Charged objects have a greater inertia than the same uncharged bodies. This is explained by an interaction of electric charges in motion with the field generated by them, called field reaction, the effect can be interpreted as an increase in the inertial mass of the body and is derived from Maxwell’s equations. The interaction of electric charges with the field depends on the geometry of the system: the inertia of a charged body assumes a tensor character, in contradiction with classical mechanics, and therefore we must distinguish between a component parallel to the motion and two transverse components. It is shown that we can divide the inertial mass of a charged body in two components, the electromagnetic mass and the non-electromagnetic mass. While the electromagnetic mass depends on the geometry of the system, the non-electromagnetic mass has the same “standard” invariance characteristics of the inertial mass, and the inertial mass is related to it if the body is uncharged.

The concept of electromagnetic mass also exists in the theory of special relativity and quantum field theory. The electromagnetic mass had a great importance in the history of physics at the turn of the nineteenth and twentieth centuries because of the attempt, carried out mainly by Max Abraham and Wilhelm Wien, initially supported by the experimental work of Walter Kaufmann, to derive the inertial mass only from the electromagnetic inertia; this interpretation of inertia was later abandoned with the acceptance of the theory of relativity; more precise experiments, performed for the first time by A. H. Bucherer in 1908, showed that the correct relationships for longitudinal mass and transverse mass were not those provided by Abraham, but those of Hendrik Antoon Lorentz.