greeting Prof Hwang!

i been trying to remix this applet, with some success. :) check out the attachment or;topicseen#msg5504

I have 2 (modeling) problems i want to add into the simulation.

1. collisions between particles ( current model is missing this, only collision with walls)
2. some way to show Maxwell distribution of speeds like

chance to work on my attachment;topic=632.0;attach=1736 below and build on each other's effort to make a fantastic Ideal Gas Model based on Kinetic Theory of Gas applet jointly?  ;D

1 and 2 seems a bit difficult for me, thanks for your consideration and let me know how should i progress.