Naked Science Forum
General Science => General Science => Topic started by: chris on 11/10/2008 09:48:53
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Clearly gravity plays a part here, because the (e.g.) water is flowing from a higher to a lower place, but isn't air pressure also involved?
Chris
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Pressure is what it's all about (caused by Gravity, of course).
The air pressure at the top is higher than the air pressure at the bottom; that's enough to lift the water 'over the top'. As long as no air is admitted into the inverted 'u' at the top then water will always be pushed up by pressure on the surface in the upper container.
The higher the water column (drop), the faster will water be pushed out at the bottom but it is Atmospheric pressure which pushes the water 'up' in the first place.
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It's the air pressure that holds the water up in the "up" side of the pipe, but it's the difference in water levels that provides the energy that moves the water. If the "up" pipe is too long it won't work, but if it's short enough you can work a syphon in an arbitrarily low air pressure (down to the vapour pressure of the liquid) and still get lots of flow.
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I thought it was gravity pulling the water down in the down side and, as nature abhors a vacuum, water from the upper container is sucked into the pipe.
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Yes - gravity pulls the water down. BUT air pressure pushes water up INTO the vertical run above the upper surface of water.
The statement "nature abhors a vacuum" is a very old idea and has been explained in much fuller terms, subsequently. Remember - there is no such word as SUCK in Science. Air molecules are not attracted to each other so they can't pull each other. Put some air into empty space and it will just spread out and out. It's always pressure difference that makes fluids flow.
If you have a hole in the top of the U, air will be pushed in and the syphon stops because there is higher pressure on the outside of the top of the U than on the inside.
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Sophiecentair, why would the air pressure be higher at the top than at the bottom? If it's "higher" then there is less atmosphere above the water and therefore the pressure would actually be lower, wouldn't it?
C
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Touchee.
I wrote that badly. The air pressure on the upper surface is higher than the air pressure at the top of the U. That is enough to keep the top of the U full of water. (There is a limit of about 10m to the height to which atmospheric pressure will push the water up and over. In practice, this limit is quite a bit less than 10m)
The pressure difference between top and bottom of the down pipe keeps the water flowing out of the bottom. The greater the 'drop' the faster the flow of water. (Think of old fashioned toilet cisterns put near the ceiling.)
Is that better, Chris?
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So nature doesn't suck [:D]
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(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fmysite.du.edu%2F%7Ejcalvert%2Ftech%2Ffluids%2Fhstat4.gif&hash=9934ebd3aee7838b02500e155d346f8d)
Pascal demonstrated that the siphon worked by atmospheric pressure, not by horror vacui, by means of the apparatus shown at the left. The two beakers of mercury are connected by a three-way tube as shown, with the upper branch open to the atmosphere. As the large container is filled with water, pressure on the free surfaces of the mercury in the beakers pushes mercury into the tubes. When the state shown is reached, the beakers are connected by a mercury column, and the siphon starts, emptying the upper beaker and filling the lower. The mercury has been open to the atmosphere all this time, so if there were any horror vacui, it could have flowed in at will to soothe itself.
http://mysite.du.edu/~jcalvert/tech/fluids/hydstat.htm
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Great demo.
Really clever to arrive at that experiment by thinking about it- and being the first to figure it out.
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(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi209.photobucket.com%2Falbums%2Fbb31%2FAndrew_K_Fletcher%2FImage13.gif&hash=5d320b82c77a2e862d6689868c726019)
Using a small amount of salt or sugar, the following experiments provide some interesting observations with changes in presure and flow in both closed loop tubing and open U tubing.
The closed loop of tubing when soft latex tube is used shows the downward flowing side with salt added bulges due to the increased pressure, while the return flow salt free side shows the latex tube necks inwards due to the reduced pressure and tension applied to the water inside as each moecule pulls on the next molecule in the bead of water.
This experiment, while simple has implications for our own circulatory system.
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The 'C' effect is noticeable when a lock gate between fresh water and sea water is opened. The gates open easily when the forces are equal but fresh water instantly starts to pour out into the sea as soon as they are open because its level is higher. It looks bizarre if you are used to canal locks.
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Great example with the locks, Another example is aquifers in desert regions close to the coast. Fresh water can be pulled up so long as the level does not fall too far. When it does, the salty ocean water floods in and contaminates the once drinkable water. The point being that some of these aquifers have maintained the relatively salt free water for hundreds if not thousands of years. Some of these well have been labled as fossil water due to their unknown age.
When you turn the C: experiment upside down that’s when the density flow becomes really interesting.
The 'C' effect is noticeable when a lock gate between fresh water and sea water is opened. The gates open easily when the forces are equal but fresh water instantly starts to pour out into the sea as soon as they are open because its level is higher. It looks bizarre if you are used to canal locks.
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"This experiment, while simple has implications for our own circulatory system."
How?
Blood etc have pretty near constant density.
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Blood filtered by the kidneys comes out from the kidneys less dense than blood flowing into the kidneys. Salts excreted in the urine prove this to be correct. This means the blood flowing back to the heart in the venous return from the kidneys is less dense than the blood flowing in the arteries. Urine density can be regulated using posture!
Respiration evaporates solute free fluid from a fluid that contains solutes, protein colloids, sugars, all of which are denser than water. Evaporating water from the respiratory tract cannot be achieved without changing the density of said solutes.
Tears, saliva and sweat show how evaporation alters the density of liquids. In dry air sweating produces salt crystals on clothing.
loading the blood by evaporating water from it during expiration will induce a movement of concentrated solutes due to the effects of gravity on said solutes to the point of excretion in the urine via the renal filtration.
http://jap.physiology.org/cgi/content/abstract/60/1/327
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The density of blood is about 1060; plasma about 1025.
Urine has a density of about 1002 to 1030.
There's not a lot of difference. But the range of body fluids seems to be about 1002 to 1060
Blood is kept under pressure in the body, the pressure varies between individuals but mine runs about 70mmHg (a bit lower than most).
The difference between a 2 metre (rather more than 6 feet) column of a liquid with a density of 1002 and one of 1060 is about the biggest pressure difference you could hope for in a person. It's about 120 mmH2O or about 8.6 mmHg.
The biggest possible effect you could get is barely clinically significant. People are not full of unusually watery urine on one side and blood on the other. The effect really isn't big.
Also the blood in the body is, in effect, well stirred- any density gradients are small.
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http://hypertextbook.com/facts/2004/MichaelShmukler.shtml
Blood density changes with body posture. Venous blood density is higher when a person is standing than when he is sitting. The following charts show the venous blood densities of 6 subjects as they change body positions during a 10 minute period.
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Those graphs show changes over the order of 10 mins. that's consistent with this hypothesis. They stand up, their blood pressure falls (it's measured near the neck). Their body notices this and seeks to correct it. Their kidneys take out water and thei blood density rises. They lie down and back diffusion from the intracellular fluid returns the blood density to near it's original value.
Nothing new.
What's not possible is that it takes 10 min for hydrostatic pressure to change.
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Showing how blood density is not a constant density.
This is not correct. Etc presumably relates to other fluids. What happens to the blood where the lymphatic system adjoins the main circulation and releases the waste from the cells? Cerebrospinal fluid flows back into the circulation too, what does that do to blood density where it takes place? Lymph for example contains proteins and sugars.
The thoracic duct carries a 1000 millilitres of lymph in 24 hours to the jugular venous return. Are you suggesting that this will not alter the density of the blood at the junction?
It is erroneous to suggest that blood has a constant density. Taking a drink alters the density at the point the fluid is absorbed. The same as removing fluid during respiration increases the density at the point where the fluid evaporates. Therefore eating a heavy meal without sufficient water would cause a dragging effect on the uptake of fluids from the gut and intestines and induce lethargy.
"This experiment, while simple has implications for our own circulatory system."
How?
Blood etc have pretty near constant density.
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A couple of points, first please learn the meaning of the word "near" as used in that quote.
Secondly, all body fluids have a sufficiently similar density that even the biggest possible effect- the one I described earlier) is less than how much your blood pressure probably changed when you read what I had posted.
The thoracic duct handles about a litre a day; but the heart handles about 5000 times more. About 20% of that is from the brain, down the jugular return, so any effect the lymphatic return has on density will be entirely negligible because they are diluted about 1000 fold.
It would be challenging to detect that change.
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How many thousands of times was the salt solution diluted in the Brixham experiment? Yet this caused water to be drawn vertical to over 24 metres in a single open ended tube. More than twice the limit believed to be possible in physics literature.
Of course there is dilution taking place. But so long as the concentration takes place in the downflow and the dilution takes place in the return flow as will be the case with respiration and drinking fluids, we have a mechanism for keeping the circulation going and for altering the pressures inside the vessels.
1 grain of sugar can initiate this flow causing a chain reaction capable of moving a comparitively huge volume of water round a single vertical suspended tube.
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What was it diluted with? Was there a bloody great pump working on it? Were the walls of the piping muscle lined? Were a whole bunch of other organs changing both the composition and the temperatur of the liquid? Was the experment widely criticised by independent scientists?
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When you turn the C: experiment upside down that’s when the density flow becomes really interesting.
We have been here before and there is not much point bringing in your 'tension' in water idea. The same forces apply whichever way up the tube may be orientated. That is only 'interesting' in the same way that all hydrostatic effects are interesting. The molecules in any experiment can only behave in the way that they will always behave. They can't 'know' what experiment they're a part of.
The medical aspects of posture are popular with the of medicine and there are a lot of people who swear by all sorts of odd therapies. The placebo effect is extremely powerful with certain people and at certain times. That doesn't mean that the effect can be explained in 'quasi mechanical' terms. The explanation is much more likely to be in the psychological direction.
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How can a varicose vein go flat by placebo effect? Ever thought of writing a paper about how a psychological direction might improve someone’s varicosed veins while they are asleep? Who knows, your hypothesis might even become a theory and supported by photographic evidence and reports from a lady who happens to be a very good psychologist. Maybe you should put it to her that watching the oedema vanish from her legs and observing the veins shrink before her eyes is psychosomatic?
She is Old Dragon on the forum and would be delighted to engage you as you obviously have some doubts about the credibility of hers and others statements on this forum.
When you turn the C: experiment upside down that’s when the density flow becomes really interesting.
We have been here before and there is not much point bringing in your 'tension' in water idea. The same forces apply whichever way up the tube may be orientated. That is only 'interesting' in the same way that all hydrostatic effects are interesting. The molecules in any experiment can only behave in the way that they will always behave. They can't 'know' what experiment they're a part of.
The medical aspects of posture are popular with the of medicine and there are a lot of people who swear by all sorts of odd therapies. The placebo effect is extremely powerful with certain people and at certain times. That doesn't mean that the effect can be explained in 'quasi mechanical' terms. The explanation is much more likely to be in the psychological direction.
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http://jeb.biologists.org/cgi/content/full/209/13/2515#FIG3
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fjeb.biologists.org%2Fcontent%2Fvol209%2Fissue13%2Fimages%2Fmedium%2FJEB02277F3.gif&hash=a259867b1ffac7ae31e1c285e65995fc)
Fig. 3. A diagram of the model of the giraffe cranial circulation used. P1, P2, P3, P4, P5, P6 were sites of pressure measurement. R1, R2, R3 and R4 were sites where external pressure could be applied using a sphygmomanometer. A submerged pump and/or jugular limb extension tube was used to generate flow through the system. The jugular tube terminated outside the bath to allow for siphon operation, and bath water level was maintained with a valve-controlled constant inflow
Add a pinch of salt and this diagram comes to life without the need of a pump!
