The particle model

The bench is drawn as in a school lab. The path of each speck is made up by the computer, at random, in the way real specks move, and each Restart gives the orange speck a new path. The view pauses at each beep so that you can mark the speck; through a real microscope it keeps moving, and you note where it is at each beep.

The lines join positions marked every 2 s. The real path between two marks is far more crooked, too small and too quick to follow.

The model in the eyepiece is not to scale. Real air molecules are far smaller, far more numerous and far faster (about 500 m/s at 20 °C), and a real speck is far heavier than the 25 molecules’ mass given to it here. Each hit keeps momentum and kinetic energy, as in a real collision between particles.

The model air can be cooled to −273 °C and stays a gas; real air turns to liquid at about −190 °C. The energies on the graph are those of an ideal gas, whose particles have kinetic energy only from moving about.

With reduced motion each step is drawn complete at once and the eyepiece shows still pictures.