We have explicitly found the moments of inertia for point masses and also for sticks, and we have even defined the parallel-axis theorem. But what about more complicated objects, such as solid disks or cylinders that spin or roll? We have been given the inertia expression of (1/2)MR^2, and have used it quite a bit in problems, but where in the world does it come from? How do we use the integral definition of inertia to solve this? That is what this video is about, as a number of people have asked about where the inertia expressions for rolling objects come from. I hope this helps and makes sense.