ah i see. Yeah I did something like that in a previous project where each particle had an x and y velocity which made the trig real easy. There were a few little querks i didn't like about doing that though, cant say i remember... so this time i thought I'd try using two variables; velocity and direction to accomplish the same thing. In some ways its better, in others it's just hard; wall collision for example is much harder than just negating the x or y velocity. Anyways... i was hoping you were using the velocity/direction method so i could get some hints... oh well.