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi209.photobucket.com%2Falbums%2Fbb31%2FAndrew_K_Fletcher%2FImage14.gif&hash=0bf5bbd1ab8df427732972604c4e92c7)
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Add a pinch of salt and this diagram comes to life without the need of a pump!
But that 'pinch' of salt has to be lifted up (requiring gravitational potential energy - the same amount that your pump would supply) and it would also need significant energy to get it to the site in the first place. It isn't free energy, is it? Of course a column of dense liquid will fall when there is a less dense liquid on the other side of the tube. It would be really surprising if it didn't - and for all the well known reasons.
The varicose vein behaves very much like any soft walled tube partially filled. Hold up one end and the air pressure will press it inwards and the hydrostatic pressure will make the water fall to the bottom; it will go flat. Isn't that just elementary stuff? We all know that the heart doesn't provide all the pumping action for the circulatory system - Leg muscles plus valves in the veins and also the arteries help in the process. What are you proposing which is significantly different? (Actual figures would help.)
The only aspect of your work which is potentially revolutionary is your apparent experience with very high siphon tubes. You would need to repeat it with scrupulous reliability and verification to get people to listen to you. Credit to you for producing your movie but it will need more than that to convince the world.
Your 'small scale' version is an entirely different matter; it just verifies what we would all expect. You can't scale an experiment validly if you don't also scale the ambient atmospheric pressure.
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Andrew, you clearly don't understand proper experiments.
I don't need to pick an argument with "name ignored by most people", I just need to point out that they are hardly independent.
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That pinch of salt does not need to be lifted. It is a result of evaporation altering the density at an elevated point. This in turn generates the force required to drive fluids to greater heights as shown in the U tube experiment that illustrates different levels and indeed on the video on youtube that shows the actual experiment. The 24 metre experiment and indeed the other experiments were designed to show that circulation takes place
1. Our varicose veins are not partially filled.
2. we lift the end up as you suggest and the blood does not pool at the bottom as you suggest but either increases or decreases circulation
3. While asleep we are not using the leg muscles so we can rule that out.
4. People who have had veins stripped surgically still observe veins going flat while on IBT so we can rule that out too.
5. The experiment is not a siphon. A siphon does not work at this height. Lowering one vessel will just apply sufficient force to break the bead of water and will not generate a siphon effect. Not surprising really considering the amount of times people have tried to do it for all sorts of reasons. Without the salt in one side you are relying on pressure to move the water and not the flow. Difficult to explain without showing it, so guess we need to do more experiments. I do have more video footage from my experiments on video tape. This will require buying some computer component to transfer the footage to digital.
6. The experiment relies on causing each water molecule to follow the next in a chain reaction generated by the falling salts. Again shown in the simple experiment on Youtube with liquids, salts and sugar dropped in a vase of water. Picture the bead of water as a length of string instead of water for a minute. Clip on a weight at the top of one side and the whole length of string rotates, not because of pressure but because it is string with a weight on one end. The resulting pressures are from the flow, not the flow caused by the pressures.
7. The only aspect of my work is? Again may I refer you to the photographic evidence in the varicose vein study. This study was designed to show the effects of IBT and indeed the pressure changes taking place inside the veins, in a way that ignorance is not an option. IBT has provided some incredible results for people with neurological conditions, yet no matter how incredible, people will find all sorts of excuses for not taking on board the evidence that is put before them. Varicose veins and oedema are simple enough to clearly show the effects of IBT.
You also state that this is common knowledge. But then have the courtesy to ask what is different, supported by actual figures.
Firstly this is not common knowledge, if it were then every single person with these conditions would be sleeping on an inclined bed. In fact the common knowledge relates to tilting a bed in the opposite direction so that the legs are higher than the heart. Ask any doctor, surgeon or scientist that has been taught about posture and varicosity, they will tell you the same.
There is a move towards showing how solutes alter the pressures inside vessels at long last. The late Professor Harold T Hammel (Ted) to his friends wrote a paper and indeed forwarded it to me when he learned about my experiments in Brixham.
Am J Physiol Heart Circ Physiol 268: H2133-H2144, 1995;
0363-6135/95 $5.00
AJP - Heart and Circulatory Physiology, Vol 268, Issue 5 2133-H2144, Copyright © 1995 by American Physiological Society
Roles of colloidal molecules in Starling's hypothesis and in returning interstitial fluid to the vasa recta
H. T. Hammel
Department of Physiology and Biophysics, Indiana University, Bloomington 47405, USA.
To begin to understand the role of colloidal molecules, a simple question requires an answer: How do the solutes alter water in an aqueous solution? Hulett's answer deserves attention, namely, the water in the solution at temperature and external pressure applied to solution (T,pe1) is altered in the same way that pure water is altered by reducing the pressure applied to it by the osmotic pressure of the water at a free surface of the solution. It is nonsense to relate the lower chemical potential of water in a solution to a lower fugacity or to a lower activity of the water in the solution, since these terms have no physical meaning. It is also incorrect to attribute the lower chemical potential of the water to a lower concentration of water in the solution. Both claims are derived from the teachings of G. N. Lewis and are erroneous. Textbook accounts of the flux of fluid to and from capillaries in the kidney and other tissues are inadequate, if not in error, as they are based on these bogus claims. An understanding of the process by which colloidal proteins in plasma affect the flux of nearly protein-free fluid across the capillary endothelium must start with insights derived from the teachings of G. Hulett and H. Dixon. The main points are 1) colloidal molecules can exert a pressure against a membrane that reflects them and, thereby, displace a distensible membrane; 2) they can alter the internal tension of the fluid through which they diffuse when there is a concentration gradient of the molecules; and 3) only by these means can they influence the flux of plasma fluid across the capillary endothelium. However, the process is complex, since both the hydrostatic pressure and protein concentrations of fluids inside and outside the capillary vary with both position and time as plasma flows through the capillary.
http://www.fasebj.org/cgi/content/full/13/2/213
Evolving ideas about osmosis and capillary fluid exchange 1
H. T. HAMMEL 2
Department of Physiology and Biophysics, Medical Sciences Program, Indiana University School of Medicine, Bloomington, Indiana 47405-4401, USA
ABSTRACT
When a solute is dissolved in water at (T, pel), the temperature and external pressure applied to the solution, the water in the solution is altered as is pure liquid water at (T, pel - H2Ol). The liquid water and the water in the solution are in equilibrium when H2Ol is the osmotic pressure of the water in the solution. Every partial molar property of the water in the solution at (T, pel), including its vapor pressure, chemical potential, volume, internal energy, enthalpy and entropy, is identical with the same molar property of pure liquid water at (T, pel - H2Ol). This elementary fact was deduced by Hulett in 1903 from a thought experiment; he concluded that the internal tension in the force bonding the water is the same in both solution and pure liquid water, in equilibrium, at these differing applied pressures. Hulett's understanding of osmosis and the means by which the water was altered by the solute were neglected and abandoned. Competing ideas included the notions that the solute attracts the water into the solution and that the solute lowers the activity (or concentration) of the water in the solution. These ideas imply that the solute acts on the solvent at the semipermeable membrane separating the solution and water. Hulett's theory of osmosis requires that the solute alter the water at the free surface of the solution where the solute exerts an internal pressure on the boundary of the solution retaining the solute. Fluid exchange across the capillary endothelium is influenced, in part, by colloidal proteins in the plasma. The role of the proteins in capillary fluid exchange must be reinterpreted based on Hulett's view, the only valid view of osmosis.—Hammel, H. T. Evolving ideas about osmosis and capillary fluid exchange.
FROM 1960 UNTIL his death in 1980, Professor Scholander and I began preparation for this lecture honoring August Krogh. Of course, we did not know then the circumstances that would become available. Few persons admired Krogh more than Scholander did. And no one, I believe, admires Pete Scholander more than I do.
During this lecture, I shall attempt to be a teacher and a provocateur. I hope to increase your understanding of osmosis with some old and some new ideas about the osmotic process. I will reexamine Starling's experiment (1) and suggest new mechanisms to account for fluid exchange across the capillary endothelium as blood flows from one end to the other. My suggestions will be incomplete; so I challenge the reader to search for additional mechanisms whereby to account for fluid exchange between a capillary and its surrounding interstitial fluid. http://www.fasebj.org/cgi/content/full/13/2/213
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Bored Chemist: A name ignored by most people?
Hardly independent? What does this mean exactly? What are you saying about this person?
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Re: "How does a siphon work ?"
Imagine a bucket on a table containing a long heavy chain, the chain is much longer than the height of the table.
Pulling one end of the chain out of the bucket and allowing it to fall to the floor could set in motion a process which could pull all the chain out of the bucket.
I believe siphoning is like this chain-in-a-bucket analogy.
Tension is possible in liquid, i.e. it can be pulled like a chain (or string), e.g. xylem tubes in trees...
Imagine a narrow tube filled with water and running to the ground from a treetop 360 feet in the air. Water is free to move in the xylem, and the walls of the xylem tube provide no direct support to the water inside. The support comes instead from the water itself. Its internal cohesiveness makes the column of water act like a long suspended string, and the tension on the molecules at any point in the column must support the weight of all the water below them. Expressed as a pressure, or force per unit area, the tension on the water in the xylem is surprisingly high: for every thirty feet of tree height, the tension increases by roughly fifteen pounds per square inch. For a xylem tube 360 feet high, the tension at the top is 180 pounds per square inch.
http://findarticles.com/p/articles/mi_m1134/is_/ai_n13606614
I believe it could be possible siphon in a vacuum. It would be necessary to pump some of the liquid initially to start the process,
(analogous to pulling an end of the chain out of the bucket and allowing it to fall to the floor), but once started the flow would be maintained by gravity, i.e. air is not necessary for a siphon to work.
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RD
So are you saying that a liquid is the same as a solid? You imply that water is just like a chain. Inter molecular forces in liquids are small - enough to produce surface tension, which is a very small effect. You tow your car with a chain and not a column of water.
Do you have evidence to the contrary?
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AKF, your post goes on too long for me to answer all the points but there are some things I need to clear up.
The salt gets up there because energy has been transferred one way or another. It's not magic just heat.
Without muscular activity in the legs, guardsmen faint and airline passengers develop dvt. The veins are distended and go flatter when the legs are elevated. Scout first aid knowledge. The veins are partially full, as I said.
If this tension exists then how can it not show itself everwhere where water is involved?
If you believe anything about the nature of molecules then you have to accept that a molecule can only interact with its close neighbours. You continue to ignore my challenge to tell me how molecules in your model 'know' that they are in your u tube and not in a simple syphon.
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Without muscular activity? A guardsman’s muscles are not relaxed. The pressure on the base of the foot is compromising the circulation. This is why they shift their weight from one foot to another to relieve the pressure and assist the circulation to get past the obstructed vessels.
Airline passengers compromise their circulation by sitting in one position for too long, often falling asleep for hours on end, The dry environment further accelerates evaporation adding to the back pressure as dissolved salts flow down to the restricted vessels. Again pressure on the buttocks compromises circulation, this same pressure is responsible for haemorrhoids developing while sitting on the loo seat for too long, or as granny used to say “don’t sit on a cold hard surface for too long as it will give you piles.
