Physicist demonstrates dictionary definition was dodgy
It is the defining moment that demonstrates a QUT physicist was correct in pointing out a 99-year-old mistake to one of the world’s most authoritative dictionaries.
QUT Senior Lecturer in Physics, Dr Stephen Hughes, sparked controversy over how a humble siphon worked when he noticed an incorrect definition in the prestigious Oxford English Dictionary.
In 2010, eagle-eyed Dr Hughes spotted the mistake, which went unnoticed for 99 years, which incorrectly described atmospheric pressure, rather than gravity, as the operating force in a siphon.
Dr Hughes demonstrated the science of siphons in a paper published yesterday in Nature Publishing Group journal Scientific Reports.
For Exploring the boundary between the siphon and barometer in a hypobaric chamber, Dr Hughes conducted an experiment in a hypobaric chamber, which simulates the effects of high altitude, at the Institute of Aviation Medicine at the Royal Australian Air Force’s Base Edinburgh in South Australia.
A siphon 1.5 metres high was set up in the chamber and when the pressure was reduced to an altitude of 40,000 feet a waterfall appeared at the top, but the water flow remained nearly constant.
At 41,000 feet, the siphon broke into two columns of water and, when returned to 40,000 feet, it reconnected as if nothing had happened.
Atmospheric pressure at 40,000 feet, which is more than 10,000 feet higher than Mount Everest, is about 18 per cent of the sea level value.
For the experiment, two buckets, one higher than the other and connected by tubing, were set up and a pool pump returned water from the lower bucket to the higher bucket.
“The fact that the water level in the upper and lower buckets is constant indicates that atmospheric pressure is not pushing water into the siphon,” Dr Hughes said.
“The stable water surfaces act like energy barriers between the atmosphere and siphon. For energy to be transferred from the atmosphere to the water the water level would have to go down, since the amount of energy transferred is equal to force times distance.
“If the water level is constant the distance is zero and therefore no energy can be transferred.”
Dr Hughes, whose previous research has taken him to Bhutan to examine how siphoning could prevent inland tsunamis, said siphons had been used since ancient times but how they work was still debated.
“If you think of a car, atmospheric pressure is like the wheels, it enables it to work. But gravity is the engine,” he said.
“It is gravity that moves the fluid in a siphon, with the water in the longer downward arm pulling the water up the shorter arm.”
The Oxford English Dictionary corrected the error and removed the reference to atmospheric pressure after Dr Hughes pointed it out. However, he said the new entry “unfortunately remains ambiguous”.
“This definition still leaves the question open as to how a siphon actually works,” Dr Hughes said.
“But at least the reference to atmospheric pressure has been removed. The vast majority of dictionaries of all languages still incorrectly assert that siphons work through atmospheric pressure and not gravity.
“I hope these findings are a useful contribution to the debate about how siphons work and will enable people to make more effective use of them.”
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george e. smith says: April 26, 2014 at 11:00 pm “No, I had no quarrel with your post; …”
Sorry, I never had any intention of implying that you did. I found your post to be an opportunity to further expound on details supporting my contention so I used it.
Patrick Schlüter says: April 27, 2014 at 3:24 am
“the atmospheric pressure is at both ends of the tubes and annuls itself each side.” Ultimately, yes it does but … so what?
“The atmospheric pressure is the same on both side and is in equilibrium, therefore not intervening in the siphon.” Just because the pressure is in equilibrium does not preclude it’s necessity for functionality at column “A”
If you were correct – that pressure is no longer needed to push the fluid up the “A” column once the siphon begins flowing – the crest could be hoisted up to any elevation, miles high, and it would continue to work – no it will NOT!
There is a maximum height beyond which the siphon will cease to function and that height is solely dependent on the pressure at the “A” side inlet. Lowering the pressure will decrease the maximum height, raising the pressure will increase the maximum height.
Work is being done on the water raising its elevation in column “A” by virtue of a pressure differential between the bottom and the top. The ONLY way to get it up there is to PUSH it up!
I can put a valve at the bottom of column B and throttle the flow to a trickle and it will not matter.
The water dropping in column “B” is the substitute for lips drawing the water up in column “A”.
