Moment of gyration

The moment of gyration represents a characteristic magnitude for "rotational inertia"of a rigid body, such as the rotating assembly of a centrifugal pump or drive (see Starting method. It is designated and calculated by means of mD² from the mass (m) of the rotating body and the diameter of gyration (D). The unit is kg • m². The diameter of gyration is:

The moment of gyration (mD²) is often replaced by the moment of inertia (J).