On linear momentum in quasistatic electromagnetic systems

The analysis of Aguirregabiria, Hernandez, and Rivas [2004 Eur. J. Phys. 25, 555--567] of the electromagnetic linear momentum in quasistatic systems omits the presence of an equal and opposite hidden mechanical momentum in such systems. The existence of hidden mechanical momentum ensures that the action--reaction law holds for the forces between the charge- and current-carrying bodies of a quasistatic system, and thus the total mechanical momentum associated with the motion of such bodies in a closed quasistatic system is conserved.