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Skills Worksheet

Chapter Review USING VOCABULARY ______ 1. Academic Vocabulary In the sentence “Gravity has an important role in maintaining the shape of the solar system,” what does the word role mean? a. a part played by an actor b. a function c. a socially expected behavior pattern d. a character assigned or taken on Complete each of the following sentences by choosing the correct term from the word bank.

gravity terminal velocity

projectile motion mass

2. An object in motion has

inertia weight , so it tends to stay

in motion. 3. An object is falling at its

if it falls at a constant

velocity. 4.

is a measure of the gravitational force on an object.

UNDERSTANDING CONCEPTS Multiple Choice

______ 5. The gravitational force between 1 kg of lead and Earth is the _____ gravitational force between 1 kg of marshmallows and Earth. a. greater than b. less than c. the same as d. None of the above ______ 6. Newton’s first law of motion applies to a. moving objects. b. objects that are not moving. c. objects that are accelerating. d. Both (a) and (b)

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Chapter Review continued ______ 7. To accelerate two objects at the same rate, the force used to push the object that has more mass should be a. smaller than the force used to push the object that has less mass. b. larger than the force used to push the object that has less mass. c. the same as the force used to push the object that has less mass. d. equal to the object’s weight. Short Answer

8. Identifying Give an example of an object that is in free fall.

9. Summarizing Describe how the cumulative effect of gravity and air resistance is related to an object’s terminal velocity.

10. Describing Explain why friction changes the velocity of objects and why friction can make observing Newton’s first law of motion difficult.

11. Concluding What would happen to the magnitude of the gravitational force between the sun and Earth if Earth were placed in Pluto’s orbit?

12. Analyzing Explain why action and reaction forces do not cancel out, even though they have equal magnitudes and act in opposite directions.

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Chapter Review continued INTERPRETING GRAPHICS Use the image below to answer the next two questions.

13. Identifying The arrows in the image indicate two separate forces that are acting in the upward and downward directions on the static light bulb. Identify these two forces.

14. Justifying Are the forces on the light bulb balanced or unbalanced? Explain your answer by considering the motion of the light bulb.

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Chapter Review continued INTERPRETING GRAPHICS Use the table below to answer the next question. Force

Acceleration

35 N

5 m/s2

70 N

10 m/s2

105 N

15 m/s2

15. Evaluating The table shows the acceleration produced by applying different forces on a 7 kg mass. Assuming that the pattern continues, predict what force would be needed to produce an acceleration of 25 m/s2 .

WRITING SKILLS 16. Writing a Biography Describe the significance of Newton’s Principia books. Describe what information was presented in Principia and why this information was important to scientists everywhere.

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Chapter Review continued CRITICAL THINKING 17. Concept Mapping Use the following terms to create a concept map: gravity, free fall, terminal velocity, projectile motion, and air resistance.

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Chapter Review continued 18. Identifying Relationships During a space-shuttle launch, about 830,000 kg of fuel are burned in 8 min. The fuel provides the shuttle with a constant thrust, or forward force. How does Newton’s second law of motion explain why the shuttle’s acceleration increases as the fuel is burned?

19. Applying Concepts Suppose that you are standing on a skateboard and you toss a backpack full of books toward your friend. What do you think will happen to you? Explain your answer in terms of Newton’s third law of motion.

INTERPRETING GRAPHICS Use the image below to answer the next two questions. Earth

Moon

Sun

20. Applying Concepts The image shows the paths of Earth and the moon. Explain how you can use the image to prove that Earth and the moon are accelerating.

21. Identifying Relationships Identify the forces responsible for maintaining the relative positions of these bodies in the solar system.

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Chapter Review continued INTERPRETING GRAPHICS Use the image below to answer the next two questions.

22. Applying Concepts The arrows in the image show the force of gravity and the force of air resistance on an acorn. Is the acorn accelerating? Explain your answer.

23. Making Inferences Under what conditions would the acorn stop accelerating yet still continue to fall?

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Chapter Review continued MATH SKILLS 24. Using Equations A rock falls from rest off a cliff and hits the ground in 1.5 s. Without considering air resistance, determine the rock’s velocity as the rock hits the ground. Show your work below.

CHALLENGE 25. Forming Hypotheses Suppose that you are looking at an orange tree. Several oranges are hanging from the tree. Suddenly, an orange falls to the ground. Form a hypothesis that explains why the orange fell. Use Newton’s first law of motion in your hypothesis.

