That's because when you take off your shoes the molecules of air trap in your socks and in your shoes escape and move at very high speeds in all different directions. So the person sitting across the room from you will definitely smell you. So you better keep those shoes on. So the second assumption about high velocities also accounts for the fact that gases will expand into any container quickly and completely. Let's look at our third assumption. So, gas molecules exert no forces on one another due to mass and charge.