# Calculating Moment of Inertia

1. Apr 13, 2009

### Dweirdo

EDIT:
Damn! wrote that in the wrong forum!!
mods please move to introductory physics!
thanks

Hi,
I'm learning by myself physics of rigid bodies , and I find it kinda hard.
Well, I know calculating the moments of Inertia is useless cause You have a table with all the MoI.
This is not a specific problem i ran into but I'll write it anyway:
1. The problem statement, all variables and given/known data
Calculate the Moment of inertia of a rotating(about it's center of mass) solid wheel of mass M( assume it's homogeneous)

2. Relevant equations

I= integral of something :PPP

3. The attempt at a solution
well i just know that the moment of inertia of a ring of mass M is MR^2/2
seems kinda intuitive,I'd like to know how do I (using integrals) calculate the MoI of a solid sphere as stated above.

2. Apr 13, 2009

### latentcorpse

$I_{ij}(O)=\int_V dV \rho(r) \left( r^2 \delta_{ij} -r_i r_j \right)$

3. Apr 13, 2009

### Dweirdo

Could You explain/expand about the formula? how did You pick the limits and etc.
thanks :D appreciated