This article presents a proposed unified description of physical interactions within the framework of the special theory of relativity. The starting point is the principle of minimum potential energy, interpreted equivalently as the principle of minimum rest mass. According to this approach, every interaction can be described by a general force formula containing the charges of the given interaction, an interaction constant, and a dimensionless function of distance. The commonly used inverse-square dependence is treated here as an experimentally established approximation valid only within a limited range of distances, rather than as a universal law extending from zero to infinity.After the finite propagation speed of interactions is taken into account, interactions become one-sided: the force exerted by a source charge on another charge is determined by the state of the source at the point from which its interaction ray reaches the affected object. Therefore, the interaction must first be described in the rest frame of the source charge and then transformed to other inertial frames by means of Lorentz transformations. Using general vectorial Lorentz transformation formulas for U-spaces of arbitrary dimension, together with a relativistic form of Newton's second law of motion, unified vector formulas are derived for the acceleration and force acting on a point object carrying an arbitrary interaction charge. The appendix presents the derivation of the rest-mass derivative used in these formulas and provides numerical checks confirming the consistency of the transformations.