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Directed Reading B Section: Gravity and Motion GRAVITY AND FALLING OBJECTS Circle the letter of the best answer for each question.
1. How does gravity affect how objects fall to the ground? a. Heavy objects fall faster.
b. Light objects fall faster. c. They fall at the same rate. d. Bigger objects fall faster. Acceleration Due to Gravity
2. What do you call the change in velocity over time? a. force b. acceleration c. mass d. gravity 3. Which of the following figures is the rate at which objects fall toward Earth? a. 9.8 m/s2 b. 29.4 m/s2 c. 19.6 m/s2 d. 0 m/s2 4. What happens to the rate at which falling objects accelerate over time? a. It depends on how far the object falls. b. The object accelerates at a constant rate. c. The downward velocity decreases. d. The downward velocity stays the same.
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Forces and Motion
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Directed Reading B continued Velocity of Falling Objects Read the description. Then, draw a line from the dot next to each description to the matching symbol.
• • •
5. the symbol for acceleration due to gravity 6. the symbol for time the object takes to fall 7. the symbol for change in velocity
a. ∆v b. g c. t
AIR RESISTANCE AND FALLING OBJECTS Read the words in the box. Read the sentences. Fill in each blank with the word or phrase that best completes the sentence.
terminal velocity
free fall
8. Because of
air resistance
, a flat piece of paper
takes longer to fall than a crumpled piece of paper. Acceleration Stops at the Terminal Velocity
9. A falling object stops accelerating at . Free Fall Occurs When There Is No Air Resistance
10. Gravity is the only force on an object in .
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Forces and Motion
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Directed Reading B continued
ORBITING OBJECTS ARE IN FREE FALL Circle the letter of the best answer for each question.
11. Why do astronauts in orbiting spacecraft seem weightless? a. Nothing produces gravity in space. b. The astronauts and the ship are in free fall together. c. The astronauts have no mass in space. d. Air resistance balances the force of gravity. Two Motions Combine to Cause Orbiting Read the description. Then, draw a line from the dot next to each description to the matching path.
12. the path of an orbiting spacecraft 13. the path of spacecraft in freefall due to gravity. 14. the path of the spacecraft without gravity
• • •
a. straight down toward Earth b. straight line forward c. curved path following curve of Earth
Orbiting and Centripetal Force Circle the letter of the best answer for each question.
15. Which of the following is orbiting? a. a planet moving around the sun b. a plane in flight c. a balloon d. a rocket flying straight up and returning to Earth 16. Which is NOT true of centripetal force? a. It is an unbalanced force. b. It can hold objects in nearly circular paths. c. It pushes outward. d. It means “a force toward the center.” Copyright © by Holt, Rinehart and Winston. All rights reserved.
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Forces and Motion
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Directed Reading B continued PROJECTILE MOTION AND GRAVITY
Circle the letter of the best answer for each question.
17. Which is not an example of projectile motion? a. a frog leaping
b. a swimmer diving into water c. balls being juggled d. a soccer ball rolling on flat ground 18. How many directions make up projectile motion? a. one
c. three
b. two
d. four
Horizontal Motion
19. Which is NOT an example of something with horizontal motion? a. a pitcher throwing a ball b. someone shooting an arrow at a target c. a leaf falling from a tree d. a bowling ball rolling toward the pins Vertical Motion
20. What is vertical motion? a. motion that is circular b. motion that is parallel with the ground c. motion that is perpendicular to the ground d. motion that can’t be seen 21. Which of the following affects only the vertical motion of projectile motion? a. gravity
c. air resistance
b. unbalanced forces
d. centripetal force
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Forces and Motion
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Directed Reading B
15. The action force is your weight push-
ing down on the chair. The reaction force is the force exerted by the chair that pushes up on your body and is equal to your weight. 16. The hands of the swimmer pushing against the water is the action force. The reaction force is the water pushing on the hands, which is the force that moves the swimmer forward. 17. The bat doesn’t move backwards because the batter is exerting another force on the bat. 18. It is hard to see the effect of the reaction force, which is the Earth being pulled upward., because Earth’s mass is so much larger than the ball’s mass. Earth’s acceleration is thus so small, you can’t see or feel it.
SECTION: GRAVITY AND MOTION 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21.
SECTION: MOMENTUM 1. The truck has more mass, and thus
2. 3. 4.
5. 6. 7. 8. 9.
10.
11.
more momentum, than the car has. The truck needs a larger force to stop it. momentum the faster car By multiplying the value for mass of the automobile by its the velocity, its momentum can be calculated. Kilograms multiplied by meters per second, or Kg•m/s. C B the law of conservation of momentum Because the combined mass of the board and skateboarder is greater than the mass of the skateboarder alone, the velocity of the skateboarder and board must be less than that of the skateboarder alone. When mass increases, velocity decreases. Momentum is transferred from one object to another, causing objects to move in different directions at different speeds. But the total momentum of all objects stays the same. The action force of the cue ball on the billiard ball, and the reaction force of the billiard ball on the cue ball, are equal and opposite. Momentum is not gained or lost.
C B A B B C A air resistance terminal velocity free fall B C A B A C D B C C A
SECTION: NEWTON’S LAWS OF MOTION 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.
B D C A C B A C D C B D B D C B A
SECTION: MOMENTUM 1. 2. 3. 4. 5. 6. 7.
B A C D C A B
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