Thats why you run it in reverse.

😂

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

"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.

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

Sounds more like an ego problem than anything else

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

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

Sure thing, Einstein

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.

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

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).

Rest in Peace

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

lol

precisely.

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.

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

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

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

and a huge sexist at the same time

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

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

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.

They also called the simulation PIV...

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.

exactly my point - you said it clearer.

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

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.

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

* overpowering

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

Magnetic bearing: No.

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

@@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.

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.

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.

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.

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.

​@@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.

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.

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.

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

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

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!?

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?

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

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.

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

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

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..

Ooh that's neat

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

What are you yapping about

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

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.

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

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

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.

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.

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?

@@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.

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.

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

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

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

It was his calling

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

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.

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.

@@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.

@@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.

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

@@Ghredle You didn't read the paper

Thank you

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

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.

That's what I thought.

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

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?

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.

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.

Unless you're talking ferrofluid and magnets.

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?

@@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

But they need to make it unnecessary complicated

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.

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

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

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."

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.

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

@@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

@@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."

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

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

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.

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

Because it is possible ?

YES, YES, YES. He is not very clear. The RED, up and down arrows show that. . Here's more detail if you care to try: .. The tangential [to the rotation] change in momentum of the flow around the bend when blowing is the cause of the 'normal' rotation. Then. . . The inward Sucking flow has the same force at the bend and is pushing the arm rotate the *SAME* direction as Blowing [clockwise here]. HOWEVER. . . When sucking, the change in momentum as fluid enters the tube-end from ALL directions is accelerating all that fluid from a a stand-still, into one direction into the tube end. That fluid goes from ZERO speed in the free atmosphere, to the tangential speed INTO the tube end [a.k.a. nozzle] THEN, After the flow goes around the bend, it has NO tangential component. Thus it is back to zero in that tangent to rotation direction. THEREFORE, Because that air goes from zero to zero *tangential* momentum [for the arm/pipe. The pressure changes[reduction] as the air rounds the edge of the tube opening, must equal the 'reaction' force caused in the bend. See time 6:02. Dr. Miles simply says it happens without justifying it more clearly. . Thinking only of the pressure change at the tube outlet, I didn't see this until I considered the momentum of that air going from a standstill to radially inward after the bend. Got it. The weak counter, sucking spin is due to the This could actually be measured with a single bent tube and no rotating joint elimination the confusion of that center manifold with the asymmetric flow causing the tiny torque. SO. . . My conclusion is that IF you build it with a rotating joint that eliminates teh sucking imbalance at the center, it should not rotate at all. TL;DR: In the vertical dimension: The air entering from all directions outside the Sucking tube starts with an average of zero vertical momentum. Then it speed up vertically entering the tube. After the bend it once again has zero vertical momentum. THEREFORE, the force around the bend MUST BE fully cancelled by the force of the pressure changes {reduction} of the fluid curving into the tube end. See time 6:02.

It's the varied velocity across the incoming flow

Yes. If you can eliminate that central mess when sucking, It won't rotate at all.