Lorentz transformation of a system carrying "Hidden Momentum", E. Comay, Am. J. Phys., 68(11), November 2000
The relations between energy-momentum tensor and its corresponding four-vector are discussed. A particular emphasis is put in conditions guaranteeing that spatial integrals of the energy-momentum densities pertain to a true four-vector. Cases where such integrals are not components of a true four-vector are analyzed and the usefulness of the notion of a false four-vector is pointed out. Results are used for explaining Lorentz transformation properties of "hidden momentum."