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.

(In reply to solution by adam)

I can agree with more mass leading to more expansion. But the amount of expansion depends most on the material. We are only told that the density of the solid material of the hollow ball is higher. But I don't know how that affects the degree of expansion. Unless we are given more information, I don't think this method would work.

Posted by np_rt on 2005-03-31 20:26:11