Moments of Inertia--Big Confusion Hey, 1. Using the conventional method to calculate moments of inertia of rigid objects which says we should divide the object into small pieces each of mass dm and then calculate the integral. is it an exact calculation or an approxximation? so far my understanding has led me to think its STILL an approximation, because whenever e do it, we ASSUME something, like for example in the case of a solid ring, we assume the thickness to bne infinitely small. 2. in calculating I for a solid disk, here's what i did: divide the disck (radially) into an infinite number of pieces each of mass dm and radius R/2 from the centre, and then calculate the integral which ends up being = MR^2 / 4 which is wrong seeing how the real answer should be MR^2 / 2 what am i doing wrong here? please guide me/!