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

@SidneyPatrickson

2 ай бұрын

Thats why you run it in reverse.

@unknowngamer37415

2 ай бұрын

😂

@jackmclane1826

2 ай бұрын

This is why they want to pump the water back out... ;)

@garymemetoo2238

2 ай бұрын

"If SOME is GOOD and MORE is BETTER then absolutely TOO MUCH should be just about RIGHT." Had some tee shirts made up years ago memorializing a meeting where a senior VP went around basically chanting the first two-thirds of this quote in his presentation. When I added the last third during a lull in the chanting, the VP just stared at me with a stunned look. The President took a liking to me right then and there and made sure I was included in more meetings, which were occasionally not fun.

@TheRealFOSFOR

2 ай бұрын

Yeah. And besides needing a reverse sprinkler you'd have to invest in a seaweedwacker.

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

@williamtopping

2 ай бұрын

Sounds more like an ego problem than anything else

@gerryjamesedwards1227

2 ай бұрын

I think Mr. Sprinkle got involved in case it gets to be known as the Sprinkle Sprinkler.

@MichaelWinter-ss6lx

2 ай бұрын

I don't see the ego problem when Feynman didn't name it himself.

@custos3249

2 ай бұрын

Sure thing, Einstein

@tikaanipippin

2 ай бұрын

Most mathematical problems that are waiting for a solution are named after smart mathematicians who could not find a solution. Q.E.D. Once the problem is solved, it does not take on the name of the successful first solver.

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!!!!

@S3IIL3CT

Ай бұрын

that is awesome, having been able to ask feynman about your problem :D

@jeffk8019

Ай бұрын

I was a chem/physics student at UC Irvine in the 80s. Any chance you could hint at the prof's name? (Edited to clarify university).

@NightVisixn

27 күн бұрын

Rest in Peace

@jbtait4268

5 күн бұрын

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.

@001variation

Ай бұрын

Makes a lot more sense, I'm sitting here wondering how on earth he broke the tank by just sucking in water

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

@yarati4584

2 ай бұрын

For me it was this one: "... and this year's entry for nominative determinism, Brennan Sprinkle."

@tamask001

2 ай бұрын

Yep, that was firmly in second place for me too!

@oxiosophy

2 ай бұрын

and a huge sexist at the same time

@harshvardhan4771

2 ай бұрын

​@@oxiosophy let me guess, you don't believe that Feynman was a great person academically and otherwise, right?

@frohnatur9806

2 ай бұрын

How does modesty burden one, except for the burden on the ego?

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

@TankR

2 ай бұрын

For the same reason it took them so long to.....just freaking build an apparatus and test it..... Because physicists aren't as smart as engineers ;) Id argue if this is the effect at play then they obviously could manipulate the tube runs to reverse the reversed reversal of the reversed flow....ya know, but backwards.

@LeeBrenton

2 ай бұрын

exactly my point - you said it clearer.

@ThePaulv12

2 ай бұрын

@@TankR Yeah they could've just used the local swimming pool at the deep end. Mythbusters would've.

@ThePaulv12

2 ай бұрын

I just wrote that above. You beat me to it lol. I have a couple of variations in my comment. One was to use pressure instead of suction.

@LeeBrenton

2 ай бұрын

yes, it shouldn't matter hey.@@ThePaulv12

"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.

@jacksimpson-rogers1069

Ай бұрын

I think you're not quite right. He really really wished to avoid being given any credit for one skill on the basis of something that had nothing to do with it. He didn't put his name Feynman on the drawings and portraits he was good at.

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.

@metalheadmax09

Ай бұрын

They also called the simulation PIV...

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.

@clockworkvanhellsing372

2 ай бұрын

Yeah, after watching the video, I still have the feeling that this massivly depends on thd design of the sprinkler. Of you'd add an infinite ammount of arms, you'd end up with something simmelar to a tesla turbine, which would possibly spin in the other direction. And a different hub layout might also form the center vortecies in a different way.

@lockeisback

2 ай бұрын

my thought exactly. they could even bend them parallel before joining along their sides to preserve laminar flow. to the point that even there the cumulative outer track of water would still move faster and might still cause slight asymmetries: then there is probably a way to angle the inlet jets entering the central chamber to compensate for the lopsided velocities. just angle them until all 4 vortices are equal. there's probably a million variations you could build, but I'm betting per design, there is a small adjustment which preserves the behavior with water flowing out, but which is balanced when water flows in. its not about principle, its about which of like 7 minute balancing acts your current design happens to be failing the most, and that is the latent rotation being seen.

