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Name ANSWERS

STUDY GUIDE

UNIT 10-Newton’s Third Law

Date Agenda HW

Tues, Jan 5 Review Video

Read Section 6.1-6.3

Fill in Reading Notes (p. 2)

Worksheet - Action-Reaction Pairs (p. 3)

Video Notes - Part 1 (p. 4-5)

Wed., Jan 6 Go over worksheet - Action-Reaction Pairs

Video Clips- (p. 6-7)

Read Section 6.4-6.6

Fill in Reading Notes (p. 9-10)

Video Notes - Part 2 (p. 11)

Thurs., Jan 7 Problem Set 1 (p. 12-13) Problem Set 2 (p. 14-16)

Study for Quest

Fri., Jan 8 Go over Problem Sets 1 and 2

Quest

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CP Physics

Reading Notes

Section 6.1-6.3

1. Newton realized that a force is not a thing in itself but part of a mutual action, an

INTERACTION, between one thing and another

2. Describe the interaction between a hammer and a nail:

THE INTERACTION THAT DRIVES THE NAIL IS THE WSAME AS THE ONE THAT

STOPS THE HAMMER

3. State Newton’s Third Law:

WHENEVER ONE OBJECT EXERTS A FORCE ON A SECONDS OBJECT, THE

SECOND OBJECT EXERTS AN EQUAL AND OPPOSITE FORCE ON THE FIRST

OBJECT

4. One force is called the ACTION force, and the other iS called the REACTION force

5. To every ACTION there is always an equal and opposing REACTION

6. Forces are equal in STRENGTH and opposite in DIRECTION

7. In figure 6.5, describe the action and reaction for each force pair.

ACTION: TIRE PUSHES ROAD REACTION; ROAD PUSHES TIRE

ACTION: ROCKET PUSHES GAS REACTION GAS PUSHED ROCKET

ACTION: EARTH PULLS BALL REACTION: BALL PULLS EARTH

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Video Notes-Part 1

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Newton's Third Law of Motion - "Action and Reaction"

Directions: Take notes on this organizer as we discuss these topics in class.

I. Force:

∙

∙

II. Newton's Third Law

∙

∙

●

III. Identifying Action and Reaction Force Pairs

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IV. Equal and Opposite Forces are NOT ALWAYS an Action – Reaction Pair

Example – Cup Resting on a Table

Newton's Third Law of Motion – Collisions

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In a collision between a minivan and a train locomotive:

● Which experiences the largest (in magnitude) force? Explain.

● Which experiences the largest effect (i.e. largest acceleration) and

why?

Newton's Third Law of Motion – How Rockets Work

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CP Physics

Reading Notes

Section 6.4-6.6

1. Figure 6.6: Earth is pulled by the boulder with JUST AS MUCH FORCE as the boulder

is pulled down by the Earth

2. Newton’s Second Law states that ACCELERATION is not only proportional to the

NET FORCE, but it is also inversely proportional to the MASS

3. Figure 6.7: The force exerted against the recoiling cannon is just as great as the force that

drives the cannonball along the barrel. Why, then does the cannonball undergo more

acceleration than the cannon?

THE CANNONBALL OF THE CANNON BALL IS MUCH LESS THAN THE MASS OF

THE CANNON

4. Since action and reaction forces are equal and opposite, why don’t they cancel out to

zero?

ACTION AND REACTION DO NOT CANCEL OUT BECAUSE EACH ACTS ON A

DIFFERENT OBJECT

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5. Look at the Horse-Cart Problem

a. What is the net force that acts on the cart in Figure 6.13?

THE NET FORCE ON THE CART IS THE DIFFERENCE BETWEEN THE PULL

OF THE HORSE AND THE FRICTION FORCE ON THE CART WHEELS

b. What is the net force that acts on the horse in Figure 6.13?

