excellent advise!

variable added:
sound // boolean  true for play false for no play
t_on // time of sound to be play

Constraints:
if (Math.abs(t-t_on)>0.04) sound=false; // turn the sound off when it has been play for 0.04s

Evolution
Event
Action page added
sound = true; // sound produced
t_on = t;

work like a charm :)
i will post my derived newton cradle from prof paco in the community board as a download-able jar file
http://www.phy.ntnu.edu.tw/ntnujava/index.php?action=dlattach;topic=824.0;attach=499

you are the best, prof hwang