@tinkerstrade3553

2 ай бұрын

​@@clockworkvanhellsing372directional baffles could align all the vortices, I would think. Such a setup should eliminate now dampened speed, and making it more relative omnidirectionally.

@oldmech619

2 ай бұрын

The tip of the nozzle has a lower pressure than the surrounding water will pull the nozzles forward

@pingnick

2 ай бұрын

Excellent thought ALSO the fact that the outer curve away from the center has more surface area against which the incoming fluid would press against would seem to be relevant too (I’m not sure why it would matter vs fluid already in the tube though to be clear…) - even altering the laminar vs turbulent friction with varying materials there would impact things etc!?

It took 140 years to put a sprinkler underwater.

@bananaman3851

2 ай бұрын

lol

@fariesz6786

2 ай бұрын

precisely.

@salsamancer

2 ай бұрын

Well the optics might have been available to scientists 140 years ago but the lasers are a more recent invention. And the computer required to crunch the data for PIV even more so.

@Broockle

26 күн бұрын

@@salsamancer none of which is needed to put a sprinkler underwater

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

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

@ralph3333

Ай бұрын

Magnetic bearing: No.

@otm646

Ай бұрын

Fluid bearings like this are common in industry, both water, oil and the classic air bearing.

@crispinmiller7989

7 күн бұрын

@@otm646 FLUID bearings are common, but I don't think this concentric-MENISCUS bearing is -- did you actually look closely at how it works? I don't think it would provide enough radial stiffness for any uses except sensitive instrumentation.

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

@qazmatron

2 ай бұрын

* overpowering

@gannonruby1119

Ай бұрын

I don’t think he needs an explanation for every like

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.

@tikaanipippin

2 ай бұрын

If there was a suitably shaped baffle inside the sprinkler head, it could be therefore made to rotate slowly in any direction, or not at all, it seems. Normal sprinkler rotation, including overcoming friction, is surely mostly rocket science - reaction to the mass of the water sprayed in the opposite direction of rotation of the sprinkler head.

@utoddl

2 ай бұрын

They should have directed the internal jets upwards so all the incoming water streams are flowing in parallel before they are allowed to interact to avoid "spooky actions in a (hidden) vortex". IMO this experiment has not effectively addressed the original question.

@Qwarzz

2 ай бұрын

Yea, I have no idea why they had two tubes in this experiment. I assume three would cause similar vortices but how about just one tube so there wouldn't even be a need for a chamber like that? Could even have just round corners so there shouldn't be any noticeable vortices at any point.

@lisabenden

2 ай бұрын

Yeah, that's what I was thinking. I want to see what happens if they design a system to nullify these internal forces, and focus only on the water in the arms of the sprinkler.

@meateaw

2 ай бұрын

​@@lisabenden If you nullify the internal forces then you aren't actually testing the problem :) The internal forces are a result of the bends in the pipe. If you nullify them, then you will have to by definition design your "reverse" sprinkler, to impart forces onto the sprinkler system to counteract the "natural" designs rotation. By having pipes that bend, you end up with water flow that is not "centrered" in the pipe. This "non uniform flow" is the effect that causes the rotation.

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.

A while ago I saw a KZread 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.

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.

@D3nn1s

2 ай бұрын

Ye i thought the same. So if the sprinkler doesnt have cnc quality openings but instead a janky mold of some sort the answer would be completely different? How would the scenario play out if you used turbulent flow?

@TheSadowdragonGroup

2 ай бұрын

@@D3nn1sor if you had more than two intakes at various angles.

@invisalats841

2 ай бұрын

They basically engineered a sprinkler to get a result. That particular sprinkler design didn't exist until they made it. Its result is rather inconsequential. As the question was concise and the parameters were quite clear, the experiment used methods that eliminated mechanical friction, which exists in all functioning sprinklers. The mechanical friction was not a variable that needed elimination. The question was not "what would happen to a specially designed sprinkler submerged underwater if it sucked in water." It's a nice little experiment, but I don't think it actually answered the question. In fact, the design probably fails miserably at being an actual sprinkler.

