Talk:Feynman sprinkler

"E pur si muove!"

I'm pretty sure that I read somewhere that atleast one very sensitive experiment showed that the feynman sprinkler does actually turn- but the effect is very small. I don't have a ref though.WolfKeeper 15:28, 8 April 2006 (UTC)

This is probably due to friction, a property which is ignored in the thought experiment. -- Rmrfstar 18:39, 8 April 2006 (UTC)

Probably something like that, or there's a bit of angular momentum being transfered due to twisting in the air leaving the pipe. The University of Maryland experiment is actually mentioned in 'An elementary treatment of the reverse sprinkler' reference, but I was unable to currently locate the video on the web; although I have seen it previously, if anyone finds it, please add it as a reference.WolfKeeper 22:23, 21 July 2006 (UTC)

(Excuse my English)

The University of Maryland has put up videos [1] that show that the inverse sprinkler does in fact rotate quite fast (I assume that the flow rates were the same blowing and sucking). On a related page [2], they mention that the question after the expected behaviour of the inverse sprinkler has been answered contradictory in the physics literature.

This Wikipedia article says that many experiments have shown that the inverse sprinkler stands still. If this is the case, I think the article should cite more sources to back up this statement. 62.152.162.188 (talk) 11:05, 15 February 2008 (UTC)

Originator

So if Feynman did not come up with this thought experiment, who did? It would be nice if the article could mention this. -Verdatum (talk) 15:17, 15 January 2008 (UTC)

Dates wrong?

In the article it says the problem appeared in "Science of Mechanics" by Earnest Mach in 1893, but seeing as Feynman was BORN in 1918, that would be impossible. Did Mach publish a similar article or is this just incorrect? —Preceding unsigned comment added by 67.121.208.184 (talk) 02:37, 17 September 2008 (UTC)

It fits when you consider that Feynman "did not come up with the problem or ever publish a solution to it, only help popularize it". Mike Peel (talk) 08:12, 17 September 2008 (UTC)

Huh?

Even though I have physics qualifications, I'm kinda tired at the moment, and somehow this is the first time I've come across this one.

Can anyone tell me why the automatic assumption isn't that it would spin backwards? A fluid dispensing/sucking-up nozzle is still a nozzle regardless of what media it is or has going through it and will still concentrate and have reaction forces, surely? there's still a partial vacuum created by the pump that will have an uneven effect, same as the overpressure of forcing fluid through it. And if it's operating in the reverse direction to normal, why wouldn't the incident forces (which make it spin forwards normally) be reversed also?

Maybe i'm just being thick, but then i am also semiconcuoo... conciuo...... consciou... goddamn it... half-asleep by medical and legal standards. 77.102.101.220 (talk) 22:17, 8 October 2008 (UTC)

"Most correctly"?

Why is that name most correct? --anon —Preceding unsigned comment added by 86.167.96.25 (talk) 22:19, 14 October 2008 (UTC)

"Lawn Sprinklers in Reverse?

The usual lawn sprinkler problem is tough enough for students to understand. But, it involves water injected into air, so all sorts of effects can be ignored, because the density ratio is 1000:1.

The reverse sprinkler demands at least the consideration of added mass, and possibly other effects.

Does anyone have a good explanation of the physics of the usual sprinkler? Other than an obscure explanation involving rotating coordinate systems in Batchelor, I have not seen one. —Preceding unsigned comment added by 71.227.99.180 (talk) 05:53, 4 May 2009 (UTC)

Having been the boy that took a ball sprinkler head (2, actually) and mounted them on the arms of a regular sprinkler, I think I see where the confusion comes from. It's pure momentum of a rocket nozzle type being constrained by the sprinklers construction. But, with the all direction ball heads, the sprinkler barely rotated at all. That is the sole reason why the sprinkler works one way but not in reverse. In the usual direction the fluid is working like a rocket exhaust and all the momentum is in one direction. When reversed, the fluid is sucked in by the nozzles *from all directions*, including from the reverse direction as well as the sideways direction. A frictionless ideal fluid might make it turn a little, but hardly with the same speed or force. What you really need is a very peculiar anisotropic fluid. 50.247.247.81 (talk) 19:28, 20 January 2015 (UTC)

Surely you mean the (dynamic) viscosity ratio? 131.111.17.143 (talk) 12:28, 2 December 2009 (UTC)

"It is now understood, however, that an ideal reverse sprinkler (i.e., one which can turn without friction and is surrounded by an ideal fluid) will accelerate towards the incoming fluid as the suction is being switched on, and come to a stop as the suction is switched off."

In this sentence,if the entire system is without friction, wouldn't the sprinkler spin forever? Or are they talking about the sprinkler bearing only?

Bikepbp2011 (talk) 18:54, 2 March 2010 (UTC)

The word "ideal" implies there is no friction. -- Rmrfstar (talk) 23:01, 9 March 2010 (UTC)

Î think what they mean is that it accelerates while the flow is ramping up, then maintains a steady speed (due to no friction) while the flow is steady, then decelerates again when the flow ebbs off. M-O-W (talk) 22:45, 15 March 2024 (UTC)

I agree with "Huh?"

I have a physics degree, and I am confused as to why it isn't obvious that the sprinkler would rotate in the "reverse" direction (i.e. advancing toward the nozzle openings). —Preceding unsigned comment added by 74.138.132.28 (talk) 21:08, 25 July 2010 (UTC)

You're forgetting something...

This article has a "Solution" section, but it lacks a "statement of the question" section! The question is never stated in detail. The introductory paragraph says a few things about the problem, and includes such false statements as "A regular sprinkler has nozzles arranged at angles on a freely rotating wheel such that when water is pumped out of them, the resulting jets cause the wheel to rotate". (This is hardly a "regular sprinkler" -- less than 1% of all sprinklers in the world contain any moving parts.)

If this sprinkler has ports that suck in fluid, then one of the following must also be true: (1) It also has ports that expel liquid and which therefore create a force and/or torque; (2) It has a "hose" that expels liquid somewhere beyond the field of the problem -- this would be analogous to the hose that feeds a rotating sprinker; (3) it has a magic teleportation device that causes the liquid to disappear from its interior instead of accumulating; (4) liquid accumulates inside this device, causing the volume of the sprinkler's shell to expand; (5) liquid accumulates inside this device, but the device's volume is constant, and therefore the density of the enclosed liquid increases constantly. You need to tell us which of the assumptions is part of the problem, or else you haven't told us the problem at all. — Lawrence King ^(talk) 20:40, 11 October 2013 (UTC)

Split off and bolded. Someone please fix this rather crippling problem with the current page, pref. by blockquoting Feynman's specific formulation of the question. — LlywelynII 02:00, 31 October 2013 (UTC)

Biography/autobiography

The book "Surely You're Joking Mr. Feynman" was written by Ralph Leighton, so it is misleading to call it an autobiography. Fixed this but because the book was written in the first person, I understand if this is a controversial change. — Preceding unsigned comment added by 67.194.41.148 (talk) 01:19, 26 December 2013 (UTC)

In the preface, Leighton explains that he prepared the text from recordings of Feynman talking about his life. In the introduction, Hibbs writes of the book as Feynman's "memoirs". I don't see anything wrong about using the term "autobiography", but I'll stick with "memoirs" since the term appears in the book itself. - Eb.hoop (talk) 05:12, 28 December 2013 (UTC)