The equation IMG = Hg states that the O resultant moment about the mass center of the external forces on the body equals the time rate of change of the angular momentum of the body about its center of mass. resultant moment about the mass center of the external forces on the body equals the time rate of change of the linear momentum of the body. resultant moment about the mass center of the internal forces on the body equals the time rate of change of the angular momentum of the body about its center of mass. resultant moment about the mass center of the internal forces on the body equals the time rate of change of the linear momentum of the body