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.”
Thanks, A. This is a superb post.
I think it is gravity that makes a siphon work, not atmospheric pressure that is somewhat lower at the high reservoir.
J Calvert N(UK) says: April 26, 2014 at 6:00 am “This paper is a travesty! And the journal ‘Nature’ published it – amazing! They have already got a poor reputation and this won’t help. It will be interesting to see what response it gets when serious physicists read it.”
Reply: Completely agree! As I wrote above, I find it frightening.
Ric Werme says: April 26, 2014 at 6:45 am “Why all this talk about connectivity? I reiterate that getting the liquid to the crest of the tube is the key requirement in starting the flow from the higher container to the lower. ”
Reply: Yes, precisely so. Perhaps another succinct way to challenge those who refuse to accept that fact is for them to ruminate two questions:
(1) Why does water go up a soda straw when you drink from it?
(2) Why would the explanation for #1 magically change to “connectivity” when we exchange another but longer column of water for a mouth/lips?
Greg says April 25, 2014 at 6:05 am
“So you’re saying you don’t need a ground/neutral for your house wiring to work…. interesting take.”
No I’m saying you need more that one wire.
Ah, strictly a “DC” (Direct Current) man I see. Tesla would disagree with you as would I …
.
re: Tom Trevor says April 25, 2014 at 9:57 pm
It seems to me that without gravity you have no atmospheric pressure. …
Minimum requirements: Two different fluids (or a gas and a fluid) of sufficiently differing densities in a given, fixed gravitational field such that at least one of the fluids may be ‘corralled’ and encouraged to occupy specific volumes defined by, say, a pair of (upper and lower) buckets …
.
Anthony: “A drinking straw is NOT the same setup, and is not self sustaining like a siphon. ”
A drinking straw is indeed exactly one half of the setup Anthony. There is pressure on each end of the straw. The pressure at the top is lower than the pressure at the bottom. To get the water to the top the difference in pressure must exceed the pressure exerted by the water at the bottom. The higher the column, the greater will be the pressure at the bottom, the more differential will be needed to drive it to the top. If you don’t believe that try sucking water up ~10 feet vertically.
REPLY: Yes 1/2 but not the same. Take the typical “siphoning gas out of a gas tank” problem. Suction is applied at one end of the hose to get the liquid “over the hump”. Once that is done, suction is terminated, and flow self-sustains due to gravity. As pointed out upthread, without gravity, such as in the space station, a siphon won’t work even though there is air pressure. – Anthony
No Anthony, the suction is still there! The column of descending fluid is providing the SAME suction that you provided for initiation.
Put a shut-off valve at the discharge end and shut off the flow. What is holding up the water on the other side, (shorter column)?
Anthony: “If you break connectivity of the water in the hose at the top, no siphon.”
Not true. You CAN have a bubble of air pass through a siphon. I do that when I change my waterbed water every couple years. It’s a siphon to get the water over the window sill which is higher than the top of the waterbed. There is usually a quantity of air in the waterbed and I push it over to the hose inlet and let it gulp air intermittently but quite a bit at a time because the hose is draped out the window and down the ground two stories below thus generating a lot of suction.
Those bubbles break your “connectivity” altogether thus disproving you.
This has been fun. Nothing wrong with reexamining what you think you know.
I used to keep a small garden. Just 4 to 6 plants. I didn’t want to drag the hose out to water it everyday so I took a trash can and drill a hole about an inch or two below the top. The hole was the diameter of some aquarium airline tubing I bought. I ran a line from the bottom of inside of the trash can to the ground a gang valve I bought. Then I ran a tube from the valve to each plant.
I’d fill the trash can above the hole and a siphon would start. Then all I had to do each day is adjust the valves so I had a slow drip and check the water level in the can periodically.
Mike M says: April 26, 2014 at 9:01 am “Put a shut-off valve at the discharge end and shut off the flow. What is holding up the water on the other side, (shorter column)?
Mike M says: April 26, 2014 at 9:18 am “You CAN have a bubble of air pass through a siphon.”
