Hidden momentum and the electromagnetic mass of a charge and current carrying body, V. Hnizdo, Am. J. Phys. 65(1) January 1997
The contribution of the electromagnetic self-field to the energy and momentum of a charge and/or current carrying body is considered within classical physics and discussed in simple terms using nontrivial exactly solvable examples. The Lorentz-transformation properties of the energy and momentum of the body can be maintained by taking into account the relativistic effects of the mechanical stresses due to the sources of the self field, or by separating the energy and momentum of a moving self-field from those of a nonelectromagnetic origin in a relativistically covariant way. In either procedure, a proper account must be taken of the hidden mechanical momentum that, in general, is contained in a stationary body that carries both charge and current, and which is equal and opposite momentum to the static electromagnetic field. Hidden momentum and the momentum of a static field are indispensable concepts of a direct physical significance in classical electrodynamics.