  From the equilibrium condition $\delta S=0$ applied to an isolated
thermodynamic system of electrically charged particles and the fundamental
equation of thermodynamics ($dU = T dS-(\mathbf{f}\cdot d\mathbf{r})$) subject
to a new procedure, it is obtained the Lorentz's force together with
non-inertial terms of mechanical nature. Other well known ponderomotive forces,
like the Stern-Gerlach's force and a force term related to the Einstein-de
Haas's effect are also obtained. In addition, a new force term appears,
possibly related to a change in weight when a system of charged particles is
accelerated.
