How Physicists FINALLY Solved the Feynman Sprinkler Problem - Explained

I think if your sprinkler is underwater then your grass is probably wet enough.

Imagine being so smart that a Problem gets Your name because you could NOT solve it.

When I was a physics grad student in the 80s I disagreed with a professor about an E&M problem - the prof was a real *sshole about it and I was sure I was right. I phoned up Feynman at his home (he was in the directory!) and asked him his opinion. He told me I was right (this story ended up doing the rounds at UCI) and he asked me the sprinkler problem. I gave a few different answers that I said were naïve answers (which are covered in your video!), and that I was unsure. He told me to call him back when I had my answer. Overall we had a 45 minute conversation - I felt very honored. I became disappointed in myself as I never got a fully convincing answer so never called him back, and he died in 1988. I felt like I had failed the great man - until I saw your video today!!!!

Am I the first person to notice that the description of Feynman's experiment is wrong? Actually, he tried to pump air into the top of the carboy to push the water backwards through the tubing; he didn't suck the water out of the tube. Eventually the pressure blew the carboy apart. See "Surely You're Joking, Mr. Feynman" at the end of Part 2: The Princeton Years.

Why didn't they repeat the experiment with internal tubes pointing upwards to cancel the vortex?

"Feynman was keenly aware of his own abilities and almost entirely unburdened with modesty" - the sentence where I clicked Subscribe.

"almost entirely unburdened by modesty." That is the greatest description of Feynman! He wasn't so much arrogant as bereft of any desire to not be arrogant.

6:42 "Sucking is not the opposite of blowing" lol

This seems more a function of the specific design of the sprinkler internals. If the pipes were angled to have the vortices' sizes inverted it could be made to rotate in the other direction.

I'm giving you a thumbs up for excellent audio quality, no over powering music and clear responses. Great work here.

These are the types of videos that make me glad to study physics in college. I guessed right in the first part, surmised the opposite in the second part, and I was happy with the result in the third part. Always adapting to new information and ideas.

Me, skipping randomly on work through the video: 7:37 "[...] Interestingly here due to our slightly imprecise use of language when we describe sucking and blowing [...]" With a humor stuck stil in puberty this line without context humours me a little.

I wish they would have redesigned the test so the arms of the sprinkler don't have that central cavity for the vortexes to form. They could have brought the two tubes together in an upside down Y with the leg of the inverted Y pointing straight up in the center -- that should eliminate those vortexes that were contributing rotational forces.

TLDR: The 100 year old answer of "depends on what engineering choices you pick to have the most effect" is the right one and nothing was actually discovered beyond why small house vacuums often have the intake opening on the side which was also known for quite a while.

That meniscus bearing is cool. I wonder where this idea came from? Can this be used to create frictionless bearings for more practical applications?

A while ago I saw a YouTube video that immediately came to mind. My first thought was also that pressure is equally everywhere in every direction, by the way. But the video was about a simple vertical (PVC) pipe connected to a vacuum cleaner. It was mounted to the side of a table, but not actually fixated in place. When the vacuum cleaner turns on, the pipe moves up a bit. Conclusion was that the air that is right next to the pipe gets sucked in with a sling-shot motion and the centrifugal force that came with it, pulls the pipe up. It also heavily depends on the shape of the rim: a well rounded edge pulls less.

It took 140 years to put a sprinkler underwater.

to the people saying they only got this answer because of the way they designed their sprinkler: they also did all of the calculations and math derivations so you can now predict the movement of many sprinkler designs, not just the one they actually built.

i had a feeling the fan topic was gonna be brought up and lo and behold, 6:42 comes up

It would have been interesting for the researchers to simplify the validation of the force that rotates the "sucking" sprinkler backwards by building a second and third sprinkler that has the arms exiting the the reservoir body at both an obtuse and acute angle relative to the axis of rotation while the arm exit into the open water chamber is in the identical location as the main experiment. This would confirm that changing this specific variable alters the direction of the "sucking" sprinkler, without needing to visually interpret the laser-illuminated particle flows. Very cool and enlightening problem !