moment of inertia (l) The kinematic properties of a rotating body; a measure of the rotational inertia of an object around a specific axis of rotation, in units of kg/m². In the Earth, the principal moment of inertia lies close to the axis of rotation and passes through the centre of mass of the Earth. Changes in the mass distribution, e.g. ice sheets, seasonal atmospheric changes, etc., cause changes in the location of the moments of inertia.

moment of inertia (symbol I) For a rotating object, the sum of the products formed by multiplying the point masses of the rotating object by the squares of their distances from the axis of rotation.