Physics 101

General Physics

Who am I?Dr. BrutonI may be teaching the remainder of

this course for Mr. Carlton.We have similar teaching styles.There will be extra credit.I will “teach to” Mr. Carlton’s test.I will hit the highlights of the chapters

with PowerPoint presentations.

Let’s take notes…

Chapter 6Chapter 6

MomentumMomentum

Momentum and CollisionsMomentum and Collisions

This chapter is concerned with inertia and motion.

Momentum helps us understand collisions.

Momentum and CollisionsMomentum and Collisions Elastic Collisions– objects rebound– e.g. superball

Inelastic Collisions– object stick together an usually

become distorted and generate heat– e.g. clay ball

Momentum

Momentum = mass velocity

p = mv

Momentum is a vector quantity.

A large truck has more momentum than a car moving at the same speed because it has a greater mass.

Which is more difficult to slow down? The car or the large truck?

Large Momentum Examples:

– Huge ship moving at a small velocity

– High velocity bullet

P = mv

P = mv

Impulse

In order to change the momentum of an object you must apply a force over some time interval.

Impulse = Force time interval = F t

Impulse and Momentum

Impulse = Change in Momentum = Final (mv) - Initial (mv)

F t = (mv)

Case 1: Increasing Momentum– Apply a force for a long time. – Examples: • Follow through on a golf swing.• Pushing a car.

Ft

Case 2: Decreasing Momentum – Apply a force for a long time.– Examples:• Air bags in cars. • Catching an egg.• Boxing, Figure 6.6• Soft collisions, Figure 6.3.

Ft

Case 3: Decreasing Momentum– Apply a force for a short time.– Examples: • Boxing• Karate

Ft

Conservation of MomentumThis means that the momentum doesn’t

change.

Recall that F t = mv)

In this equation, F is the "external force".

Internal forces cannot cause a change in momentum.

ExamplesConservation of Momentum: If

there are no external forces, the total momentum for a system remains unchanged.

Example 1: a person sitting inside a car pushing against the dashboard

Example 2: a bullet fired from a rifleExample 3: a rocket is space

Example Problems...