3.6 Law of Conservation of Angular Momentum

3.6 Law of Conservation of Angular Momentum

The law of conservation of angular momentum states that if no external torque acts on a system, the total angular momentum of the system remains constant.

The law of conservation of angular momentum is one of the fundamental principles of Physics. It has been verified from the cosmological to the sub-microscopic level. The effect of the law of conservation of angular momentum is readily apparent if a single isolated spinning body alters its moment of inertia.

If a body of moment of inertia $I_{1}$ spinning with angular speed $\omega_{1}$ alters its moment of inertia to $I_{2}$, then its angular speed $\omega_{2}$ also changes so that its angular momentum remains constant.

Hence

The angular momentum is a vector quantity with direction along the axis of rotation. Hence, the direction of angular momentum along the axis of rotation also remains fixed. This is illustrated by the fact given below:

The axis of rotation of an object will not change its orientation unless an external torque causes it to do so.

This fact is of great importance for the Earth as it moves around the Sun. No other sizeable torque is experienced by the Earth, because the major force acting on it is the pull of the Sun. The Earth's axis of rotation, therefore, remains fixed in one direction with reference to the universe around us.