My son is learning about the phases of matter, so I made a quick tic80 simulation of matter.

I'm using the Lennard Jones potential to simulate the interatomic forces, using a leapfrog integrator to try to conserve energy. The boundary conditions are implemented with springs. There is gravity to get things to fall. I'm using a Nose-Hoover thermostat in order to set the temperature.

Use the arrow keys to adjust the temperature, shown in the upper left corner.

To play with the simulation, check it out here and check out the repo.