The inertia of rotational motion is called moment of inertia. It is denoted by L. Moment of inertia is the property of an object by virtue of which it opposes any change in its state of rotation about an axis.

The moment of inertia of a body about a given axis is equal to the sum of the products of the masses of its constituent particles and the square of their respective distances from the axis of rotation.

Its unit is kg.m²

and its dimensional formula is [ML²].

The moment of inertia of a body depends upon

• • position of the axis of rotation
  • orientation of the axis of rotation
  • shape and size of the body
  • Distribution of mass of the body about the axis of rotation.

The physical significance of the moment of inertia is same in rotational motion as the mass in linear motion.