So let's go back to this example, right? So when I take my ball and I push this ball, I can only push it to a certain extent at some point. I can't push it any further unless I exert a stronger force. Well, why is that? Well, the reason for that is because all these molecules are moving at tremendous velocities and every time they hit the container, hit the walls, they exert a force or a pressure. Pressure is simply force per some given area.