Unit 1 Answer Key: Motion, Forces, and Energy

ANSWER KEY

Chapter 1 Chapter 1 Project Worksheet 1 (p. 6) 1a. Answers may vary. Sample: Marvin might not have started running as soon as Keisha called. Repeating measurements lets you get an average speed, and average speed may be more representative of an animal’s speed than just one measurement. 1b. Answers may vary. Sample: You may want to include the first measurement because it increases the number of measurements, and the more measurements used, the more accurate the speed calculation. You may want to exclude the first measurement because it is atypical. 2a. about 47.1 cm 2b. about 2.17 m Chapter 1 Project Worksheet 2 (p. 7) 1m ; 8.9 m/s 1,000 mm 1m 365 d 3 ; 109.5 m/yr 100 cm 1 yr 1,000 m 1 yr 3 ; 2.5 m/d 1 km 365 days 365 d 1 km 3 ; 2.19 km/yr 1 yr 1,000 m

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Section 1-2 Review and Reinforce (p. 15) 1. The Nazca Plate 2. The Juan de Fuca Plate 3. 290 m 4. about 9 cm 5. The theory of plate tectonics states that the surface of Earth is divided into a number of sections, or plates, which move slowly in relation to each other. Section 1-2 Enrich (p. 16) 1. mountains 2. Students should notice the Andes mountain range on the western edge of South America. 3. Question 1: The North American, Pacific, and Juan de Fuca; Question 2: South American and Nazca 4. Yes. When plates run into each other or slide past each other, earthquakes are a result. For example, earthquakes occur along a plate boundary in California, on the San Andreas Fault. Section 1-3 Review and Reinforce (p. 19) 1. true 2. velocity 3. is 4. 50 5. true

Science Explorer Focus on Physical Science

© Prentice-Hall, Inc.

Section 1-1 Review and Reinforce (p. 11) 1. 200 m/min 2. 160 m/min 3. 160 m/min east 4. 800 m 5. slope = 2 m/s; The slope is the same as her speed. 6. International System of Units 7. motion; reference point 8. velocity 9. speed 10. meter

Section 1-1 Enrich (p. 12) 1. Downward. It appears to follow a straight path. 2. four seconds 3. The average speed is 20 meters per second. During the last second in which it fell it was moving about 35 meters per second. 4. From the reference point of the person on the ground, the ball appears to follow a curved path.

ANSWER KEY

6. 0 7. acceleration 8. velocity Section 1-3 Enrich (p. 20) 1. 2.0 cm 2. About 2.0 cm 3. 0.5 cm 4. Point D 5. Point E 6. About 2.0 cm; greater. 7. If the object had traveled in a straight line for 6.28 s, it would be 25.1 cm away. If it traveled around the circle for 6.28 s, it would be back where it started. Chapter 1 Skills Lab (pp. 21–22) For answers, see Teacher’s Edition, pp. 18–19. Chapter 1 Real-World Lab (pp. 23–25) For answers, see Teacher’s Edition, pp. 24–25.


Chapter 2 Chapter 2 Project Worksheet 1 (p. 30) Part I 1. The stretched rubber of the balloon rapidly squeezes air molecules out the nozzle. This rapid expulsion of air in one direction results in an equal force in the opposite direction. 2. A squid fills an internal pouch with water and then rapidly expels it. This water quickly being pushed in one direction results in an equal push in the opposite direction, and the squid moves forward. 3. The flipping of the salmon’s tail pushes water downstream. The water being pushed pushes back with an equal force, propelling the salmon upstream. 4. The hummingbird flaps its wings rapidly, pushing air downward. The air being pushed down pushes up with equal force, keeping the hummingbird suspended in the air, against the pull of gravity.


