Such Derivation About Viscosity's Calculation Formula of Verticul Capillary Tube Viscometer is Wrong

Objective:People do not know when the viscosity calculating formula of vertical capillary viscometer derived from Poiseuille Law in physical experiment teaching materials of medical colleges.In fact,this derivation is wrong and has deceived people of generations.In this article,the error is revealed and the correct derivation is given.Methods:First of all,in virtue of people's living experiences,the article reveals that the liquid flow rate in nonhorizontal pipes and vertical pipes don't comply with the law of Poiseuille,from which we know that the liquid flow rate in nonhorizontal pipes couldn't calculated by the Poiseuille's Law.And then,the paper illustrates that pressure at both ends of capillary of vertical viscometer approximately equals atmospheric pressure,and the pressure discrepancy P of both two ends is zero,thus we can know that P = ρgl is wrong.Results:By the two points mentioned above,it can be proved that we couldn't derive the viscosity calculating formula of vertical capillary viscometer by using of the Poiseuille's Law.Conclusions:The viscosity Calculating formula of vertical capillary viscometer can not choose but be deduced by using the liquid flow rate formula of nonhorizontal pipe,and this method is correct.