p5d momentum
TRANSCRIPT
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P5d - MomentumCollisions, crashes and
cannons
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P5d - Momentum
Opposite reaction forces
• When one body exerts a force on a second body, the second body exerts an _________ and ____________ force on the first
• In other words: If you push something, it pushes back just as hard
“For every action, there is an equal and opposite reaction.”
Isaac Newton
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Spot the action & reaction forces!
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Spot the action & reaction forces!
beam
10 kg
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Spot the action & reaction forces!
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Spot the action & reaction forces!
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Opposite reaction forces
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Opposite reaction forces
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Forces and momentum revision• If forces are balanced…
• If forces are unbalanced…
• Forces and velocities are vectors and must have…
• Momentum =
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MomentumQ ~ What would do more damage: a 6 kg
bowling ball traveling at 6 m/s or a 10 g ping-pong ball traveling at 6 m/s?
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What’s the momentum?
A 20000 kg elephant charging at 10 m/s
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What’s the momentum?
Lewis Hamilton’s 400 kg car traveling at 80 m/s
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What’s the momentum?
A 6 kg bowling ball traveling at 6 m/s
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What’s the momentum?
A 10 g ping-pong ball traveling at 6 m/s
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Collisions• There is no change in momentum during a
collision - momentum is always conserved
Ptotal(before) = Ptotal(after) = 0
Pred(before) + Pblue(before) = Pred(after) + Pblue(after) = 0
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Recoil• Many guns and cannons recoil when fired
Ptotal(before) = Ptotal(after) = 0
Pgun(before) + Pbullet(before) = Pgun(after) + Pbullet(after) = 0
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Explosions - Total momentum is zero
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Preventing injury in crashes
• Seatbelts, airbags and crumple zones are all safety features of cars
• They reduce the risk of injury in the event of a crash
• They do this by slowing the collision down…
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Slowing collisions down
Force = change in momentum
time