Animation of the distribution of energies in the particles of a gas. The energy of each gas particle is colour-coded, from dark blue (least) through purple, pink and red to bright orange (most energetic). The energies relate to their velocities: more energetic particles move more quickly. Initially all the particles have an average energy, but this quickly distributes itself unevenly amongst the particles as the system reaches equilibrium. The graph at bottom left shows the distribution of energies, with energy increasing on the horizontal axis, and the number of particles with each energy on the vertical axis. It is seen that although the levels fluctuate as particles exchange energy during collisions, on average most particles have low to middling energies, with only a few at the highest level. This describes a Maxwell-Boltzmann distribution.