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Physicist unmasks 99-year-old mistake in English dictionaries
The Register ^

Posted on 05/11/2010 9:03:35 AM PDT by Gomez

An Australian physics prof has discovered a 99-year-old error in the Oxford English Dictionary - repeated in most dictionaries worldwide - and is having it corrected.

The error is in the definition of the noun "siphon", a tube used to draw fluid from a higher location to a lower one - as when emptying a vehicle fuel tank, an aquarium or other vessel difficult to empty by other means.

Liquid is, of course, drawn up the shorter limb of the siphon by the weight of that in the longer downward one: thus the operating force is gravity. However most dictionaries follow the OED in stating that atmospheric pressure drives the process.*

Dr Stephen Hughes of Queensland University of Technology noted the error after visiting a massive siphon project in South Australia which was being used to transfer gigalitres of water into a depleted lake.

On returning, the prof decided to write an article about the siphon for use by school science teachers, and discovered to his dismay that most dictionaries described the process wrongly.

"An extensive check of online and offline dictionaries did not reveal a single dictionary that correctly referred to gravity being the operative force in a siphon," grumbled the physicist.

The OED currently says:

A pipe or tube of glass, metal or other material, bent so that one leg is longer than the other, and used for drawing off liquids by means of atmospheric pressure, which forces the liquid up the shorter leg and over the bend in the pipe.

"The OED entry for siphon dates from 1911 and was written by editors who were not scientists," explained Margot Charlton of the Dictionary's staff. Amazingly, it seems that in 99 years nobody had ever queried the definition.

The next edition of the OED will be corrected.

According to Hughes some encyclopaedias - though not the Encyclopaedia Britannica - repeat the error. The doc has written a paper with more detail on siphons which the interested can read here.

Bootnote

*This may be true during the process of starting the siphon off, which is usually done by creating a temporary suction on the outflow end of the pipe so as to draw fluid up and over the hump. This works by the action of atmospheric pressure on the surface in the to-be-emptied vessel: but once the siphon is flowing this force is countered by atmospheric pressure at the other end of the pipe.


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To: James C. Bennett; BitWielder1

A siphon is driven by atmospheric pressure on the upside unless the liquid adheres to the tube. Then it can be raised higher than atmospheric pressure or in a vacuum if you start with a full tube and not suction. Suction will raise it over a hump no higher than atmospheric pressure, i.e. 33 feet of water or 30 inches of mercury.

It is explained in detail in Wikipedia.


41 posted on 05/11/2010 9:46:10 AM PDT by UnbelievingScumOnTheOtherSide (NEW TAG ====> **REPEAL OR REBEL!** -- Islam Delenda Est! -- Rumble thee forth)
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To: mlocher
The government right now is siphoning off huge amounts of job creating capital from the private sector into government coffers to fund an unbalanced budget. The government is a black hole. I therefore vote with the professor and go with gravity.

Oh, I don't know. The government sucks, does it not? Thus pressure might be the driving force in that case.

42 posted on 05/11/2010 9:46:25 AM PDT by El Gato ("The second amendment is the reset button of the US constitution"-Doug McKay)
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To: James C. Bennett

“Are you sure siphons don’t work in a vacuum?”

I question this too. The atmospheric pressure is exactly equal at both ends of the tube. The only reason it might not work in a “perfect” vacuum is that many liquids boil in vacuum.


43 posted on 05/11/2010 9:46:56 AM PDT by bitterohiogunclinger (America held hostage - day 393)
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To: aquila48
I would think that the type of liquid would have something to do with it working or not ... surface tension of different liquids varies appreciably.
44 posted on 05/11/2010 9:47:16 AM PDT by MHGinTN (Obots, believing they cannot be deceived, it is impossible to convince them when they are deceived.)
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To: Yo-Yo
You're wasting your time describing an experiment.

The scientific method doesn't work by hypothesis and experimental proof. It proceeds by consensus and by considerations of social justice. Oh, and the assertions of C-list celebrities.

The debate is over. Siphons used to work by air pressure 99 years ago, but man's destruction of air pressure's native habitat has changed the way they work, for ever.

P.S. I have Siphon Credits to sell.

45 posted on 05/11/2010 9:48:15 AM PDT by agere_contra
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To: BitWielder1

Back in high school physics, we had a kid in the class that insisted atmospheric pressure was part of the siphon. The teacher set up an experiment: He started a siphon and plugged it with a stopper that could be released from outside a bell jar through a stopper in the top. He then evacuated the bell jar and released the plug in the siphon. The siphon flowed (despite the fact the water was boiling at room temperature), but there was no pressure.

Therefore, the siphon is all gravity, pressure has nothing to do with it.


46 posted on 05/11/2010 9:48:24 AM PDT by Cyber Liberty (Build a man a fire; he'll be warm for a night. Set a man on fire; he'll be warm the rest of his life)
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To: James C. Bennett
The top of the siphon has a lower pressure than the ends.
Make the siphon tall enough and that low pressure will reach zero.
Make it even taller and the liquid will split and stop moving.