5. The canoeist pushes water backward with the paddles. The pushed water pushes back with equal force, causing the canoeist and the canoe to go down the river. 6. The rotating propeller pushes water backward. The pushed water pushes back with the same force, causing the motor and the boat to go forward, across the lake. 7. The monkey pushes against the limb, and the limb pushes back on the monkey with equal force. 8. When the first ball hits a second ball, the second ball pushes back with the same amount of force. This causes the first ball to stop and the second ball to move forward. Part II Answers may vary. Samples: spring pushing off back of a ramp, mousetrap pushing off the ground, windup clock turning wheels that push against the ground, rubber band turning propeller that pushes against the air. Chapter 2 Project Worksheet 2 (p. 31) Part I Answers may vary. Samples: shape of vehicle, length of ramp, length of spring, type of wheels Part II Answers may vary. Students should include at least one experiment for every variable they list in their table. Section 2-1 Review and Reinforce (p. 35) 1. Unbalanced Balanced push Forces Forces or pull net force 5 0 net force not 5 0 do not have change change an an object's direction object's motion motion

2. Accept any clear statement of the law: objects at rest or moving at constant speed remain as such unless acted upon by an unbalanced force. Accept any examples that clearly illustrate the concept.

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2.

c a d e f b

1.0 0.8

Section 2-1 Enrich (p. 36) Angles of greatest acceleration will vary. However, riding in a elevator (or lifting the accelerometer) should yield an angle of 0°. 1. The acceleration is not constant. 2. Greatest angles will vary. However, you would not expect to see a 90° angle, because, regardless of horizontal acceleration, the force of gravity is also pulling the washers down. 3. The accelerometer was accelerated vertically, but no acceleration was recorded because the accelerometer only measures horizontal accelerations. 4. You would need to accelerate the accelerometer by known amounts, and then observe the angles seen on it. In this way, known accelerations could be matched with angles on the accelerometer.

Section 2-2 Enrich (p. 40) 1. Acceleration Mass 2

1m/s 1m/s2 1m/s2 1m/s2 1m/s2

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0.1 kg 0.2 kg 0.5 kg 0.7 kg 1.0 kg

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Force 0.1N 0.2N 0.5N 0.7N 1.0N

0.6 0.4 0.2 0.0 0.0

0.2

0.4 0.6 Mass (kg)

0.8

1.0

3. They are directly proportional. As force increases, objects of greater mass must be used to maintain constant acceleration. As force decreases, objects of lesser mass must be used to maintain constant acceleration. 4. Brightness and distance from the bulb are inversely proportional, because as one value becomes greater, the other becomes less. Section 2-3 Review and Reinforce (p. 43) 1. The types of surfaces; how hard the surfaces are pushed against each other 2. Answers may vary. Example: put oil on the surfaces 3. Objects fall at a different rate when the air resistance acting on them is different. 4. Mass is the amount of matter in an object; weight is a measure of the pull of gravity on an object. 5. All matter in the universe is attracted by all other matter. 6. c 7. g 8. f 9. b 10. h 11. e 12. a 13. i 14. d



Section 2-2 Review and Reinforce (p. 39) 1. Force 5 Mass 3 Acceleration or Acceleration 5 Force/Mass 2. c 3. a 4. d 5. c 6. a 7. force 8. m/s2

Force (N)

3. 4. 5. 6. 7. 8.

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Section 2-3 Enrich (p. 44) 1. The blocks were very heavy and they were rough, which made the friction high. 2. They might have reduced friction by changing it from sliding friction to rolling friction. The pencils underneath the book act as a model of how the Egyptians could have used logs. 3. Answers may vary. Samples: Pour olive oil and slide the blocks. Build a canal to float the blocks on barges. 4. Sample: It isn’t a fact because we don’t know that the Egyptians used the method. It is possible the Egyptians used the log method, so it is a hypothesis. Section 2-4 Review and Reinforce (p. 47) 1. It stays the same before and after an event. 2. Newton’s third law of motion says that if an object, such as a foot, exerts a force on another object, such as a soccer ball, the second object (the soccer ball) exerts a force of equal strength in the opposite direction on the first object (the foot). 3. Since momentum equals mass times velocity, a very slow-moving elephant could have the same momentum as a very fast-moving golf ball. 4. 160 kg•m/s 5. momentum of moving car 5 0.04 kg 3 4 m/s 5 0.16 kg•m/s The momentum of the coupled cars is 0.16 kg•m/s because momentum is conserved. 6. Momentum is mass times velocity. 7. The total momentum of a group of objects remains the same unless outside forces act on the objects. Section 2-4 Enrich (p. 48) 1. C; 32,000 kg•m/s 2. B; It has the least momentum. 3. Answers may vary. Sample: the forces are equal and opposite to the forces applied by the cars and are the same for both cars. The equal forces, however, are applied over different times. The force exerted by the wall is applied


