Duplicate problem

im trying t make a simple effect. what i want to do is when you moev the mouse a duplicate of a ball is made to the position of the mouse and then it falls down towards the bottom of the screen. my problem is that i cant figure out the code to get all of my duplicate balls falling down at once. im not sure whether it needs a for function but im not really sure on what that is. my code is this :


i = 1;
onMouseMove = function () {
 i = i+1;
 duplicateMovieClip(_root.ball, "ball"+i, i+1);
 _root["ball"+i]._x = _root._xmouse;
 _root["ball"+i]._y = _root._ymouse;
 onEnterFrame = function () { _root["ball"+i]._y += 10;};
};

any help is appreciated
thanks
woopsedoo