Oscillations of Liquid Helium in a U-Tube

Abstract

Frictional forces in He II were studied by observing the decay of free oscillations in a U-tube. The decay, unlike that for ordinary liquids (including He I), is characterized by two logarithmic decrements: one for amplitudes of oscillation below about 0.1 cm, and another for amplitudes between about 0.2 and 1 cm. The values of these two decrements agree with the results of a hydrodynamical calculation which assumes that for the lower range of amplitudes the two-fluid equations of Landau and Tisza hold, and that for the other range of amplitudes the normal and superfluid components have identical velocity fields. The values for the viscosity coefficient deduced from the observations agree roughly with each other and with the published results of other methods. Despite the large experimental error, there is evidence that the viscosity when the two components move together is higher than the viscosity of the normal component when the two-fluid equations hold, the ratio being about 1.33:1.