over a shorter time than the force exerted by the Fitch Barriers. 4. Answers may vary. Sample: Fitch Barriers will more slowly absorb the momentum of car B than will the solid concrete wall on car A. The Fitch Barriers will have a gradual braking effect in contrast to the sudden stop against the concrete wall. Therefore, the force with which the people in car B are thrown forward will be distributed over a greater period of time than would be the case of the people in car A. This will reduce the probability of serious injury to the people in car B versus those in car A. Section 2-5 Review and Reinforce (p. 51) 1. Newton’s third law of motion—every time there is an action force on an object, the object will exert an equal and opposite reaction force. 2.

3. Any object moving around another object in space. 4. Gravity; it would no longer orbit Earth. It would move in a straight line. Section 2-5 Enrich (p. 52) 1. You don’t feel Earth moving because all objects around you, including the atmosphere, are moving with you at the same speed. 2. No. The direction of Earth’s rotation is west to east, exactly perpendicular to the direction in which you would launch a satellite into polar orbit, so the rotation would have no effect on the launch.

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3. The launch location would be traveling “backwards” in relation to the direction of the orbit. So, you’d have to accelerate the satellite to a speed of 19,200 km/hr 1 1,700 km/hr 5 20,900 km/hr relative to the launch point. 4. The satellites would continue to orbit Earth. Chapter 2 Skills Lab (pp. 53–54) For answers, see Teacher’s Edition, pp. 42–43. Chapter 2 Real-World Lab (pp. 55–57) For answers, see Teacher’s Edition, pp. 54–55.

Chapter 3

Chapter 3 Project Worksheet 2 (p. 63) 1. Answers may vary. Sample: I found the best materials to be the lightest. Aluminum cans worked better than aluminum foil because they are stronger and did not change shape when the pennies were added.

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Section 3-1 Review and Reinforce (p. 67) 1. All of the forces exerted by the individual molecules in the fluid add together to create pressure in a fluid. Force 2. Pressure = Area 3. Air pressure decreases as elevation increases. 4. Water pressure increases as depth increases. 5. G, A, D, B, F, C, E 6. Pressure is a measure of force exerted on an area. 7. A fluid is any substance that can easily change its shape or flow. 8. One pascal is one newton of force applied to one square meter of area. Section 3-1 Enrich (p. 68) 1. No. 2. The paper was lifted up by the stick. The middle of the paper, over the stick, lifted off the paper first. While this happened, air had time to rush under the paper, so the pressure should have been about equal. 3. Yes. With the newspaper on top, it was much more difficult to press down hard and fast on the stick. 4. No. Because the movement was so fast, air had less time to flow under the paper. For this reason, there would have been more air pressure on the top of the paper than on the bottom. 5. The downward force was caused by atmospheric pressure. Because the paper was being lifted so quickly, the pressure above it was not balanced by the pressure of the air beneath the paper.



Chapter 3 Project Worksheet 1 (p. 62) 1. Answers may vary. Sample: Materials are aluminum cans and aluminum foil. The cans will be used as floats and the aluminum foil will be used as a deck. I chose these materials because they are lightweight metal. 2. Answers may vary. Check students’ diagrams to see if they are thoughtfully designed. 3. Answers may vary. Sample: The boat will be tested in a dishpan of water. If the boat floats, pennies will be added until 50 have been added or the boat sinks. 4. Answers may vary. Sample: Boats will be made from different materials. Each boat will be tested in a dishpan and pennies will be added as cargo. The best designs will be the boats that carry the cargo. 5. Answers may vary. Sample: I will make a balance from a meter stick, string, and two plastic bowls. The boat will be weighed using pennies for weights.

2. Answers may vary. Sample: The boat made from aluminum cans was the best. It held its shape and carried the pennies. The boat was the lightest and the easiest to make. 3. Answers may vary. Sample: I plan to show the class my different boat designs and describe the strengths and weaknesses of each. Then I will show the class my best design and demonstrate it.

