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Directed Reading B Section: Measuring Motion OBSERVING MOTION BY USING A REFERENCE POINT Circle the letter of the best answer for each question.
1. Which of the following helps us to see if something is moving? a. a position b. a reference point c. speed d. velocity 2. What is a reference point? a. something that appears to stay in place b. something that appears to keep moving c. something that stays at the same velocity d. something that stays at the same acceleration 3. What is an object’s change in position over time called? a. speed b. acceleration c. friction d. motion Common Reference Points
4. What can a mountain become for a hot air balloon flying past? a. a reference point b. a starting point c. a finishing point d. a mid-point
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Directed Reading B continued
SPEED DEPENDS ON DISTANCE AND TIME Read the words in the box. Read the sentences. Fill in each blank with the word that best completes the sentence.
direction distance
meters velocity
speed time
5. The SI unit for speed is
per second.
6. The distance traveled divided by the time taken to travel is
. Determining Average Speed
7. In three hours, a driver usually covers a different each hour. Recognizing Speed on a Graph
8. On the graph in your textbook, the blue line represents actual . VELOCITY: DIRECTION MATTERS 9. Speed in a particular direction is called . 10. Velocity is speed in a given
.
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Directed Reading B continued Read the words in the box. Read the sentences. Fill in each blank with the word that best completes the sentence.
same
opposite
direction
Changing Velocity
11. Your velocity changes when your speed or changes. Combining Velocities
12. Objects moving in the
direction are
added together to find the velocity. 13. Objects moving in
directions are
subtracted to find the velocity. ACCELERATION accelerating acceleration
increasing decreasing
14. The rate at which velocity changes is . 15. If your speed is not changing but your direction is, you are . 16. When a driver’s acceleration is positive, the velocity is . 17. Negative acceleration means that the velocity is .
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Directed Reading B continued Calculating Average Acceleration Circle the letter of the best answer for each question.
18. How is acceleration expressed? a. in seconds b. in meters per second c. in meters per second per second d. in seconds per meter Recognizing Acceleration on a Graph
19. On the roller coaster acceleration graph, what does the line showing positive acceleration look like? a. It moves straight across horizontally. b. It moves upward. c. It moves downward. d. It moves straight up vertically. Circular Motion: Continuous Acceleration
20. Why is an object traveling in a circular motion accelerating? a. because its direction is always changing b. because Earth is rotating c. because nothing else is traveling the same direction d. because its reference points are also changing 21. What is the acceleration that occurs in circular motion called? a. velocity b. positive acceleration c. negative acceleration d. centripetal acceleration
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Lesson Print PAGE TEACHER RESOURCE SECTION: FRICTION: A FORCE THAT OPPOSES MOTION
7. Earth has an enormous mass, so its
1. The force of friction causes a ball to
stop rolling. 2. friction 3. The two forces are (1) the force push-
4. 5.
6. 7. 8.
9. 10.
11. 12. 13. 14. 15. 16. 17.
18.
ing the surfaces together and (2) the roughness of the surfaces. Pavement is rougher than ice. The weight of the larger book on the table creates more friction than the smaller book. The friction is less when the surface is less rough. Kinetic friction is friction between two moving surfaces. Two types of kinetic friction are sliding kinetic friction and rolling kinetic friction. Sliding kinetic friction is usually greater than rolling kinetic friction. Static friction occurs when force applied to an object does not cause the object to move. static friction kinetic friction B A C D Answers will vary. Sample answer: Friction harms the engine of a car by creating heat between moving parts and causing the parts to wear down. Answers will vary. Sample answer: Without friction, you would slip and fall when you tried to walk.
SECTION: GRAVITY: A FORCE OF ATTRACTION 1. gravity 2. Astronauts on the moon bounce when
3. 4.
5. 6.
they walk because the moon has less gravity than the Earth does. As the masses become greater, the force of gravity increases. Yes. All matter experiences gravity, because all matter has mass. Gravity is proportional to mass. gravity The mass of most objects is too small to cause a force large enough to move objects toward each other.
8.
9.
10. 11. 12.
13. 14.
15.
16.
17. 18. 19. 20. 21. 22. 23. 24. 25.
gravitational force is very large. Therefore, objects are pulled by Earth’s gravity toward Earth’s center rather than being pulled by a smaller force of gravity toward its center. The two questions were: (1) Why do objects fall toward Earth, and (2) what keeps the planets moving in the sky? Newton proposed that the same unbalanced force that pulled an apple toward Earth was the same unbalanced force that kept the moon in orbit around Earth. the law of universal gravitation C The gravitational force between two bowling balls is greater. The reason is that the greater the masses are, the greater the gravitational pull will be. The gravitational force between them decreases rapidly. The cat has less gravitational force acting on it than the elephant has, because it has less mass. The sun is too far away for its gravitational force to have much of an effect on me. Without the sun’s gravitational force, planets would not stay in orbit around the sun. mass weight weight W W M W M M
Directed Reading B SECTION: MEASURING MOTION 1. 2. 3. 4. 5. 6. 7. 8. 9.
B A D A meters time distance speed velocity
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Lesson Print PAGE TEACHER RESOURCE 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21.
direction direction same opposite acceleration accelerating increasing decreasing C B A D
SECTION: WHAT IS A FORCE? 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.
force motion newton B C B D A A D A B B
SECTION: FRICTION: A FORCE THAT OPPOSES MOTION 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.
A D B D C A C B C B A C B A C B A A B
SECTION: GRAVITY: A FORCE OF ATTRACTION 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21.
A A C D B A B Earth planet force gravitation C D A B C D B D A B
Vocabulary and Section Summary SECTION: MEASURING MOTION 1. motion: an object’s change in position
relative to a reference point 2. speed: the distance traveled divided by
the time interval during which the motion occurred 3. velocity: the speed of an object in a particular direction 4. acceleration: the rate at which velocity changes over time; an object accelerates if its speed, direction, or both change
SECTION: WHAT IS A FORCE? 1. force: a push or a pull exerted on an
object in order to change the motion of the object; force has size and direction 2. newton: the SI unit for force (symbol, N) 3. net force: the combination of all of the forces acting on an object
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