Before you are two balls, one solid and one hollow. They are to all appearences completely identical: same size, same weight, same outer material (though one might assume, correctly, that the hollow ball would need a higher-density material on the inside to make it the same weight).

Without breaking either of the balls, how can you easily determine which is hollow?

Assume that the material is solid enough that a hitting the side of the hollow ball will not result in any noticeable echo or vibrations.

Supposing that there is a ball of higher density material, reguardless of weight, you should be able to try a floating test in water.  The higher density one should sink, or sink lower, should both balls sink. 

Posted by David on 2005-03-28 05:41:07