I was watching a physics lecture and the instructor made the statement that "for a given mass, decreasing the diameter of the body makes it harder to spin up". In one way this makes sense, as with a smaller diameter one has a shorter torque arm to work with... however, I seem to recall from my physics that the moment of inertia goes as r^2. Which would say that it would be easier to spin up as the size decreases. What am I missing? Thanks!