*********************
Anthony – Putting those two points together have an experiment for you. Construct my ‘extreme’ waterbed siphon, the short inlet side column is only 6″ and the discharge side column is 20 feet, (5/8 garden hose). Have shut-off valve on the discharge end below in the open position. Get the siphon going then shut off the valve.
Now remove the inlet from the water and allow all the water to pour out (allowing a bubble to rise to the crest). The short 6″ column now has only air, no water in it at all.
Now re-immerse it into the water and open the valve – the siphoning will resume.
“REPLY: Sorry, no. Actually the definitive experiment to show that siphoning works by gravity alone has been done, see this siphon made with bead chain. Gravity and inertia is all it needs, and it wouldn’t work if the beads weren’t connected, just like water molecules are with bonds. – Anthony”
Analogies can be tricky, especially if the analogy has little in common with the concept in question. If the bead chain were a good analogy to a water siphon, you wouldn’t need the water siphon’s tube, would you? If you must use a bead analogy, make the beads very small individual ball bearings, and you’ll be closer to the actual case of your typical water siphon. Oops, now it doesn’t work…
I gave three links earlier (April 25, 2014 at 1:24 pm). As Mindbuilder has pointed out, the Wiki article on siphons is excellent, with several examples showing why atmospheric pressure is necessary (but not sufficient) for the typical water siphon. If still not convinced, read the second link, Richert & Binder’s reply to Dr. Hughes, complete with photos. If still not convinced, watch the CO2 siphon video. See? No chain required.
Misconceptions aside, this is an excellent article and discussion, which illustrate the misconceptions that bedevil even real life honest-to-goodness scientists, let alone us poor benighted laymen. I’m reminded of the commenters who couldn’t wrap their minds around concepts like “the steel greenhouse”
http://wattsupwiththat.com/2009/11/17/the-steel-greenhouse/
or Dr. Spencer’s “Yes, Virginia” article
http://www.drroyspencer.com/2010/07/yes-virginia-cooler-objects-can-make-warmer-objects-even-warmer-still/
or Anthony’s videotaped “backradiation” experiment
http://wattsupwiththat.com/2013/05/27/new-wuwt-tv-segment-slaying-the-slayers-with-watts/
(Remember some of the comments on that thread, Anthony?) Sometimes I despair for the future of the human race.
But it’s kind of funny, too. 🙂
PS OMG, how could I forget the tar pits thread?
http://wattsupwiththat.com/2014/04/10/the-la-brea-tars-pits-gets-themselves-in-a-sticky-wicket-over-climate-change-and-adaptation/
REPLY: Thanks, if you used highly magnetized ball bearings, to simulate the molecular bonds of water, instead of bead chain, it might work just the same. – Anthony
Anthony,
Interestingly, that statement brings us full circle – back to the dictionary from whence this whole hubbub began.
Your statement is incorrect. The dictionary demonstrates that quite nicely. It does that not by telling us how a siphon works. Dictionaries are not the proper reference for that question. Rather, the dictionary does its proper job by telling us what a siphon is. If one uses ellipsis to pull the OED’s nose out of the realm of the encyclopedia that it is not, the dictionary that it is defines a siphon as:
Fundamentally, that is what a siphon is. Thus, it is not correct to say that a siphon will not work in zero G. Rather, a siphon cannot exist in zero G, because a “siphon” is undefined in zero G. Irrespective of its disputed role as the force that operates a siphon, it is without question that it is gravity that provides the “up” and the “over” that fundamentally define what a siphon is. No gravity, no up. No up, no over. Without gravity, there is no siphon, “working” or not. There is just a tube with a bend in it.
🙂
Ric Werme says: April 26, 2014 at 6:45 am “Why all this talk about connectivity? I reiterate that getting the liquid to the crest of the tube is the key requirement in starting the flow from the higher container to the lower. ”
Reply: I have to slightly walk back my earlier reply, (my fault for not thoroughly digesting your comment). That is not quite correct, the liquid has to be beyond that point, brought up and over the crest then back down to be below the level of the of the feed water in order for the siphon to start functioning.
Well If one defines a “siphon” as a device that continuously (ally) transports a material over a rim at a higher altitude without artificial assistance, then I believe the chain bead demonstration, establishes, that “pure” siphon action requires only gravitational energy to run.
