Observation of Torque Exerted by Pure Superflow

Pure superflow is observed to exert a torque in flowing about an object of arbitrary shape. The magnitude of such torque agrees in every respect with expectations based on pure potential flow theory. The present results indicating pure potential flow for superfluid are considered to constitute the complementary experiment to the earlier Craig-Pellam investigation of zero lift for superflow. We consider that these two experiments taken together establish completely the pure potential flow property for superfluid by verifying that (a) zero force, but (b) a prescribed torque are exerted upon an object of arbitrary shape and orientation. As a by-product to the present investigation, an independent evaluation of $\frac{{\rho }_s}{\rho }$ for liquid helium is obtained in conformity with earlier measurements.