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TEACHER RESOURCES 11. The feather and the hammer would hit

7. Sample answer: During a head-on

the moon’s surface at the same time because there is no air resistance. 12. A parachute reduces the acceleration of a skydiver by increasing air resistance, which allows a skydiver to descend with less velocity. Without the parachute, acceleration due to gravity would cause the skydiver’s velocity to increase as he or she approaches the ground. If a skydiver opens the parachute too close to the ground, he or she may have already reached such a high velocity that there is not enough time for the parachute to reduce the velocity before landing. In that case, it is too late for the parachute to be effective.

collision, an unbalanced force stops the motion of the car. But because no unbalanced force immediately acts on the people inside the car, they continue to move forward. Air bags are important because they provide unbalanced forces to stop the motion of the people in the car. The air bags prevent the people from hitting the dashboard or windshield of the car. 8. The black arrow represents the force that the hand exerts on the table. The white arrow represents the equal and opposite force that the table exerts on the hand. 9. The acceleration of the wagon will be less with my friend’s brother in the wagon than it was before he climbed in because he added more mass to the wagon. Because the wagon containing both people has a greater mass than the wagon containing only my friend, I must apply more force to achieve the same rate of change in motion.

SECTION: NEWTON’S LAWS OF MOTION 1. Sample answer: Inertia is the

2.

3.

4.

5.

6.

tendency of an object to resist changes in motion. When the forces on an object are unbalanced, the velocity of the object could increase, the velocity could decrease, or the object’s direction of motion could change. When the forces on an object are balanced, the motion of the object will not change. Objects that are at rest will stay at rest and objects that are in motion will stay in motion. Newton’s second law states that the acceleration of an object increases as the force acting on the object increases, but the acceleration decreases as the mass of the object increases. If there were no friction between a rolling ball and the ground, the ball would not stop rolling. Friction is the unbalanced force acting on the ball to change its motion. The action and reaction forces do not balance each other because the forces are acting on two different objects. Because they act on two different objects, you cannot combine them to determine the net force.

Chapter Review 1. 2. 3. 4. 5. 6. 7. 8.

B inertia terminal velocity weight C D B Sample answer: A feather falling inside a vacuum is in free fall. An object dropped on the moon is in free fall. 9. Gravity and air resistance combine to give a net force on the falling object. When gravity and air resistance are the same size but in opposite directions, the object stops accelerating downward and reaches its terminal velocity. 10. Friction is a force that opposes the motion of objects. Friction slows the motion of objects so you don’t see objects moving forever in a straight line. 11. The magnitude of the gravitational force would decrease because the distance between the sun and Earth would be greater than the current distance between the sun and Earth.

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TEACHER RESOURCES 12. Action and reaction forces do not can-

23. The acorn will stop accelerating when

cel out because these forces do not act on the same object. The down arrow indicates the force of gravity; the up arrow indicates the elastic forces due to tension in the electric cord. Because the motion of the light bulb is not changing, we know that the forces are balanced. 175 N; For every 35 N of force that is applied, the acceleration increases by 5 m/s2 . (25 m/s2 )/(5 m/s2 )
5 and 5  35 N
175 N or (25 m/s2  15 m/s2 )
10 m/s2 105 N  70 N
175 N Students’ biographies should state that the Principia books included Newton’s laws of motion and the universal law of gravitation. Answers should also indicate that scientists still use the ideas presented in Principia to do research and solve problems. An answer to this exercise can be found at the end of the Teacher Edition. During takeoff, the shuttle burns fuel and therefore loses mass. However, the forward force on the shuttle remains the same. So, the shuttle’s acceleration increases because its mass constantly decreases during takeoff. I will move away from my friend (in the opposite direction of the backpack). The action force is my pushing the backpack toward my friend. The reaction force is the backpack pushing me away from my friend. Neither Earth nor the moon is traveling in a straight path, so an unbalanced force must be acting on each. Therefore, each must be accelerating. Gravity provides the centripetal force that keeps the moon in orbit around Earth, and Earth in orbit around the sun. Yes, it is accelerating. The downward force of gravity indicated by the down arrow is greater than the upward force of air resistance indicated by the up arrow. So, the acorn is accelerating downward.

it reaches its terminal velocity. This would occur if the upward force of air resistance becomes equal to the downward force of gravity. Then, the acorn would stop accelerating and continue to fall at a constant velocity. 24. v
g  t
9.8 m/s2  1.5 s
14.7 m/s 25. Sample answer: If the forces on the orange were unbalanced, the orange would fall from the tree. While the orange is static, the upward force of the tree on the orange balances the force of gravity. When the orange breaks away from the tree, the force of gravity is an unbalanced force that acts on the orange and causes the motion of the orange to change.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

Section Quizzes SECTION: GRAVITY: A FORCE OF ATTRACTION 1. 2. 3. 4. 5. 6. 7. 8. 9.

B C A B D C A C B

SECTION: GRAVITY AND MOTION 1. 2. 3. 4. 5. 6. 7. 8. 9.

C B A B A C C B B

SECTION: NEWTON’S LAWS OF MOTION 1. 2. 3. 4. 5. 6.

D A C B B C

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