'Feynman and followers, you guys are off': Physicists disprove decades-old Richard Feynman theory on 'silly' sprinklers
Physics & Mathematics
Seven "silly" sprinklers with spiral and counter-bent arms just dismantled both Feynman's and Ernst Mach's decades-old theories about which way a reverse sprinkler spins.
Angular Momentum ConservationFluid DynamicsFalsificationismNewton's Third Law
Theory Briefing
- Feynman's own 1940s experiment ended with a shattered glass sprinkler and no clear answer — leaving the reverse-sprinkler question open for 80 years.
- NYU physicist Leif Ristroph built seven deliberately weird sprinkler shapes, including one with arms spiraling multiple times, to pit the leading theories head-to-head.
- Feynman's theory predicted that reversing the nozzle bend would flip the spin direction — it didn't, forcing the team to declare 'Feynman and followers, you guys are off.'
- Mach's rival theory predicted the spiral design would spin dramatically differently due to extra angular momentum inside the arms — the solid structure 'barely cared.'
- The real driver turned out to be the central hub, where colliding water generates a momentum flux that the sprinkler pushes back against — the same physics as a forward sprinkler, just flipped inside-out.