Rigid Body

The equilibrium position is along the radius, when the center of mass moves on the circular orbit. The angular velocity on the orbit is obtained from , that is, . Since the graviational force and the centrifugal force depend on the radius, different forces are applied to the two masses. The total force on a mass at the radius , rotating with the rod, is , so that the difference is . If the rod rotates by a small angle the resulting torque is , so that one has

where . Thus,