@justlola417

Ай бұрын

No, the question is what is the result of the forces in that system. Mechanical friction and unaligned tubes would obscure the actual results, while this set up is what an "ideal" sprinkler would act like. This way, we discovered what actually had a predominant effect on the direction of rotation, which is the flow in the internal parts of the sprinkler, more than the liquid actually being sucked in or hitting that wall in the first bend in the tube

@justlola417

Ай бұрын

I would've loved it if they did other designs too to see how the angles and types of flow contribute to those vortexes, but this is still an interesting result

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.

@gg-gn3re

2 ай бұрын

Yea that's the most important part of this study IMO. The results were obvious and it's embarrassing this wasn't "solved" earlier as vacuums knew and solved this internal vortex issue several decades ago, thus I already knew the results. I figured this video was going over something that was solved in the 1990s or something but it's pretty sad looking at that date..

@mowskeeto2602

2 ай бұрын

Ooh that's neat

This was real fun to watch. Thank you a lot for this video.

That was actually remarkably informative and entertaining. Thank you.

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.

@marvin.marciano

2 ай бұрын

Hey English isn't my first language and I didn't understand your suggestion. Could you draw it and send a link?

@chicklucas6682

2 ай бұрын

What are you yapping about

@MelvinSabu

2 ай бұрын

Its simple, the video author explained about how the submerged sprinkler sucks in water and the individual legs of the sucking tubes are ending inside in a mutual opposite alignment (which is the reason for the submerged sprinler rotating backwards) But inorder to truly find out the sppinning effect by avoinding this new disturbance, both the sprinkler tubes can be bend 90 degrees and be taken entirely out from the water so that the problem of momentum interaction of water molecules inside the submerged sprinkler head will not arise. The true motive of the experiment can be served justice. Now did you get the idea ?@@marvin.marciano

@ferrumignis

2 ай бұрын

It wouldn't necessarily remove the vortices, just change their orientation. Any asymmetry means they could still provide a net force. I would rather see a design with just one nozzle (and a counterweight for balance) with the pipe having, as far as practical, a constant diameter from pump to nozzle.

@ferrumignis

2 ай бұрын

​@@chicklucas6682Are you genuinely unable to visualise what the OP describes?

I think it's because the geometry of the plenum wasn't specified, and the effect would disappear depending on the plenum's geometry. This seems more like experimental error unless the problem specifically states that the sprinkler has to have this specific plenum geometry. I assumed the sprinkler wouldn't move, but i also assumed the experiment would provide a suction via a 2:1 header with decent flow characteristics rather than dumping asymmetrical flow into an internal volume. Of course it would spin in revere in that case, but arbitrary changes to the internal volume can give any result. Care was taken to isolate the system from pump vibration, meniuscus bearing for lower friction, all this is pretty obvious and what i'd assume would be the setup, but i also would assume that the experiment would account for the internal geometry by using a low turbulence Y connection to the suction. As the problem was being described, i already thought of a siphon and meniscus bearing, as well as a fairly laminar internal structure. The experiment is specifically designed to give this result, and it can give the opposite result if the internal geometry contained baffles, guide fins, a rounded feature in which an axle/pivot bolt runs, or any number of possible configurations. When i design hovercraft hulls i use all kinds of tricks like this to negate lift motor torque by adjusting the plenum geometry.

@pixelsort

2 ай бұрын

Haha, I just read your comment after basically posting the same exact thing.

@jakeaurod

2 ай бұрын

I wonder, if they were able to perfectly match everything to minimize design biases influencing fluid dynamics, would we see outside forces acting to create a spin, such as Coriolis and gravitational effects from mass concentrations.

@emptyshirt

2 ай бұрын

I'd like to see the arms be offset from the axis of rotation to create an internal vortex that is opposite the observed head rotation direction. Make the arms reversible as well so they can create the forward internal vortex and see if there is a difference in speed. To me the rotation is obviously attributed to different pressure at the suction face and reverse side of each arm. That is where the external system interacts most strongly with the internal system.

@fnamelname9077

2 ай бұрын

In this case, though, isn't the force ultimately from the different total curvature of the inside and outside paths of the pipes? I know that the differential vortices are apparent at the center, but it seemed to me that the force arises as an imbalance in the suction experienced across the inside walls of the pipes. (The different speeds and sizes of the central vortices are therefor a result and not a cause.) It's surely true that you could overcome that by introducing other geometric facts at other locations. However, it would seem to remain true, that in a truly symmetric system, that the result obtained here should remain. Do you not think it so?

