  A very simple system like a parallel-plate capacitor reveals striking
features when we examine the peculiar phenomena appearing when it is moving at
low speed in different directions. Both hidden momentum and hidden energy
appear and their addition, with their sign, to the corresponding
electromagnetic component results in the expected ordinary kinetic momentum or
energy of the electrostatic mass equivalent. What's happening is that passing
from one inertial reference frame to another, part of the energy or momentum is
transferred from the electromagnetic component to the material part of the
system or the other way around. A paradoxical self-accelerating behavior is
evidenced if one admits that the capacitor is discharging through an electrical
resistance during its motion. It is shown that one must take into account the
mass of the produced heat.
