Feynman sprinkler

The device generally remains steady with no rotation, though with sufficiently low friction and high rate of inflow, it has been seen to turn weakly in the opposite direction of a conventional sprinkler.

"[2] In the early 1940s (and apparently without awareness of Mach's earlier discussion), the problem began to circulate among members of the physics department at Princeton University, generating a lively debate.

Richard Feynman, at the time a young graduate student at Princeton, built a makeshift experiment within the facilities of the university's cyclotron laboratory.

In an article written shortly after Feynman's death in 1988, John Wheeler, who had been his doctoral advisor at Princeton, revealed that the experiment at the cyclotron had shown “a little tremor as the pressure was first applied [...] but as the flow continued there was no reaction.”[5] The sprinkler incident is also discussed in James Gleick's biography of Feynman, Genius, published in 1992 where Gleick claims that a sprinkler will not turn at all if made to suck in fluid.

[6] In 2005, physicist Edward Creutz (who was in charge of the Princeton cyclotron at the time of the incident) revealed in print that he had assisted Feynman in setting up his experiment and that, when pressure was applied to force water out of the carboy through the sprinkler head, There was a little tremor, as [Feynman] called it, and the sprinkler head rapidly moved back to its original position and stayed there.

Most of the published theoretical treatments of this problem have concluded that the ideal reverse sprinkler will not experience any torque in its steady state.

[12] An analysis of the actual distribution of forces and pressure in a non-ideal reverse sprinkler provides the theoretical basis to explain this: Differences in the regions over which internal and external forces act constitute a force-couple with different moment arms consistent with reverse rotation... the resulting flow-field asymmetry developed downstream from the sprinkler-arm bends supports the role of vortices in reverse sprinkler rotation by suggesting a mechanism for generating vortices in a consistent direction.