ANSWER KEY

Section 3-2 Review and Reinforce (p. 71) 1. When pressure on a confined fluid is increased, the increase is transmitted equally to all parts of the fluid. 2. hydraulic device 3. Moving a fluid from one place to another 4. 2 Pa 5. 20 N


Section 3-2 Enrich (p. 72) 1. Water will stop moving through the siphon when the level of water in container A falls to the level of the intake end of the siphon. 2. Only siphon 2 will function. 3. Siphon 1 will not work because the discharge end is higher than the intake end. This means the water will flow back into container A. Siphon 3 will not work because the intake end is above the surface of the water in container A, so water from container A cannot be pulled into the siphon. Section 3-3 Review and Reinforce (p. 75) 1. The buoyant force pushes up against gravity and makes the object feel lighter. 2. According to Archimedes’ principle, the weight of the water displaced by the object equals the weight of the object. Because water weighs 1 g per cm3, the object must weigh 10 g. 3. greater 4. less 5. equal to 6. The buoyant force on an object is equal to the weight of the fluid displaced by the object. 7. Density is the mass of an object per unit volume. 8. A force acting on an object in a fluid in the direction opposite to gravity


Section 3-3 Enrich (p. 76)

Sample 1. 2. 3. 4. 5.

Pressure

Volume

10 N/cm2 20 N/cm2 2.0 N/cm2 1.0 N/cm2 100 N/cm2 40 N/cm2

1 m3 0.5m3 5 m3 10 m3 0.1 m3 0.25 m3

6. 80 N/cm2 4 10 N/cm2 5 8, so you would expect the air in the tire to occupy 8 times the tire’s volume once it is released at normal pressure. 1,200 cm3 3 8 5 9,600 cm3. Section 3-4 Review and Reinforce (p. 79) 1. Below the wing 2. Above the wing 3. It is being pushed downward. 4. The push becomes stronger. 5. As the wind speeds up, pressure on top of the chimney will decrease, according to Bernoulli’s principle. Smoke will move faster, going from a higher-pressure area to a lower-pressure area. 6. The pressure exerted by a moving stream of fluid is less than the pressure of the surrounding fluid. Section 3-4 Enrich (p. 80) 1. A bat would use airfoil a, because more lift would be important while landing. However, since it would be moving more slowly, drag would be less important. 2. A bat might use airfoil c, because drag must be low to fly as fast as possible. At such high speeds, getting enough lift would not be a problem. 3. A bat might use airfoil b. It’s less curved than a, so it would give less lift, but it is more curved than airfoil c, which is shaped for fastest flight. 4. If the bat did this, the wing held in shape a would have more lift than the wing in shape c. One wing would rise, which would cause the bat to roll over.

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5. You probably would not see the bat use this wing shape because it would generate a lot of drag that might slow the bat down to the point where it could not fly. Chapter 3 Real-World Lab (pp. 81–83) For answers, see Teacher’s Edition, pp. 76–77. Chapter 3 Skills Lab (pp. 84–85) For answers, see Teacher’s Edition, pp. 84–85.

Chapter 4 Chapter 4 Project Worksheet 1 (p. 90) 1. inclined plane, wedge, screw, lever, wheel and axle, pulley 2. pulley 3. lever 4. inclined plane 5. Answers will vary: top, side or bottom. 6. Answers will vary: only one of six simple machines must be mentioned. 7. Answers will vary: only one of six simple machines must be mentioned. 8–10. Students’ designs will vary.

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Total Work (in Joules) 50 J 43.5 J 35.5 J 25 J 0J 1. As the angle increases, the fraction of the force that contributes to the work decreases. 2. None of the force applied to the object contributed to its movement because the directions of the force and movement were at right angles to one another. 3. No. Section 4-2 Review and Reinforce (p. 99) 1. true 2. multiplying 3. true 4. without 5. mechanical advantage 6. input force 7. machine 8. ideal mechanical advantage 9. actual mechanical advantage 10. efficiency 11. output force Section 4-2 Enrich (p. 100) 1. The person is pulled downward by the force of gravity. 2. Force: 75 kg 3 9.8 m/s2 5 735 N Work: 735 N 3 0.5 m 5 367.5 J 3. Force: 750 kg 3 9.8 m/s2 5 7,350 N Work: 7,350 N 3 0.05 m 5 367.5 J It is the same amount of work.



