private function onEnterFrame(event:Event):void
    {
     var x1:Number = ball.x - stage.stageWidth / 2;
     var y1:Number = ball.y - stage.stageHeight / 2;
     var x2:Number = cos * x1 - sin * y1;
     var y2:Number = cos * y1 + sin * x1;
     ball.x = stage.stageWidth / 2 + x2;
     ball.y = stage.stageHeight / 2 + y2;
    }
   }
  }