private function init():void
    {
     stage.scaleMode = StageScaleMode.NO_SCALE;
     stage.align=StageAlign.TOP_LEFT;
     
     stage.frameRate = 100;
     ball = new animation_ch19_Ball();
     ball.x = stage.stageWidth / 2;
     ball.y = stage.stageHeight / 2;
     vx = 300;
     vy = -300;
     addChild(ball);
     time = getTimer();
     addEventListener(Event.ENTER_FRAME, onEnterFrame);
    }