# Moment of inertia of a uniform solid sphere

1. Jun 10, 2012

### david456103

For calculating I of a uniform solid sphere, why can't we use thin spherical shells? When I try to use spherical shells I get (3/5)MR^2. Every single derivation uses thin cylindrical shells and end up with the correct expression((2/5)MR^2) but they never explain why it is correct to use cylindrical shells and not spherical shells.
Thanks!

2. Jun 10, 2012

### haruspex

You certainly can get there via spherical shells, but it produces the same answer: 2/5.
What do you get for the MI of the shell?