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Apr7-06, 01:02 PM
P: 10
Wow I see the light (I think) :P

I'll just take a quick guess here, and say that a small addition to your answer to my second question would be 'only if your element is a point mass, or the element has moment of inertia = dm(r^2) ' ?

I think this follows, looking at the working for a solid cylinder, my textbook uses shells, which each have moment of inertia dm(r^2), and that derivation just uses I = integral of r^2 dm, which is the same working for a point mass element as you point out.

Anyhow, I'll go and review this stuff. Thank you for your explanation!