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.

Roll them down a ramp.  I don't remember my physics that well, but they have different moments of inertia.  The hollow one has its mass concentrated away from the centre of mass, and so it should provide more resistance to rolling, so the solid one will beat it in a race down a ramp.

This might be wrong, it might be the other way around, like I said, I don't remember my physics that well.  Seems right to me.  Either way, rolling them down a ramp will separate them.

Posted by iamkobe on 2005-03-25 15:43:08