Download answers to packet

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 Notes - Part 2 (p. 11)
Video Clips- (p. 6-7)
Read Section 6.4-6.6
Fill in Reading Notes (p. 9-10)
Thurs., Jan 7
Problem Set 1 (p. 12-13)
Fri., Jan 8
Go over Problem Sets 1 and 2
Quest
Problem Set 2 (p. 14-16)
Study for Quest
1
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
ACTION: ROCKET PUSHES GAS
ACTION: EARTH PULLS BALL
REACTION; ROAD PUSHES TIRE
REACTION GAS PUSHED ROCKET
REACTION: BALL PULLS EARTH
2
Video Notes-Part 1
3
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
4
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
5
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
6
7
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
8
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
9
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.
10
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:
II.
=
______
Rifle:
=
______
Why Don't Action and Reaction Forces Cancel?
∙
BUT
∙
Action Reaction Pair
ACTION:
Forces on the Ball
RESULT:
REACTION:
11
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
12
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
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?
10.
THE FORCE IS THAT WHICH THE EXHAUST EXERTS. IT IS THE REACTION TO THE
FORCE THE ROCKET EXERTS ON THE EXHAUST GASES.
13
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
14
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
15
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.
16