THE NET FORCE ON THE HORSE IS THE DIFFERENCE BETWEEN THE

PUSH OF THE HORSE AND THE GROUND ON EACH OTHER AND THE

PULL OF THE HORSE AND THE CART ON EACH OTHER

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c. What is the net force that acts on the ground in Figure 6.13?

THE NET FORCE ON THE GROUND IS THE DIFFERENCE BETWEEN THE

PUSH OF THE HORSE AND THE GROUND ON EACH OTHER AND THE

FRICTION FORCE BETWEEN THE CART WHEELS AND THE GROUND.

d. Explain, using forces, why the horse-cart system accelerates:

THE HORSE CARE SYSTEM ACCELERATES DUE TO THE DIFFERENCE BETWEEN THE PUSH OF THE HORSE AND THE GROUND ON EACH OTHER AND THE FRICTION FORCE BETWEEN THE CART WHEELS AND THE GROUND.

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Video Notes-Part 2

Newton's Third Law of Motion - "Action and Reaction"

I. Action-Reaction Forces Acting on Objects of Different Masses

∙ Newton's 2nd Law:

∙ Newton's 3rd Law:

∙ Acceleration of each object

Bullet: = ______ Rifle: = ______

II. Why Don't Action and Reaction Forces Cancel?

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BUT

∙

Action Reaction Pair Forces on the Ball

ACTION: RESULT:

REACTION:

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Problem Set 1 Newton's 3rd Law Questions Directions: Answer the following questions in complete sentences

1. In the interaction between a hammer and the nail it hits, is a force

exerted on the nail? On the hammer? How many forces occur in this

interaction?

THE HAMMER EXERTS A FORCE ON THE NAIL AND THE NAIL EXERTS A FORCE ON THE HAMMER. THEY ARE EQUAL AND OPPOSITE. THERE ARE TWO FORCES.

2. When a hammer exerts a force on a nail, how does the amount of force compare with that of the

nail on the hammer?

THE FORCES ARE THE SAME. BOTH THE HAMMER AND THE NAIL ARE PART OF ONE INTERATION.

3. When you walk along a floor, what pushes you along? Include a diagram in your answer.

YOU PUSH ON THE FLOOR AND THE FLOOR PUSHES YOU FORWARD

4. When you jump up, the world really does recoil downward. Why can’t this motion of the world

be noticed?

THE ACCELERATION IT TOO SMALL BECAUSE OF THE WORLD’S LARGE MASS

5. When a rifle is fired, how does the size of the force of the rifle on the bullet compare with the

force of the bullet on the rifle? How does the acceleration of the rifle compare with that of the bullet?

Explain your answer.

THE FORCE THE RIFLE APPLIES TO THE BULLET IS EQUAL AND OPPOSITE TO THE FORCE THE BULLET APPLIES TO THE RIFLE. THE ACCELERATION IS SMALL FOR THE RIFLE BECAUSE OF ITS LARGER MASS, AND THE ACCLEREATION OF THE BULLET IS LARGE BECAUSE OF ITS SMALLER MASS

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6. Your weight is the result of the gravitational force of the earth on your body. What is the

corresponding reaction force?

THE REACTION FORCE IS THE FORCE EXERTED BY YOU ON THE EARTH 7. If you walk on a log that is floating in the water, the log moves backward. Why?

YOU APPLY OF FORCE TO THE LOG AND THE LOG EXERTS AN EQUAL AND OPPOSITE FORCE ON YOU. THE FORCE OF THE LOG ON YOU ACCELERATED YOU FORWARD AND THE FORCE OF YOU ON THE LOG ACCELERATED IT BACKWARDS 8. If a bicycle and a massive truck have a head-on collision, upon which vehicle is the impact force

greater? Which vehicle undergoes the greater change in its motion? Defend your answers.

