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Directed Reading A Section: Gravity and Motion 1. Suppose a baseball and a marble are dropped at the same time from the same height. Which ball would land first according to Aristotle? Explain.
GRAVITY AND FALLING OBJECTS ______ 2. Which of the following statements describes what happened when Galileo dropped two cannonballs with different masses from the same height? a. The more massive cannonball reached the ground first. b. The less massive cannonball reached the ground first. c. Both cannonballs reached the ground at the same time. d. The results depended on the volumes of the cannonballs as well as their masses. 3. Why do objects fall to the ground with the same acceleration?
4. What is the meaning of the acceleration value 9.8 m/s2 ?
5. How does the velocity of a falling object change over time?
AIR RESISTANCE AND FALLING OBJECTS ______ 6. A crumpled piece of paper hits the ground before a flat sheet of paper because a. the acceleration of gravity is greater on the crumpled paper. b. there is more air resistance against the flat paper. c. the crumpled paper is more massive. d. the crumpled paper is less massive. 7. The force that opposes the motion of objects through air is called
.
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Directed Reading A continued 8. What three factors affect the amount of air resistance acting on an object?
9. What do you get when you subtract the force of air resistance from the force of gravity?
10. When a falling object stops accelerating, it has reached
velocity. 11. If there were no air resistance, what would happen to hailstones?
12. The motion of a body when only the force of gravity is acting on the body is
called
.
13. Why is a skydiver not really in free fall? Explain your answer.
ORBITING OBJECTS ARE IN FREE FALL 14. Is it true that an astronaut is weightless in space? Explain your answer.
15. An orbiting shuttle follows the curve of the Earth’s surface as it moves at
a constant speed, and so is said to be
Earth.
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Directed Reading A continued 16. Why don’t astronauts hit their heads on the ceiling of the falling shuttle?
17. What is centripetal force?
PROJECTILE MOTION AND GRAVITY ______18. Which of the following is NOT an example of projectile motion? a. the path of a juggled ball b. the path of a ball rolling on a flat surface c. the path of water from a sprinkler d. the path of an arrow through the air 19. The curved path that an object follows when thrown near the surface of the
Earth is called
.
20. What are the two components of projectile motion?
21. What is the horizontal motion of an object?
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Directed Reading A continued 22. What is the vertical motion of an object?
23. How does gravity affect objects in projectile motion?
24. If you shoot an arrow aimed directly at the bull’s-eye of your target, where will the arrow hit your target? Why?
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Answer Key Directed Reading A
23. Gravity pulls objects in projectile
motion down at an acceleration of 9.8 m/s 2 , the rate for all falling objects. 24. The arrow will hit below the bull’s eye because the arrow accelerates downward as it moves forward.
SECTION: GRAVITY AND MOTION 1. According to Aristotle, the baseball
2. 3.
4.
5. 6. 7. 8. 9. 10. 11. 12. 13.
14.
15. 16.
17.
18. 19. 20. 21. 22.
would drop first. He thought the rate at which an object falls depends on its mass. C The force of gravity is greater on more massive objects, but those objects are harder to accelerate because they are more massive. These two effects balance each other, so the acceleration is the same on all objects. For every second an object falls, its downward velocity increases by 9.8 m/s. The object falls faster and farther each second than it did the second before. B air resistance size, shape, speed net force terminal Hailstorms would hit the Earth at a velocity near 350 m/s. free fall Free fall occurs when gravity is the only force acting on an object. Therefore, skydivers cannot be in free fall because there is air resistance. No. An astronaut has mass, and so has some gravitational force exerted on him or her. Therefore, the astronaut has some weight. orbiting Astronauts don’t hit their heads on the falling shuttle because they are in free fall just like the shuttle is. Centripetal force is the unbalanced force that causes objects to move in a circular path. The word centripetal means “toward the center.” B projectile motion horizontal motion and vertical motion motion that is parallel to the ground motion that is perpendicular to the ground
SECTION: NEWTON’S LAWS OF MOTION 1. the relationship between force and the
motion of an object 2. An object at rest remains at rest, and an
3. 4.
5. 6.
7. 8.
9. 10. 11.
12. 13.
14.
object in motion remains in motion at a constant speed and in a straight line unless acted on by an unbalanced force. 0N In both cases, the objects will not change its motion unless acted upon by an unbalanced force. friction Inertia is the tendency of an object to resist being moved, or to resist a change in speed or direction. B The acceleration of an object depends on the mass of the object and the amount of force applied. Its acceleration increases. Its acceleration increases. To have equal acceleration, the force on the more massive car must be greater than the force on the car with smaller mass. If the ratio of the force applied to the mass of each car is the same, then both cars will have the same acceleration. The apple is easier to accelerate because it has less mass. Whenever an object exerts a force on a second object, the second object exerts an equal and opposite force on the first. For each force that acts on an object, another force occurs that is equal to the first force and is exerted in the opposite direction. In this way, every force is paired with an opposing force.
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