Newton's Laws for Rotation.

1st Law : The rotational principle of inertia:
The rotational principle of inertia: In the absence of a net applied torque, the angular velocity remains unchanged.

2nd Law: The rate of change of Angular Momentum:

τ = I α

This is not as general a relationship as the linear one because the moment of inertia, I, is not strictly a scalar quantity. The rotational equation is limited to rotation about a single principal axis, which in simple cases is an axis of symmetry.

3rd Law: Reaction Torque:

For every applied torque, there is an equal and opposite reaction torque. (A result of Newton's 3^rd law of linear motion.)

If we can somehow cheat any of these laws we can have perpetual machines requiring no energy inputs.