code: def vel_critical(self):
          
          return (4 / (3 * math.pi) * (2 * pc.gravity * self.hl) ** (1 / 2)).to(u.m/u.s)
docs: The average vertical velocity of the water inside the LFOM pipe
          at the very bottom of the bottom row of orifices The speed of
          falling water is 0.841 m/s for all linear flow orifice meters of
          height 20 cm, independent of total plant flow rate.