The Moment of Inertia is the rotational analogue of Mass.  Where mass resists acceleration, Moment of Inertia is the physical quantity that resists angular acceleration.  Moment of Inertia is expressed in units of mass times length squared: `I = m*r^2` and this expression, `I = m*r^2`. also represents the Moment of Inertia of a point mass, m, at a distance, r, from the axis of rotation.