@rustymustard7798

2 ай бұрын

@@fnamelname9077In this specific internal geometry a rotation is imparted. The question isn't asked in terms of the effects of the internal geometry, but in terms of what effect the suction has in terms of imparting rotation. In this configuration the signal to noise ratio doesn't allow a valid result in terms of suction. If the internal geometry isn't fixed as a constant and can be anything that causes suction through the arms, i can easily design a range of internal geometry configurations to impart any desired rotation. And as for the differential in the pipe, it becomes a larger effect only because there are colliding differential flows. This will not hold true if there is only one tube, or three, or seven, or if the tubes were flush to the inside, or if those tubes were tapered, or angled, or mitered at the ends or, or and on and on. Unless the internal geometry of all sprinklers are an ansi standard, then all sprinklers will act differently, and the answer only applies t this specific case. The answer is that they answered the wrong question and call it solved because noise caused the result. This might just bother me enough to run this experiment myself with a setup capable of giving a result, it's not like it's hard to 3d print some tubes and siphon some water. And in the case that the confounding factor of internal vortices is accounted for, there's a whole other can of worms with the nozzle shape. Is the sprinkler arm tip just a cut off section of pipe? Does it have an internal taper? Beveled outer edges inducing Coanda effect? Something else like decorative plastic flowers that the water shoots out from? Everyone in Feynman's class disagreed because they all have different brand sprinklers a home lol.

nicely done and brilliantly scripted, illustrated, and produced ty for posting!

Thank you for this great insight in how to analyze and tes problems, great stuff.

"entry for nominative determinism" slayed me sir. bravo

I remember hearing about a problem that early jet aircraft had, especially those with intakes in the nose. It was called "inlet lift". At high angles of attack the air entering the inlet had to turn a corner, and this created a nose up force. This made stall recovery tough because adding power, i.e. afterburner, increased the effect.

@darkracer1252

2 ай бұрын

stall is a lack of lift. and you're saying now that increasing the total net lift is making stall worse.. are you daft? not to mention that same effect is happening at the bottom of the engine aswel in the opposite direction. and thus cancels itself out. you must be on drugs or something.

That was an eye opening demonstration of forces that I never thought about.

What a banger video! Excellent summary of their paper, there's so much to this

8:35 of course, Brennan _had_ to work this problem. fascinating 🖖

@Inimbrium

2 ай бұрын

There's a long history in the UK of people who's namesake became their job. My metalworking teacher was called Mr. Bolt.

@Intrafacial86

2 ай бұрын

For some reason, YT wanted my “feedback” on this comment.

@michaelgreco202

2 ай бұрын

Knowing him, 90% of his motivation for this was the joke.

@thecompanioncube4211

Ай бұрын

It was his calling

What a fascinating result. Fluid dynamics - elegantly simple rules that often defy expert intuition.

The simplest sprinklers are composed of hoses with holes punctured at regular intervals. Great presentation and delivery of the material. Only 4 minutes in but I appreciate the thought and craftsmanship that has been invested in communicating this problem.

Thank you for this. Amazing visualizations and explanations. I love having my brain scratched.

It would be interesting to have the tubes inside the central cavity turn so that they are pointing vertically (up or down) compared with the axis of rotation.

This was already solved a decade ago at Harvard. They knew about the votices inside the hub and that the rotation depends on the geometry. Wang's contribution is more subtle and the new "solution" is pop science sensationalism

@Ghredle

2 ай бұрын

The Harvard study did not include the internal geometry and how this can change the rotational direction

@shanent5793

2 ай бұрын

@@Ghredle You didn't read the paper

@anguismemes1666

2 ай бұрын

Thank you

@Ghredle

2 ай бұрын

@@shanent5793 no i did not …just had access to one drawing which shows the water intake… my assumption was based on incomplete knowledge,

@ANDELE3025

2 ай бұрын

Seeing as the real solution (aka depends on what you engineer the sprinker for/emphasis on what forces) was already present during RPFs lecture, it was solved more than just a decade ago and not at Harvard.

Thank you. “Experimental design” questions answered that occurred to me as you were presenting the facts, possible solutions and attempted proofs. Very clearly demonstrated and well explained for a visual, life long learner.

