  In this paper we prove, by expressing the energy as a function of the wave
propagation speed, it is highlighted the existence of an equivalent mass of the
wave, as well as of an Einstein type relations between the energy and this
mass. Also, we establish a relation between angular frequency and energy
similar to that of the Planck relation. For the propagating wave, there is a de
Broglie type relationship between the linear momentum and the action variable
(the angular momentum), i.e. the wave linear momentum is proportional to the
wave number, the proportionality coefficient being the action.
