NEW YORK, NY – For over a century, physicists have been fascinated by the question of how a sprinkler would rotate if it were underwater, drawing in water instead of expelling it. This long-standing puzzle, known as “Feynman’s sprinkler,” has finally been answered by a team of researchers at New York University.
The inquiry into the rotation of a reverse sprinkler dates back to the 1880s, but it resurfaced in the mid-20th century thanks to renowned physicist Richard Feynman. Despite various attempts to address the question, it remained a mystery for decades.
Now, NYU researchers have conducted groundbreaking experiments to uncover the mechanics behind the rotation of a reverse sprinkler. Using an underwater setup with ultra-low-friction bearings, they were able to observe water flow through the device as it freely spun, shedding light on its rotational behavior.
To capture the phenomenon, the team dyed the water, added microparticles, and illuminated it with bright green lasers, recording the process with high-resolution, high-speed cameras. The resulting footage provided captivating insight into the peculiar rotation of the reverse sprinkler.
Published in Physical Review Letters, the team’s findings revealed that the reverse sprinkler indeed rotates in the opposite direction of a regular sprinkler. Lead researcher Leif Ristroph explained that while a forward sprinkler propels itself by shooting out jets of water, a reverse sprinkler’s rotation is driven by the inward water flow and the internal collisions of sucked-in jets.
Furthermore, the experiment’s methods hold promise for practical applications involving devices responding to flowing air or water, according to co-author Brennan Sprinkle of the Colorado School of Mines. This research marks a significant milestone in the study of fluid dynamics, providing a long-awaited answer to a question that has puzzled scientists for well over a century.