//MovieClip:ball1_mc,ball2_mc
onClipEvent (load) {
    speed = 0;
    accel = 1;
    boundPos = 200;
}
onClipEvent (enterFrame) {
    this._y += speed;
    if (this._y >= boundPos) {
        speed *= -1;
    } else {
        speed += accel;
    }
}

var speed = 0;
var accel = 1;
var boundPos = 200;
function bound () {
    this._y += speed;
    if (this._y >= boundPos) {
        speed *= -1;
    } else {
        speed += accel;
    }
}

ball1_mc.onEnterFrame = bound;
ball2_mc.onEnterFrame = bound;