ball1_mc.speed = ball2_mc.speed = 0;
var accel = 1;
var boundPos = 200;
function bound () {
	this._y += this.speed;
	if (this._y >= boundPos) {
		this.speed *= -1;
	} else {
		this.speed += accel;
	}
}
ball1_mc.onEnterFrame = bound;
ball2_mc.onEnterFrame = bound;