  We study the force between two circular electrodes in different
configurations. A formula analogous to Kelvin's formula for the spheres is
given in the case of equal disks held at the same potential and when one plate
is earthed. An expression for the force at short distance between two
arbitrarily charged disks is found: the generic case shows a logarithmic
repulsive force, also for disks carrying charges of opposite sign. Some
numerical computations support the results. A classification for the possible
behaviors of the force is proposed on the basis of a decomposition of the
capacitance matrix. It is shown that the forces depend strongly on the
dimensionality of the contact zone between the conductors. The analysis is
supported by a numerical computation carried for the case of two disks of
different radii.
