A common example from intermediate‐level electromagnetic theory, the calculation of the force acting on a dielectric slab partially inserted into a parallel‐plate capacitor, is examined in detail. The physical origin of the force, ignored in most textbooks, is shown to be due to the fringe field. The standard textbook calculation, in which the fringe field is explicitly ignored, is examined. An analysis which includes the presence of the fringe field indicates that the standard result is valid, but under conditions other than those generally presented.