Date: Mon, 11 Oct 1999 11:04:55 -0500 (CDT)

Author: Dale Stille

Subject: Re: Ball jumping out of water cup


Hello from Iowa,

Experimental success !!!! (although just quick and dirty).

We first theorized that what was needed was to

1) Have a ball with high buoyancy (such as a ping-pong ball).
2) Keep the ball at the center of the water surface at all times.
3) Have the bottom of the water container hit the floor evenly.

So, here is what we did :

1) We took a 1/2-gallon wide-mouth polyethylene bottle with an outside
diameter of 5 inches, and filled it with 3 1/2 inches of water.

2) We placed 7 floating ping-pong balls, which arrange themselves neatly
in a hexagonal array with one in the middle. The ball in the middle is of
a different color than the other six. We had all white balls except for
the one in the middle which was orange.

3) To insure than the bottom of the container would hit the floor evenly,
we guided the free fall of the container with a 5 1/2 inch (outside
diameter) plexiglass tube (3 1/2 feet long, but you can make it longer).
It might be necessary (if the water container fits too tightly in the
tube) to raise the plexiglass tube about two inches off the ground to
prevent any air pressure build-up in the tube. We did not need to do this
in our setup.

4) When we drop the container through the plexiglass tube and it hits the
floor we can clearly see the orange ball jump first (about 1 1/2 - 2

We also recommend (and will try this as soon as we can) to use
videocapturing to more clearly see the jump.

Dale Stille and Ramon Torres-Isea
The University of Iowa.

On Sat, 9 Oct 1999, Urs Lauterburg wrote:

> Dear TAPlers,
> One of our Profs wants to show how a ball would be ejected out of a cup
> filled with water when dropped. He says he heard it should be possible but
> all I have tried so far failed. The idea is to have a ball float inside the
> water and when the water cup hits the floor the ball is supposed to be
> ejected due to the suddenly changing water pressure at the moment of the
> impact which should force the ball to fly back up again.
> Has anyone achieved this and if yes how ?
> Thank you for any related comments on this subject.
> Cheers
> Urs
> Urs Lauterburg
> Physics Edutainer
> University of Bern
> Switzerland