What is the law of circumference?

The law of circumference (also known as the law of conservation of angular momentum) is a physical law that describes the motion law of a rotating system. The law stipulates that when an object rotates around a fixed axis, the angular momentum remains unchanged unless there is an external force.

More specifically, the law of circle shows that the angular momentum L of a rotating system is conserved, that is, the magnitude of L remains unchanged until an external torque acts on the system. The external torque changes the angular momentum of the rotating system, thus changing its motion state.

The law of circumference is a basic law in classical mechanics, which is applicable to various situations of rotating motion systems, such as rotating rigid bodies, particles moving in a circle, charged particles moving in a magnetic field, etc.