“exactly like a chain on a pulley. ” – is not a “siphon” because it is in tension and therefore does not require pressure/force to push it up the “A” column. It WILL work in a vacuum and to any height, (within the tensile limits of the material.) The bubble scenario eliminates the “chain over the pulley” description because it is a missing link unable to pull the water up column “A”.
Not only will a siphon work with an single air bubble but will work with a continuous injection of air bubbles at the intake pipe that separate the water into uniform individual segments. All that is required to make the water move in either direction is that one side has an additively deeper column of water in the pipe. Furthermore, if the two sides are not in balance with regards to the the amount of air vs. water then the column will shift in the siphon even if the water level in the to reserviors are at the exact same height. I find it amazing that people who have obviously never experimented with siphons are making claims about how they work when they haven’t a clue.
the pumps that were installed in New Orleans at the beginning of the 20 th century are a combination of syphon and propeller pump and are still in use to clear the city of rain water.
Patrick Schlüter, A response of TL:DR is a quite a bit offensive considering he’s right and you are wrong. I read all of Mike M’s comments and he, so far, has gotten everything correct.
I can’t believe the simple concepts here that people are not getting like the fact that air bubbles are under pressure even when at the top of a siphon. Air if not confinded in some way will just keep expanding because the molecules will just drift apart via inertia. Mike has shown and understanding of these concepts.
Patrick Schlüter says:
Redundantly incorrect.
Unclear as to what “rupture the flow” means, but it does not seem to address the fact that a standard siphon can function just fine with air bubble(s) in the tube that completely disconnect the water column.
You are confusing concepts. Cohesion is not a function of external pressure. To the contrary, cohesion is exactly the opposite of external pressure. Cohesion is the internal attraction of the liquid molecules to each other.
What happens to an ionic liquid siphon under vacuum, if you introduce a small but tube-spanning bubble into the tube? It stops.
What happens to an ionic liquid siphon under atmospheric pressure, if you introduce a small but tube-spanning bubble into the tube? It continues to operate.
Of course it is.
It is gravity that causes the liquid in the descending leg of the siphon to fall, lowering the pressure within the tube to something less than atmospheric.
And it is gravity that creates the atmospheric pressure that pushes the liquid from the upper reservoir toward that lower pressure and up the tube.
This dispute is largely semantic. Ultimately (and by definition), it is the difference in gravitational potential between the upper and lower ends of the tube that drives a siphon. In a typical siphon (constructed in an atmosphere, from a non-ionic liquid with dissolved and entrained gas) the difference in gravitational potential can and most frequently does operate via the action of (also gravitationally induced) atmospheric pressure.
Brian Macker says:
April 27, 2014 at 8:47 am
“All that is required to make the water move in either direction is that one side has an additively deeper column of water in the pipe. ”
That is not true. Try placing the inlet tube to the bottom of the water tank. Then the siphon works with the mouth of the outlet tube just below the water’s surface level and the flow rate from the siphon is proportional to the pressure of water above the outlet of the tube. In this case the mass of water in the tube is much greater than the mass of water in the outlet tube since the outlet tube is shorter than the inlet tube which reaches to the bottom of the water in the water tank.
Adding gas bubbles may or may not stop the flow depending upon whether the gas volume is able to increase too much as pressure decreases on the bubbles as water flows down the outlet tube.
Mike M says:
Not true. The maximum height is also dependent on the properties of the liquid in the siphon.
JJ says: April 27, 2014 at 12:07 pm ” Not true. The maximum height is also dependent on the properties of the liquid in the siphon.”
Pedantic much? For any given fluid … “There is a maximum height….” Of course it’s going to be something less for mercury than for water, I think everyone understands that, thanks for sharing.
JJ says: April 27, 2014 at 11:45 am “This dispute is largely semantic. ”
That’s true and several others above have stated the same thing. The dictionary definition describes the apparatus and a general idea of it’s function without getting into exceptions involving cohesive fluids, air bubbles and chains over pulleys. Such issues are the domain of physics books not dictionaries IMO.
I think Dr. Hughes is a notoriety seeker who has deluded himself into believeing that he alone has discovered something “wrong” with the dictionary definition which appears to me to be thoroughly adequate as written:
“a tube bent to form two legs of unequal length by which a liquid can be transferred to a lower level over an intermediate elevation by the pressure of the atmosphere in forcing the liquid up the shorter branch of the tube immersed in it while the excess of weight of the liquid in the longer branch when once filled causes a continuous flow.”
