On the contrary, on solids and liquids the density is much higher and so there is not too much space for them to move. And that's why we can't compress them easily. And that's exactly why when we take this inflated ball, we see that we can easily compress it because there's lots of space for the molecules to move. 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.