Animation of the distribution of energies in the particles of a gas as it is heated. The energy of each gas particle is colour-coded, from dark blue (least) through purple, pink and red to bright orange (most energetic). Initially all the particles have the lowest energy, but when the centre is suddenly heated, the energy distributes itself amongst the particles. The energies relate to their velocities: more energetic particles move more quickly. 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, as time progresses, on average most particles have low to middling energies, with only a few at the highest level. This describes a Maxwell-Boltzmann distribution.