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9 - Force and Momentum (9.1 - Momentum and impulse (Momentum and…
9 - Force and Momentum
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9.2 - Impact forces
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Rebound impacts
When a ball hits a wall and rebounds, its momentum changes direction due to the impact. If the ball hits the wall normally, it rebounds normally so the direction of its momentum is reversed. The velocity and therefore the momentum after the impact is in the opposite direction to the velocity before the impact and therefore has the opposite sign.
Suppose the ball hits the wall normally with an initial speed u and it rebounds at speed v in the opposite direction. Since its direction of motion reverses on impact, a sign convention is necessary to represent the two directions. Its initial momentum is +mu and its final momentum is -mv. F = change in momentum / change in time. F = -mv - mu / change in time = The impact force
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9.5 - Explosions
When two objects fly apart after being initially at rest, they recoil from each other with equal and opposite amounts of momentum. So they move away from each other in opposite directions