It does show itself everywhere water is involved. Here is the ultimate demonstration for you:
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RD
So are you saying that a liquid is the same as a solid? You imply that water is just like a chain. Inter molecular forces in liquids are her small - enough to produce surface tension, which is a very small effect. You tow your car with a chain and not a column of water.
Do you have evidence to the contrary?
The xylem example above is evidence of the tension water can withstand...
tension at the top [of 360 foot tree] is 180 pounds per square inch.
180 psi is quite substantial, not a "very small effect". If you had a tube of water with two freely moving,
(and snugly fitting) pistons, you could tow your car with it if it had a diameter of about three inches.
[ Invalid Attachment ]
(the I shapes are the freely moving pistons).
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Without muscular activity? A guardsman’s muscles are not relaxed. The pressure on the base of the foot is compromising the circulation. This is why they shift their weight from one foot to another to relieve the pressure and assist the circulation to get past the obstructed vessels.
Airline passengers compromise their circulation by sitting in one position for too long, often falling asleep for hours on end,
So are you agreeing or disagreeing that muscular activity (that means movement) aids circulation?
I'm afraid that you've been wasting my time. You give me a link which is supposed to be demonstrating the existence of tension in water. I patiently looked at it all (btw, it was a Kids programme and not a Scientific Presentation - which is about all you can expect on U tube). Nowhere in the link does 'Dr Bob' mention tension. He merely talks in terms of density and classical hydrostatic pressure effects. You have chosen to quote a phenomenon as proof of a fanciful idea you have. That is no evidence, in any way, that you are correct. It can be explained perfectly on the basis of density changes and a resulting pressure difference.
As for the phisiological bits, if you want me to I could calculate the power available from the pressure difference on different sides of your circulation system. The estimated output power of the heart is a couple of Watts (look it up - there's a lot of stuff about it). I should estimate your 'osmotic' power to be in the region of milliWatts. So the heart dominates - other effects are there and probably measurable but . . . so what (WATT)?
Can you accept arguments based on things like power and energy with actual quantities quoted? Or does it smack too much of 'conventional, chauvinistic' Science?
Again, I ask you to give me some evidence of a properly documented phenomenon in which 'tension' is the only explanation?
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tension at the top [of 360 foot tree] is 180 pounds per square inch.
That is not evidence - it is a statement.
If you had a tube of water with two freely moving, (and snugly fitting) pistons,
you could tow your car with it if it had a diameter of about three inches.
That has been explained in terms of atmospheric pressure by Otto von Guericke years ago. See this link among many others.
http://en.wikipedia.org/wiki/Magdeburg_hemispheres (http://en.wikipedia.org/wiki/Magdeburg_hemispheres)
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A californian redwood?
The cohesion tension theory?
My experiment at 24 metres?
No matter how much evidence is before you you will never accept it!
The following letter came from Professor Hammel:
INDIANA UNIVERSITY
SCHOOL OF MEDIICINE date September 6/ 1995
Dear Mr Fletcher:
I received the information you sent me regarding your ideas about fluid
transport in trees, in tubing and in the vascular system in humans.
I will study your ideas and comment upon them as soon as possible. A Quick
scan of your Brixham experiment prompts me to ask if you conducted this
experiment with boiled water without any solute added to the tubing on
either side of the central point which you raise 24 meters? I expect that
you could raise the tubing to the same height with or without solute in the
water. In any case , your experiment confirms that clean water (water that
is unbroken water, water that is without a single minute bubble of vapour)
can support tension of several hundreds of atmospheres. The record tension
obtained experimentally is 270 atmospheres. At 10 degrees C. (c.f. Briggs,
L. Limiting negative pressure of water. Journal of Applied Physics 21:
721-722 1950).
I expect even this tension at brake point can be exceeded by careful
cleansing of the water, to remove even the most minute region of gas phase.
When the water is already broken, as occurs when gas is entrapped on
particulate matter in ordinary water, the water will expand around even a
single break when tension (negative Pressure) is applied to the water. When
you boil the water, prior to applying (2.4-1) ATM negative pressure to the
water in the highest point of the tubing, you eliminate some of these breaks
in ordinary water. I expect that dissolving NaCl or other solutes in the
water will have little or no effect on the way you measure the tensile
strength of water.
I am enclosing some reprints that may interest you. Some of these deal with
negative pressures we have measured in tall trees, mangroves and desert
shrubs. Other reprints deal with how solutes alter water in aqueous
solutions and how colloidal solutes (proteins) affect the flux of protein
free fluid between plasma in capillaries and interstitial fluid.
Sincerely H.T. Hammel Ph.D.
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If you had a tube of water with two freely moving, (and snugly fitting) pistons,
you could tow your car with it if it had a diameter of about three inches.
That has been explained in terms of atmospheric pressure by Otto von Guericke years ago. See this link among many others.
http://en.wikipedia.org/wiki/Magdeburg_hemispheres (http://en.wikipedia.org/wiki/Magdeburg_hemispheres)
It is intermolecular forces, not atmospheric pressure, which permits water to withstand tension.
If you want an experiment try separating two sheets of wet glass each about a foot square.
The intermolecular forces between the water molecules act like glue holding the two sheets of glass together,
atmospheric pressure is not required: this glass-sheet demonstration would work in a vacuum.
(The Magdeburg hemispheres demonstration would not work in a vacuum).
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this glass-sheet demonstration would work in a vacuum.
That, again, is merely a statement. Have you any evidence of this.
You might bear in mind that the force which has been measured can be explained by atmospheric pressure.
What value do these inter molecular forces have, btw? Can you quote a value from somewhere. You imply that it has been measured. It would have huge implications on things like the boiling point of water, for instance.
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this glass-sheet demonstration would work in a vacuum.
That, again, is merely a statement. Have you any evidence of this.
The wet glass sheets stick together because of the cohesive (and adhesive) properties of water..
Cohesion (n. lat. cohaerere "stick or stay together") or cohesive attraction or cohesive force is a physical property of a substance, caused by the intermolecular attraction between like-molecules within a body or substance that acts to unite them. Water, for example, is strongly cohesive as each molecule may make four hydrogen bonds to other water molecules in a tetrahedral configuration. This results in a relatively strong Coulomb force between molecules.
http://en.wikipedia.org/wiki/Cohesion_(chemistry)
The water really does act like strong glue. Glue does not require atmospheric pressure to function: glue works in a vacuum.
What value do these inter molecular forces have, btw? Can you quote a value from somewhere. You imply that it has been measured.
It would have huge implications on things like the boiling point of water, for instance.
The strong intermolecular forces between (polar) water molecules are why water has higher boiling point than similar sized molecules, e.g. water (H20) is liquid at room temperature, whereas ammonia (NH3) and methane (CH4) are gases at room temperature.
Hydrogen cyanide (HCN) boils at 26oC.
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this glass-sheet demonstration would work in a vacuum.
That, again, is merely a statement. Have you any evidence of this.
You might bear in mind that the force which has been measured can be explained by atmospheric pressure.
What value do these inter molecular forces have, btw? Can you quote a value from somewhere. You imply that it has been measured. It would have huge implications on things like the boiling point of water, for instance.
The value has been measured- it's about 2.5KJ/g
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The value has been measured- it's about 2.5KJ/g
KJ/g is not a unit of force.
Do you have a reference so that I could look at your source? It may make more sense than the bald statement.
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The strong intermolecular forces between (polar) water molecules are why water has higher boiling point than similar sized molecules, e.g. water (H20) is liquid at room temperature, whereas ammonia (NH3) and methane (CH4) are gases at room temperature.
Hydrogen cyanide (HCN) boils at 26oC.
But water boils at room temperature at an ambient pressure at about 0.1 Atmospheres. A volume of water inside the cylinder would boil once the pressure difference was reduced to that amount - with about 90% of the force which would be needed to separate the Magdeburg Hemispheres under the same conditions.
It is very easy to show the effect of depressing the boiling point of water under reduced pressure - I have done it in a bell jar with lukewarm water. It just boils when you reduce the pressure with a vacuum pump. If you conduct your experiment at room temperature, why would the same thing not happen at an appropriate pressure?
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A 1966 paper on the tensile strength of water...
[ Invalid Attachment ]
http://resources.metapress.com/pdf-preview.axd?code=q221256030087858&size=largest
http://www.springerlink.com/content/q221256030087858/
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The figure I gave is the latent heat of evaporation. It's a measure of the energy required to separate the molecules against the force that holds them together. As such it is an indirect measure of that force.
To convert it to a force is tricky because you need to know the form of the force/ distance curve so you can differentiate it.
However you can convert the figure from KJ/g to KJ/mol then to J/ molecule and, knowing how many molecules there are in a given area (from the density etc) you can work out the energy required to separate the molecules in a given area. If you assume that the potential is roughly linear over some small distance you can get an estimate of the force required.
I gave that figure just to show that the force and be calculated (it will be very large).
RD has cited a direct experimental value.
The point is that the force can be (and has been ) measured and calculated.
The other point- that the boiling point of water is dependent on atmospheric pressure is a red herring. The other liquids' boiling points also depend on pressure. However water will always have a much higer boiling point because it has strong bonds holding the molecules together whereas things like methane don't.
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That's fair enough. I was trying to relate it to a possible 'tensile strength' so the number would be handy.
I don't think that pressure vs boiling point is irrelevant. Doesn't it relate to the energy needed to make a surface molecule break free? If there is even a hint of a surface anywhere within the liquid bulk then it can form a bubble at a low enough pressure and any tension you might have had will not count. This argument would not prohibit dynamic tension, as long as the load is applied briefly enough.
But, if a normal lift pump will not operate over a greater height than that which corresponds to atmospheric pressure for the liquid density, then how can an inverted u tube support a greater head?
I appreciate that, in a small bore tube, the effects of the tube surface could make a difference but, in a bulk liquid, what can keep a column above that which is supported by the AP difference?
The paper quoted above agrees with my point - it doesn't work for static pressures below the saturated vapour pressure.
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6 mil bore tubing was used. The reason the inverted tube works is the bead of water remains unbroken s0 at no point is water relying on adhesion to a surface other than the walls of the tube which does not affect the tension applied to the water inside it.
The water has no surface to be pulled from. Having a pump at the top would require the adhesive properties of water to stick to the diaphragm or piston, which in effect is the same as capping one end of a water filled tube and raising it vertically. Adhesion in water while very strong does not come close to the cohesive properties of water molecules.
The inverted tube worked as it was envisaged to do and supports the weight of two columns of water suspended vertically in the smooth bore tough nylon tubing.
The bead of water remains intact for a long time until water vapour forms into bubbles, these join together and cause the beads of water to separate. Now both levels fall back to the 10 meter limit at sea level and the space above is vacuum. As was the case in the original water pump problem that Galileo and Toricelli were faced with at the castle of the Grand Duke of Tuscany. The barometer was born later from trying to resolve this problem, but the problem to this date stands unless we change the parameters a little by using an inverted single open ended tube.
Andrew
That's fair enough. I was trying to relate it to a possible 'tensile strength' so the number would be handy.
I don't think that pressure vs boiling point is irrelevant. Doesn't it relate to the energy needed to make a surface molecule break free? If there is even a hint of a surface anywhere within the liquid bulk then it can form a bubble at a low enough pressure and any tension you might have had will not count. This argument would not prohibit dynamic tension, as long as the load is applied briefly enough.
