This applet highlights the activity of detecting collision pairs and advancing particles to collisions during the simulation of a system modeled using a hard potential.
The simulated system is surrounded by hard walls. At any instant the two disks (or one, for an incipient wall collision) that are next to collide are colored red and blue, respectively.
Adjustment of the particle number halts the simulation. Press the "Continue" button to restart. Adjust the temperature to speed up or slow down the simulation.