siphon, an instrument, usually in the form of a tube bent to form two legs of unequal length, for conveying liquid over the edge of a vessel and delivering it at a lower level. Siphons may be of any size. The action depends upon the influence of gravity (not, as sometimes thought, on the difference in atmospheric pressure; a siphon will work in a vacuum) and upon the cohesive forces that prevent the columns of liquid in the legs of the siphon from breaking under their own weight.
@ashlawn10h Sorry, but I still disagree. Under your definition, I should be able to cut my tube in half lengthways (i.e. so it is long, with a c-shaped cross-section) and expect water to flow. This only works if the entire stretch is downhill, any uphill section stops it working. A closed tube is needed, and this highlights the need for a difference in pressure (note carefully I say pressure and not atmospheric pressure) to drive the siphon...
I'm disappointed to see that the Bernoulli equation was not mentioned in any of these comments... And more shocked that a Professor at a University came to such conclusions.
@FirajaNinja I'm sorry that I didn't try to baboozle everyone with a sea of algebra just to ensure you wouldn't be disappointed. The whole point was to explain it in a way that people without a working knowledge of Bernoulli's equation can understand.
@micolich Hahahah, I wasn't critiquing your video at the slightest. This demonstration would be key to begin any fluid dynamics course. :D It was in reference to the youtube user comments. I was yearning for another engineer or physicist to at least bring it up.
@FirajaNinja That's not how I think most people would have read your original comment, but that's ok. Now that I see your point I couldn't agree more. Bernoulli's equation is vital to really understanding a siphon, almost all of the physics for it is contained in that one equation alone (esp. if you can safely ignore cavitation effects).
Professor Stephen Hughes continues to deny the primacy of atmospheric pressure in the practical siphon. Google for Stephen Hughes, siphon, and Oxford University Press, to get to the oup blog with the discussion.
My reply failed to clear the moderator. I suspect because I linked to two files at the Wikimedia commons. One of which I call an air launch siphon, where the entire siphoning process is carried out without tensile strength coming into play. Search WikiMedia org for AirLaunchSiphon
Found a reference to another article on vacuum siphons, this one from a University of California professor:
MINOR, RALPH SMITH, Associate Professor of Physics. Would a Siphon flow in a Vacuum! Experimental Answers. School Science and Mathematics, vol. 14, no. 2, p. 152; Feb., 1914.
Oops, a stray mouse click resulted in one of my previous comments being trashed. Oh well, no big deal I guess.
Dr Hughes reports that this article demonstrated a siphon of mercury in vacuum up to 16cm! This article is so old that I'm guessing it's no longer under copyright. That means we may be able to post a scan of it for all to download.
I was looking for Nylon tubing in the hardware store, but they didn't have it. They only had vinyl and polyethlene tubing. Unknown adhesion there. Then it occurred to me Fletcher used beverage service tubing because regulations require such things to be clean, whereas hardware store tubing could be contaminated. Fletcher said he tried putting a t-fitting at the top of his tubes but couldn't get over 10m. A tall siphon may have to be a smooth tube at top.
@micolich Andrew K Fletcher makes some strange and interesting claims about his inverted U-tubes (google thenakedscientists and 200829)
I wonder if water forms into an expanded ice like structure when it's under negative pressures and how that might complicate the issue. Not that that would necessarily explain this stuff.
Got the SchSciRev article yet? If not, what method are you pursuing it with? Stanford's got it.
@micolich The Z-tube is a clever device. See Wikipedia. The fact that the Z-tube has to be spun up to a certain speed before it even starts to measure water's tensile strength demonstrates that tensile strength usually contributes nothing at all to holding siphon stream together. Vacuum siphons are supposedly demonstrated. I haven't read it but See Nokes 1948 "Vacuum Siphons". For siphon 24m tall, see video sz9eddGw8vg but beware AndrewKFletcher is selling miracle medical device.
