In this paper we construct such a physical model with a continuous distribution of relaxations. It is based on the phenomenological theory of relaxation processes which have a long history in physics literature and was recently summarized in a monograph in which references to other relevant publications can be found, [24]; also see [25]. The present work is confined to relaxation mechanisms which result from changes in normal stresses. More specifically, we are interested in the local mechanisms of irreversible energy loss caused by uniform compression or expansion of a medium for which all components remain unchanged, rather than the losses caused by friction between different layers of a medium which move with different velocities (for a more detailed discussion of this issue see [26]). No attempt is made to model effects of shear viscosity and heat conduction beyond the conventional Navier–Stokes approach, since this topic goes far beyond the scope of this paper.
