The Principle of Material Frame Indifference

Abstract

The principles of invariance and symmetry have played an important role ever since the early days of science. This chapter presents what many believe is an appropriate spacetime invariance principle for the continuum thermodynamics: the principle of material frame indifference, also called the principle of objectivity. This principle establishes a link between the general thermodynamic assertions such as the equation of balance of energy and the boundedness of energy from below on the one hand and the specific continuum thermodynamic concepts on the other. Among the latter concepts will be the mass, its positiveness, the equations of balance of linear and angular momenta, and the concepts of internal and kinetic energies. Apart from this theoretical role, the principle of material frame indifference is also important in the constitutive theory where it restricts the form of the constitutive functions. This feature of the principle of material frame indifference will be explained in Part III; here we shall concentrate on the fundamental aspects.