But, if a normal lift pump will not operate over a greater height than that which corresponds to atmospheric pressure for the liquid density, then how can an inverted u tube support a greater head?
I appreciate that, in a small bore tube, the effects of the tube surface could make a difference but, in a bulk liquid, what can keep a column above that which is supported by the AP difference?
The paper quoted above agrees with my point - it doesn't work for static pressures below the saturated vapour pressure.
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I wish you could tell me the difference between the top of a U tube and the top of a single tube. Particularly if the tube had a 'domed' top. Assume that the vertical height is greater than the 10m , conventional, limit.
The molecules need to stick to the top surface whether it's a U or just the top of the tube.
On the attached diagram, the region in the upper section of both the single vertical and the U tube are under exactly the same conditions. How is the water supposed to stick to the top of one yet not to the other? How do the molecules 'know' that they are in different bits of apparatus so that they can behave differently? A loop of string stuck to the top of either curve would pull away from the upper surface just as easily. Whatever the tension may have been, the liquid would not 'stick' to the top any easier for either case.
Can't you see my problem?
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I wish you could tell me the difference between the top of a U tube and the top of a single tube...
With reference to my chain-in-a-bucket-on-a-table analogy...
If an end of the chain is lifted to the brim of the bucket and released it will fall back into the bucket.
If an end of the chain is pulled over the brim and out of the bucket and below the level of the table then released, it could set off a process which pulls the entire chain out of the bucket.
The top of a siphon's U tube is analogous the brim of the bucket, and the water, (which can have tension), analogous to the chain.
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RD. All you have done is to repeat the 'analogy'. That is not an explanation in any sense. Of course what you say about a chain is correct. We can all measure the tensile strength of a chain; it's what we call a solid and the molecules are very well stuck together. If the tensile strength of water was as high then it would behave like a solid in many ways - it wouldn't flow, for a start. Or perhaps you would like to reclassify materials in some way.
Siphons don't work in a vacuum, in any case. You can't ignore the way a mercury barometer functions; it actually tells you about how the atmospheric pressure is acting. Without pressure pushing on the reservoir surface, the column collapses. Are you suggesting that a siphon would work at the same rate irrespective of the ambient atmospheric pressure? Is there something about the conditions in the tube leading up to a lift pump which is different from the conditions in the 'up' tube of a siphon? I ask again "How do the molecules 'know' what they are supposed to do in each case?" Do they know where they are? Can they ignore the atmospheric pressure in one case and yet totally rely on it in another case?
Dip your hand into a bowl of water. Can you draw up a thread of water by 'tension?
If you want to justify / explain how this phenomenon is going to work as you predict then you have to say, not only how these intermolecular tensions work to keep the column of water stuck together but what happens on the TOP surface / interface with the material of the tube? Are the molecules stuck to that too? If not, why won't they drop off due to the low (negative?) hydrostatic pressure in that region and form a void? Forces act in three dimensions and all directions count.
You could, perhaps, also tell me what the limit to this effect could be. You could imagine making the top section tube wider and wider until the width of the top channel was almost as great as the total height of the loop. Your 'tension' should then also be present. When would the effect stop? At the very last instant when the lower face of the horizontal section dips under the level of the water in the reservoir?
AKF, at least, has seen a phenomenon which needs some explanation and which doesn't confirm normal textbook models. All that you are doing, RD, is to assert a naive idea which is not in accord with the overwhelming opinion and a huge body of evidence.
BTW, there is a great little demonstration to show that air pressure is needed in order for water to be 'drawn' up a tube. If you try to suck up a drink through a straw when an airtight lid (sealed round the straw too, of course) is put on the beaker. If you didn't need atmospheric pressure, then you could suck all the water up with no problem. Try it. Try getting your outboard / lawn mower motor to operate without undoing the breather into the fuel tank. Air has to get in or the reduced pressure will soon stop liquid flowing.
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AFK. Re your Brixham experiment. Did you, at the same time, do a control experiment in which you lifted a single sealed, water-filled tube up to the same height? It would be interesting to have compared the two situations.
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Sophiecentaur
Your domed tube is still a capped end tube. This still relies on the ability of water molecules to adhere to the dome. The weight of the column of water will tear it away at the 10 meter limit. There is no point repeating what is known.
There is adhesion to the top of the U tube, but it equates to the same adhesion the water has on all of the internal wall of the tube. We know that if the top end is open the water flows freely out so adhesion to the walls of the tube is not required to hold the water up. However adhesion is important to prevent the water from necking as it is placed under tension. in that I mean water molecules being pulled away from the inside of the tube so that vacuum can replace it. Adhesion here is important. What we have with the inverted U tube is water molecules cohesively joined to water molecules in an unbroken column of water from one vessel to another.
If we raise our water filled tubes open ends from the two vessels while the tube is suspended vertically the water in both sides appears to be elasticised and rises up both sides equally.
Now the water could flow out one side or the other as one would expect based on current thinking about liquids. Yet it does not! It remains suspended because the water has been stretched down both sides held only by the link to other water molecules.
If we then blow up one side to increase the pressure you would expect the water to flow out the other side immediately. It does not! The water level on the side you increase the pressure rises but not enough to tip the balance and cause water to empty from the other side.
These experiments have been repeated many times, even at greater heights than the 24 metres at Brixham.
If you would like me to bring a demonstration to your school I would be delighted to do so. Or you could phone Mr Smith (head of science at Paignton Community College and ask him what he thought about water flowing up to the top floor of the college. Mr Smith added; “I have no problem whatsoever with this experiment. This is exactly how trees lift water, but what can I do about it? I still have to teach the curriculum!”
To understand the experiment one needs to abandon pre conceptions about how water behaves under tension and think of it as stretching and contracting.
The video link about the ocean circulation was readily dismissed by yourself. That video shows clearly how a sinking denser ocean water can cause a dragging effect on water from the equator pulling up warm less dense water thousands of miles.
This is highly significant in understanding the U tube experiment. The same downward flowing salt in the one side causes the dilute fluid to flow up the other side. Nothing to do with pressure either. We can eliminate air / atmospheric pressure in the closed loop experiment.
I wish you could tell me the difference between the top of a U tube and the top of a single tube. Particularly if the tube had a 'domed' top. Assume that the vertical height is greater than the 10m , conventional, limit.
The molecules need to stick to the top surface whether it's a U or just the top of the tube.
On the attached diagram, the region in the upper section of both the single vertical and the U tube are under exactly the same conditions. How is the water supposed to stick to the top of one yet not to the other? How do the molecules 'know' that they are in different bits of apparatus so that they can behave differently? A loop of string stuck to the top of either curve would pull away from the upper surface just as easily. Whatever the tension may have been, the liquid would not 'stick' to the top any easier for either case.
Can't you see my problem?
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I still don't see how your U tube experiment relates to how water is pulled up a tree - a tree is not a closed system - we know that water transpires from the leaves. Fair enough, this would increase the solutes in the leaves, which would then flow back down, but as it's not closed, it can't be the mechanism you suggest. Would your tube experiment still work if you put holes in the top of the tube, out of which some water could evaporate?
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Ben
This flow and return system does not need any tubes to operate. The experiment was to show how strong the tension is and how efficient the density flow system is, not to represent a perfect mechanical tree.
If my experiment was inside a sleeve filled with water to represent an outer bark, then yes we could have pores in the top of the tube and yes it would cause water to exude at the top as the downard flow would drive the dilute fluid higher as shown in the video exp on youtube.
In fact as I said before Strasburger's experiment used an actual tree that had been killed by picric acid and showed circulation continuing for weeks after the tree had died, eliminating any living processes involved with transport. Killing the tree inevitably liberated solutes and this trickle down of salts from top to bottom maintained the circulation, generating the suction at the base of the trunk submerged in the tub of acid required to draw in the fluid. acid exuded from the dead branches for several weeks and this can also be addressed by using the U spirit level demonstration again on Youtube.
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The problem with this thread is that it involves three or more topics which have been drawn together in order to 'prove' something. In reality, they should be discussed separately as they do not necessarily support each other.
Much of the previous post (the reply to my post, that is) is fine BUT. You still do not say how the molecules (I assume you subscribe to molecular theory) behave.
Pressure in a fluid acts equally in all directions (I think you will agree). There are forces between the water molecules and the inner surface of the tube. If there were not, then there would be nothing to keep them in contact when there was low / negative pressure in the tube. Take a piece of dough, say, and stretch it. The sides move in as the length increases. That is the effect of tension. If you wanted to oppose these forces, then you would have to stick the sides to the inside of a tube - with some other forces. If your column of water is to stay at the same width (i.e. fitting the inside of the tube) there must be forces keeping the surface of the water in contact with the tube wall. These can either be due to pressure (pushing) or adhesion (pulling) but they have to exist. You have already said that there must be negative pressure because it is at a height greater than 10m so the forces must be adhesive. These forces must exist whether the tube is single or a U.
The temporary tensile strength of an unbroken volume of water is one issue and it has been shown and measured. The conditions for it to work are very critical and it is not a common phenomenon to observe because, once the saturated vapor pressure is reached, evaporation can occur and cause bubbles. That's fine.
BUT you need to do much better than you have done if you want to explain the totality of your experiments in the terms you have done so far.
You surely agree that we need any explanations to be as consistent as possible over all situations and that the behaviour of a substance depends upon local molecular conditions. Liquids can exist as liquids even when their temperature is above the normal boiling point - well known. That situation breaks down as soon as there is a nucleus around which a bubble can form. Well known.
The situation of a molecule next to the wall of a tube of any shape, under the same pressure conditions must be the same. How can you dispute that? If you cannot tell me how the situations are different then how can your explanation be satisfactory? I take it that you did not try the experiment with a single tube? You 'assumed' the outcome of that experiment?
The video link about the ocean circulation was readily dismissed by yourself. That video shows clearly how a sinking denser ocean water can cause a dragging effect on water from the equator pulling up warm less dense water thousands of miles.
Your argument would also imply that it is the hot air 'pulling' cold air in underneath it that causes convection - i.e that even gases can exhibit tension. The more sustainable explanation is that the more dense, cooler air displaces the warmer, less dense air due to pressure.
Why do you need tension to explain the ocean circulation when all you need is to realise that there is a bit of excess pressure (the more dense stuff sinks and PUSHES the less dense stuff upwards)? You seem to be confusing cause and effect, here.
Benv's comments make good sense. The structure of the equivalent 'tube' in a tree is very different. Not only is there some venting at the top but the Xylem 'tubes' are much thinner than your plastic tubing. Furthermore, they are very irregular and they have connections with the plant all the way up via perforations. It is surely the extremely small size of the tubes which gives a clue as to how they work. Adhesive forces between water and many substances are stronger than cohesive forces between water molecules. Narrow tubes (capillary) in the Xylem make use of this difference.
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For anyone who doesn't know exactly 'how trees work' or has their own ideas about it, I suggest you take a look at this link. It is a Google Book review and does not show all the pages but there is plenty of evidence which you can read of a well thought out bit of Science which takes the magic out of the mechanisms used by plants to raise water.
The main point about it, as far as I am concerned, is that it depends upon the Xylem tubes being extremely thin. Cavitation is always a problem and can stop the process.
