Computation of horizontal force normal to the axis of a spheroidal conducting particle in a field gradient

When a cylindrical or spheroidal conducting particle resides in an electric field which is quasi-homogeneous over the axis of symmetry of the particle but inhomogeneous in the direction normal to the particle, the particle is subject to a force normal to its axis in the direction of the field gradient. In the 1980's, Cooke treated this problem experimentally, based on an expression for the force in terms of an empirical constant times the product of the field times the derivative of the electric field a direction normal to the particle axis. The present contribution provides a general analytical expression this force which agrees with that determined by Cooke for his experimental configuration.