47 posted on 05/11/2010 9:48:36 AM PDT by BitWielder1 (Corporate Profits are better than Government Waste)
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To: aquila48; drangundsturm; MHGinTN
So would siphons work in a vacuum?

See 41
48 posted on 05/11/2010 9:49:18 AM PDT by UnbelievingScumOnTheOtherSide (NEW TAG ====> **REPEAL OR REBEL!** -- Islam Delenda Est! -- Rumble thee forth)
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To: BitWielder1
A siphon will not work in vacuum, it takes external atmospheric pressure to push the liquid up the shorter leg.

Of course it would, other than the little problem of the liquid boiling off. You could fill the long leg in the liquid resevoir, cap the end, and lift it up over the lip of the container. It would work just fine via gravity alone.

49 posted on 05/11/2010 9:49:21 AM PDT by El Gato ("The second amendment is the reset button of the US constitution"-Doug McKay)
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To: aquila48
So would siphons work in a vacuum?

Yes, but not in zero G.

50 posted on 05/11/2010 9:50:47 AM PDT by Cyber Liberty (Build a man a fire; he'll be warm for a night. Set a man on fire; he'll be warm the rest of his life)
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To: BitWielder1

Not exactly. See 41.
See Wikipedia re trees higher than 33 ft.


51 posted on 05/11/2010 9:51:13 AM PDT by UnbelievingScumOnTheOtherSide (NEW TAG ====> **REPEAL OR REBEL!** -- Islam Delenda Est! -- Rumble thee forth)
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To: sima_yi
Gravity causes the liquid in the long end of the tube to fall, which creates a pressure differential along the length of the tube, which atmospheric pressure on the to-be-emptied liquid attempts to "correct".

Doesn't need to be atmospheric pressure, the weight, and thus pressure of the liquid in the tank would be enough.

52 posted on 05/11/2010 9:51:15 AM PDT by El Gato ("The second amendment is the reset button of the US constitution"-Doug McKay)
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To: goseminoles
Siphons are used frequently in irrigation around here, rather than use the huge sprinkler setups. I have used them draining boats, cheap above ground pools and for a host of other applications, including 'fuel transfer'.

How useful the principle is to you depends on the opportunities you have to apply it.

53 posted on 05/11/2010 9:52:11 AM PDT by Smokin' Joe (How often God must weep at humans' folly. Stand fast. God knows what He is doing.)
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To: James C. Bennett

“Besides, just by an energy equivalence analysis, atmospheric pressure cannot drive a work process in that manner. Gravity-based potential energy by way of the relative difference in liquid levels, is the main source of energy causing the flow.”

The problem with that is the reason you are “Siphoning” is because in order to get the liquid from the higher spot to the lower spot, you need to get the liquid from the higher spot a little bit higher first.

In order to do that you are decreasing the pressure in the tube (relative to the pressure pushing down on the top of the liquid) in order to bring liquid to the high point in the tube, where after the force of gravity will keep the pressure in the tube at its lesser state by itself (which continues to draw more liquid uphill.

If it was in a vacuum, there would be no way to force the liquid to defy gravity and go up, either to start the process, or after the process got started. You are relying on differential pressure between the atmosphere and the tube to make the liquid go “uphill” first.


54 posted on 05/11/2010 9:52:13 AM PDT by dsrtsage (One half of all people have below average IQ...In the US the number is 54%)
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To: Cyber Liberty
There was probably enough steam pressure and/or air left to make it work in that small volume.
Try it again with mercury.

55 posted on 05/11/2010 9:53:51 AM PDT by BitWielder1 (Corporate Profits are better than Government Waste)
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To: El Gato

Excellent point El Gato.

The higher end of the siphon would have to be very close to the top of the liquid in a vacuum bell-jar to remove that possibility.


56 posted on 05/11/2010 9:54:19 AM PDT by agere_contra
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To: BitWielder1
A siphon will not work in vacuum

Mainly because, by definition, there's nothing to siphon in a vacuum.

57 posted on 05/11/2010 9:54:46 AM PDT by dead (I've got my eye out for Mullah Omar.)
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To: UnbelievingScumOnTheOtherSide

Water goes higher than 33 feet in trees because of capillary action. An entirely different phenomena called “surface tension.”


58 posted on 05/11/2010 9:54:50 AM PDT by Cyber Liberty (Build a man a fire; he'll be warm for a night. Set a man on fire; he'll be warm the rest of his life)
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To: Gomez; a fool in paradise
Party pooper!


59 posted on 05/11/2010 9:56:18 AM PDT by Revolting cat! (Let us prey!)
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To: El Gato; BitWielder1

You are both not quite right. See 41

Water has tensile strength and viscosity depending on the tube material that can overcome negative pressure.


60 posted on 05/11/2010 9:56:43 AM PDT by UnbelievingScumOnTheOtherSide (NEW TAG ====> **REPEAL OR REBEL!** -- Islam Delenda Est! -- Rumble thee forth)
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