Leif Ristroph and Applied Mathematics Lab Team Settle Feynman’s Sprinkler Problem

July 15, 2026

Professor Leif Ristroph and collaborators Jesse Etan Smith, Mingxuan Zuo, Will Kuhlke, and Brennan Sprinkle have settled the long-standing Feynman Sprinkler Problem in a new research paper published this week. The question—debated since the 1880s and made famous in the 1980s by physicist Richard Feynman—revolves around reverse sprinklers. Feynman asked whether submerged sprinklers sucking in water would rotate at all or spin in the opposite direction of standard lawn sprinklers. Turns out it's a surprisingly difficult question to answer, and one with many potential applications to fluid and air flow problems.

In a series of experiments in Courant's Applied Mathematics Laboratory, the team found that the submerged sprinkler sucking in water spun in the opposite direction to a typical sprinkler expelling water and at a much slower speed. Their new paper in journal Proceedings of the National Academy of Sciences confirmed this is true even for "silly sprinkler" shapes with additional arms or bends in those arms. With the publication, "This Feynman problem, as put by Feynman — this is solved,” Professor Detlef Lohse told the The New York Times, whose coverage of the breakthrough currently leads their Science section.

You can read more about the research process and potential applications on NYU News.