We have performed an experiment in which we have determined the viscosity of air using the
Hagen–Poiseuille equation in the proper range of the Reynolds number (Re). The experiment is novel
and simple which students even at high school level can perform with minimal equipment.The
experiment brings out the fact that determination of viscosity of a fluid is possible only when its
Reynolds number is sufficiently small. At very large Reynolds number, the gas behaves more like an
inviscid fluid and its flow rate satisfies Bernoulli’s equation. In the intermediate range of the
Reynolds number, the flow rate satisfies neither the Hagen–Poiseuille equation nor the Bernoulli
equation. A wide range of Reynolds numbers from 40 to about 5000 has been studied. In the case of
air, this large range has not shown any sign of turbulence.