Question

define moment of inertia obtain an expression

Answer 1

Moment of inertia, in physics, quantitative measure of the rotational inertia of a body
ie., the opposition that the body exhibits to having its speed of rotation about an axis altered by the application of a torque (turning force)




Basically, for any rotating object, the moment of inertia can be calculated by taking the distance of each particle from the axis of rotation (r in the eqn), squaring that value (r^2 term), and multiplying it times the mass of the particle.

Answer 2

The moment of inertia of a point mass with respect to an axis is defined as the product of the mass times the distance from the axis squared. The moment of inertia of any extended object is built up from that basic definition