@mindbuilder2 I'll take a look at the 24m siphon video, but a question. Have you ever *seen* a copy of Nokes paper? I followed the reference on the Am. J. Phys. website, and there is no such article!
@micolich I Haven't really tried yet to get my hands on the vacuum siphon article. Looking at vapor pressure and surface tension pressure just above zero, a water siphon might work in vacuum for very small heights in a tube like glass that it could adhere to. I wonder what tubing material AKF used to 24m. Better luck in vacuum might be had with something less volatile like oil. Normal siphons are under atmospheric pressure and so their molecules are repelling rather than pulling anyway.
@micolich On AJP homepage I clicked "all issues" under "browse content" then vol 16 and pdf toc of issue 4. It was listed near bottom, but no apparent way to access it. Interestingly it's not listed in html toc. The discussion at Wiki says "The Nokes citation is actually just a short digest of Nokes, M C, 1948, Vacuum Siphons, School Science Review 29 p. 233"
@mindbuilder2 True, I managed to get my hands on the copy of the Am. J. Phys. article. Now I need this School Science Review article, which might be a little harder to get...
@micolich A guy in the Wiki discussion said the Nokes article didn't even actually involve a siphon in vacuum, just a vacuum used to prime the siphon. Is that true?
@mindbuilder2 From my reading, I suspect it is actually a demonstration of a siphon operating in vacuum, although the detail is sparse as its a short review of another paper that supposedly does contain enough detail. Claim is that it works with mercury, dibutyl phthalate (low vapour pressure liquid) and de-aired water, and the pipework needs to be really clean.
I suspect more detail is in the Sch. Sci. Rev. article, which I'm still trying to get...
@micolich Consider a siphon experiment that could empty an entire bucket of water without the water on either side of the siphon ever touching. Water shot up into the air from a nozzle separates into a series of disconnected droplets. Construct a siphon where the top is a transparent box and the intake leg could enter one side of the box at 45deg and launch the liquid into the air inside the box. A slow motion camera may be required for proof. A fast shutter still photo might suffice.
@gm255 Yes, there are two. The first is Pascal's equation Delta_P = rho*g*Delta_h, and it provides equivalence between gravity and pressure. In other words, gravity is nothing special, it is just contributing to a pressure differential that drives a flow. The second is Bernoulli's equation v^2/2 + gz + P/rho = constant, and here again there is both pressure and gravity. That pressure can be a difference in atmospheric pressure, it can be gravitational, it can come about by other means.
Well we are approaching what exactly is the definition of a siphon here, but I still think that for an everyday siphon.....the g term is the driver.
If there is a great difference in atmospheric pressure (probably impractical) then is this not the same as a pressure vessel just pushing out fluid, like an aerosol can, or an O2 bottle.
@gm255 First, its completely practical, its exactly how a 'popper' (i.e., fruit-juice in a cardboard tetrapak container) works. Its also how the squeeze bottles in chemistry labs work, and not surprisingly, those bottles are called 'siphon bottles'.
I agree though, it depends how you want to define siphon, I'll leave that to the dictionary experts.
I mean a difference in atmospheric pressure.......Delta P = rho g h, where h is the variable (probably rho too). Thats not so practical. Applying an extermnal force, like in a squeeze bottle is not "atmospheric" I think.
@gm255 Why not? Imagine, for example, an enclosed vessel with a boiling liquid in it, that 'atmosphere' can provide an overpressure that drives a liquid through a tube. Its exactly how a helium transfer siphon works (which, incidentally, is what got me caught up in this whole siphon debacle in the first place. ;) It was the first counterexample I thought of when I heard the news article on the radio).
@gm255 Regarding your 'dodgy science' accusation, if you don't like it, go do your own experiments and present them to back your own conclusions. I have tried to correct misconceptions by providing experiments (on real siphons mind you, not bits of chain over PVC pipe) that highlight failings in an explanation being presented in the media.
Science not about authoritarianism and accusations, it is about continual improvements in explanation by testing those explanations with experiment.
