Stopping movie clips

Hi

I have a problem stopping movie clips in flash. I have two move clips on main time line. One name for script is ball other is ball1. They are two different movie clip simbols they are not just different instances. If i put stop(); on the first frame it stops both of them. How do i stop only one. I tried:

ball.stop();

and

ball.addEventListener(Event:ENTER_FRAME, stop_ball)
function stop_ball(evt:Event):void {
stop();
}

and

ball.addEventListener(Event:ENTER_FRAME, stop_ball)
function stop_ball(evt:Event):void {
ball.stop();
}

It does not work. What am i doing wrong? Please i need some advice. Tnx in advance.