Transcript Impulse and Momentum

Impulse and Momentum
• Newton’s third law not mentioned in
energy treatment reason: gives rise to
another conservation principle
Ex. Explosion of object into 2 unequal
masses (use to show via Newton’s Laws)
to get statement of Momentum
Conservation
• Momentum = mass * velocity [vector]
• Impulse = force * time interval
Examples of Impulse
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Baseball : barehanded vs. glove
Boxing : bare-knuckle vs. glove
“Rolling with punch”
1941 Chevy dashboard
Gym mats
Impulse : Airplane and Bird
• Bird : mass = 0.5 kg and length = 20 cm
• Airplane: speed = 300 m/s = 650 mi/hr
– Impulse = F∆t = ∆mv = (0.5 kg)(300 m/s)
∆t = ∆s/v = (0.20m)/(300m/s) = 6.7 * 10 - 4 s
F = (150)/(6.7 * 10 – 4) = 2 * 105 N ≈ 20 tons!
Cite: B-1B Bomber (stealth); Israeli Combat Jet
Conservation of Momentum:
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Total momentum of a system is not changed if
there are no external forces. Vector Statement
• Applications
1. Explosions: guns, cannons (fort in western
Pa), buccaneers, tanks, and Hollywood.
2. Collisions (extremes)
A. Complete Inelastic – Momentum conserved,
energy lost; objects collide and stick together
moving as one after collision.
Ex. Football, trains, traffic accidents, and
ballistic pendulum.
B. Complete Elastic – Energy and
Momentum conserved; objects collide and
rebound (separate) with no energy lost.
Ex. Pool table or marbles
*** Look at 2-Dimensional Examples***