Inertia

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 movement 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.