depents on the collision.

for instance a collision with a block

function bounce_event
{
if (EVENT_TYPE == Event_impact)
{
... // do what you want.
}
}

action bounceball
{
...
my.enable_impact = ON; // sensible for impact
my.EVENT = bounce_event;
...
}

hope this is what you mean, check the help file in the SED and type enable, you'll find al sorts of collision detections.