I wanted to write about a Java molecular simulation that I made a while ago, before I became entranced by Python. The program is a simple 2D physics simulation, with circles representing billiard ball-style atoms. The idea before the simulation was initially an attempt to create a virtual lava lamp. In its first incarnation, there were two types of atom. Each atom was attracted to nearby atoms of the same type (with a force proportional one over distance squared). If the distance between any two atoms was below a threshold then the two atoms repel each other.