I just couldn't see how the tree height was linked in. Thats a pretty complex analogy to be introducing into a simple siphon system. There are a myriad of forces and phenomena taking place in the tree...and that paper also cites a list of other factors as possible inhibitants to tree height. I thought it was a nebulous idea to introduce.
However...you certainly are challenging...one has to challenge as a scientist!..I retract my dodgy science statement.
@gm255 I definitely agree that the tree is a very complex system to compare to, but it was the best example I could find that would give me some estimate for how high you can raise water against gravity when its tensile strength starts to play an important role.
Consider it a very loose Fermi problem that I did there, estimation is an important skill in physics, especially when trying to design experiments.
@gm255 You've got it backwards. Equations don't make physics proofs. The equations are the theories and the real world experiments like micolich's are the proofs. Or in the case of Dr Hughes liquid tensile strength theory of siphons, the disproofs.
In an experiment we observe. We cannot disagree with that. But we can disagree about what we think is happening in the experiment. How do we tell someone what we think is happening? Thats in the equation.
Just want to correct a minor error, the tree paper in Nature was 2004 not 2009. For anyone curious, its Koch et al., "The limits to tree height", Nature 428, 851 (2004).
siphon, an instrument, usually in the form of a tube bent to form two legs of unequal length, for conveying liquid over the edge of a vessel and delivering it at a lower level. Siphons may be of any size. The action depends upon the influence of gravity (not, as sometimes thought, on the difference in atmospheric pressure; a siphon will work in a vacuum) and upon the cohesive forces that prevent the columns of liquid in the legs of the siphon from breaking under their own weight.
ashlawn10h 2 months ago
@ashlawn10h Sorry, but I still disagree. Under your definition, I should be able to cut my tube in half lengthways (i.e. so it is long, with a c-shaped cross-section) and expect water to flow. This only works if the entire stretch is downhill, any uphill section stops it working. A closed tube is needed, and this highlights the need for a difference in pressure (note carefully I say pressure and not atmospheric pressure) to drive the siphon...
micolich 2 months ago
@ashlawn10h A siphon cannot work by gravity and cohesion alone, hydrostatic pressure is a vital component.
micolich 2 months ago
I'm disappointed to see that the Bernoulli equation was not mentioned in any of these comments... And more shocked that a Professor at a University came to such conclusions.
FirajaNinja 10 months ago
@FirajaNinja I'm sorry that I didn't try to baboozle everyone with a sea of algebra just to ensure you wouldn't be disappointed. The whole point was to explain it in a way that people without a working knowledge of Bernoulli's equation can understand.
micolich 10 months ago
@micolich Hahahah, I wasn't critiquing your video at the slightest. This demonstration would be key to begin any fluid dynamics course. :D It was in reference to the youtube user comments. I was yearning for another engineer or physicist to at least bring it up.
FirajaNinja 10 months ago
@FirajaNinja That's not how I think most people would have read your original comment, but that's ok. Now that I see your point I couldn't agree more. Bernoulli's equation is vital to really understanding a siphon, almost all of the physics for it is contained in that one equation alone (esp. if you can safely ignore cavitation effects).
micolich 10 months ago
@FirajaNinja
It was mentioned!! By micolich himself, in one of his early replies to one of my comments.
gm255 8 months ago
Professor Stephen Hughes continues to deny the primacy of atmospheric pressure in the practical siphon. Google for Stephen Hughes, siphon, and Oxford University Press, to get to the oup blog with the discussion.
My reply failed to clear the moderator. I suspect because I linked to two files at the Wikimedia commons. One of which I call an air launch siphon, where the entire siphoning process is carried out without tensile strength coming into play. Search WikiMedia org for AirLaunchSiphon
mindbuilder2 1 year ago
Found a reference to another article on vacuum siphons, this one from a University of California professor:
MINOR, RALPH SMITH, Associate Professor of Physics. Would a Siphon flow in a Vacuum! Experimental Answers. School Science and Mathematics, vol. 14, no. 2, p. 152; Feb., 1914.