Thanks for the video! I found the paper too dense for a leisurely read, but this was perfect for my curiosity.

Did Mach's theoretical sprinkler have the attitude of the internal ends of the tubes defined? Thanks to all who work on this problem, it has been spinning around my brain for decades now, since I read Feynman's book.

Not so convinced.. since you talked about the opposite effects of sucking and inertial forces in the pipe corners, Reynolds should be an important factor. The pressure gradients involved in sucking are influenced by viscosity, while the force imparted on the tube due to the fluid changing direction are not. I expect it would spin in the normal way at sufficiently high Re.

@pingnick

2 ай бұрын

Yeah that and changing the dynamics of the center fluid removal would seem highly relevant etc

@milanpetrik7419

2 ай бұрын

I'm satisfied with the above explanation neither. Imagine sprinkler mouth sucking a thick jelly, so it will cut itself into a jelly. And water may behave like such a thin jelly in this regard.

@vast634

2 ай бұрын

Kind of a random addition to the experiment to allow the fluids to collide inside the sprinkler. This should not be part of the experiment, and mitigated with the pipes being fed / sucked by separate tubes. Or them being bend upwards before joining. The whole experiment lacks a certain clarity of its definition.

@milanpetrik7419

2 ай бұрын

@@vast634 Yes, the turbulence effects inside of sprinkler should be eliminated by experimental arrangement in similar way, like the described experiment already does outside of it.

@williamwightman8409

Ай бұрын

@@vast634 I agree, the internals are irrelevant to the problem. At the very least the internals should have been isolated to be nonconsequential. Otherwise too many variables.

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 !

That answer is actually really fascinating, and it just goes to show you that it's not always outside, but what's inside that really counts

Next experiment: stop those vortexes from forming within the center of the hub

@williamwightman8409

Ай бұрын

That's what I thought.

also, there is no "sucking" only pressure differentials. meaning fluids always get pushed, never pulled.

@starfishsystems

2 ай бұрын

Well, it's a straightforward problem in the case of something like a bow thruster, which is a "ducted fan": a symmetrical arrangement of a propellor in the middle of a duct open at both ends. It's not hard to argue that most of the force transfer here is at the surface of the propellor itself, which in turn is transferred via the mounting frame to the vessel. In an open environment, very little force can be said to result from the thruster developing higher ambient pressure on one side of the vessel relative to the other. But that "very little" difference is still NONZERO and, significantly, it has the SAME SIGN as that of the blade thrust. The Feynman sprinkler, for obvious reasons, develops perhaps HALF of that pressure difference in the best case. We might say that the entire ambient environment is at a common pressure, but in the area close to the vent, the pressure is lower. If you put your finger over the vent, you can easily feel it being drawn toward the vent. That's a rough measure of the available motive force in this negative pressure scenario. The fluid in that region has mass and therefore resists being accelerated. The various resulting force vectors in the neighborhood cancel except for the component along the axis of the vent. In short, this force may be modest but it is NONZERO, and it has the SAME SIGN as the flow through the duct, which is inwards in the case of a Feynman sprinkler. A broadly conical vent will tend to contain this negative pressure and direct its force more in line with the vent axis. It will still be more diffuse, therefore less directed and effectively weaker, relative to what is possible with a positive pressure through the vent. But if you imagine making the vent into a diffuser, you can see how easily the positive pressure scenario can be weakened as well, until the two scenarios become quite closely comparable.

@brianthibodeau2960

2 ай бұрын

How does this apply in a situation where you suck on a straw? You are creating a pressure differential between your mouth and the water, at which point the water travels up the straw to enter your mouth thus balancing the differential. I would consider that a pull.

@InfinityOrNone

2 ай бұрын

Unless you're talking ferrofluid and magnets.

@brianthibodeau2960

2 ай бұрын

Ohh wait is it becasue the pressure of the world outside the straw is now greater than the pressure in your mouth and it pushes the water up the straw?

@Scotty-vs4lf

2 ай бұрын

@@brianthibodeau2960 yeah, when you arent sucking the air pressure inside the straw and outside are the same. once you start sucking, theres less air pressing down on the liquid inside the straw vs outside, so the air outside is able to push the liquid up the straw to try and equalize the pressure. if you had a straw going all the way to space (so just a tall straw with a vacuum inside it) it would only be able to push the liquid up a certain distance before the weight of the water in the straw is too much for the atmosphere to keep lifting. so you could put a tube from the ocean to space and it wouldnt drain the ocean

Perfect to watch at 3am, when you think you'll just peak at the result, but end up staying for the amazing video as a whole!

