Within our ball, we have lots of different molecules. But the difference between any two molecules is much greater than the size of the molecule itself. And that's why we can compress it because when we compress it, there's lots of space for the molecules to move. 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.