Section 4-1 Review and Reinforce (p. 95) 1. She is doing work if the force causes the box to move some distance in the direction of the force. 2. Use this formula: Work 5 Force 3 Distance 3. 80 J 4. The result produced by a force exerted on an object that causes the object to move some distance in the direction of the force 5. Amount of work done when you exert a force of 1 newton to move an object a distance of 1 meter

Section 4-1 Enrich (p. 96) Table values:

ANSWER KEY

4. Input force: 735 N Output force: 7,350 N Mechanical advantage: 7,350 N 5 10 735 N 5. Efficiency: 367.5 J 3 100% 5 100% 367.5 J This is complete efficiency and is very unlikely. Friction would cause a real treadmill to be less efficient.


Section 4-3 Review and Reinforce (p. 103) 1. wedge 2. wheel and axle 3. lever 4. inclined plane 5. pulley 6. screw 7. compound machine 8. lever 9. pulley 10. gear 11. screw 12. inclined plane 13. fulcrum 14. wedge 15. wheel and axle Section 4-3 Enrich (p. 104) 1. lever 2. inclined plane 3. pulley 4. wheel and axle 5. first class lever 6. the magnifying glass (A) and paper bag (B) Section 4-4 Review and Reinforce (p. 107) 1. a lever 2. It bends. 3. It extends. 4. a wedge 5. the jaw muscles 6. Tough connective tissue that attaches muscles to bone


7. The tendon pulls on the bone, making it work as a lever. Section 4-4 Enrich (p. 108) 1. Without lubrication, the friction of the tendon moving through the pulley would irritate the tendon. 2. Yes. The pulleys are attached to the bones of the thumb. They direct the force exerted by the tendon so that the joints of the thumb will move properly. 3. Answers may vary. Samples: in the toes, in the ankles, in the knees, in the elbows Chapter 4 Skills Lab (pp. 109–111) For answers, see Teacher’s Edition, pp. 108–109. Chapter 4 Real–World Lab (pp. 112–113) For answers, see Teacher’s Edition, pp. 122–123.

Chapter 5 Chapter 5 Project Worksheet 1 (p. 118) 1. The vehicle will not have enough energy to get up the second hill. The potential energy of a vehicle on the first hill would be less than the potential energy of a vehicle on the second hill. The vehicle would require energy input to get up the second hill. 2. In a frictionless system, this would work; however, the vehicle will lose energy because of friction against both the track and the air. The vehicle would not make it up the second hill. 3. It might be possible for the vehicle to complete this type of track. However, success will depend on the height of the first hill and the distance between the hills. If the vehicle has enough potential energy on the first hill and does not expend the energy on long distances between the hills, this setup would work. 4. The materials that the students select may vary. Make sure that they are readily available to the students at a reasonable price. Also, make sure that the students have selected materials that are easy to modify.

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5. The students’ vehicle choices will vary. Again, make sure that they are readily available to the students at a reasonable price. Also, be sure that the students’ vehicles are compatible with their choice of track. 6. This measurement will vary, depending on the student’s vehicle. Students may need help measuring the mass of their vehicles. 7. Make sure that students draw their sketches to scale. The scale that they use should be clearly indicated on their sketches. 8. Heights of hills and distances between hills should conform to the scale that the student selected. The point of maximum potential energy is at the top of the first hill. The point of maximum kinetic energy is at the bottom of the first hill.

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Section 5-1 Enrich (p. 124) 1. potential energy 2. When the kinetic energy given the can by your initial push is converted to potential energy, the can comes to a stop. 3. The rubber band unwinds as the can rolls back to you. 4. The can gains kinetic energy as it rolls back. 5. When you first push the can, you are adding kinetic energy. 6. The harder you push the can, the more times the can will rotate. The more rotations the can makes, the more the rubber band twists and the greater the potential energy it stores. Section 5-2 Review and Reinforce (p. 127) 1. at all points 2. no energy is lost 3. true 4. true 5. point 2 6. A change from one form of energy to another 7. When one form of energy is converted to another, no energy is destroyed in the process



Chapter 5 Project Worksheet 2 (p. 119) Part I Make sure that students keep thorough records of their modifications. 1. If the second hill is shorter, the vehicle will travel further up the third hill. 2. The answer to this question will vary depending on the type of track that the student has designed. 3. The students’ answers will vary depending on the track, vehicle choices, and the distances between hills. Part II Make sure that students keep thorough records of their modifications. 4. The answer to this question will vary depending on the type of track that the student has designed. 5. It is likely that the student will need to change the heights of the hills to include additional features. 6. The answer to this question will vary depending on the type of track that the student has designed.

