We can learn something no less important by comparing Equation 14-12 with the ideal gas law in terms of number of molecules, Equation 14-6: \(pV = NkT\), or \(p = (N/V)kT\). In order for both Equations 14-6 and 14-12 to be correct, it must be true that \((2/3)K_{\mathrm{translational,\ average}} = kT\), or
In words, Equation 14-13 says that the average translational kinetic energy of a molecule in an ideal gas is directly proportional to the Kelvin temperature of the gas. This justifies the statement we made in Section 14-2 about the physical meaning of temperature.