code: def resistance(self):
          
          self.total_resistance_coef = frictional_resistance_coef(self.length, self.speed) + \
                                  residual_resistance_coef(self.slenderness_coefficient,
                                                           self.prismatic_coefficient,
                                                           froude_number(self.speed, self.length))
          RT = 1 / 2 * self.total_resistance_coef * 1025 * self.surface_area * self.speed ** 2
          return RT
docs: Return resistance of the vehicle.
  
          :return: newton the resistance of the ship