Section 5-1 Review and Reinforce (p. 123) 1. Work is the transfer of energy. 2. Kinetic energy is the energy of a moving object. Potential energy is energy stored and held in readiness. (Note: For items 3–8, there are multiple possible answers. Students do not need to have all the answers shown for each item to receive credit.) 3. c, and b or e, depending whether it’s a gas or electric stove. 4. a 5. a, b, c, f 6. b, c, f 7. c, d, f 8. a, c, e, f 9. b 10. c 11. a

ANSWER KEY

Section 5-2 Enrich (p. 128) 1. A, E 2. E, A 3. The comet is losing gravitational potential energy as it gets closer to the sun, but is gaining kinetic energy as it speeds up. 4. The comet is losing kinetic energy as it slows, but is gaining gravitational potential energy as it moves farther away from the sun. 5. Potential energy has been converted to kinetic energy, but total energy is constant. 6. Kinetic energy has been converted to potential energy, but total energy is constant.


Section 5-3 Review and Reinforce (p. 131) 1. The sun converts nuclear energy to electromagnetic energy. 2. electromagnetic energy from the sun 3. a fossil fuel; petroleum or natural gas 4. The stored chemical energy in coal is converted to thermal energy when the coal is burned to produce steam. 5. The steam has thermal energy. The turbines have mechanical energy. 6. Mechanical energy is converted to electrical energy as turbines turn electric generators. 7. Answers may vary. Sample: Electrical energy can be converted into thermal energy in your toaster. Section 5-3 Enrich (p. 132) 1. petroleum and coal 2. petroleum 3. Yes. There is a sharp drop in the use of petroleum in the 1970s. 4. 1960s 5. Hydroelectric power is the energy produced by converting the energy of running water into electrical energy. No, it is not a fossil fuel. 6. Because fossil fuels took hundreds of millions of years to form, we generally think of them as not being renewable.


Section 5-4 Review and Reinforce (p. 135) Force 3 Distance 1. Power = and Time Work Power = Time 2. Ignacio does not perform any work nor use any power. Because the crate does not move, no work is done on the crate, and there is no power used. 3. You need to know the time Ignacio took to move the crate. 4. 10 W 5. 20 J/s 6. 40 W Section 5-4 Enrich (p. 136) Answers for table will vary. Samples: Microwave oven—0.5 h; $0.08 Stove/oven—2 h; $2.40 Clothes dryer—1 h; $0.50 Vacuum cleaner—0.25 h; $0.02 Clothes washer—1 h; $0.05 Color television—3 h; $0.06 Dishwasher—2 h; $0.26 1. Answers will vary. For samples above: Daily total cost: $3.37 Weekly total cost: $23.59 2. Answers will vary. Sample: watch less television; only run the dishwasher when it is full; only wash or dry full loads; use the microwave more than the conventional oven. Chapter 5 Skills Lab (pp. 137–139) For answers, see Teacher’s Edition, pp. 138–139. Chapter 5 Real-World Lab (pp. 140–141) For answers, see Teacher’s Edition, pp. 152–153.

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Chapter 6 Chapter 6 Project Worksheet 1 (p. 146) Part I Data will vary depending on the materials tested. Materials should be ranked according to difference between starting and ending temperatures. Part II Data will vary depending on the design features tested. Features should be ranked according to difference between starting and ending temperatures.