Oops, a stray mouse click resulted in one of my previous comments being trashed. Oh well, no big deal I guess.
mindbuilder2 1 year ago
Dr Hughes reports that this article demonstrated a siphon of mercury in vacuum up to 16cm! This article is so old that I'm guessing it's no longer under copyright. That means we may be able to post a scan of it for all to download.
mindbuilder2 1 year ago
I was looking for Nylon tubing in the hardware store, but they didn't have it. They only had vinyl and polyethlene tubing. Unknown adhesion there. Then it occurred to me Fletcher used beverage service tubing because regulations require such things to be clean, whereas hardware store tubing could be contaminated. Fletcher said he tried putting a t-fitting at the top of his tubes but couldn't get over 10m. A tall siphon may have to be a smooth tube at top.
mindbuilder2 1 year ago
@micolich Andrew K Fletcher makes some strange and interesting claims about his inverted U-tubes (google thenakedscientists and 200829)
I wonder if water forms into an expanded ice like structure when it's under negative pressures and how that might complicate the issue. Not that that would necessarily explain this stuff.
Got the SchSciRev article yet? If not, what method are you pursuing it with? Stanford's got it.
mindbuilder2 1 year ago
@micolich The Z-tube is a clever device. See Wikipedia. The fact that the Z-tube has to be spun up to a certain speed before it even starts to measure water's tensile strength demonstrates that tensile strength usually contributes nothing at all to holding siphon stream together. Vacuum siphons are supposedly demonstrated. I haven't read it but See Nokes 1948 "Vacuum Siphons". For siphon 24m tall, see video sz9eddGw8vg but beware AndrewKFletcher is selling miracle medical device.
mindbuilder2 1 year ago
@mindbuilder2 I'll take a look at the 24m siphon video, but a question. Have you ever *seen* a copy of Nokes paper? I followed the reference on the Am. J. Phys. website, and there is no such article!
micolich 1 year ago
@micolich I Haven't really tried yet to get my hands on the vacuum siphon article. Looking at vapor pressure and surface tension pressure just above zero, a water siphon might work in vacuum for very small heights in a tube like glass that it could adhere to. I wonder what tubing material AKF used to 24m. Better luck in vacuum might be had with something less volatile like oil. Normal siphons are under atmospheric pressure and so their molecules are repelling rather than pulling anyway.
mindbuilder2 1 year ago
@micolich On AJP homepage I clicked "all issues" under "browse content" then vol 16 and pdf toc of issue 4. It was listed near bottom, but no apparent way to access it. Interestingly it's not listed in html toc. The discussion at Wiki says "The Nokes citation is actually just a short digest of Nokes, M C, 1948, Vacuum Siphons, School Science Review 29 p. 233"
mindbuilder2 1 year ago
@mindbuilder2 True, I managed to get my hands on the copy of the Am. J. Phys. article. Now I need this School Science Review article, which might be a little harder to get...
micolich 1 year ago
@micolich A guy in the Wiki discussion said the Nokes article didn't even actually involve a siphon in vacuum, just a vacuum used to prime the siphon. Is that true?
mindbuilder2 1 year ago
@mindbuilder2 From my reading, I suspect it is actually a demonstration of a siphon operating in vacuum, although the detail is sparse as its a short review of another paper that supposedly does contain enough detail. Claim is that it works with mercury, dibutyl phthalate (low vapour pressure liquid) and de-aired water, and the pipework needs to be really clean.
I suspect more detail is in the Sch. Sci. Rev. article, which I'm still trying to get...
micolich 1 year ago
Comment removed
mindbuilder2 1 year ago
@mindbuilder2 Yeah, that's basically what Nokes does.
micolich 1 year ago
@micolich Consider a siphon experiment that could empty an entire bucket of water without the water on either side of the siphon ever touching. Water shot up into the air from a nozzle separates into a series of disconnected droplets. Construct a siphon where the top is a transparent box and the intake leg could enter one side of the box at 45deg and launch the liquid into the air inside the box. A slow motion camera may be required for proof. A fast shutter still photo might suffice.
mindbuilder2 1 year ago
...can you give the equations to prove it is a mixture of gravity and atmospheric pressure?
