kinetic co-energy

Based on the principle of symmetry, we  propose a universal expression of the energy of  physical system. If we accept a generalized coordinate as an argument, we come to potential energy; if we accept a generalized velocity as an argument, we come to kinetic co-energy. Here, like in the variational principle, the concept of kinetic energy does not work. The examples of application relate to electromagnetic fields, electro­magnetic circuits, and mechanics of concentrated masses.

It is shown that motion is accompanied by energy and co-energy, which are inseparable. In a linear media they are equal and can replace each other. In a nonlinear media they are different, and each of them executes its own functions. Universal expression for co-energy of the physical system is offered. The concept of kinetic energy in variation principles does not fit. Examples refer to the electromagnetic field and relativistic theory of gravitation. The paradox of transversal and longitudinal relativistic masses is refuted.