There is one aspect of this debate that is not semantic – the “attraction” between water molecules, i.e. water possessing tensile strength in an amount capable of “pulling” molecules up the siphon. If water did possess tensile strength anywhere near this proportion, you would feel this when you removed your hand from a pool of water. If there is any molecular attraction there, it is so small that you can’t feel it, and certainly not substantial enough to have a material effect on the operation of a siphon.
Thank you Brian Macker and the several others who agree with you for helping me maintain hope that scientific intellect is not dead. I am deeply disturbed and saddened by what I have read here, particularly from people whom I had come to respect for their scientific acumen.
Here is a simple experiment I would like to see someone carry out, perhaps I will buy the stuff and do it myself but hopefully someone has already done it somewhere saving me the effort. Set up two containers of water, say around a gallon in size, and a rigid pipe in a “U” shape to form a siphon tube, something that will not collapse under atmospheric pressure if a vacuum were drawn in it, perhaps 1/2″ schedule 40 pvc pipe, with elbows to form a U shape, and a valve in the middle of the U to turn flow on/off. Set up water column barometers to read the pressure, one for each tank. At normal barometric pressure you will need a column around 35 feet high for this. Or, seal each container, with a tube connecting them going to a vacuum pump and draw a vacuum to reduce the height required for the water column barometers, if you can draw a vacuum down to around 2 ft of water it obviously makes the experiment easier to setup. The actual vacuum doesn’t matter, what matters is that it is the same in both containers. Now, here is the critical part of this experiment. Set up the upside down U tube so that it’s center is above the water level in the water column barometers, say perhaps a foot or two above. Fill the inverted-U tube with water with the valve shut off to prevent water flow, and the ends of the U are submerged below the water line in each respective container. If pulling a vacuum obviously this will all need to be sealed, or do the experiment at regular atmosphere pressure with an inverted U thats close to 40 ft high. Either way is a lot of work, but certainly do-able. Lot easier to see results if using a vacuum. This would be so easy to sketch but I don’t know how to do that here so bear with my word description.
Now here is the key part. The two water columns barometers should be same height showing pressure is the same on both sides, and the inverted U is filled with water with each end submerged in water of the respective container. One container is set perhaps a foot or so higher than the other, enough to produce a significant siphon flow. If the top of the inverted U is lower than the water column level in the barometers, and the valve is opened, water will flow. But, if the U is higher than the water columns, what will happen? I say, the amount that the U can be raised above the water columns is a measure of the “tensile strength” of the water, i.e. the strength of the “chain”. And I say, this level, if not zero, is close to it. I’m not sure what it would be, but I predict it wouldn’t be more than an inch or so, which could be attributed to surface tension and capillary effects and not molecule attraction.
So, anyone ever done anything like this, or game to try? Bets anyone?
Mike M says:
Not pedantic at all. You did not say “For any given fluid” and among the fluid properties that differ and matter to the maximum height of a siphon is the fluid’s molecular cohesion. You will note that bit is at the crux of the discussion.
This link from a comment above:
“A water siphon can work at over 10 meters, though its delicate and and the water needs to be degassed first. this one got to 24m http://www.youtube.com/watch?v=sz9eddGw8vg”
This is interesting experiment, similar to what I attempted to describe in my post above, however not near carefully controlled enough for my taste. I may try this myself when I get some time. It wouldn’t surprise me if the tubing above the level of barometric water column was crushed from atmospheric pressure which would distort the experiment, just like a straw crushes when sucked to hard on a thick milkshake, one atm pressure actually has a lot of crushing force, tubing needs to be strong, I would suspect even fairly rigid hdpe tubing would crush under full atm pressure. Crushing would decrease the diameter and make surface tension and capillary effects more pronounced. I will say it again, surface tension and capillary effects are real, but I am highly doubtful of the presence of any significant molecular attraction leading to a “chain over pulley” effect with water. I am very interested to experiment with this, if there are any significant “chain pull” effects with water siphon (more than maybe an inch) I will happily eat my words.
LRshultis,
“That is not true. Try placing the inlet tube to the bottom of the water tank.”
