ch7-momentum.pdf

7/29/2019 ch7-momentum.pdf

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Momentum

Part 1

Chapter 7

Momentum

Read Sections 7.1 Momentum

7.2 Impulse Changes Momentum

7.3 Bouncing

7.4 Conservation of Momentum 7.5 Collisions

7.6 The Horse Cart


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Momentum

Momentum is Inertia in Motion Or Mass in Motion

We know it is harder to stop a Hummer rather than a

Mini

This is because the Hummer has a greater Momentum

Momentum is measured by mass X velocity or:

Momentum=Momentum=mvmv

Therefore there are two components to momentum

lets think about that..

Impulse Changes Momentum

If there is a change in an objects momentum there must be a

change in its mass or its velocity

Usually it is the velocity that changes

Therefore a change in velocity (acceleration) is caused by a force

f=ma Think of the braking force in a car

How long the force acts is important

The longer the force acts the greater the change in momentum The quantity force X time is called Impulse and

Impulse = Change in Momentum or

Ft=Ft=((mvmv))

This relationship helps us analyze a variety of situation


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Increasing Momentum

A golfer swings his club as fast as possible.

In doing this he will impact the ball and for the time theclub is in contact with ball the force of the club will causethe ball to accelerate This is called an Impulse

Impulse= Force x time or = FtImpulse= Force x time or = Ft

The ball shoots away with increased momentum ( whatabout the club?)

This is why follow through is very important as it increasesthe time when the ball is in contact with club

What other sports is this an important action?

Impulse Changes MomentumDecreasing Momentum

You have just got your learners permit

and your parents have foolishly let you

borrow the car

In order to impress the person sitting next

to you, you are DRIVING TOO FAST!!!!!

You must stop the car and there is a policeroad block in front of you

Do you run off the road and hit a concrete

wall or run off the road and plough through

a haystack

Lets think about Impulse! Impulse=Ft

What are some other examples?


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Momentum

Part2

Chapter 7

Bouncing

Why is a flower pot that falls off a shelf bouncing onyour head worse than when it just crashes on yourhead? Because if it were to just crash there would be a single impulse

of the pot being stopped by your head.

But if it bounces it will need the impulse to push off your head,thus making the total impulse even greater and your headeven sorer.

Impulse Ft=(mv) and in the case of a bounce v will greater

than if it just landed on your head.

Look at this Who has the larger (mv) ?

Therefore who has the larger Impulse?

Where is the greatest force?


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How does the boxer on the receiving endsoften the blow?

If the climber slips and falls, what kind of rope

do you think she would want and why?

If the batter wants to hit a home run describehis follow though and why?

Conservation of Momentum

In bringing Newtons 2nd and 3rd Laws together we can

understand the principle of Conservation of Momentum

Lets examine this by looking at some models.

http://www.physicsclassroom.com/mmedia/momentum/cbb.html

From these we can see that momentum is conserved.


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The Law of Momentum Conservation is

In the absence of an external force, the momentum of a

system remains unchanged

But always try to define the system!!!


Momentum is a VECTOR!!

Can you think of other vector objects with momentum?


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Strange systems

Momentum

Part 3

Chapter 7


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Collisions

There are two types of collisions

Elastic this is where a pool ball will hit another ball and

bounce off each other

Inelastic this is where two colliding objects get tangled

together and head off as one new object like a car crash

where the cars become mangled together

In both of these the Law of conservation is obeyed

What are some Elastic and Inelastic collisions?

Collisions

http://www.glenbrook.k12.il.us/gbssci/phys/mmedia/index.html#carcra

sh


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Collisions

Momentum Vectors

Who can define a Vector?

As with force, momentum also obeys the vector rules

Think of a game of pool

A Safety lining up on a wide receiver

What else?


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Momentum

Concept Summary

Momentum of an object is the product of its Mass andVelocity

Changes in Momentum depends on forces that act and

the length of time they act

Impulse is the average force multiplied by the time it acts

The impulse exerted on something is equal to its change

in Momentum

The Law of Conservation of Momentum states that it is

conserved when there is no net external force.

Momentum is a vector quantity

MomentumKey Terms

Conserved

Elastic Collision

Inelastic Collision

ImpulseLaw of Conservation of Momentum

Momentum


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Momentum

Part 4

Chapter 7

Formulae

F=ma

Momentum=mv

Impulse=ft= (mv)


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Math Problems

Similar to Q19

a. What is the momentum of an 10kg bowling ball rolling at 3m/s?

b. If the bowling ball rolls into a pillow and stops in 0.75s, calculate

the average force it exerts on the pillow.

c. What is the average force the pillow exerts on the ball?

Math Problems

Similar to Q22

A 3 kg blob of putty moving at 4m/s slams into a 6kg

blob of putty at rest

a. Calculate the speed of the 2 stuck together blobs of putty

immediately after collision

b. Calculate the speed of the 2 blobs if the one at rest was 9kg

ch7-momentum.pdf

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