# A Decades-Old Conundrum: Mathematicians Finally Solve Feynman's "Reverse Sprinkler" Problem

Mathematicians have finally cracked the reverse sprinkler problem, a conundrum that has puzzled scientists since the 1940s. The solution challenges conventional wisdom and could have implications for controlling fluid flows.

## The Reverse Sprinkler Problem

Physicists have long been perplexed by the "reverse sprinkler" problem. While a typical lawn sprinkler releases jets of water to rotate the wheel, what would happen if the water were sucked into the sprinkler instead? Would the wheel turn in the opposite direction or not at all? This problem has intrigued scientists since the 1940s.

Recently, mathematicians at New York University published a paper in the journal Physical Review Letters claiming to have solved the conundrum. They combined precision lab experiments with mathematical modeling to explain how a reverse sprinkler operates.

The surprising result is that the reverse sprinkler spins in the opposite direction when taking in water as it does when ejecting it. The cause of this unexpected behavior is subtle and challenges conventional wisdom on the matter.

## The Work of Leif Ristroph's Lab

The lab of co-author Leif Ristroph at NYU's Courant Institute frequently tackles real-world puzzles. In the past, they have fine-tuned the recipe for the perfect bubble and studied the formation processes of stone forests in China and Madagascar. Ristroph's lab also built a working Tesla valve and delved into the aerodynamics of paper airplanes.

Their diverse range of research projects demonstrates their expertise in solving complex scientific problems. By combining experimental data and mathematical modeling, they are able to unravel the mysteries behind these phenomena.

## History of the Reverse Sprinkler Problem

Although the reverse sprinkler problem is often associated with Richard Feynman, it actually dates back to a chapter in Ernst Mach's 1883 textbook. Mach's thought experiment remained relatively unknown until a group of physicists at Princeton University started debating the issue in the 1940s.

Feynman, who was a graduate student at Princeton at the time, became heavily involved in the discussion and even conducted an experiment in the cyclotron laboratory to test his hypothesis. The problem continued to baffle scientists due to the differing interpretations of the physics involved.