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.

I live in India, and theoritical cats don't seem to be available here.So I tried to use my neighbour's cat,but she did not seem too cooperative.Ah!For people do not understand the joys of experimental biophysics! (cat+moment of inertia=biophysics, what else ?)

And now to business.I take the hint from biophysics-pass ultrasonic waves through the balls,and the ultrasound images of the two shall tell you which is hollow -that's the principle on which sonography works.When sound waves moving in a medium with a certain density encounter a medium of different density they get reflected.

Posted by Rex on 2005-03-26 14:59:48