1. MOMENTUM AND IMPULSE PHYSICS 2007-2008

2. 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

3. 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

4. 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.

5. HEAD ON COLLISIONS Cars exchange momentum via impulse Total momentum remains unchanged. The least-massive car experiences the largest change in velocity.

6. MOMENTUM AND FORCE Momentum is closely related to force. Force = change in momentum/time interval F  t =  p = mv f – mv i 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.

7. 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?

8. 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).

9. HOMEWORK PAGE 209 # 1 – 3 PAGE 211 # 1 - 4