// put gravity on box
scene.addForce( new GravityForce(box));
// create a trigger to detect contact forces with some threshold
scene.addTrigger(new ContactTrigger(box, 2.0, new Callback(){
@Override
public void contactAboveThreshold(Body interactingBody,
ContactConstraint constraint) {
System.out.println("In contact with " + interactingBody );
}