The mechanism does not rely on 'flow' or inverted U tubes. It is described and explained in terms which make sense and do not go against any established ideas.
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A nice sweeping blanket statement as per usual. For a start, you do not know exactly how trees work!
Cavitation is not a problem for trees and does not stop the process, because every single xylem will cavitate and repair the cavitation!
It is not discribed in terms which make sense. Why do you think there is as much debate on the acent of sap in tall trees as there has ever been? Just because it is in the curriculum does not make it correct!
BTW: Didn't assume anything. Tried a T junction at the top of the U tube and found it failed at 10 metres as the junction simply caused the water to fall rapidly to the 10 metres and vacuum above it as expected. Thought I could have got away with it. However, even with the valve closed the join caused a seed point for the water to boil.
It is possible that there is a delay between a sink and a return flow that could be measured to prove whether it's tension or pressure changes that causes the Atlantic conveyor to function the way it does.
Gas could be tested in the same inverted U tube to determine if it also has a tension added to it. Something I have thought about doing with Co2 due to it’s weight. If the gas flows out of the U tube then you are correct. What do you think should happen if we test Co2 in this way? BTW, I am not sure what will happen with gas either so would rather wait to see what happens. Though the atmospheric pressure will equalise at the same height as the water so we would need a much higher U tube to compensate for this. Interesting.
Andrew K Fletcher
For anyone who doesn't know exactly 'how trees work' or has their own ideas about it, I suggest you take a look at this link. It is a Google Book review and does not show all the pages but there is plenty of evidence which you can read of a well thought out bit of Science which takes the magic out of the mechanisms used by plants to raise water.
The main point about it, as far as I am concerned, is that it depends upon the Xylem tubes being extremely thin. Cavitation is always a problem and can stop the process.
The mechanism does not rely on 'flow' or inverted U tubes. It is described and explained in terms which make sense and do not go against any established ideas.
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I am, basically, a reductionist. If there is a theory which explains a phenomenon and it doesn't involve needlessly new complications then I tend to find it acceptable. Science, in general, looks to explain the World with a minimum of 'laws'.
The book in that link manages to give explanations for the phenomena involved with tree sap movement which don't need to introduce any new 'fanciful' ideas. Actual numerical values are quoted and that always reassures me that someone knows what they are talking about. The effect of adhesion and cohesion, taken together is considered and there is a very reasoned discussion of the actual forces involved and the requirement for tubes of the sort of size that Xylem uses. No magic and nothing actually new - just an intelligent approach which uses values drawn from elsewhere in Science.
I mention cavitation because that is something which couldn't be dealt with if the cavities were large.
I did not suggest a T piece should be added; it would obviously be a nucleus for local boiling. I suggested a smooth termination to the top of the tube. Your use of an unbroken length of u tube gave you the best chance of a smooth internal surface in the higher sections. Your explanation that you need tension all round the loop is not the only one which explains the phenomenon.
Yet again, I ask you to tell me the difference in the situation for my two molecules at the top of the two tubes. If you can't either assure me that you did the experiment I suggested or come up with some adequate theory about my two molecules then your explanation (being the 'new' one) is not proven.
As far as I am concerned, there is no need to use your 'cohesion - not- adhesion' idea until you prove it. Conventional arguments about tree sap use adhesion and cohesion and make good sense.
Measuring the delay in the Atlantic Conveyor could be difficult; the time involved is over 1000 years. Why do you want to find tension everywhere? Pressure differences explain all these phenomena - even the Brixham experiments (the indoor and the outdoor ones) where the two ends are exposed to the atmosphere and one column just happens to be heavier than the other. If you adjusted the heights of the two reservoirs, you could stop the flow or even reverse it. The pressure at the bottom of a column of fluid is ρgh (h is height and ρ is density) If ρ is greater then h will be smaller for the same pressure.
It is not surprising that there is still some 'debate' about the tree sap thing; it is not straightforward, there is a sort of 'magic' about it because it is counter intuitive, in many ways and it is the sort of topic beloved of fringe Science.
There is also a lot of aimless debate about Income Tax, personal health and the Moon Landing 'conspiracy'. It doesn't meant that all views are equally valid.
Have you heard of the Van der Vaal forces? They apply in gases and in liquids. They modify the gas laws, particularly at high pressure and are caused by the asymmetry of charges around electrically neutral molecules. What sort of experiment did you have in mind which could reveal gas tension? Gases are usually only too happy to expand as much as you let them. They have already boiled.
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I am, basically, a reductionist. If there is a theory which explains a phenomenon and it doesn't involve needlessly new complications then I tend to find it acceptable. Science, in general, looks to explain the World with a minimum of 'laws'.
The book in that link manages to give explanations for the phenomena involved with tree sap movement which don't need to introduce any new 'fanciful' ideas. Actual numerical values are quoted and that always reassures me that someone knows what they are talking about. The effect of adhesion and cohesion, taken together is considered and there is a very reasoned discussion of the actual forces involved and the requirement for tubes of the sort of size that Xylem uses. No magic and nothing actually new - just an intelligent approach which uses values drawn from elsewhere in Science.
1st Paragraph beginning with the word Basically adds nothing intelligible.
I mention cavitation because that is something which couldn't be dealt with if the cavities were large.
2nd paragraph on the other hand admits there is one big problem for the cohesion tension theory as it stands today. Cavitations. Yes, these tiny bubbles have a habit of forming bigger ones and when they form in the fine xylem tubes, which incidentally are much larger than capillary tubes used experimentally to show capillary action, fail to function because of the same 10 metre limit shown in the barometer and Water pump puzzle: Galileo, Toricelli.
This completely destroys the tension theory as it stands. Another problem is and I have said it time and time again, there are 40 metre trees here in Devon, Larch and some Ash-growing in close proximity to each other that have few branches on the top and very few leaves, yet obviously are capable of surviving for many years. The argument for the cohesion tension theory is that the collective loss of moisture from the leaves causes more water to be pulled up and out of the tree. How pathetic is that?
Capillary action. Well is the tree towering a hundred metres able to cause water to be soaked up through the massive trunk of a Californian Redwood at 5 thousand litres a day? I don’t think so. If this were the case then rising damp in walls would do the same and it does not.
Root pressure: Don’t even get me started on this one.
And then we have Strasburger’s experiments which you failed to address in my previous post. Just in case you missed it. Here it goes again. Take one large tree. Suspend it over a bath of picric acid after it has been recently removed from the soil. While submerged in the toxic soup, saw off the roots, or indeed leave them intact. The acid rises and kills all the living processes in the tree. Now for some 3 weeks or more the tree continues to draw acid up and transpiration continues, even though for all intensive purposes the tree is a skeleton.
Now somewhere I think you mentioned a straw analogy. Take one straw, say 10 metres or more tall. Suck as much as your lungs can bare to suck and se if water rises and flows out the end. But this is not quite like the leaves and branches on the tree is it? As you pointed out in other posts my experiments are too simple to represent a tree. (which incidentally was never my intention) But let us make our straw we are frantically sucking on more like a tree. The leaf for example has pores in it that allow gas to escape. So we stab a few holes in it. Some are closed and some are open, so like a flute we place a few fingers on some of the holes and suck. Do we suck air in or do we suck water up when we couldn’t even suck water up without the holes in it?
Now let us look at the barometer. Here we have a glass tube as you suggested we should try. Mercury has been added instead of water so that the it can be scaled down, after all mercury is a liquid much denser than water and it was good enough for Toricelli and the barometer, which incidentally was a happy accident while trying to sort out the age old 10 metre limit problem, has indeed already got the rounded end you suggested should be tried with water. Let us not forget also that Galileo used a longer tube with water. You fail to accept that what this brilliant man concluded about his own experiments and your suggestion was indeed correct in a single suspended vertical capped tube. The barometer does not show mercury adhering to the top of the tube but shows vacuum above it. Toricelli was trying to recreate the pump problem using this set up and failed, but found the reason why it fails and there was born the barometer.
Now for your analogy of lowering one vessel to initiate a siphon.
Our suspended U tube filled with water, ignore the salt for a minute.
We lower one vessel. Remember the observed elastic properties of water I mentioned in a previous post, again ignored by yourself? Well all that is going to happen is that the water will stretch until it breaks. Note you will not pull the water up the other side. Yes I have tested it.
And no there is no “sort of magic” about how trees lift water just a lot of stupid people that can’t see the wood for the trees.
Andrew K Fletcher
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----- Original Message -----
From: Andrew K Fletcher
Sent: Friday, June 02, 2006 2:15 PM
Subject: [IAWA Forum] More questions on Circulation within a tree.
A while ago, the question of density changes in residual leaf and
branch fluids as a direct result of the efficient transpiration from the
leaves of a tree was put to the group. Judging from the responses which
were also posted at the request of one of the groups members, it would
be fair to deduce that there is a general acceptance that density
changes would be an inevitable consequence of the evaporation of 98% of
the water from the leaves.
several members also began to question what would happen to the sap
once the density had increased and indeed it was suggested that it would
be acted upon by gravity and that the sap would be moved as a result of
this interaction with gravity.
This brings me to the next part of this important question for the
group.
Explaining the results of Eduard Strasburger's experiment
Andrew K Fletcher
Evaporation from the leaves alters the density of the sap at the leaf,
and gravity pulls the denser sap down. This generates a positive
pressure in front of the falling sap, and a tension / negative pressure
behind the falling sap, which initiates a simple flow and return, much
the same as found in a simple flow and return domestic central heating
system, where the heat from the boiler alters the density of the water
causing the heated water to rise, where it is cooled inside the hot
water tank via a coiled copper tube, returning the cooled water back to
the boiler.
The German botanist Eduard Strasburger's famous experiment - where he
killed all of the cells in a tree by cutting off the roots, while
submerged in a bath of picric acid - demonstrated that transpiration and
circulation was maintained for three weeks, after the death of the tree.
I put it to the group that either the picric acid or the copper
sulphate solution used by Strasburger, caused the minerals and sugars
held within the dying leaves and branches to be released over the 2
weeks and that this was all that would be required for a simple flow and
return system to maintain the circulation and transpiration.
Furthermore, the experiment does suggest that no living process need be
involved in the bulk flow of a tree.
This would result in a downward flow caused by the liberated solutes
and this would in turn generated suction at the base of the tree
sufficient to draw in more dilute solution from the bath, and that this
flow would continue until the liberated salts and sugars had either all
reached the picric acid / copper sulphate bath, or that the liberated
salts and sugars had changed the density of the fluid within the tub to
counterbalance any falling solutes.
Andrew K Fletcher, UK
http://4e.plantphys.net/article.php?ch=4&id=98
Strasburger himself was an adherent of the school of physics and provided some strikingly efficient demonstrations of water being lifted to considerable heights without any involvement of living cells (Figure 1). He showed that woody stems with their lower end immersed in concentrated solutions of copper sulfate or picric acid and severed by a cut made below the surface of the liquid, will readily suck the solution up. Immediately upon contact, the poisonous fluid kills all living cells in its way, but the copper or the acid arrive in the transpiring leaves and kill them as well. The uptake of the solution and the loss of water from the dead leaves may continue for several weeks, and new solutions of a different color may be lifted in a dead stem.