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

7:55 "Timmy, close the window" "Oh, sorry dad."

I remember seeing a model of the inverse sprinkler years ago with air being sucked in. The result was that it was sensitive to disturbances and it was possible to get it going in both directions. It wasn't going that far to reduce the disturbances though.

Mesmerising and stimulating : Thank you for sharing

That was a brilliant video - Thanks!

When water is spit out it all goes one direction (due to its momentum inside pipe) but when sucked in, it comes in from almost every direction (except for the direction of the pipe) since its initial momentum is close to zero. This is why “put-put” boats work.

@anguismemes1666

2 ай бұрын

But they need to make it unnecessary complicated

So, if you added a 90 degree bend pointing up to the suction area then all rotation should stop. Right?

@nsnick199

2 ай бұрын

And you could change the direction of rotation by changing the angle the pipes enter the central chamber, right?

@scotthammond3230

2 ай бұрын

And the direction of rotation actually wouldnt be affected by the external angle of the pipes, assuming the vortices still formed in the same manner, right?

Wow, very interesting and a lot more complex than I was thinking it would be!

A wonderful problem. I had not heard of that one. Well done 👍

6:40 - yes. Sucking and blowing can be the same thing. However. Context is really important

@tikaanipippin

2 ай бұрын

A vacuum cleaner can be made to suck or blow, however the suction is very local and directed into the head, but blowing is always at a distance, and the effects are much more random, which is why I object to council road and park maintenance operatives using fossil-fuel driven leaf blowers to scatter the leaves in a general direction, before being picked up by other means. If they had vacuum cleaners, the leaves would be sucked into receptacles on site or by hoses connected directly to their vehicle's leaf collector directly.

@Fivizzz

Ай бұрын

12-year-old me: "he he he"

Commenting at 0:53, before watching your report. Many years ago, in the early days of the worldwide web, I was curious about this. I searched online and found groups that reproduced the experiment and even had video! These were done in various ways, e.g. with gas instead of water, and other fluids. Also, the sprinkler arm shape varied. The empirical results were all over the place! Some went one way, some the other, some had no discernible movement. I also found a draft of a paper analyzing the physics, and with simplifying assumptions, concludes that in the steady state there should be no motion. I emailed them with the experiments I had found, and later found that not only had they updated the paper but I got thanked in the list of credits at the end! So, with the forces in opposite directions cancelling, these "simplifying assumptions" will be all that's left. Due to viscosity and friction and the arm shape and whatnot, tiny imperfections cause the cancellation to be less than perfect. Whether the real-world sprinkler moves one way or the other depends on the precise design, the fluid viscosity, friction, resident time inside the arm, and who knows what else. So, if this experiment claims to be the first/only people to try it, they are _so_ wrong. If it claims to be the first detailed analysis of the physics, they are wrong by a few decades. So I wonder what is meant by "breakthrough" and why it's "finally" solved when it was solved more than twenty years ago IIRC. Is this all not on the Wikipedia page, perhaps, so nobody else knows about it? I wonder if ChatGPT knows about it? ...

@JohnDlugosz

2 ай бұрын

Yes, ChatGPT remarks, "... This is because the system's behavior when water is sucked in can be counterintuitive and is influenced by various factors, such as the design of the sprinkler, the viscosity of the fluid, and the specifics of the fluid flow (laminar vs. turbulent)." Asking about specific results, it notes, "...small differences in experimental setup can significantly affect the outcome, and theoretical analyses often rely on idealized assumptions that may not fully capture the complexities of real fluid dynamics." and, "...but the direction and magnitude of this motion often depended on specific details like the shape of the sprinkler arms, the presence of nozzles, and the rate of fluid flow."

@HenrikMyrhaug

2 ай бұрын

ChatGPT was trained on lots of content from the internet, so it can maybe be used to compile the general gist of what people on the internet are saying about the topic. Just a little reminder ChatGPT is a language model, not a general intelligence.

@MichaelWinter-ss6lx

2 ай бұрын

Yep, the AI is still far from obtaining it's"I".

