Date: Mon, 11 Oct 1999 09:59:23 -0600

Author: The Lahrs

Subject: Re: Ball jumping out of water cup


Gordon writes:
"True, but for some reason I had the impression that the ball was fully
submerged at the start of this. So, surface tension effects shouldn't come
into play for this case?"

Yes, I think you're right. I must have missed that point!

So the demonstration would be:
First pull the ball down to the bottom of the cup of water,
perhaps using a magnet attached to the ball and another one
under the cup. Simultaneously release the cup and pull away
the exterior magnet. The cup will fall and the ball will
remain on the bottom during the fall as both are weightless
from the point of view of the accelerating frame of reference.

When the cup hits the floor the ball will pop up to the
surface. Now whether or not the ball is ejected from the cup
is another question < perhaps the original question! >. I
tried just now releasing a ping pong ball from a depth of
a few inches and it didn't leave the surface of the water.
Breaking away from the surface may be where surface tension
comes into play. Perhaps a ball coated with wax would have
an easier time of it.


* John C. and Jan H. Lahr *
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* 1925 Foothills Road *
* Golden, Colorado 80401-1718 *
* (303) 215-9913 *
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