In that sense, I believe that OED and the good Dr. are correct in deleting the atmospheric pressure as the mechanism.
Obviously, the bead chain experiment will work perfectly in a complete high vacuum, but it won’t work, absent gravity.
But when applied to the more common case of a liquid, it would seem to be necessary for most ordinary liquids to maintain positive pressure (>0) in the entire upward side of the loop, or at least a pressure greater than the vapor pressure at the prevailing Temperature. But I’m not totally sold on that restriction yet. The upward momentum thing needs consideration.
From an experimental point of view, I have siphoned liquids, at least water, and gasoline, by totally immersing the tubing, in the liquid, so it fills, and excludes all bubbles of air. Then with my thumb blocking the outlet end of the tube, that end is lifted over the rim, and brought below the liquid level, before releasing. The other end of course must remain submerged. That has always worked for me. No I don’t steal gas, but if you have a boat with a 75 gallon fuel tank, you often use a siphon to remove gas for winter storage for example. In my case, said gas, went into my car to be used up.
Now in that case, I can’t get my hand in the gas tank, to use the above process. Well of course, I suck on it, but you clamp the tube end, before the gas gets to your mouth; so use a transparent plastic tubing.
I have to think some more about how the momentum thing allows for an increased loop elevation.
Now just for kicks, having dealt with bead chains and gasoline.
I wonder if you can siphon empty a vat full of sulphur hexafluoride gas, by just swilling some over the edge (no tube).
PS. Don’t have the boat anymore; got stolen out of my yard.
G
I’m going to invest in some bead chain, so my kiddiegarden teacher can demonstrate pure siphon physics to her munchkins; all of whom, were not responsible for being here.
“””””…..Mike M says:
April 26, 2014 at 9:49 am
Mike M says: April 26, 2014 at 9:01 am “Put a shut-off valve at the discharge end and shut off the flow. What is holding up the water on the other side, (shorter column)?
Mike M says: April 26, 2014 at 9:18 am “You CAN have a bubble of air pass through a siphon.”…..”””””
So Mike; you let in an air bubble that completely fills the up side of the siphon AT ATMOSPHERIC PRESSURE.
Now you immerse, and open the valve.
Water starts flowing, and air bubble too, which starts expanding, and bubble pressure drops as volume expands. Air has low mass, so low momentum, so very little turbo boost from falling water column, coupled through air bubble , to get the upwater going again.
Pretty much falls to ambient air pressure to send water up the upside, so it would seem that upside tube length must be less than the 10 meter limit, and down tube would need to be much longer, to allow for air bubble expansion. For a 9 meter uptube, you’d need of the order of 90 meters of downtube to refill the uptube with water.
This problem is getting totally out of hand; somebody better call a halt, before we all go nuts.
“REPLY: Thanks, if you used highly magnetized ball bearings, to simulate the molecular bonds of water, instead of bead chain, it might work just the same. – Anthony”
It might indeed, but again, if water acted like that you wouldn’t need the tube. You can even build 3D structures with the magnetic balls; try that with liquid water.
http://www.tealco.net/bucky_balls_buckyballs.html
There probably is more going on here than a “siphon” but take an empty glass and place it next to the sink. Take a strip of paper towel and place it so one end is at the bottom of the glass and the other end is in the sink but lower than the bottom of the glass. Fill the glass with water and be sure the towel is also wet all the way to the sink end. The glass will empty.
Reply to Brian Macker
BeauGatun says:
April 25, 2014 at 3:00 pm
The pressure per unit area in the higher chamber is greater due to the greater potential energy of the water than that of the lower chamber. Once the flow is established, it will keep flowing. Air pressure will actually tend to counter this as the lower chamber has a higher surface pressure. As a simple Engineer, am I missing something?
Brian Macker says: April 25, 2014 at 3:35 pm
BeauGatun,
“The pressure per unit area in the higher chamber is greater due to the greater potential energy of the water than that of the lower chamber.”
