" At every instant ,there is just one point of contact between the body and the plane and this point has no relative motion, hence ideally the friction should be zero" --from my textbook Firstly, I don't understand the "relative motion" part. Can someone please explain. And we do know in fact that there is some friction that exists int he form of rolling friction. But what exactly causes it when there is hardly any surface area of contact? Why is there any rolling friction at all?