hi prof
i found some bugs
3 made the Radius work
5 fix bug in equation d(omega)/dt = kv*kw*mu*g/R, kw missing
11 fix bug the trace is position correctly now at the fixed point on the rim of the object

i also improved it here http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1953.0
http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1953.0[img]http://www.phy.ntnu.edu.tw/ntnujava/index.php?action=dlattach;topic=1953.0;attach=3413;image[/img]