Non-parallel currents and the Newton’s third law of motion

Abstract

Abstract We provide an explicit calculation to check that Newtown’s third law holds for non-parallel currents if the field momentum is accounted for. In textbooks of electrodynamics, it is usually noted that in the interaction of non-parallel current elements, the action force is not balanced by the reaction force, though these forces are balanced in the interaction of two closed current-carrying loops. In the case of non-closed current segments the change in the momentum stored in the field should be taken into account. Using a simple model of two non-parallel straight current segments we show how it works. As such a model, two straight orthogonal to each other conductors are considered, with equal charges of opposite signs at the ends of each conductor. For some interval of time, a direct current is supported in the conductors. We show that the total momentum of the system is conserved.