So what happens in a system of gas molecules that is under constant temperature? Well, then, on average, the kinetic energy of any gas molecule, say gas molecule one, is the same as the kinetic energy, gas molecule number two. So let's equate these guys and let's see where that leads us. Let's suppose the kinetic energy of some gas molecule one is equal to kinetic energy of gas molecule two because they have the same temperature. Now, let's also assume that gas molecule two has a larger mass than gas molecule one. So gas molecule two is heavier.