 But there is an altogether different way of looking at that same gas; that is, as consisting of a large number of molecules (a vessel on a laboratory table contains something like \(10^{23}\) molecules). These molecules bounce around under the influence of the forces exerted onto them when they crash into the walls of the vessel and collide with each other. The motion of each molecule is governed by the laws of classical mechanics in the same way as the motion of the bouncing ball. So rather than attributing some macro variables to the gas and focussing on them, we could try to understand the gas’ behaviour by studying the dynamics of its micro constituents.