I'm a bit confused about the speed of objects rolling down slopes. In my textbook, it says "Neither the mass nor the size of the object will affect its speed when rolling downhill." And that solid balls of different masses/sizes will all reach the bottom of the slope together. And then it goes on to say that because a hollow cylinder has mass far from the centre, it has a large rotational intertia, so gains a larger proportion of rotational Ek, so a smaller proportion of linear Ek, so it will have a slower speed when rolling downhill. Hence a solid ball (smaller I) will reach the bottom of the slope before the hollow cylinder. My ques is - if rotational inertia is what determines the speed of objects rolling down slopes, won't a larger solid ball have a larger rotational inertia than a smaller solid ball? So a larger solid ball should (by the reasoning above) have a slower speed, so will reach the bottom of the slope AFTER (not at the same time as) a smaller solid ball? Yet my textbook says "Large or small, light or heavy, all of these solid balls will reach the bottom of the slope together". Can someone help me clear up my confusion?