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2F4e.plantphys.net%2Fimages%2Fch04%2Fwe0401a_s.png&hash=096f40e6cdfb172c34782ccb002d5cb8)
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It's a shame that you don't appreciate my point about Science being reductionist. But, having seen your approach, which tends to be the inverse of this, I should not be surprised. If one is going to have any chance of improving one's understanding of Science then you need as few factors as possible in the treatment of any situation.
I do not propose to have any strong opinions about the way trees work and I think that there are too many facets for the amateur to understand the process in detail.
What I do feel qualified to have an opinion on is the basic way in which your experiment with elevated tubes experiment may work.
Adhesion is not going to happen with a liquid metal because of the delocalised electrons. You won't get any bonding forces like the water molecules exhibit. That's why you get an inverted meniuscus with mercury. It wouldn't stick to the top a a tube any more than it sticks to the sides. It's not a candidate for a scale model.
I notice that, yet again, you avoid the issue of what molecules actually 'do'. Toricelli, brilliant as he was, knew nothing of molecular bonds so he can't be expected to get it all right. In 2008, I should expect anyone to include the idea in explaining virtually anything.
Do you 'suck'in the air or is it pushed in by the external pressure? Interestingly, in my suggested experiment, there is no air pressure and no water goes up the tube and, in your suggested experiment, there is air pressure and the water moves.
Quoting endless instances of very high trees doesn't make your case better - just one tree would be enough and we all accept that the phenomenon does happen. What we are after, I thought, was some sort of explanation which is consistent with other explanations of other phenomena. That's what Science is all about isn't it?
There are so many differences between your experiments and what goes on in trees that, without some more detailed treatment (involving the molecular level) there is little chance of really improving our understanding of what goes on.
Trees may function after they are dead, for a while, but the structures and materials were put there whilst it was alive - millions of years of development.
I'm afraid that I find it very hard to give credence to many of your personal Scientific models because you just don't apply the very basic concepts of cause and effect in your explanations. Dense fluids SINK through less dense fluids - explicable in historical and modern terms. Yet, on your video, you claim that they are pulled down. This is right, if you say that it is Gravity which is pulling - but Gravity is pulling everything down. It is the difference in density which makes it happen, the same as in the Oceans.
I leave you with my usual question. "How do the molecules know where they are?" I look forward to an answer. Don't bother with stuff about trees. Let's do one thing at a time.
"Wood for the trees" nice one (LOL), does your theory hold water tho?
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Your question about how molecules know where they are has been ignored because molecules cannot know where they are. If you could re-word your question so it makes more sense, maybe I can understand where you are coming from better.
I have tried to explain that the bead of water behaves how water and other liquids behave under tension. This is cohesion in water. The ability of water to stick to water is stronger than water sticking to the tube. This is why the loop works and the single upright tube close at the top either rounded off or flat, or twice as big at the top than the bottom is only as strong as 1 molecule sticking to the tube. As soon as one molecule pulls away more follow, just like blue tack pulling away from a wall, the water tears away from the top of the tube because of the weight of the water column below. The higher the tube goes the greater the weight of the water column. Obvious really.
The unbroken bead of water has a continued unbroken water cohesive bond, at no point is this bond relying solely on adhesion as is the case with your rounded closed end tube thought experiment.
Having a glass tube made to test your experiment is impractical, will inevitably fail, And I see no point in considering testing it given the failings of Galileo on the same subject and many more that have followed.
It’s difficult to ask trees whether this flow and return system is holding water. On the other hand it is easy to ask people if it holds water in human physiology and circulation. More to the point it is even more fruitful to ask people with varicose veins to photograph them as they shrink using an inclined bed, when doctors and nurses predict the opposite will happen.
I would love a chance to talk to you and show these experiments so you can see them for yourself. They are quite humbling to physicists, one in particular a good friend and water engineer to boot sat on the floor with his hands on his face shaking his head saying this cannot be. Why have I not been shown this before. Why have I accepted without question what I have been taught? This same man also benefited tremendously from tilting his bed when he realised the significance of this discovery.
Andrew tel: 01803524117
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Your question about how molecules know where they are has been ignored because molecules cannot know where they are. If you could re-word your question so it makes more sense, maybe I can understand where you are coming from better.
Here lies the crux of our problem. The molecules in the water are what determine what it is going to do. A molecule at the top of your U tube will be in exactly the same situation as one at the top of a single tube; they will both have water molecules below them and plastic molecules above them. You have kept on insisting that they will behave differently in each case. I ask the question because there is no difference in the situations for each of the molecules so how can they behave differently? i.e How could they know where they are? You have acknowledged that that is a nonsense question.
Try to read the following carefully and, if you want to answer it, please keep strictly to the content. Neither trees nor human bodies play any part of the argument or the context here.
Let us consider what is happening at the top of your u tube. First of all, a liquid will flow and cannot 'keep its shape' without some sort of container - that's the definition of any fluid. Furthermore there is a fundamental principle of pressure / stress in fluids and that is it acts in all directions, equally. If you don't accept those two then we must part company - don't bother to read on.
At the top wall of the tube there can either be positive, zero or negative pressure.
If there is positive pressure then the force on the walls will be outwards and balanced by the force from the walls of the (rigid) tube.
If the pressure is negative then there will be an inwards force as well as one 'along' the bead. The liquid will flow 'inwards' or away from the walls unless it is acted on by some other, balancing, force . This force must be due to the attraction of the molecules of water to the molecules on the sides of the tube.
The third option is that there is no force at all - in which case you could take the wall of the tube away and the bead of water would stay intact and behave as it did before.
You must believe that the presence of the tube is necessary for the thing to work - that's the only totally "obvious, really" thing about any of this, actually. We can agree that option three does not apply, I'm sure.
The pressure can hardly be greater at the top than at the bottom. I think you would agree - so the first option cannot apply either.
So we are left with the fact that there must be negative pressure at the top - whether it is a U or a single tube- once the 10m height has been reached. The molecules and the way they interact with their neighbours are what determines how the water will behave. Left to itself, with or without tension between the water molecules, the bead of water would become thinner and thinner (the 'tension' acting equally in all directions) unless the molecules at the interface stick to the molecules on the tube surface. Unless you acknowledge that you may as well say that water is like a solid and that you could replace it with a steel wire running through the tube and expect the same behaviour for steel as water when it emerged at the other end.
Your model implies that the tube is not interacting with the water - or you would have taken the tube into consideration - involving the forces on the molecules. That just cannot be correct or, by the same argument, you would be able to scoop up a handful of water and raise a column - like treacle (and even that will flow back down unless contained within a tube).
If water were like a' chain' then it would not need a tube to guide it - you could just pass it over a pulley. The tube must be doing something which you don't seem prepared to discuss in Scientific terms.
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Didn't think anyone was interested in my experiments on the forum enough to go into them in more depth. I agree with the molecules of water interacting with the molecules of the inside of the tube. And indeed called this adhesion. Adhesion in a resin requires the same interaction between the adhesive and the tubular wall.
Trees must make use of this by producing resins in the sap. This must also contribute to the heights achieved by some tree species. One only has to have this resin between the finger and thumb and pull them apart to see how the resin forms fluid strands, much the same as a spiders silk.
Without any tube. The flow and return will take place in or out of a vessel as gravity causes a density flow, which in turn causes other molecules to be dragged behind it, completing a flow and return. Constant evaporation from the surface of a container filled with fluid containing denser solutes will alter the density at the surface.
There are a number of other anomalies going on in the tubular experiment too, for example, when the salt solution flows down and becomes diluted down the flow leg of the U tube, the flow appears to accelerate. I am not sure what is happening here, but having a stab at it, I think that gravity is able to align / polarise the salt molecules and the water to improve the flow. Conjecture I know, but have no idea what else could be introducing a boost because the upward flow of pre boiled / degassed water is maintained, and no further salt is added to the downward flow side. Another possibility is that gravity interacts better with the same amount of salt as it moves down towards the ground (sea level). Any ideas?
The simple boiled sugar solution video shows how the concentrated solution at the bottom of a pan of water on a gas ring operates a flow and return system that prevents water vapour from reaching the surface. Looking closely we can see active boiling below the surface yet the surface is free from bubbles breaking the surface.
Cavitations have been observed in a scaled down flow and return system consisting of a catheter bag, a bladder wash bag, a drip bag, and a network of vessels designed to show how circulation works in the body at the London International Inventions Fair 1997. This circuit worked very well with the drip bag introducing coloured salt solution at the top of the tubular circulation system. The downward flow caused the whole system to circulate and could be operated by, and indeed was, many thousands of visitors. The salts flowed down through a T junction at the bottom was a bladder wash bag to collect the salts, the coloured solution flowed through a catheter bag using a T junction again and the concentrated solution flowed to the bottom of the bag, as clean water flowed out to replace the salt solution lost. A convenient tap on the bladder bag represented the urine being released from the system. Many doctors, nurses, inventors, scientists and government officials for several countries were entertaining the circuit and discussing the implications with me. Yet none of those people were prepared to rock the boat and do something with it. Anyway, that’s history now. The point I was making is that this flow and return model produced it’s own cavitations. Everyone could see that the flow continued around them with out problem. Bubbles forming, even 5 mil long were observed to flow down instead of up using small pulsate amounts of salt solution released from the bag to drive the circuit.
Once you have observed this and look at a diagram of either the human body, and animal, insect, plant, tree, or the ocean current, or indeed the experiment at Brixham, it all comes alive in front of you. You don’t see inanimate drawings any longer, but a coherent flow and return. It is everywhere in nature, one just needs to understand it to see it.
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There is no point in my replying to your comments because you have avoided addressing the one serious scientific point which would help to solve what is really going on. Another string of instances have not advanced the topic in any way. Clearly your Science is too fuzzy to discuss the issues I brought up. Did you not read what I wrote?
Pity.
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Would anyone else like to contribute some sense?
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You are stating the obvious. Of course the water interacts with the tube, why else would we have performed this experiment had it not?
The analogy of a rope or chain is merely to show the dragging effect of each molecule on it's neighbour. This reaction to movement will make the water flow up or down and even up and down in the same side of the tube if required. Yes a two way flow in the same tube. So how does this fit with your tubular interaction?
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If, as you say, the cohesion is stronger than the adhesion, why does the water not stick to itself and pull away from the tube walls to form an ever-narrowing bead?
Why should the water interact differently with the walls of the U tube and the single tube? I don't think that you have actually considered this in detail.
Most of the links I can find imply that the adhesion between water and glass (as an example) is stronger than the cohesion between water molecules. That explains the positive meniscus with water in glassware. The negative meniscus for mercury is because the adhesion is much less.
But you clearly don't want to discuss what is happening between molecules. You'd rather use generalised 'chat' ideas which don't help with the Science at all.
What is this 'reaction' you quote in your last post? Is it the Third Law 'reaction' or what?
The only reference I have read from elsewhere which actually discusses your 'tension' (several posts earlier) implies that it is 1. Dynamic (it won't last) and 2. Less than the adhesion. Neither of those facts predict your u tube behaving any differently to a smoothly terminated single tube.
BTW, i will repeat another question - how wide can your u tube before the effect will cease? From your arguments, I would infer that there is no limit - even the total height of the U.
And, please, no more trees until this is sorted out.
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As you said earlier, the tension must be acting on all the water, so why do you expect it to be acting closer to the wall? The fact that cavitations take place and can be observed taking place is good enough for me. Even with water vapour bubbles in the column of water the bead does not give up immediately. It is irrelevent whether you believe it or not unless you go ahead and repeat the experiments.
