In solids there are crests and troughs. In highly polished surfaces there are molecular forces. But what creates friction during rolling where there is only line contact (in case of cylinder) or point contact (inn case of a ring)? I read somewhere that when an object is rolling it forms a hump in front of it on the surface on which it is rolling. Thats what opposes it and hence is a cause of friction. I don't really buy that. Please help me understand.