Transcript MOMENTUM AND IMPULSE - Greenwich Public Schools

MOMENTUM AND IMPULSE
PHYSICS 2007-2008
BUMPER CARS
Observations
About Bumper Cars
• Moving cars tend to stay moving
• It takes time to change a car’s motion
• Impacts alter velocities & ang. velocities
• Cars seem to exchange their motions
• Heavily loaded cars are hardest to redirect
• Heavily loaded cars pack the most wallop
MOMENTUM
Translating bumper car carries momentum
Momentum
– A conserved quantity (can’t create or destroy)
– A directed (vector) quantity
– Measures difficulty reaching velocity
Momentum = Mass · Velocity
EXCHANGING MOMENTUM = IMPULSE
Impulse
– The only way to transfer momentum
– Impulse is a directed (vector) quantity
Impulse = Force · Time
Because of Newton’s third law, if obj1 gives an
impulse to obj2 , then obj2 gives an equal but
oppositely directed impulse to obj1 .
HEAD ON COLLISIONS
Cars exchange momentum via impulse
Total momentum remains unchanged.
The least-massive car experiences the largest
change in velocity.
MOMENTUM AND FORCE
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Momentum is closely related to force.
Force = change in momentum/time interval
FDt = Dp = mvf – mvi
Force x time interval = change in momentum
This equation explains why follow-through is
important in sports, the longer the contact
between objects, the greater the momentum
transferred.
SAMPLE PROBLEM
• An astronaut with a mass of 45 kg wears a 32
kg suit and moves at 5.7 m/s on the moon.
What is the magnitude of the total momentum
of the astronaut in the suit?
What is the magnitude of the astronaut’s
momentum?
What is the magnitude of the momentum of the
same astronaut jogging at 5.7 m/s on Earth?
SAMPLE PROBLEM
• Air bags are designed to protect passengers
during collisions. Compare the magnitude of
the force required to stop a moving passenger
in 0.75 s (by a deployed air bag) with the
magnitude of the force required to stop the
same passenger at the same speed in 0.026 s
(by the dashboard).
HOMEWORK
• PAGE 209 # 1 – 3
• PAGE 211 # 1 - 4