{"id":761097,"date":"2026-07-13T21:27:08","date_gmt":"2026-07-13T21:27:08","guid":{"rendered":"https:\/\/www.newsbeep.com\/us\/761097\/"},"modified":"2026-07-13T21:27:08","modified_gmt":"2026-07-13T21:27:08","slug":"solution-to-feynmans-reverse-sprinkler-puzzle-also-applies-to-silly-sprinklers","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/us\/761097\/","title":{"rendered":"Solution to Feynman’s reverse sprinkler puzzle also applies to “silly sprinklers”"},"content":{"rendered":"

Watering your lawn in the summer can be both pragmatic and fun with so-called \u201csilly sprinklers<\/a>,\u201d designed to create amusing loops and spirals of water jets. And there\u2019s some fascinating physics at work to boot. Researchers at New York University\u2019s Courant Institute conducted a series of experiments with different silly sprinkler designs to find the answer to a longstanding problem in fluid dynamics, according to a new paper published in the Proceedings of the National Academy of Sciences.<\/p>\n

As previously reported<\/a>, the reverse sprinkler problem is associated with physicist Richard Feynman because he popularized the concept, but it actually dates back to a chapter in Ernst Mach\u2019s 1883 textbook The Science of Mechanics (Die Mechanik in Ihrer Entwicklung Historisch-Kritisch Dargerstellt). Mach\u2019s thought experiment languished in relative obscurity until a group of Princeton University physicists began debating the issue in the 1940s.<\/p>\n

Feynman was a graduate student there at the time and threw himself into the debate with gusto, even devising an experiment in the cyclotron laboratory to test his hypothesis.\u00a0One might intuit that a reverse sprinkler would work just like a regular sprinkler, merely played backward, so to speak. But the physics turns out to be more complicated. \u201cThe answer is perfectly clear at first sight,\u201d Feynman wrote in Surely You\u2019re Joking, Mr. Feynman<\/a> (1985). \u201cThe trouble was, some guy would think it was perfectly clear [that the rotation would be] one way, and another guy would think it was perfectly clear the other way.\u201d<\/p>\n

Mach proposed that there would be no rotation with a reverse sprinkler: the reaction force on the nozzle as it sucks in water pulls the nozzle counter-clockwise, while the water flowing into the inside of the nozzle pushes it clockwise. The two forces cancel each other out in this steady-state scenario. Feynman\u2019s own experiment showed a slight tremor when pressure was first applied to pump water through the nozzle, and then the sprinkler returned to its original position and remained still.<\/p>\n","protected":false},"excerpt":{"rendered":"Watering your lawn in the summer can be both pragmatic and fun with so-called \u201csilly sprinklers,\u201d designed to…\n","protected":false},"author":2,"featured_media":761098,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[32],"tags":[79],"class_list":["post-761097","post","type-post","status-publish","format-standard","has-post-thumbnail","category-science","tag-science"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts\/761097","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/comments?post=761097"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts\/761097\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/media\/761098"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/media?parent=761097"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/categories?post=761097"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/tags?post=761097"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}