Molecular Dynamics Applet

[Trouble loading the applet? Check that Java is enabled in your security settings, or try a different browser, or make sure you're on a real computer and not a mobile device. You may need to download and install the Java plugin. If all else fails, you can try this rudimentary HTML5 version, which doesn't use Java.]

This applet simulates the dynamics of simple atoms and molecules in a two-dimensional universe. The force between the molecules is weakly attractive at short distances, but strongly repulsive when they touch. Use the applet to explore phases of matter, emergent behavior, irreversibility, and thermal effects at the nanoscale.

The physics:

The user interface:

The fine print:

Of related interest:

If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generation of creatures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis (or the atomic fact, or whatever you wish to call it) that all things are made of atoms&mdashlittle particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another. In that one sentence, you will see, there is an enormous amount of information about the world, if just a little imagination and thinking are applied.”

Richard Feynman