@fritt_wastaken

2 ай бұрын

@@HenrikMyrhaug the notion that GPT just "compiles the general gist" is straight up wrong. Neural nets can generalize, systematize and extrapolate information. They can deduce something entirely new and can develop task-specific emergent properties. GPT isn't a reliable source because it doesn't do what we expect it to do, not because it doesn't do anything remarkable

@somdudewillson

2 ай бұрын

@@HenrikMyrhaug This is something of an arbitrary distinction given that it can solve very nearly entirely arbitrary problems, as long as they can be phrased in a textual manner. _So many_ papers are "we presented x problem to a big language model and it turns out it can solve it pretty well."

Subscribed. What a great video. I guessed it would not move at all. I did not see Dean flow coming as the solution.

Fascinating! I spotted the first two forces, but (fluid dynamics being largely over my head) didn't know whether the force due to the pressure difference and the force due to water going around the bend would inherently cancel out. Hadn't even considered the behavior of water inside the hub.

That sprinkler should be in a museum somewhere with an explanation of the design constraints and how this specific design solves them. That is a thing of pure art

I don't know who pointed the editor to that Simpsons clip, but you need to give them a big fat raise.

@001variation

Ай бұрын

And fire the dude who did the volume levels for that part

Super fascinating great experiment and video

Was REALLY looking forward to you going over the "friendly fluid dynamic equations" in Wang's paper.🤭

It's obvious that it wouldn't spin if the liquid is drawn uniformally from the system (which can be achieved through inner arrangement of the sprinkler) because there is no net change in the angular momentum of the water. Basically the way it spins depends on how the water is leaving the system, not how it enters. Same as with regular sprinkler. Edit: The answer given in the video is only correct if you want to know what forces do sprinkler arms contribute and ignore everything else. Which is not quite the same as the original question

Living in 2024 is phenomenal, in terms of how deeply informative content just casually drops when you may most conveniently want/need it. Just a couple days back I was contemplating the problem in leisure, and after having settled on my answer, looking around the internet for confirmation. To my surprise, there was a paper...lo and behold...from 2024 itself! And to my even greater surprise just now, a KZread video on the topic tips its hat in my path. Internet was always known to be powerful, but something wonderfully invigorating is making it powerful still!

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

Fantastic experiement!! Huge thanks to the scientific team and God Bless you!

Maybe there is no sprinkler??

2 ай бұрын

The paper proved there's at least one, as one of the authors 😄

"How Physicists FINALLY Solved the Feynman Sprinkler Problem" - I didn't even know it existed.... lol... 😂

@Mrbfgray

2 ай бұрын

One of his books has entertaining story around that--as a student he first convinced his professor that it must spin in one direction then later equally convinced him that it would spin in the opposite direction.

That laser sheet imaging is one of the coolest things I've ever seen in my entire life

That is utterly fascinating.

I would expect it to spin the other way , but very slowly because if you've ever tried to use a box fan to "suck air" you know that the air isn't sucked out in a clean column . So suction is NOT the inverse of blowing .

@echelonrank3927

2 ай бұрын

cmon, its somewhat like the inverse of blowing, precisely why i also expect it to go slow the other way

Yeah, but why would you want to suck anything with a sprinkler...? 🤔😂

@seanhewitt603

2 ай бұрын

It has greater implications to physics and the universe...

@marchurnik

2 ай бұрын

Because it is possible ?

I think the mass difference exiting or entering tube is a crucial reason for the rotation of a sprinkler other that the obvious other reasons and that changes the outcome of suction. It's just amazing they didn't use something else to compare the problem to

OK I'll play ball and engage because you showed me an interesting problem :) My hypothesis at the start of the video is that the sprinkle-sucker will rotate counter to its above-water counterpart. I visualized the forces of a space ship to arrive at this answer. The water jet of a sprinker has essentially the same properties as a rocket. It's just a jet of water instead of a jet of fire. So, the inverse seems to be the most likely outcome, since we have inverted the forces at play.

12:59 if you don't want a 13 minute history of sprinklers.

This was a great video!

Fantastic problem; interesting investigation. I have a problem, for wich I had no luck searching for a good explanation: forces in vacuum. You get a suction cup, press against the well finished surface of something heavy, make vacuum ...and it can be moved upwards. Or remember the historical event at Magdeburg, with horses playing tug of war. Wich forces are present, with such a strong value? Intramolecular?

hilarious and interesting. you win the internet today sir

8:00 Wait a sec, did you use battered side down footage??? Awesome!!!

