Saturday, December 01, 2007

Coefficient of Restitution - Questions from Neighbors

Ashley asks (See original document):

Does this make sense?

In a, you can see that the ketchup in the bottle is a rest. When you turn the bottle upside down, thrust it at a high speed and quickly stop it, the ketchup flies to the bottom of the bottle. Since you’ve applied a force on the bottle and then stopped it, the force causes the ketchup to go down even after you’ve stopped the bottle because of its inertia of the initial force.

In b, you can see the ball is in motion. When the ball hits the wall, the unbalanced force, it will bounce off and continue in a different direction. Even if the ball wasn’t stopped by the wall, gravity and air resistance would have eventually stopped it.

My Answer:

Are you saying that the ketchup continues in the direction it was traveling, even after you stopped the bottle? If so, this is an example of F=MA, Mass times Acceleration equals force. Or an object in motion will stay in motion until another force acts upon it.

When the ketchup hits the end of the bottle, or the ball hits the wall, and returns. This return is called coefficient of restitution. The coefficient of restitution is the ratio of speeds of a falling object, from when it hits a given surface to when it leaves the surface, or the amount of return or bounciness. A superball may have a high coefficient of restitution, or return of about 90% of it's original starting point, ketchup may only have a < 2% return.


The Physics Factbook

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