The law of conservation of angular momentum is a basic principle in physics, which points out that the angular momentum of a closed system is constant without external torque.

The mathematical expression of the law of conservation of angular momentum is: L=Iω, where L is angular momentum, I is the moment of inertia of the rotating object, and ω is the angular velocity of the rotating object. This formula shows that the angular momentum will not change if an object is not acted by any external torque. The rotation speed and direction are constant.