No, the pressure at the surface of the higher chamber is lower than the pressure at the surface of the lower chamber. You don’t even need any chambers for a siphon to work as long as you have a thin enough tube, or a movable plug in the uphill end of the tube. All the water will flow out the lower end. The pressure differential is in the tube, not the chambers.
Brian Macker from BeauGatun
Yes, you are quite correct air pressure has nothing to do with it. I was being a bit simplistic when I said “The pressure per unit area in the higher chamber is greater due to the greater potential energy of the water than that of the lower chamber” I was not referring to air pressure or a closed system of chambers. What I meant and should have made clear was the potential liquid pressure once the siphon has been established, the difference being between the ends of the tube. The siphon has to be established, it is not spontaneous, which seems to be the thought of some posters. Although I am sure, someone has an example of it. Think of the fun you have establishing the flow of gas out of the car for the lawn mower, that bit uses differential air pressure but only to fill the tube, there are many ways to establish a siphon. The water is going from a higher to a lower potential, that is what all matter will do if it is given the chance, all thanks to four-dimensional space-time aka gravity.
george e. smith says: April 26, 2014 at 12:35 pm:
** So Mike; you let in an air bubble that completely fills the up side of the siphon AT ATMOSPHERIC PRESSURE. Yes
** Now you immerse, and open the valve.Yes
** Water starts flowing, and air bubble too, which starts expanding, and bubble pressure drops as volume expands. Yes, yes, yes & yes. The bubble expands as it’s pressure drops. As it’s pressure drops the differential pressure between it and atmospheric at the inlet increases so water immediately begins going up the inlet the moment the bubble begins expanding.
**Air has low mass, so low momentum, so very little turbo boost from falling water column, coupled through air bubble , to get the upwater going again. Yes. Momentum has some influence on how quickly everything responds but has no affect on the steady state flow once it is established.
** Pretty much falls to ambient air pressure to send water up the upside, Not exactly certain what you are stating here? It started at ambient so now it’s well below ambient as you pointed out above.
** ..so it would seem that upside tube length must be less than the 10 meter limit, Yes, 6 inches is less than 10 meters. 6″ was chosen for demonstrable proof; no need to test limits.
** .. and down tube would need to be much longer, to allow for air bubble expansion. Yes EXACTLY SO! The bigger the bubble, the greater the volume that bubble will have to expand to to reach a low enough pressure for the water to get up to the crest and back down to below the inlet elevation – that’s WHY I picked a very short column going up and a very long one going down – to be certain it would work.
** For a 9 meter uptube, you’d need of the order of 90 meters of downtube to refill the uptube with water. Yes and no. Again, such are longer than needed for demonstration purposes. My description was solely an experiment to disprove the contention that a siphon cannot work with a bubble going through. That’s all it was meant for – not to examine limits.
Hmmmn.
With all of this erudite and deep “thought experiment” discussion ..
1. Has any one actually done the experiment with a pressure gage mounted at the high point between the two ends of the siphon? What is the measured change in rise height pressure w/r height of rise?
2. Across different rise-heights (top of suction fluid level) to (height of rise point), what is the plot of internal pressure to external pressure (gage d/p) at the top of the siphon tube?
3. For different fluids of different vapor pressures at the (room temperature) time of the experiment, what is the d/p with respect to different vapor pressures?
4. For a given height of the siphon rise point, and a single fluid type (ie, a constant vapor pressure) ,what is the relationship between rise height and existing bubble size? (At what point will a given size bubble break the siphon?)
5. What is the relationship between bubble size and tube diameter? Does it matter?
6. For a given rise height and fluid type and fluid vapor pressure, does tube diameter affect rise height?
RACookPE1978 says: April 26, 2014 at 2:11 pm ” 5. What is the relationship between bubble size and tube diameter? Does it matter? ”
No it does not matter at all because having ANY bubble at all disproves the contention that some magical cohesive property in water is dragging the water up and over the crest like a chain going over a pulley. Atmospheric or some other amount of pressure is required at the inlet in order to push the fluid up the ascending tube for a true “siphon” to work. Yes there are cohesive bonds but so trivially insignificant in strength that they are no factor in any discussion of ordinary water siphoned with a garden hose as proven when a bubble goes through.
