What you Need
What to do
Hold the tennis ball directly on top of the basket ball, and then try to drop both balls together as smoothly as possible onto a hard surface. Make sure you stay a long way away from anything delicate!
What may happen
You should find that the tennis ball bounces far higher than the height it was dropped from.
Why does it happen?
If you drop a ball it will only ever bounce up nearly as high as it was dropped from. However if you drop two balls more interesting things can happen. The basketball hits the ground and bounces first so the the tennis ball hit the basketball coming back up. This is like hitting it with a tennis racket so it bounces off much faster than it was coming down and it flies up into the air.