         gameView.addSubview(dropView)
         
         gravity.addItem(dropView)
+        collider.addItem(dropView)
     }
 }
 

    
    let gravity = UIGravityBehavior()
    
    lazy var animator: UIDynamicAnimator = {
        let lazilyCreatedDynamicAnimator = UIDynamicAnimator(referenceView: self.gameView)
        return lazilyCreatedDynamicAnimator

    override func viewDidLoad() {
        super.viewDidLoad()
        animator.addBehavior(gravity)
        animator.addBehavior(collider)
    }
    
    var dropSize: CGSize {
