Nonclassical continua, pseudobalance, and the law of action and reaction

The procedure followed in constructing models for gene- ralized continua is revisited. It is shown that the microforce ba- lance equations required for the description of generalized continua are not in fact expressions of the balance of physical quantities, but consequences of the regularity assumed for the systems of contact actions. In the proposed approach the law of action and reaction, which in classical continuum mechanics is a consequence of Euler's balance laws, recovers the status of a basic principle held in Newto- nian mechanics. Some examples of generalized continua taken from the literature are discussed.