I said depth, not mass. When the tubes go deep below surface The numbers you need to add depend on depth to surface. Water depth in the tube below the respective surface are added as zero, and air as negative. A siphon can move water in one direction, either direction, before stopping, depending on how the air bubbles are situated in the tube. Their are aquarium filters that operate by injecting bubbles into tubes to move water up a siphon and over the edge that is higher. This requires that the outlet it the filter (where the water level is higher ) not be below the water line too far so the bubbles can escape.
When I wrote my previous posts I had not read Dr. Hughes papers themselves, only this WUWT blog post about it. Now I have read Dr. Hughes papers themselves, and all I can say is OMG. Here are links:
http://www.nature.com/srep/2014/140422/srep04741/full/srep04741.html
http://eprints.qut.edu.au/31098/25/31098.pdf
http://eprints.qut.edu.au/31098/
It appears the hyperbolic chamber experiment is pretty much the same as what I was trying to describe above, about pulling a vacuum. What he didn’t have in his experiment that I would use in mine, are the barometric water columns for reference, one in each of the two water tanks. It appears to me that his results actually disprove the molecular bond “chain” theory he is promoting, I’m happy to get into details of why if anyone is interested. I’m not a regular poster here (or anywhere for that matter) but I do enjoy reading WUWT. The whole climate science/activism things we have today makes my fur bristle, because I have a pretty good BS detector, and it frequently goes off with the CAGW chicken-littles but it usually doesn’t go off at WUWT, keep up the good work! This siphon thing, though, it has my fur bristling, not because I don’t believe in freedom of speech, but rather the tone of this Dr. Hughes publicly claiming these dictionary definitions are wrong, based on what I see as incorrect interpretation of his own experimental results. And what really gets me going, is the credentials of this guy – he is the expert in the field, no less. Think about this. IF I am right (which I may not be, but on this one I’m pretty sure I am), then this means a senior university PhD in a published paper(s) in peer reviewed journal(s) has made claims that are incorrect, and can easily and repeatably be falsified through lab experiments. If I am wrong on this I will tuck my tail between my legs and skulk off in shame. I’m pretty dang sure I’m not wrong on this, though, and I desire to prove it.
Consider for a moment, IF I am right (and that is still a big IF at this point) then this is an example that could, and maybe should, be used to show what can go wrong with science. To me this is a direct parallel with the problems with climate science, professors not skeptical enough of their own opinions to discern between reality and what they may believe is real.
Here is my interpretation of Dr. Hughes hyperbolic chamber experiment (link above):
1. The siphon quit functioning and turned into a pair of water column barometers when the pressure was lowered to the point where a reference “real” water barometer would show a water level at about the same level as the top of the siphon hose – i.e. exactly what I would expect to happen when barometric pressure is what is responsible for “pushing” the water up the column, and NOT being “pulled” by molecular attraction.
2. The “waterfall” effect he describes is exactly what I would expect to happen as the pressure is lowered such that the reference water barometer (that he should have included in the experiment) shows a level just slightly above the height of the siphon tube. The reason for the “waterfall” is that the pressure differential pushing the water up the tube becomes small enough such that the friction effects of water flowing in the tube become noticable. There is no longer enough flow to fill the tube, and thus it trickles over the top with the tube only partially filled.
3. The height of the “pool” at the bottom of the “waterfall” is approximately where the water level of the other reference barometric water column installed in the lower tank is at – i.e. above the “pool” it is a near complete vacuum, thus corresponding with a reference water barometer placed next to it.
I would appreciate comments or debate on this topic. I don’t personally know this Dr Hughes, and have no personal beef with him. However, if I am correct, this is a big deal to me, and should be to you as well.
One more thing (sorry if I’m becoming a nuisance) Wikipedia has what is IMHO a great writeup on this topic, with a debunk of the chain analogy.
http://en.wikipedia.org/wiki/Siphon
Mike
Unfortunately Dr. Hughes’ explanation is inadequate. Gravity alone cannot completely explain how siphon works. For example, cover the higher or lower reservoir to make it air tight and the flow stops. Why? Decrease the diameter of the tube and flow stops. Why? Gravity cannot explain these because the weight of the fluid is the same.
