  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.