THE IMPACT FORCE IS THE SAME ON BOTH. BECAUSE OF THE BICYCLE’S SMALLER MASS, THE CHANGE IN MOTION (ACCELERATION) IS GREATER FOR THE BICYCLE. 9. A speeding bus makes contact with a bug that splatters onto the windshield. Because of the

sudden force, the unfortunate bug undergoes a sudden deceleration. Is the corresponding force that

the bug exerts against the windshield greater, less, or the same? Is the resulting deceleration of the bus

greater than, less than, or the same as that of bug?

THE FORCE OF THE BUG ON THE BUS IS EQUAL AND OPPOSITE TO THE FORCE OF THE BUS ON THE BUG. THE BUG UNDERGOES A MUCH GREATER DECELERATION THAN THE BUS BECAUSE IT HAS A MUCH SMALLER MASS

10. Some people used to think that a rocket could not travel to the moon because it would

have no air to push against once it left the earth’s atmosphere. We now know that idea was

mistaken. What force propels a rocket when it is in a vacuum?

THE FORCE IS THAT WHICH THE EXHAUST EXERTS. IT IS THE REACTION TO THE

FORCE THE ROCKET EXERTS ON THE EXHAUST GASES.

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Problem Set 2

Newton’s Third Law

Think and Explain

1. Why is it easier to walk on a carpeted floor than on a smooth, polished floor?

YOU CAN EXERT A GREATER HORIZONTAL FORCE ON A CARPET THAN ON A

POLISHED FLOOR BECAUSE OF THE GREATER FRICTION. THIS IN TURN

PROVIDES A GREATER REACTION FORCE TO PROVIDE TRACTION FOR

WALKING

2. If you step off a ledge, you accelerate noticeably toward the earth because of the

gravitational interaction between you and the earth. Does the earth accelerate toward you

as well? Explain.

YES, THE EARTH ACCELERATED TOWARD YOU AS WELL, BUT THE

ACCELERATION PRODUCED BY THESE EQUAL FORCES ARE QUITE UNEQUAL

BECAUSE OF THE GREAT DIFFERENCE IN MASSES BEING ACCELERATED

3. Suppose you’re weighing yourself while standing next to the bathroom sink.

Using the idea of action and reaction, explain why the scale reading will be less when

you push down on the top of the sink.

WHEN YOU PUSH DOWN ON THE SINK, THE SINK PUSHES YOU UPWARD. THIS

TENDS TO LIFT YOU OFF THE SCALE AND DECREASE THE READING ON THE

SCALE

Why will the scale reading be more if you pull up on the bottom of the sink

IF YOU PULL UPWARD ON THE SINK, IT WILL PUSH DOWNWARD ON YOU AND

INCREASE THE READING

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6. When a high jumper leaves the ground, what is the source of the upward force that

accelerates her?

THE GROUND PUSHES UPWARD ON THE JUMPER, WHICH IS THE FORCE THAT

PROVIDES AN UPWARD ACCELERATION.

What force acts after her feet are no longer in contact with the ground?

IN THE AIR, ONLY THE FORCE OF GRAVITY ACTS ON THE JUMPER. UPWARD

ACCELERATION CEASES AND THE ACCELERATION IS DOWNWARD (g)

7. Since the force that acts on a bullet when a gun is fired is equal and opposite to the force

that acts on the gun, does this imply a zero net force and therefore the impossibility of an

accelerating bullet? Explain.

IN THIS CASE, THERE ARE TWO SETS OF INTERACTIONS. THE EXPANDING

GASES IN THE GUN AT ON BOTH THE BULLET AND THE GUN. ACTION AND

REACTION DO NOT CANCEL BECAUSE EACH ACTS ON A DIFFERENT OBJECT

ONE ON THE BULLET AND ON THE GUN

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8. The strong man can withstand the tension force exerted by the two horses pulling in

opposite directions.

How would the tension compare if only one horse pulled and the left rope were tied to tree?

THE TENSION WOULD BE THE SAME

How would the tension compare if the two horses pulled in the same direction, with the left rope

tied to the tree?

SINCE THERE IS TWICE THE FORCE, THERE WOULD BE TWICE THE TENSION ON THE

ROPE.