Use eqn 35.22 to derive the energy density of a gas of (i) non-relativistic particles (γ = \frac{5}{3}) and (ii) relativistic particles (γ = \frac{4}{3}).
u =\frac{p}{γ −1}. (35.22)
Straightforward substitution into eqn 35.22 yields
u =\frac{3}{2} p for γ = \frac{5}{3} , (35.23)
u =3 p for γ = \frac{4}{3} , (35.24)
in agreement with eqns 6.25 and 25.21.
p = \frac{2}{3} u. (6.25)
p = \frac{u}{3}, (25.21)