private function init():void
    {
     stage.scaleMode = StageScaleMode.NO_SCALE;
     stage.align = StageAlign.TOP_LEFT;
     ball = new animation_ch10_Ball(20);
     addChild(ball);
     ball.x = 100;
     ball.y = 50;
     
     // create five lines
     lines = new Array();
     for(var i:uint = 0; i < numLines; i++)
     {
      var line:Sprite = new Sprite();
      line.graphics.lineStyle(1);
      line.graphics.moveTo(-50, 0)
      line.graphics.lineTo(50, 0);
      addChild(line);
      lines.push(line);
     }