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Napkin ring problem
Problem in geometry / From Wikipedia, the free encyclopedia
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In geometry, the napkin-ring problem involves finding the volume of a "band" of specified height around a sphere, i.e. the part that remains after a hole in the shape of a circular cylinder is drilled through the center of the sphere. It is a counterintuitive fact that this volume does not depend on the original sphere's radius but only on the resulting band's height.
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/2/27/Sphere_bands.svg/640px-Sphere_bands.svg.png)
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/f/f8/Cut_Napkin_ring_problem_Animation_created_with_openscad.gif/320px-Cut_Napkin_ring_problem_Animation_created_with_openscad.gif)
The problem is so called because after removing a cylinder from the sphere, the remaining band resembles the shape of a napkin ring.