Every summer, lawns fill with colorful "silly sprinklers," whose looping and twisting tubes send water spraying in unusual patterns. Their designs may look playful, but researchers have now used these backyard devices to investigate a serious and decades-old question in physics.
The mystery is known as Feynman's Sprinkler Problem. It asks what happens when a sprinkler operates in reverse, pulling water into its arms instead of forcing water outward. By building and testing sprinklers with a variety of shapes, a team of mathematicians has now produced a clear experimental answer. Their results also offer broader insight into how moving fluids push, twist, and rotate physical structures.
"This work provides the experimental answer for Feynman's Sprinkler Problem by showing, across several sprinkler types, how the angular momentum of water flows drives sprinklers' rotation," explains Leif Ristroph, an associate professor at New York University's Courant Institute School of Mathematics, Computing, and Data Science and the senior author of the paper, which appears in the journal Proceedings of the National Academy of Sciences.
Why the Sprinkler Problem Matters
The researchers say the findings are useful for more than settling a famous scientific puzzle. Understanding how objects react to moving fluids could help engineers improve machines that capture or convert energy from flowing liquids.
