A relation betweenp and e in the form/7 = /?(p, e) or e = e(p,p) is called an equation of state (EOS). In particular, the EOS of an ideal perfect gas is


The quantity T = (7 - \)e is the temperature in energy units and 7 > 1 is the adiabatic index. A more complicated, so-called two-term EOS has the form


This EOS sometimes allows one to describe approximately the properties of solid state of materials. In (3.1.5) the quantities p0 and c0 are constants such that for e = 0 the relation p = 0 must hold; hence p0 — POCQ/J. The condition p = 0 for e = 0 and p = p0 provides the initial static equilibrium of the medium. Particularly, in modelling of explosive welding of metals (Godunov et al. 1970; Godunov et al. 1979) it was assumed p0 = 8.93 g/cm3 and c0 = 3.97 km/s for copper and p0 = 7.87 g/cm3 and c0 = 5.0km/s for iron. Equation (3.1.4) can be obtained from Eq. (3.1.5) for c0 = 0 and/?0 = 0.