1. The problem statement, all variables and given/known data Find the moment of inertia of a solid sphere of uniform mass density (like a billiard ball) about an axis through its center 2. Relevant equations I = ∫rρdV 3. The attempt at a solution I =ρ ∫r4πr2dr = ρ4π∫r4 Then I integrate this from 0 (the center) to R, so I = (ρ4π)*(R5/5) And ρ = mv so ρ = M/(4/3)πR3 = 3M/4πR3. Put ρ into the equation for moment of inertia to get I = 3MR2/5. My book tells me the answer is (2/5)MR^2. Where did I go wrong?