But if this a ball was filled with solid or liquid, I would not be able to compress it without changing its shape or volume. Let's look at the second assumption. Gases move at high velocities in all different directions. So what's the observation or what's the experience from everyday life that tells us that gas is, in fact move at high velocities? Well, for example, if you forgot to wash your feet or you've been wearing your shoes for way too long, you know that if you take off your shoes and there's a girl or a voice sitting across the room, they will definitely smell you instantaneously. That's why you better keep your shoes on.