docs: def force(self, Ly=None):
          '''
          Estimate the applied force (in Newtons) on a drop according to the
          electromechanical model [1].
  
              Ly is the length of the actuated electrode along the y-axis
                  (perpendicular to the direction of motion) in milimeters. By
                  default, use the square root of the actuated electrode area,
                  i.e.,
                      Ly=Lx=sqrt(Area)
                  To get the force normalized by electrode width (i.e., in units
                  of N/mm), set Ly=1.0.
  
          1. Chatterjee et al., "Electromechanical model for actuating liquids in
             a two-plate droplet microfluidic device," Lab on a Chip, no. 9
             (2009): 1219-1229.
          '''
          if self.calibration._c_drop:
              c_drop = self.calibration.c_drop(self.frequency)
          else:
              c_drop = self.capacitance()[-1] / self.area
          if self.calibration._c_filler:
              c_filler = self.calibration.c_filler(self.frequency)
          else:
              c_filler = 0
          if Ly is None:
              Ly = np.sqrt(self.area)
          return 1e3 * Ly * 0.5 * (c_drop - c_filler) * self.V_actuation()**2