Gravitational potential energy of a rigid body E,=∑△m,g,=m ∑△m,21=mg2e m The gravitational potential energy of a rigid body is as same as the energy of one particle on its center of mass with same weight The work-energy theorem of rotation e02 2 二J0 Gravitational potential energy of a rigid body c i i p i i mgz m m z E m gz m g      The gravitational potential energy of a rigid body is as same as the energy of one particle on its center of mass with same weight The work-energy theorem of rotation                  2 1 1 2 2 2 2 1 2 2 1 1       d mgz J mgz J ext c c