If you cant, then you are just supposing. Dodgy science!
gm255 1 year ago
@gm255 Yes, there are two. The first is Pascal's equation Delta_P = rho*g*Delta_h, and it provides equivalence between gravity and pressure. In other words, gravity is nothing special, it is just contributing to a pressure differential that drives a flow. The second is Bernoulli's equation v^2/2 + gz + P/rho = constant, and here again there is both pressure and gravity. That pressure can be a difference in atmospheric pressure, it can be gravitational, it can come about by other means.
micolich 1 year ago
@micolich
Well we are approaching what exactly is the definition of a siphon here, but I still think that for an everyday siphon.....the g term is the driver.
If there is a great difference in atmospheric pressure (probably impractical) then is this not the same as a pressure vessel just pushing out fluid, like an aerosol can, or an O2 bottle.
gm255 1 year ago
@gm255 First, its completely practical, its exactly how a 'popper' (i.e., fruit-juice in a cardboard tetrapak container) works. Its also how the squeeze bottles in chemistry labs work, and not surprisingly, those bottles are called 'siphon bottles'.
I agree though, it depends how you want to define siphon, I'll leave that to the dictionary experts.
micolich 1 year ago
@micolich
I mean a difference in atmospheric pressure.......Delta P = rho g h, where h is the variable (probably rho too). Thats not so practical. Applying an extermnal force, like in a squeeze bottle is not "atmospheric" I think.
gm255 1 year ago
@gm255 Why not? Imagine, for example, an enclosed vessel with a boiling liquid in it, that 'atmosphere' can provide an overpressure that drives a liquid through a tube. Its exactly how a helium transfer siphon works (which, incidentally, is what got me caught up in this whole siphon debacle in the first place. ;) It was the first counterexample I thought of when I heard the news article on the radio).
micolich 1 year ago
@gm255 Regarding your 'dodgy science' accusation, if you don't like it, go do your own experiments and present them to back your own conclusions. I have tried to correct misconceptions by providing experiments (on real siphons mind you, not bits of chain over PVC pipe) that highlight failings in an explanation being presented in the media.
Science not about authoritarianism and accusations, it is about continual improvements in explanation by testing those explanations with experiment.
micolich 1 year ago
@micolich
Hi micolich again.
I just couldn't see how the tree height was linked in. Thats a pretty complex analogy to be introducing into a simple siphon system. There are a myriad of forces and phenomena taking place in the tree...and that paper also cites a list of other factors as possible inhibitants to tree height. I thought it was a nebulous idea to introduce.
However...you certainly are challenging...one has to challenge as a scientist!..I retract my dodgy science statement.
gm255 1 year ago
@gm255 I definitely agree that the tree is a very complex system to compare to, but it was the best example I could find that would give me some estimate for how high you can raise water against gravity when its tensile strength starts to play an important role.
Consider it a very loose Fermi problem that I did there, estimation is an important skill in physics, especially when trying to design experiments.
micolich 1 year ago
@gm255 You've got it backwards. Equations don't make physics proofs. The equations are the theories and the real world experiments like micolich's are the proofs. Or in the case of Dr Hughes liquid tensile strength theory of siphons, the disproofs.
mindbuilder2 1 year ago
@mindbuilder2
In an experiment we observe. We cannot disagree with that. But we can disagree about what we think is happening in the experiment. How do we tell someone what we think is happening? Thats in the equation.
gm255 1 year ago
Just want to correct a minor error, the tree paper in Nature was 2004 not 2009. For anyone curious, its Koch et al., "The limits to tree height", Nature 428, 851 (2004).
micolich 1 year ago
You answered the questions I was about to ask from the previous video. Glad I waited. Cant wait to see the experiment. Cheers
cryotwin 1 year ago