MOMENTUM AND IMPULSE
Momentum
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Momentum is mass in motion. It tells you how difficult
it is to stop an object.
mass x velocity is its momentum
p  mv
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p, momentum (kg m/s)
m, mass (kg)
v, velocity (m/s)
Momentum is a vector, it needs
magnitude and direction. It will have
the same direction as the object’s
velocity.
Example Questions:
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What has more momentum?
1) A large truck moving 20 mph, or a small car
moving 20 mph?
2) An Olympic walker or an Olympic runner?
Example Question:
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Calculate the momentum of a 1.5 kg Frisbee
traveling through the air at 4 m/s.
Calculate the velocity of a 4 kg football with 20
𝑘𝑔 ∙𝑚
of momentum.
𝑠
Impulse
Impulse is the change in momentum.
In order to change an object’s momentum
(velocity, mass or both), you must apply
p
a force over some time.
p  Ft
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J, impulse (kg m/s)
F, Force (Newtons, N)
t, time (s)
 mv
p  m(v f  vi )
m(v f  vi )  Ft
Questions:
1) A .2 kg arrow is shot out of a bow at 80 m/s.
a) What is the change in momentum of the arrow?
b) How great was the force of the bow string if it was
applied for .1 seconds?
c) How great was the force of the bow string if it was
applied for .05 seconds?
Youtube videos:
 Egg vs Sheet
 Football 1
Football 2
How are modern cars designed to keep you safer in a collision?
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Crash 1
Crash 2
https://www.youtube.com/watch?v=Z8Rl0xd6qhs
https://www.youtube.com/watch?v=dkMCFcEkQ0w
Maybe too much crumple zone…
They lived: Subaru they lived commercial
Momentum Video
http://www.nbclearn.com/science-of-nfl-football
Impulse Changes Momentum
If the change in momentum occurs over a long time, the
force of impact is small.
Impulse Changes Momentum
If the change in momentum occurs over a short time, the force of impact is large.
Impulse Example
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A 500-kg car traveling at 9.1 m/s strikes a brick wall and comes to a stop in 0.1 s.
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What is the impulse?
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What is the change in momentum?
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What is the amount of force when the car hits the brick wall?
Impulse Changes Momentum
Increasing Momentum
To increase the momentum of an object,
apply the greatest force possible for as
long as possible.
** A golfer teeing off and a baseball
player trying for a home run do both of
these things when they swing as hard as
possible and follow through with their
swing. **
Impulse Changes Momentum
If the change in momentum occurs over a long time, the force of impact is small.
Impulse Changes Momentum
If the change in momentum occurs over a short time, the force of impact is large.