time over a long fetch. In general, longer blowing, stronger winds produce waves with greater wave heights, longer wavelengths, and longer periods, but a given wind produces waves with a wide range of sizes and speeds.

13. As water waves approach the shore, the bottom of the wave begins to reach the bottom.

Friction between the moving particles of water at the bottom of the wave and the bottom result in a slower-moving wave as the wave height increases. The wave front becomes progressively steeper as the bottom part of the wave moves slower than the top.

Eventually the top part becomes so steep that it breaks forward and becomes a breaker.

The zone where breakers occur is called surf.

14. Water accumulated on shore returns to the ocean by moving beneath the breakers. This weak current might be pushed along the shore by the waves. If the current finds a lower place or channel deeper than the adjacent bottom, a strong stream of water called a ―rip current‖ bursts out against the waves and returns water through the surf to the sea. A lack of surf and darker-looking water indicate a deeper channel, and a turbid or muddy streak of water indicate the presence of a rip current.

For Further Analysis 49. Answers will vary but could include such ideas as towing glaciers or purifying seawater through the use of solar energy.

50. Answers will vary but could include such ideas as building retention basins where runoff will soak into the ground.

51. Answers will vary, but the two letters should both be convincing.

52. The oceans are well mixed and there are chemical processes at work that remove dissolved materials.

53. Answers will vary.

54. Similarities – both are large moving streams of water. Differences – a river generally moves in a channel on land and an ocean current is a moving stream of water that moves in the water of the ocean.

Group B Solutions