def update_balloon(self, b):
        b.x += b.vx
        b.y += b.vy 

        if b.x < 100 or b.x >= self.bounds.width - 100:
            b.vx = -b.vx

        if b.y < -100:
            self.balloons.remove(b)

        self.queue_draw_balloon(b)