"entirely unburdened by modesty" hahahahaha. I'm stealing that line. Also, I initially assumed, the same vacuum hose/shirt effect was in effect. Fascinating video.

Brilliant! Amazing experiment

Great Explanation

I love science. I was thinking it won't move because suction isn't the reverse of blowing and intake is slow compared to repellent and it's just intaking inside the same material. But then of course, slight inconsistancies in fluent motion causing a slight spinning angle. It's so simple yet so complicated.

Alright, I'm convinced that these vortices impart their momentum on the central body, however I'm not quite convinced yet that the negative pressure at the point of ingress is completely overruled by the positive momentum imparted on these tubes by their internal flow's directional change. How about redoing this setup with a longer straight closed-off tube with a 90deg smaller soldered-on jet, and increase the flow to the turbulent realm? That should mix up the flows enough in the core that eddies should be randomized and cancelled, and due to the lack of bend, it'll only be about the effects of the negative pressure at the jet start, and positive at the reaction wall.

thank you, this video is super interesting, especially serj tankian explaining it to me

Great, I'm currently sitting in my laboratory and as a postdoc I'm continuing to work on my work "Experimental study of thermohaline stairs in double-diffusive convection", but now in a rotating reference system. My experimental setup shows significantly more effects than this actually quite simple Feynman sprinkler problem. There are also many technical solutions in my structure, including the PIV system! Nevertheless, it's nice to see how much thought had to be invested to solve the Feynman sprinkler problem and that it is by no means easy to have to think outside the box 1000 times when the problem becomes even more complex! Thanks for this great video! Dr. Axel Rosenthal from Institute for Astrophysics and Geophysics in Göttingen .

I was not expecting youtube to remind me about vorticity today. I clearly needed it, though!

awesome video! loev the green particles!

does this change at all if the sprinkler pipes are connected in the center and not attached to a cylinder where the water can create vorticies?

I like to think Feynman would have loved this. The closer you look, the more interesting it becomes!

Wow! As a former fluid physics student, this was a lot of fun to see if my intuition would hold up. My gut predicted counterrotation, and giving it some thought I predicted a net rotation in the water to impart angular momentum. It was probably a lucky guess though!

This was quite interesting- in the end I found the answer a little confusing, but it’s nice to know it does spin reverse to when water is flowing the other way. Have you ever studied the “chain fountain” problem? Similarly related to momentum imparted, we see chain will rise from a pile as chain is dropped over the edge of a container. Where does the upward momentum come from? I’d appreciate your discussion if this.

I appreciated the buttered side down reference at 8:00

I love that the result is 1 - what any rando would have expected 2 - due to forces that hadn't even occurred to Feynman et al.

absolutely brilliant

very informative. Non physicists can see this complicated problems solution ( without the math). ( I hear I forget, I see I remember ( I do, I understand).

this seems like an answer to this one specific case. if there were three arms, would the nature of the vortex lobes in the central chamber be different? and what's the behavior in the limit as you add more and more arms? is the acceleration constant or does it get faster and faster or does symmetry or turbulence in the internal chamber's vortices produce some other effect?

This made my day! My little brain guessed this right years ago. thank you.

That leaves a couple of design to look at to verify the experiment. 1) Make the tubes perfectly straight. 2) Angle their direction entering the center portion.

An important concept is the _friction_ of water particles against the internal tube linings. This friction delivers a force causing the sprinkler to rotate in reverse while sucking. This is the same concept that I would teach Elon Musk: instead of using only 33 boosters on the starship rocket, use thousands of mini- or micro-boosters instead. The _friction_ of the jet exiting the nozel creates an additional lift that in turn increases the rocket's efficiency drastically.

My initial conclusion when hearing the problem was that it wouldn’t spin for the same intuitive reasons that explained why the force from sucking in fluid is much much weaker than expelling fluid. Now I also made an assumption that those tubes that went into the sprinkler housing, didn’t just terminate immediately into an empty cavity where vortices can form. I assumed the tubes would bend downwards. If the tubes did bend downwards once inside the housing, would the sprinkler rotate at all in this case?

Loved it. Thanks.