Torques without Rotation: the Right-Angle Lever

Abstract

An extended body subject to external forces which exert zero net force and zero total torque in the rest frame, may experience a nonzero torque in another inertial frame, and nonetheless does not rotate. Long known as the Trouton-Noble or right-angle lever paradox, there has been extensive discussion and indeed controversy, but a clear understanding comes from a suitable treatment of angular momentum and simultaneity.