A measure of a body’s resistance to changes in velocity, whether the body is at rest or moving at a constant velocity. The velocity can be either linear or rotational. The moment of inertia (WK2) is the product of the weight (W) of an object and the square of the radius of gyration (K2). The radius of gyration is a measure of how the mass of the object is distributed about the axis of rotation. WK2 is usually expressed in units of lb-ft2.