   var animator: UIDynamicAnimator?
   var gravity: UIGravityBehavior?
   var collision: UICollisionBehavior?
+  
+  var panGesture: UIPanGestureRecognizer?
   
   override func viewDidLoad() {
     super.viewDidLoad()

    // Dispose of any resources that can be recreated.
  }
  
}

    // Add gravity to the animator
    self.animator!.addBehavior(self.gravity)
    self.animator!.addBehavior(self.collision)
    
    // add pan getsture recognizer
    self.panGesture = UIPanGestureRecognizer(target: self, action: "panning:")
    self.greenBox!.addGestureRecognizer(panGesture!)
  }
  
  override func didReceiveMemoryWarning() {
