A Feynman Sprinkler, Feynman inverse sprinkler or most correctly reverse sprinkler began as a thought experiment in explaining the workings of the reverse of a typical rotary lawn sprinkler. This experiment is commonly associated with and named after Richard Feynman though he did not come up with the problem or ever publish a solution to it, only helped popularize it in Surely You're Joking, Mr. Feynman! and other writings of his. It appeared in Science of Mechanics by Ernst Mach, published in 1893.

Explanation

The problem concerns what would happen if such a lawn sprinkler were submerged in water and water were sucked through it, flowing backwards. The possible outcomes are as follows: the sprinkler will spin forward; the sprinkler will spin backward; the sprinkler will not spin at all. There has been much debate in the past century over the solution. Feynman once attempted the experiment, "which ended in a minor catastrophic explosion". In recent years, the experiment has been performed many times, with air as the medium of the sprinkler, demonstrating that the "reverse" sprinkler does spin in the steady state. The University of Maryland also did the experiment on a very low friction bearing underwater and found that the sprinkler did indeed turn very slowly as if being sucked forwards. Although many experiments have been done, the scientific community still debates the validity of them because of the complex forces involved.

References

External links

• The Edgerton Center Corridor Lab: Feynman Sprinkler