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Q & A: Conservative Forces (Gravity)

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Most recent answer: 10/22/2007
Q:
Hi, We have done an experiment (physics) where a ball bearing is placed in a u-shaped tube and been told that if there was no friction, the ball bearing would continue rolling back and forth forever. My son would like to Know why gravity would not eventually cause the ball bearing to stop in the middle of the tube closest to the ground. Help please.
- Brenda
Homeschooling parent, New Zealand
A:
When gravity acts on an object, in this case a bearing ball, it speeds it up on the way down, and then slows it down on the way up. Gravity does this in an equal amount both ways (because it is constant).
An other good example would be when someone throws a ball straight upwards. If it is just thrown a little, then when it comes back down it lands with a low speed. If it is thrown way up in the air, it comes down very fast. So gravity must be slowing it down as much as it is speeding up the ball.

If you wanted to you could introduce energy and show how energy is conserved. But that is a whole different topic (although a lot simpler).

(published on 10/22/2007)

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