But it is worth considering that a molecule has an affect on it's neighbour. This must also apply when the bead of water fails.
How wide will it go? This is a new one for me. I have no idea having never considered it. We have gone higher than 24 metres though only by a few metres more, though with careful hoisting we could I am sure go higher still. The other video's I have show the experiment more clearly. I must find a way of changing them to digital format for the web.
We have not tested the experiment with a larger bore than 6 mil. But I suspect the diameter increasing more will reduce the stability of the experiment due to the inevitable increase in the weight of each column placing more tension on the water if this is what you mean. So diameter should be on a sliding scale to height achieved. logially that is.
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As you said earlier, the tension must be acting on all the water, so why do you expect it to be acting closer to the wall?
It acts everywhere, as I said. The molecules which are in the bulk of the water will only act on the water molecules immediately around them. The tension will be acting in all directions there but not 'on all the water', just on adjacent molecules. I was interested in what happens at the interface - because that will be where there are molecules of water right next to molecules of plastic. If there are no attractive forces between these molecules then the water will part company with the plastic, pulled away by cohesion. You don't seem to think that this is relevant but, once the water and plastic are separate, the bead will collapse due to its cohesion. If you try this with mercury it won't work at all because the cohesion in mercury is so much higher than the adhesion to the tube.
How can you not see this? If the tension 'within' the water is greater than the adhesive forces (stress) then the column will collapse and fall. Whatever the shape of the water container below the surface we are considering this will apply. As long as there are no rough edges, the column will be supported in both the U and the single tube (I have said this so many times) because the molecules on the surface are under precisely the same conditions. What is your problem with understanding that - or in seeing the relevance of it?
If you believe that a liquid can behave in any other way then you must also believe that water ( and liquids in general) behave totally differently from the way they actually do. You seem to be so attached to the notion that the U tube is essential, rather than just happening to work better because of its inherently unbroken surface and because it is so much easier to fill with liquid without bubbles etc.
If you were to melt the end of some tube and blow a good, smooth, bulb on the end, it would allow just the same thing to happen as happens at the top of your U.
Just because you have produced an interesting and novel effect it doesn't mean that you have explained it correctly.
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You are totally and utterly wrong about the shape of the tube not making any difference.
Let me put it in simple terms for you.
On either side of the tube we have suspended a column of water, which stretches like elastic under tension! The walls of the tube cannot collapse and account for the changes in water level when the open ends of the tube are pulled out of the container filled with water.
Now let us deal with the two plates of glass sticking together due to what you, et al say is showing the strength of adhesion in water molecules.
You are obviously adhering to what you teach in physics relating to adhesion being the stronger force so let me clear things up a little for you.
Question 1. Are you assuming that when two plates of glass are pressed together with water between them, the glass is close enough to have only the molecules that are stuck to each other and in contact with the glass. Or are we saying that there is water between the glass which has many water molecules that do not make contact with the glass too?
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The walls of the tube cannot collapse and account for the changes in water level when the open ends of the tube are pulled out of the container filled with water.
Can we not agree that a force is needed in order for the tube to be having an effect? If there's no force involved then you could take the tube away and there would be no difference - clearly nonsense, so this must be true.
The tube must be doing something. Just 'being there' does not describe what it does.
What does "like elastic" mean?
Elastic ( I think you mean a rubber band) is a solid which needs no container for it to stay in shape. As you stretch a piece of rubber, you distort the bonds throughout the bulk until the forces balance out. The length increases and the width reduces - keeping the volume constant. What is there in a piece of water which will achieve the same thing? All the water I have seen (0-100C) flows, except for small water drops - which we aren't discussing here.
How can your forces only apply 'along' the length of column yet not apply across the width of it? ("like a piece of elastic")
Re your 'glass plate' question: An ''ideal' pair of glass sheets, which are totally flat (to within the thickness of one molecule) would probably stick together in any case, without water - welding, effectively. In practice, there will be many spaces between. The addition of water molecules would increase the adhesive force because they would provide thousands of times more molecules 'in contact' with each face. That will increasing the 'temporary' bonding between the faces - adhesion at work???
If you look at any picture of menisci at a glass - water interface, you will notice that the water is pulled upwards at an angle of greater than 45 degrees. How can you explain this if you deny that the water molecules attract each other more than their attraction to the glass molecules? Also, how do you square your idea with the behaviour of mercury in glass? Do you subscribe to the normal ideas of vectorial addition of forces or do we part company here also?
Real Science does not use Metaphor and Simile to describe what is going on. Can you give a reply which doesn't rely on either of these?
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I put it to you that the two not so ideal sheets of glass have many more molecules of water between them, many of which are not in contact with the glass on either side and only have contact with each other. So we are not only looking at adhesion but also at cohesion and each is as strong as each other until the water parts company with the glass. In fact there is little chance of the water being able to share 1 molecule with the other sheet of glass is there? So cohesion conveniently ignored here is very relevant. And when the water does separate from the glass sheets it is because water has been pulled away from the glass, not pulled away from other water molecules.
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I do get a little tired of sneering remarks about the teaching of Science. Unlike the mass of fringe and fanciful approaches to Science which ignore selected bits of conventional Science yet use other bits, where they suit, good Science and Science teaching try to be consistent and rigorous. If a new idea comes to a 'true' scientist, it will be examined thoroughly to see where it agrees with and where it clashes with the rest of our experience. THAT is the sort of questioning that advances our understanding. Any serious Science teacher will use the conventions because they have stood against many tests, unlike 'alternative' and unproved ideas which come along and pass as frequently as No. 39 buses.
Alternative proponents tend to have an amazing arrogance about their abilities to understand things. We have to protect young minds from a lot of misinformation which presents itself as a crusade against the establishment.
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and each is as strong as each other until the water parts company with the glass
That is merely a statement. How do you 'know' that water will part company with the glass before some water molecules part? On what evidence is it based? A simple piece of evidence which refutes what you say is the angle of a water meniscus. Does that not weigh in your assessment? Are you going to ignore the most basic ideas in mechanics, now?
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Nice try SophieCentaur. But you fail to address the fact that the water volume between the two plates of glass has a massive number of molecules that do not come into contact with the glass and stretch from the molecules that do. So if the two plates of glass are stuck together it is not just because of adhesion is it? If you agree with this, then you must also accept that cohesion in this experiment is = to the adhesion, because this has been used to state the strength of adhesion.
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UH?
You have a chain which breaks. One of the middle links is weaker than the rest. You do an experiment to determine the relative strengths and, low and behold, you choose to say that one of the stronger, end, links broke first.
That just doesn't make sense to me.
Whilst you have some tension then all the links are holding. When the weaker links break, the chain breaks.
Do you contest the evidence of the shape of a meniscus which implies that the adhesion is stronger than the cohesion?
Did you learn any Science (or even some logic) at School, or did you reject it even then?
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http://www.imss.fi.it/vuoto/eberti.html#
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.imss.fi.it%2Fvuoto%2F2775_30.jpg&hash=0bae56b197b7389dedcef7e83b14e19a)
Experiment by Gaspare Berti in the Minim Convent at Pincio.
Gaspar Schott, Technica curiosa, sive, Mirabilia artis, Würzburg 1664
Three and a half centuries ago, most scientists didn't believe in the concept of a vacuum, or a place with no air. But there were a few renegade researchers including Gasparo Berti, who set out to make a vacuum. Berti rigged up a huge glass tube, several stories high alongside his house, and filled the tube with water. Then he sealed off the top of the tube and opened the bottom into a pail full of water. He found that the water level in the tube dropped a few feet, but then didn’t move. Berti claimed that he had produced a vacuum in the tube above the water line, and that’s just what he did. He also made a barometer by gosh, but he didn’t realize it, so it was no big deal. But a couple years later, a guy named Torricelli after carefully eyeing Berti’s vacuum thingamajig, set out to make a barometer with mercury instead of water, because Berti’s barometer was just too big. The experiment was a success, and Torricelli became the creator of the barometer. So, a classic mercury barometer is only about 2 1/2 feet high and much easier to deal with than Berti’s water barometer which would be about the size of your average house. So, on a beautiful spring day, if you used Berti’s barometer, the pressure would read about 30 feet, instead of 30 inches.
The Weather Notebook is underwritten by Subaru, the beauty of all wheel drive with major support by the National Science Foundation. http://www.weathernotebook.org/transcripts/1998/01/30.html
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Nice picture - was it a holiday snap?
But what about my questions? They actually contain some serious Science.
p.s. Yet again you don't read your own links. It was a LEAD siphon. Adhesion to metals would be very low so even your tube experiment wouldn't work at >10m.
You could always try to repeat it with lead, I suppose. A tenner says it wouldn't have the same result as for your plastic tube.
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Im beginning to Like you SophieCentaur :)
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Love you too! Mwah.
Now for an answer?
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Ok so back to the two sheets of glass. If as you suggest cohesion is the weakest link. Then this test never did address the adhesion of water but showed the cohesion of water. Because there would be a huge amount of molecules between both sheets of glass that do not come into contact with the glass.
Now, if we sandwich two sheets of steel together with water between them do we again feel a similar bond between them. As someone who has worked in sheet metal, I can confirm that there is adhesion between the plates, as to whether it is similar to that of glass I cannot remember as it’s been many years ago now. But certainly remember struggling to part wet steel sheets and stainless steel sheets too.
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Your experiences with sheet steel and glass are not relevant because you did no measurements and could not have distinguished quantitatively between attraction or pressure. There is no evidence one way or another there.
How could the sheets of glass have been stuck together if there weren't both cohesion and adhesion? How could the test distinguish between the strengths of the two? A chain of 100 links or a chain of one link would each have the same strength (cohesion). The fixings at either end (adhesion) are just as important, though. You have no knowledge whether the chain or the fixings failed first without side information about the relative strengths.
Does the simple meniscus test not mean anything to you regarding the relative bonding forces? You keep avoiding answering that question. Why?
Is a rubber band solid or liquid? Is it a proper analogy to describe how the siphon works? The 'chain' analogy certainly doesn't either - it can only be used in the context of the 'glass plates and, even then, only in a dynamic sense.
Try thinking Science this time instead of wanting to be right. Stop shifting your ground all the time and concentrate on these few key issues.
Once they are sorted out we can move on, perhaps.
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Air & Water by Mark Denny Pages 255 266 deals with what Professor Hammel mentions in his letter. H.T. Hammel was a World Authority on circulation in trees, spending many years researching it, and a fascinating man who also worked on nuclear energy. We had some interesting conversations regarding cohesion, one of which was the spinning Z tube, and it’s commercial application.
http://books.google.co.uk/books?id=XjNS6v7q130C&pg=PA255&lpg=PA255&dq=spinning+z+tube+cohesion+water&source=web&ots=sGiBMDOEe6&sig=1DfEAi94WVJoGQlzM7-MNwUgjEY&hl=en&sa=X&oi=book_result&resnum=1&ct=result#PPA256,M1
Water flowing vertically in a single open ended tube to 24 meters using salt as the driving force.
Introduction to the experiment
Bench top scaled down version of the Brixham Experiment
Andrew K Fletcher
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why are we back on trees?
Whenever things get tight you start off in another direction. I'm quite happy to talk about trees when we've cleared up the crucial issue of you understanding the logic of my last post. No one else's input is needed for that.
