if(ball.x + ball.radius > stage.stageWidth)
     {
      ball.x = stage.stageWidth - ball.radius;
      ball.vx *= bounce;
     }
     else if(ball.x - ball.radius < 0)
     {
      ball.x = ball.radius;
      ball.vx *= bounce;
     }
     if(ball.y + ball.radius > stage.stageHeight)
     {
      ball.y = stage.stageHeight - ball.radius;
      ball.vy *= bounce;
     }
     else if(ball.y - ball.radius < 0)
     {
      ball.y = ball.radius;
      ball.vy *= bounce;
     }
     
     // check each line
     for(var i:uint = 0; i < numLines; i++)
     {
      checkLine(lines[i]);
     }
    }