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Physics 101
General Physics
Who am I?
 Dr. Bruton
 I 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 6
Momentum
Momentum and Collisions
This chapter is concerned with
inertia and motion.
Momentum helps us understand
collisions.
Momentum 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
P = mv
– High velocity bullet
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

= Ft
Impulse and Momentum
Impulse = Change in Momentum

= Final (mv) - Initial (mv)
F t = D(mv)
Case 1: Increasing Momentum
– Apply a force for a long time.
– Examples:
• Follow through on a golf swing.
• Pushing a car.
F
Dt
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.
F
Dt
Case 3: Decreasing Momentum
– Apply a force for a short time.
– Examples:
• Boxing
• Karate
F
Dt
Conservation of Momentum
This means that the momentum
doesn’t change.
Recall that F t = D(mv)
In this equation, F is the "external
force".
Internal forces cannot cause a
change in momentum.
Examples
Conservation 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 rifle
Example 3: a rocket is space
Example Problems...