Section 6-1 Review and Reinforce (p. 151) 1. Only if there is the same amount of water in each glass 2. a. Celsius (°C) b. 0 c. 0 d. 212 3. b 4. e 5. a 6. f 7. d 8. c

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Section 6-2 Review and Reinforce (p. 155) 1. convection 2. radiation 3. conduction 4. conduction 5. convection 6. radiation 7. conduction 8. conductor 9. heat 10. convection current 11. specific heat 12. insulator 13. radiation 14. convection Section 6-2 Enrich (p. 156) 1. The water in cup B cooled more than the water in cup A. 2. Answers may vary. Sample: In cup A, the melting of the ice cube immediately decreased the temperature of the water. Afterwards, the difference in temperature between the water and the room was not as great, so the rate at which the water radiated heat was not as great. In cup B, the water radiated heat to the room before the ice cube was added, so there was a greater difference between the temperature of the water and the room. As a result, the rate at



Chapter 6 Project Worksheet 2 (p. 147) 1. Keeping these two variables the same acts as a control. It allows you to use the ending temperatures of the experiments to determine the best insulators. 2. Answers may vary. Sample: The materials and designs with the highest ending temperatures will make the best insulating devices. 3. Answers may vary depending on materials tested. Students may notice that materials such as packing peanuts and foam board that contain enclosed air pockets make good insulators, and materials which hold air less tightly, such as cotton balls, are less effective as insulators. 4. Answers may vary depending on design features tested. 5. Sketches may vary. Check that students have labeled the important features of their containers. 6. Lists may vary. Check that lists are complete and feasible.

Section 6-1 Enrich (p. 152) 1. 37.0°C 2. 22°C 3. 2129°F 4. 136°F 5. 240°F 6. 177°C 7. 2795°F 8. 230°C is warmer. It converts to 222°F, which is warmer than 230°F. Check students’ work. 9. Answers may vary. Sample: The temperature scale is Fahrenheit. Because it is snowing, the air temperature is below the freezing point of water. 26°F would be below freezing, but 26°C would be close to room temperature.

ANSWER KEY


which the water in cup B radiated heat was greater. 3. Answers may vary. Sample: You should let the hot chocolate sit for five minutes and then add the ice cube. By letting the hot chocolate radiate first, the difference in temperature between the hot chocolate and the room is greater than if you added the ice cube immediately. Therefore, the hot chocolate will cool faster. 4. Answers may vary. Sample: Pancakes that are immediately covered in syrup will stay warm longer. The syrup will decrease the temperature difference between the pancakes and the room so that they will not radiate heat as quickly. Section 6-3 Review and Reinforce (p. 159) 1. The solid ice absorbed thermal energy from its surroundings and changed state, or melted, to become liquid water. 2. When a substance is changing state, its thermal energy is changing but its temperature remains the same. That’s because the change in thermal energy is changing the arrangement of the particles, but the average kinetic energy of those particles is not changing. 3. Metal expands when it heats up. If there were no gaps, the railway tracks could bend or buckle on a hot day. 4. melting 5. state 6. condensation 7. evaporation 8. boiling 9. freezing 10. thermostat 11. thermal expansion 12. change of state 13. vaporization 14. bimetallic strip Section 6-3 Enrich (p. 160) 1. Sprinklers that are set off when a link of solder melts involve a change of state. 2. As the temperature rises, the part with the lowest melting point will melt first. The link of


3.

4.

5. 6.

solder in a sprinkler should melt first, so the solder should have the lowest melting point. The glass expands less than the liquid inside it because the expansion of the liquid causes the glass to break. If each sprinkler is set off individually, only the area of the fire will be sprayed and less water damage will occur. Heat moves to the sprinkler by radiation and by convection. If sprinklers were designed to go off a few degrees above room temperature, they could go off for reasons other than a fire, such as if the building’s temperature rose due to a broken air conditioner.

Section 6-4 Review and Reinforce (p. 163) 1. Only Internal Combustion Engines: Fuel is burned inside the engine, Examples are diesel and gasoline engines; Only External Combustion Engines: Fuel is burned outside the engine, An example is a steam engine; Shared: Contains pistons and cylinders, Thermal energy is converted to mechanical energy. 2. a 3. c 4. e 5. b 6. d Section 6-4 Enrich (p. 164) 1. Tube A contains hotter water than tube B, because the water in it is coming from the hot engine. 2. Heat flows into air moving past the radiator. 3. The radiator cools the fluid. 4. Answers may vary, but should indicate some problem with overheating. Samples: It might get too hot. It might break. The oil might burn. Chapter 6 Skills Lab (pp. 165–167) For answers, see Teacher’s Edition, pp. 170–171.

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