11Reviewing Main IdeasReviewing Main Ideas

• A force is a push or a pull.

Newton’s First Law

• Newton’s first law states that objects in motion tend to stay in motion and objects at rest tend to stay at rest unless acted upon by a net force.

• Friction is a force that resists motion between surfaces that are touching each other.

22Reviewing Main IdeasReviewing Main Ideas

• Newton’s second law states that an object acted upon by a net force will accelerate in the direction of this force.

Newton’s Second Law

• The acceleration due to a net force is given by the equation a = Fnet/m.

22Reviewing Main IdeasReviewing Main Ideas

• The force of gravity between two objects depends on their masses and the distance between them.

Newton’s Second Law

• In circular motion, a force pointing toward the center of the circle acts on an object.

33Reviewing Main IdeasReviewing Main Ideas

• According to Newton’s third law, the forces two objects exert on each other are always equal but in opposite directions.

Newton’s Third Law

• Action and reaction forces don’t cancel because they act on different objects.

• Objects in orbit appear to be weightless because they are in free fall around Earth.

Chapter ReviewChapter Review

Question 1

Which of Newton’s laws explains how this rocket gets off the ground?

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Chapter ReviewChapter Review

Answer

Newton’s third law explains how a rocket moves upward. The force of the propellant being driven out the base of the rocket causes an equal but opposite force pointing in the other direction, which drives the rocket up.

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Chapter ReviewChapter Review

Question 2

When the air resistance force equals a falling object’s weight, the net force on the falling object is zero. The object has reached _______.

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Chapter ReviewChapter Review

Answer

The answer is terminal velocity. This means its acceleration is zero; it does not mean that the falling object stops moving.

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Chapter ReviewChapter Review

Question 3

If you are going around in circles, even at an unchanging speed, you are constantly _______.

A. acceleratingB. increasing in velocityC. increasing your distanceD. slowing down

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Chapter ReviewChapter Review

Answer

The answer is A. This is called circular motion.

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Question 4

When you throw a ball, why doesn’t it move in a straight line?

Answer

It would, if you were in space. On Earth, however, the force of gravity causes it to move in a curve as it falls.

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Chapter ReviewChapter Review

Question 5What is responsible for slowing down the lunch trays in this illustration?

A. accelerationB. frictionC. gravityD. inertia

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Answer

The answer is B. Friction always opposes sliding between two objects.

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Standardized Test PracticeStandardized Test Practice

Question 1

Which would remain unchanged were you to go up in the space shuttle?

A. your distance from the EarthB. your massC. your perceptionsD. your weight

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Standardized Test PracticeStandardized Test Practice

Answer

The answer is B. Your weight is relative to your distance from Earth and whether or not you are in freefall.

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Standardized Test PracticeStandardized Test Practice

Question 2

You are swimming laps in a pool. When you come to the end, you turn around underwater and push off the wall. What does the wall do?

A. it changes stateB. it does nothingC. it pushes backD. it pulls on you

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Standardized Test PracticeStandardized Test Practice

Answer

The answer is C. Newton’s third law states that the wall pushes back on you with the same amount of force you exert on it.

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Standardized Test PracticeStandardized Test Practice

Question 3Suppose you are in a space station when suddenly you realize an asteroid is headed your way. What do you need to know about the asteroid to know how forceful the impact will be?

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Standardized Test PracticeStandardized Test Practice

A. its massB. its accelerationC. its mass and its accelerationD. its mass and its acceleration and its origin

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Answer

The correct answer is C. Newton showed that f =ma. If the asteroid is moving very slowly, or if it has very little mass, the force of its impact will be much less than if it is very massive and moving quickly.

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Standardized Test PracticeStandardized Test Practice

Question 4Which object would have the least acceleration if you pushed on it with a force of 5 N?

A. bookB. canC. cupD. stapler

Object Mass (g)

Cup 380

Book 1,100

Can 240

Ruler 25

Stapler 620

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Answer

The answer is A. Acceleration is calculated using the equation a = Fnet/m.

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Standardized Test PracticeStandardized Test Practice

Question 5The type of friction that prevents an object from starting to move is known as _______.

A. static electrical frictionB. static frictionC. typical frictionD. total friction

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Standardized Test PracticeStandardized Test Practice

Answer

The answer is B. Static friction is different from sliding friction, which slows down an object that is sliding.

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