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10/03/2006
1
Momentum and Collisions
We look at another consequence of
Newton’s Laws of Motion.
This time the emphasis is on Newton’s
Third Law.
10/03/2006
2
Newton II rewritten:
Acceleration is the rate of
change of …
–
Velocity.
We call mass times velocity
momentum
–
Momentum is a vector.
–
The unit is kg m/s
F
=
ma
=
m
Δ
v
Δ
t
=
mv
f
−
mv
i
Δ
t
=
p
f
−
p
i
Δ
t
F
=
Δ
p
Δ
t
p
≡
mv
10/03/2006
3
Impulse
Multiply both sides by
Δ
t.
Force times time equals
impulse.
–
Unit is N s
Impulsemomentum
theorem:
–
1 N s = 1 kg m/s
F
=
Δ
p
Δ
t
F
Δ
t
=
Δ
p
J
=
F
Δ
t
10/03/2006
4
Nonconstant forces
Can we use the impulsemomentum theorem if the forces are not
constant?
–
Yep!
The area under the force vs. time curve is impulse.
What average force will give the same impulse (area) for the same
time?
Example: Think about landing from a jump.
–
What makes it easier?
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View Full Document10/03/2006
Problem #1
A boy kicks a football with an
average force of 90.0 N for a
time of 0.200 s.
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 Spring '11
 Chiu
 Physics, Acceleration, Mass, Momentum

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