I have enjoyed all the above. Many of the contributions have failed to clearly differentiate the “powering force” of the siphon from the physical effects taking place when it is running under different conditions. That causes a lot of misunderstanding and digression.
Mike M is correct when he in effect asks for a definition of a siphon to exclude chains-over-pulleys. He is right to do so thus some putative ionic siphons are disqualified.
it was not sufficiently clarified that multiple siphons in series will not work for water if the total “up” exceeds 10 metres which points to the need for air pressure to be present, but the air pressure is not the source of “work” as many have stated.
The comment about the pipeline being above the hydraulic gradient is incorrect, full stop. It applies if the pipeline goes above the source point *only*. Pipelines above the HG work but at a lower flow rate than the starting and endpoints alone indicate.
Mike M, I am inclined to agree with your narrower definition of a siphon as a device that requires at least some atmospheric pressure to function. The others are chain-over-pulley devices some of which look like siphons. Appearances can be deceiving.
Take a container of water. Fill a tube full of water. Place fingers over ends of tube. Place an end of the tube at bottom of the water and other end below the water level in the container and open ends of tube. Water will flow at a speed proportional to pressure of water at the depth that the outlet is relative to surface of the water. That is where gravity comes in. A dense fluid in the tube does not allow separation of the molecules of the fluid in the tube, therefore the fluid need not consist of polar molecules. Therefore, the water siphon does not depend upon any kind of hydrogen or other kind of bonding and only on pressure due to gravity and the dense fluid.
I find it useful to distinguish between a barometer and a siphon.
A water barometer made out of a capped clear flexible pipe will read some 10 meters of atmospheric pressure.
Then lower the capped end below the barometer water container, remove the cap and the pipe is now a siphon that will drain the barometer water container.
The barometer works because of atmospheric pressure, but the siphon works because of gravity.
Of course gravity is the cause of atmospheric pressure. And of course, atmospheric pressure is lower at the barometer water container than at the siphon discharge. I can not imagine how the atmospheric pressure difference might not work against the siphon effect, much less being its cause.
“””””…..Mike M says:
April 26, 2014 at 2:01 pm
george e. smith says: April 26, 2014 at 12:35 pm:
** So Mike; you let in an air bubble that completely fills the up side of the siphon AT ATMOSPHERIC PRESSURE. Yes….”””””
Mike; I was not in any way challenging your assertion that it would work with an air bubble.
I was stepping through your process, for the benefit of other readers, who might not see it, to show them how to figure the maximum up tube height versus the size of the bubble. You stated (correctly), that a bubble could pass on through the siphon. But you didn’t specifically say it wouldn’t change size doing so. I merely used your description to make that point for other readers.
Obviously, a small bubble (short) serves to disconnect the water column, so it isn’t all connected, an that kills most of the momentum transfer, because of the much lower mass of the air bubble.
No, I had no quarrel with your post; but since you gave a blow by blowof your sequence, I just used that to step through and deal with the bubble expansion. Yes, if the up tube height approached the 10 meter atmospheric limit, it will take a very large bubble expansion to get it running again.
G
@Mike M the atmospheric pressure is at both ends of the tubes and annuls itself each side. It isn’t the force that maintains the flow during the siphoning. It is true that it is this pressure that will kickstart the motion when one creates a depression one the other side of the tube, but that action is only removing the counteracting pressure from the the other side of the tube.
The point is that changing one of the pressure on one side (augmenting the pressure on the start side is called a pump) or the other side (then it’s called a straw) will start the motion, but the motion itself is maintained by gravity. That’s why you need a difference of height of the 2 basins and the sipĥon always works from the high basin to the low basin.
TL;DR
The atmospheric pressure is the same on both side and is in equilibrum, therefore not intervening in the siphon.
PS: as for the bubbles, they don’t rupture the flow when under atmosphere is because of this pressure. Under vacuum, where the air pressure is absent in “pushing from both sides” there is no force to maintain the liquid cohesive, that’s why you need a ionic liquid where the internal cohesion of the liquid is strong enough to compensate for the absence of air pressure on both ends, exactly like a chain on a pulley. But the motion of the liquid in the tubes is still due to gravity.