Electromagnetic forces on dissipative dielectric media

The standard treatment of electric and magnetic forces on material bodies, based on energy conservation through the calculation of the work done in the course of a displacement of the object, fails when media are dissipative. We emphasize that the study of these systems requires consideration of the general momentum balance that leads to obtaining the forces by integration of the Maxwell stress tensor across the body surface. We study the influence of losses in some examples, including the cases of a liquid between charged parallel plates and a dielectric sphere in a nonuniform field. An analysis of the physical origin of the differences with the corresponding loss free cases, based on the study of the electric forces on true and polarization charges, is made.