Hi all, I was wondering how to calculate the moment of inertia of a cylinder that is filled with a substance and is rolling down an inclined plane. I know that I = int(r^2 dm), and I know what r is... but I gather that dm may be a complicated function of mass density-position and some volume differential. I was wondering if someone can explain to me how this works ... I may have to find the density of the substance, right? Is that the only way I can find it? Also, I understand that I may very well end up with an approximation, but that' sfine.. as long as its reasonably accurate. I want a numerical answer (even if it is a reasonable approximation).. not an exact integral. Thanks!