Almost right, but physics collisions are EVENT_FRICTION.

Code:

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function init_sphere()

{
phent_settype(my, ph_rigid, ph_sphere); // enable physics for this ball
	phent_setmass(my, 100, ph_sphere); // the ball has 1kg (2 lbs) and behaves like a sphere
	phent_setfriction(my, 0); // friction
	phent_setelasticity(my, 100, 0); // bounce a lot
	temp.x = 0; 
      temp.y = -250; 
      temp.z = 0; // earth gravity factor, g = 9.81 m/s2
	ph_SetGravity(temp); // set gravity
my.enable_friction = on;	
my._event = bounce_event;
}

function bounce_event()
{
	if(event_type == event_friction)
	{
          //phent_addglobalforce here
	}
}  

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