The mechanical analog of an inductor is a mass. The voltage across an inductor corresponds to the force used to accelerate a mass . The current through in the inductor corresponds to the velocity of the mass. Thus, Eq. (E.4) corresponds to Newton's second law for an ideal mass:
where denotes the acceleration of the mass .
From the defining equation for an inductor [Eq. (E.3)], we see that the stored magnetic flux in an inductor is analogous to mass times velocity, or momentum. In other words, magnetic flux may be regarded as electric-charge momentum.