Started by Samuel Okafor (@samokafor) ·
what does a sprinkler do if you run it backwards
6 sources · 34 min down the hole
How I got here
- Started with
- If a sprinkler sucks water in instead of spraying it out, does it turn?
- Ended at
- “Feynman reverse sprinkler solved”
The Trail
- “reverse sprinkler which way does it spin” (google.com)
- Feynman sprinkler (en.wikipedia.org)
feynman's attempt at princeton apparently ended with a glass jug exploding
- Richard Feynman (en.wikipedia.org)
- Ernst Mach (en.wikipedia.org)
the question goes back to mach in the 1880s, way before feynman
- “nyu reverse sprinkler 2024 experiment” (google.com)
- “Feynman reverse sprinkler solved” (hn.algolia.com)
What I came away with
A 2024 NYU experiment with a very low-friction sprinkler found it does turn, slowly, in the opposite direction to a normal sprinkler. The answer comes down to subtle flows inside the body of the sprinkler, which is why simple momentum arguments kept giving people different answers.
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