Date: Mon, 11 Oct 1999 13:46:15 -0600

Author: The Lahrs

Subject: Re: Ball jumping out of water cup


OK, I was able to duplicate the effect on a small scale.

I dropped a plastic glass containing water to a depth of about
2 cm and a ping pong ball onto a counter from a height
of 8 - 10 cm. To reduce the stress on the glass I placed a
damp sponge on the counter where the glass would hit.

The ping pong ball bounces up and out of the glass! The
height seems to be higher when the ball starts out in the
center of the glass. Swirling the glass prior to dropping
it moves the ball to the center.

Does anyone have a good explanation for this effect? How
does this compare with the NASA demonstration that showed
for less abrupt changes in acceleration that a floating object
would not change it's position with respect to the surface of
the water?

Without the ping pong ball in the water, the water would
often shoot up from the center of the glass, but generally
not as high as the ping pong ball would shoot up.

Would a ping pong ball dropped from the same height onto a
hard surface shoot up just as high? I'll have to do some
more experiments!


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