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Impulse-Momentum Theorem
An impulse, J, is equal to the change in momentum of an object.
You can have a large force, but if the applied time is very small you get only a small change in momentum!
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Example
A 150g baseball is thrown with a speed of 20m/s. It is hit straight back toward the pitcher at a speed of 40m/s. If the bat is in contact with the ball for 6ms, what was the average force on the ball?
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Impulse Approximation
Other forces often act on an object during a collision.Ex: In the previous example gravity also acted during the collision.
If these forces are very small in comparison to the impulsive force, they can be neglected.
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Stopping an object
Pretend you have an object moving with initial momentum mv and you want it to come to a stop. The impulse-momentum theorem says:
Demo: Egg & Sheet
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Air Bags & Seat Belts
Air bags and seat belts are designed to increase the time it takes for you to come to a stop so that forces on you are less.
See Ch.6 #36
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Perfectly Inelastic Collisions
Perfectly Inelastic Collision: Two objects collide and stick together.