where f is a numerical factor which in general depends on the molecular model. For smooth spherically symmetric molecules, however, f is very close to 2.5 , not deviating by more than 1 % % for a variety of interparticle force laws. Since k , μ μ , and c v are each well-defined physical quantities which can be measured independent of each other, this expression provides a convenient test of the theory. For monatomic gases, such as the noble gases, the agreement with experiment is fairly good.