Rueckner, Wolfgang2016-06-292015Rueckner, Wolfgang. 2015. “The Puzzle of the Steady-State Rotation of a Reverse Sprinkler.” American Journal of Physics 83 (4) (April): 296–304. doi:10.1119/1.4901816.0002-9505http://nrs.harvard.edu/urn-3:HUL.InstRepos:27413727The continuous rotation of the reverse sprinkler has been a puzzle for over two decades. This article presents a series of experiments that demonstrate that a properly designed reverse sprinkler experiences no steady-state torque and does not rotate. Ignoring transients when the flow starts and stops, if any sustained rotation of the reverse sprinkler occurs, it is because a force couple produces a torque accompanied by vortex flow inside the body of the sprinkler. No steady-state rotation occurs if the vortex is suppressed or prevented from forming in the first place. Demonstrative proof is given that an ideal reverse sprinkler does not rotate.en-USJournal Article2016-05-0620152016-06-2910.1119/1.4901816