Why do things which spin tend to keep spinning in the absence of external forces such as friction with the environment? In order for objects to keep spinning doesn't their periphery (relative to their centre of rotation - which would be their centre of mass, right? - ) have to be constantly acted upon by forces external to it in order to constantly change its direction of travel all the while preserving its (instantaneous) speed? Where does this force come from? How come the spin doesn't immediately start to slow down after torque is no longer applied to impart spin? Think about it. At one moment in time a clump of atoms on the periphery of a flywheel spinning freely in interplanetary space is going one way and some time later (after that clump of atoms has completed half of a rotation around the centre of rotation) the same clump of atoms is now travelling the opposite way, with the same speed as before. Where did the energy for decelerating and accelerating that clump of atoms come from? Please note I am not asking whether angular momentum is conserved or not. I am asking why it is conserved. I would very much appreciate it if replies to this thread made that distinction. Thank you very much for your interest in this inquiry and your time. Especially if you decide to help elucidate this for me.