The more complete explanation is fluid flows when the hydrostatic pressure in the tube is greater than the static pressure of the fluid in lower reservoir and the friction force due to viscosity. Covering the higher reservoir, the air expands and air pressure decreases. This decreases the hydrostatic pressure. Covering the lower reservoir, the air is compressed and air pressure increases. This increases the fluid static pressure. Decreasing the tube diameter increases the fluid friction force.
Dr. Hughes’ study is of interest to hobbyists and amateur scientists. But it is trivial to engineering because the physical principles are well known to students of fluid mechanics. There is nothing new here that is not described in fluid mechanics textbooks.
Spicy Mike, Your assessment is identical to mine.
The mistake in dictionaries is the term “atmospheric pressure.” It should be “hydrostatic pressure.” How does a siphon work? In plain language, fluid flows when the difference between hydrostatic pressure and pressure loss due to fluid friction is greater than the difference between air pressure in low reservoir and high reservoir. In mathematical form:
(Ps – Pf) > (Pl – Ph)
Where: Ps = hydrostatic pressure; Pf = pressure loss due to fluid friction; Pl = air pressure at low reservoir; Ph = air pressure at high reservoir. Fluid flows when the inequality is satisfied. In Dr. Hughes’ experiment, Pl and Ph are equal so it doesn’t matter what the air pressure is because their difference is zero. Ps is always greater than zero therefore water flows.
Had he change Pl = air pressure at sea level and Ph = air pressure at 40,000 ft. Water will flow in the reverse direction – upward. Now that is something gravity alone cannot explain. This is proof that siphons work by differences in hydrostatic pressure and air pressure.
If it were possible to make a water siphon taller than the barometric height then you could discount the atmospheric effect, especially if the two reservoirs were only separated by a few inches. This would also conclusively prove the cohesion theory.
The Vacuum Siphon on Youtube is in effect taller that the barometric height. However water has surface tension and cohesion limited to about 3 to 4mm. You could have a 9.5 metre upleg on a siphon, the bottom 9m could be 2m diameter, the last 0.5m could be 5mm tube and the downleg could be 5mm tube. The up leg would contain approx. 28 tonnes of water. The siphon would work. However, don’t try and tell me that a water column just 5mm in diameter and 500mm long could support 28 tonnes because of cohesive or tensile strength. You are dreaming. The source of energy for the siphon is gravitational potential head, i.e. the height difference between the inlet and the outlet and the water moves due to the circumstances that create a pressure gradient. The different densities of the two mediums, i.e. water and air also come into play.
3 Blind Mice
That is not quite true. What you are forgetting is the bouncy force of the water on itself. I know that this is quite unusual so direct you to http://www.youtube.com/watch?v=_dQJBBklpQQ . As you can see the beads actually lift from the surface. In effect a cylinder of water does not just hang from the top as a weight on a pulley. At each level the liquid is pushing down but it is also pushing up. If you do the maths you can see that in fact it doesn’t matter that the volumes are different, with or without air.
You can see that this is true by imagining the experiment set up with an ionic liquid in the way you describe only with the bottom of both tubes in the same reservoir. e.g a u-tube barometer with one fat leg. Now put the whole device in a vacuum chamber and take away all the air. If the larger volume drags down one side you have in effect created a perpetual motion machine. Clearly this is not possible.
@ur momisugly Adrian
What is not quite true?
You mention “The bouncy force of water”???
Then you add a link with something that has no water at all, rather beads!
And exactly what are you trying to say in your message, you are just rambling.
Maybe you are one of the 3 blind mice
@ur momisugly 3 blind mice
Oh! I’m sorry that my two short paragraphs were too long for you to follow, and please feel free to ad hominem. The point was that at no point does the water need to support 28 tonnes.
@ur momisugly Adrian
My comment re “The Vacuum Siphon on Youtube is in effect taller that the barometric height” was based on the revised barometric height because atmospheric pressure within their chamber has been reduced to zero.
My original comment re tensile strength was directed at those that argue that siphons work only because of gravity and tensile strength, and use the chain analogy that the down leg pulls the up leg with it. Under such circumstances, then it would have to support 28 tonnes.
You wrote that what I said was not quite true but then go on to agree that it doesn’t have to support 28 tonnes.
I have no idea what the beads have to do with water siphons. They are physical attached to each other so it is a chain and expect it would incorporate issues such as minimum bending radius and centrifugal force.