The Law of Conservation of Angular Momentum states that if no unbalanced external torque acts on a rotating system, the angular momentum of the system is constant. An external torque is initially added to the system producing vertical angular moment in the wheel. The physicist and the wheel are now considered a closed system with no external forces. When the wheel is held vertically, horizontal spinning equals zero and the physicists doesn't rotate. When the wheel is turned horizontally, the physicist spins to counteract the wheel's rotation, thus conserving angular momentum.