if(dist < minDist)
      {
       var angle:Number = Math.atan2(dy, dx);
       var tx:Number = centerBall.x + Math.cos(angle) * minDist;
       var ty:Number = centerBall.y + Math.sin(angle) * minDist;
       ball.vx += (tx - ball.x) * spring;
       ball.vy += (ty - ball.y) * spring;
      }
     }
    }