hi, is there any difference between balls or humans when collision occur? i am trying to write a human model for collision cases... and still trying very2 hard to make it in realistic way. your applet seems like good for me and i'm impressed with it... perhaps it would be good to be applied to my project.. can u explain it in detail how's the calculation for it? dividing it into 3 condition,(1.before,2. during..,3.after.. )would be really2 great... thanks.. ref: http://www.phy.ntnu.edu.tw/ntnujava/viewtopic.php?t=19 Regards, Bazli Karim siput_tiung@yahoo.com