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We are not. Denny relates to cohesion and adhesion which is where we are at.
Read the two pages please, it answers your questions about cohesion and adhesion
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But I need YOU to answer the questions. You see, I don't think you understand my questions (or much of the stuff you keep quoting as answers).
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You first dispute tension is possible. It is proved that it has been measured. Then you dispute the stregnth of cohesion stating ashesion is stronger. Again the measturements of cohesion speak for themselves.
Then there is the evidence of a droplet of water on a surface, rising up from the surface against gravity. Nothing to stick to here is there? Unless you count water sticking to the atmosphere that is.
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Just where is the evidence which "speaks for itself". Where is the measurement of cohesion compared with the measurement of adhesion?
Where else but in the simple meniscus in a water tube?
Could you please comment on what the curve of a meniscus tells you about the relative strengths of the cohesive and adhesive effects? Do you actually understand any of this?
When does a droplet 'rise up' out of the water without being given some kinetic energy? Yet again, you bring up another issue and do not stick to the main one.
What has this to do with your understanding of the meaning of the two terms you keep using and have not yet defined or described.
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The way to settle this is for you to conduct your single six mil bore capped tube elevated vertically above the 10 meter mark and come back and let us all know how it goes. Trying to get me to jump through your hoops is a little lame.
What does the meniscus tell us? It relates to surface tension much more than adhesion. The same can be seen with a water boatman on a pond causes a clear depression in the surface. Do we conclude that the whole of the pond has rose up above the feet of the water boatman? Are you presuming that the curve shows water being pulled up the tube? If so then consider the atmospheric pressure pushing the water up the tube by pressing down on the water that the tube rests in.
You keep asking if I understand your reasoning. The answer is I understand that your reasoning about the ten meter mark that you teach from your science books is erroneous. The Brixham experiment was with a single open ended tube, stretched vertically to 24 metres and more. A tiny amount of salt causes water to flow around the tube drawing water from one vessel into another, and you have the cheek to tell me I do not know my subject. Go explain the Brixham experiment to your students and let them see that the 10 meter limit does not ring true.
You try to separate this flow and return system into boxes so it can be challenged in a way that you can deal with it. Well, this is not how this theory was born. It was born from reading a tremendous amount of open ended conclusions that still to this day attract a tremendous amount of arguments. The Cohesion tension theory as it stands to date is complete Bull***t. Why protect your students from truth?
The meniscus curve does not show water climbing out of the open ended tube now does it? Capillary action does not move water over half a meter does it? What about capillary action in a six mil bore tube for a start off, where does this leave adhesion?
And while we are at it, please explain why varicose veins go flat when a bed is tilted head up by five degrees to the horizontal.
You see SophieCentaur. I know that this theory holds water! I have seen the effects of IBT, which is based on this theory reversing spinal cord injury, multiple sclerosis, cerebral palsy, Parkinsons’s Disease, varicose veins, oedema, thrombosis, scarletina, blindness, and many more conditions. So please refrain from thinking this is some whimsical fantasy. There is a lot at stake for a lot of people and all the time I have to deal with sanctimonious condescending people who think having a qualification places them in a position to ridicule and ostracise a real scientist working on the cutting edge of science and delivering repeatable results.
If you can’t handle this then that is your problem and you have to deal with it not me.
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We'll have to leave it at that then.
When you learn some Science rather than a list of partially related instances, you may realise what I am talking about.
We usually find that people without respect for qualifications are those who have very few of their own.
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I don't have qualifications. I am not a doctor either. But I do have a an enquiring brain and use it to great effect questioning traditionally unsubstantiated guesswork .
Who else is qualified in reversing spinal cord injury and all those other illnesses that respond because a flat bed is avoided? Where are the peers when a discovery is new and contradicts the established views in science?
You put down a challenge for me to test my own theory, yet are unwilling to test your own theory about why the Brixham experiment works and would rather try to mock someone who has tested his own theory experimentally to see if it not only causes water to flow vertical to more than twice the accepted limit, and cause it to hang in mid air with both ends of the tube open to the atmosphere.
My research is challenging your teachings.
I can handle constructive criticism. But will not have you or anyone else try to belittle me. Save that skill for your pupils education and see how many become scientists.
We'll have to leave it at that then.
When you learn some Science rather than a list of partially related instances, you may realise what I am talking about.
We usually find that people without respect for qualifications are those who have very few of their own.
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If you look at the preceding posts you will see that it was not I who started with disparaging remarks. You have 'belittled' the well thought out theories of Scientists who have good track records and you have impugned my teaching. I have merely replied to criticism in kind. If you don't like that sort of thing then don't start it.
It is not up to me to 'prove' anything. I have been trying to apply one or two extremely well established ideas in order to explain your experiences. My argument with you is that your 'explanations' for a list of phenomena are just not rigorous. I tried to reduce one issue (adhesion vs cohesion) to the least complex level. That is not intended to be disparaging to you; it is just the way one needs to approach Science when one want to improve understanding.
You have clearly not seen the relevance of my questions about how your ideas relate to the most basic models in Science. The ideas I am working with are tried and tested (involving molecules, bonds, pressure, stress etc.). They work very well in other contexts so they can be expected to work in this context too.
What you have failed to grasp is that, if your model and explanation of the way water behaves in one specific situation, were correct then water would behave very differently in many other situation. You have not acknowledged the paradox. This can either be because you just don't know basic Science or that you feel so beleaguered that you are not prepared to look outside of the box.
The only way to overturn a hitherto successful scientific theory is to understand it thoroughly and then to see where it is wrong. If your ideas were really correct then you should be able to 'see where I am coming from' and explain my error in my terms. Instead, you have avoided the crux of my questions.
If I haven't expressed myself well enough then there are are plenty of textbooks which can, no doubt, put it better.
Your arguments just don't include rigour; they diverge, rather than converge on an issue. Because of this, they fail to convince.
Until you understand the existing models and all their implications more thoroughly then you are not in a position to justify your own.
Do you think that Einstein would have avoided an argument involving Newtonian Mechanics? He knew he was right with SR and GR because he understood the previous work fully and could see where it was inadequate. He could explain the content of the previous theories in terms of his new theories because he was thoroughly grounded in his subject. Where is your grounding and where does your theory take you with respect to the existing theories?
The theories about molecular attraction are not, by the way, 'unsubstantiated guesswork'.
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Adhesion in water depends on cohesion, it cannot function without cohesion. Cohesion does not need adhesion to work. Water molecules are attracted to each other whether in a rain drop falling from the sky, in the ocean, or indeed a tree.
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Is it just my imagination, or is Andrew obsessed with trees?
Perhaps he was a dog in a previous incarnation
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Imagination BC, there ain't no past life, this is a science forum.
Is it just my imagination, or is Andrew obsessed with trees?
Perhaps he was a dog in a previous incarnation
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OK, there's no evidence for a past life but I think I can find some evidence about trees.
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Successfully operating a siphon in a vacuum, using an exotic ionic liquid that can handle the extreme conditions.
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Successfully operating a siphon in a vacuum, using an exotic ionic liquid that can handle the extreme conditions.
So?
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I thought it was interesting. But, not surprising. However, they obviously did not have a perfect vacuum either.
So, my question is.
What is the limit of the height of a siphon with an ionic liquid?
With Mercury, the maximum height of a siphon is 760mm, or 1 ATM.
With Water, the maximum height of a siphon is theoretically 33.95 feet (also 1 ATM).
Does vapor pressure also play a role? So a siphon of water at 99°C would be a lot lower than one at 4°C.
With the ionic liquid, I assume one could likely calculate the maximum height of the siphon based on the density of the liquid. So, if the density was around 13.5 g/cc, then the maximum height of the siphon would be about 760mm.
If the density was about 1g/cc, then the maximum height would be about 34 feet.
In the You-Tube film, I would be curious what they would have gotten had they used a loop of material giving a height of about 3 feet or so.
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CliffordK the heights you have quoted are the theoretical predictions based on a siphon acting under atmospheric pressure. This height is proportional to the magnitude of atmospheric pressure, in the experiment I'm sure the pressure is reduced enough to make this theoretical height miniscule (much less than the height achieved in the experiment).
What is the maximum height achievable with this liquid is a good question (and how is this dependant upon air pressure), but I don't think you're predictions based on density are necessarily going to be correct.
Also nice point about vapor pressure, I can only assume that air pressure is effectively reduced with the increase of vapor pressure (either by decreasing air pressure or heating the liquid). The liquid in the video however has no significant vapour pressure, apparently it will sit in space for years.
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I'm sure the ionic liquid would be odd to work with.
If you take a Mercury barometer, the space above the liquid is essentially a pure vacuum (plus some Mercury vapor due to the vapor pressure). Lowering the pressure, and the mercury level gets lower. Raising the pressure and the mercury level goes up. However, this vacuum gap at the top would be sufficient to break a siphon.
If one made a column of the ionic liquid, one would likewise eventually reach a height where a vacuum gap would form. And, if it is part of a siphon, the vacuum gap would break the siphon. And, this would be dependent on the pressure.
However, it might be somewhat like a supercooled liquid, in that the level may raise up beyond the expected maximum, then once the gap starts to form, it would quickly drop down to the expected height.
Unlike the Mercury, the gap above the ionic liquid would be essentially a pure vacuum without vapor from the liquid.
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Touchee.
I wrote that badly. The air pressure on the upper surface is higher than the air pressure at the top of the U. That is enough to keep the top of the U full of water. (There is a limit of about 10m to the height to which atmospheric pressure will push the water up and over. In practice, this limit is quite a bit less than 10m)
The pressure difference between top and bottom of the down pipe keeps the water flowing out of the bottom. The greater the 'drop' the faster the flow of water. (Think of old fashioned toilet cisterns put near the ceiling.)
Is that better, Chris?
Because of gravity, water and most liquids seek their own level. This means that if left side by side, gravity would not be able to move the water in any direction. But if you were to move one container lower than the other then water could move in the direction of the lower level container through a tube or pipe that was attached to the bottom of the higher container. But if the tube used to move the water had to be raised higher than the upper container, suction would get the water moving in the direction of the lower container and then gravity would take over and the water would continue to move without further suction. A siphon doesn't "defy" gravity to work, but uses gravity to perform the siphoning action.
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Touchee.
I wrote that badly. The air pressure on the upper surface is higher than the air pressure at the top of the U. That is enough to keep the top of the U full of water. (There is a limit of about 10m to the height to which atmospheric pressure will push the water up and over. In practice, this limit is quite a bit less than 10m)
The pressure difference between top and bottom of the down pipe keeps the water flowing out of the bottom. The greater the 'drop' the faster the flow of water. (Think of old fashioned toilet cisterns put near the ceiling.)
Is that better, Chris?
Because of gravity, water and most liquids seek their own level. This means that if left side by side, gravity would not be able to move the water in any direction. But if you were to move one container lower than the other then water could move in the direction of the lower level container through a tube or pipe that was attached to the bottom of the higher container. But if the tube used to move the water had to be raised higher than the upper container, suction would get the water moving in the direction of the lower container and then gravity would take over and the water would continue to move without further suction. A siphon doesn't "defy" gravity to work, but uses gravity to perform the siphoning action.
Commodity Tip - please reference anything copied and pasted from another site. Your answer is entirely from
http://wiki.answers.com/Q/How_does_a_siphon_work