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705,548 Views • Mar 10, 2024 • Click to toggle off description
Read the paper here:
Centrifugal Flows Drive Reverse Rotation of Feynman’s Sprinkler; Kaizhe Wang, Brennan Sprinkle, Mingxuan Zuo, and Leif Ristroph, Phys. Rev. Lett. 132, 044003 journals.aps.org/prl/abstract/10.1103/PhysRevLett.…
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#breakthrough #physics #science #mystery
Chapters:
00:00 What Is Feynman's Reverse Sprinkler Problem?
0:48 The History Of The The Feynman Sprinkler
3:32 Why Does A Sprinkler Spin?
6:42 Suction Vs Blowing: Airflow & Velocity
8:17 The Experiment
12:37 The Results: Mystery Solved?
13:41 Explanation and Visualising The Results
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Views : 705,548
Genre: Science & Technology
Date of upload: Mar 10, 2024 ^^
Rating : 4.864 (780/22,138 LTDR)
RYD date created : 2024-05-02T13:08:09.177197Z
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YouTube Comments - 2,026 Comments
Top Comments of this video!! :3
Imagine being so smart that a Problem gets Your name because you could NOT solve it.
3.5K |
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!!!!
116 |
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.
328 |
"Feynman was keenly aware of his own abilities and almost entirely unburdened with modesty" - the sentence where I clicked Subscribe.
809 |
Why didn't they repeat the experiment with internal tubes pointing upwards to cancel the vortex?
1.1K |
"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.
29 |
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.
16 |
I'm giving you a thumbs up for excellent audio quality, no over powering music and clear responses. Great work here.
211 |
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.
913 |
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.
11 |
I think it is possible to analyze the problem in a simpler way by breaking it down.
1/ pumping fluid quickly inside a simple tube with an entry and exit generates strong pushing thrust at the exit, and weak pulling thrust at the entry. this can probably be measured independently using load cells. the thrust can be converted into movement/rotation or a stationary force/torque, it doesnt matter. this is highlighted by jet ski having the jet exit direction controling the thrust, while the intake is directed forward and downward (not straight forward) and doesnt change direction for forward or reverse operation
2/ if you now have several exits, and several entries, the overall thrust will be approximately the sum of the exit thrusts
3/ if exit thrusts cancel each others approximately, then the intake thrusts can become prevalent
4/ if exits streams point at each or at fixed objects other weird turbulence and vortices will happen and create additional secondary effects way more complicated to study and probably cant be predicted without numeric simulation and understood through experimentation
5/ even it the main exit thrusts cancel each other, those secondary effect could still outweight intake thrusts. THIS IS probably the ONLY CONCLUSIION of this experiment?
6/ the rotating part of a sprinkler should be analyzed like a freely rotating system with entries and exits for fluid to be pumped through
7/ the traditional sprinkler has several exits which combined generate a clear torque, stronger than any effec onthe sucking side, the intakes don't matter
8/ the generic sucking sprinkler achieved using any sprinkler, with reversed pumping action, is designed wihout any attention to the blowing side , and because of this, has undetermined behavior
8/ the sprinkler shown in this experiment is seemingly designed to cancel the effects of the blowing side to show the effect of the sucking side (by using symetrical exits, pointing at the center, but failed to do so because asymetrical flows and resulting asymetrical vortices
1 |
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.
429 |
It took 140 years to put a sprinkler underwater.
246 |
That meniscus bearing is cool. I wonder where this idea came from? Can this be used to create frictionless bearings for more practical applications?
8 |
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.
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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.
138 |
Are you telling me that not one person decided to bend the tubes upward toward the pump—rather than just ending them at cavity where they point at each other—in order to basically remove the vortices entirely?
It's like the question hasn't been answered at all, at this point.
379 |
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.
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Truly wonderful. Not only massively educational and interesting but presented by THE most beautiful, hypnotic imagery. Simply brilliant and full marks to all those involved. Thanks Ben. Cheers 🍺
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@lewis_r_
1 month ago
I think if your sprinkler is underwater then your grass is probably wet enough.
6.6K |