Australian physicist spots dictionary error
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From: Greg Neill on 17 May 2010 08:05 Peter Webb wrote: > I am treating tension as meaning the ability of the material to resist > materials being pulled apart. Liquids are easily "pulled apart". Liquids are easy to pull apart only if they are pemitted to "neck", that is, they can deform into a narrow enough cross section whereby the tension on the corss section can be overcome. There's plenty of examples in the literature of experimental measurements of liquid tensions. > The > characteristic of water that I am using is its incompressibility, which may > be considered a form of "negative tension". Most liquids have very strong > forces preventing their compression, but none at all preventing them being > expanded into a vapour in the absence of some othe forces (eg air or water > vapur partial pressure). > >>> >>> If water had tensile strength, and this caused the operation of the >>> siphon >>> (as others had claimed), then you would be able to start the siphon with it >>> going over an obstacle of greater than 10 metres high (= 1 atmosphere of >>> pressure) and then lift the high point of the siphon until it is more >>> than >>> 10 metres high, and the tensile strength of the water would keep it >>> operating. This does not work. >> >> You make this claim, but can you back it up with empirical >> evidence? >> > > Only the fact that pumps cannot pull water up more than 10 metres, or over > obstacles higher than 10 metres, and this has been known since the early > days of the steam engine when one of its first uses was draining water out > of mines. There are other factors at work there, in that the materials comprising water contact surfaces of the pumping mechanisms etc. are not exactly perfect at "gripping" water at the interface. > > > >> One can point to many examples of water tension operating >> over more than 10m height differential -- just look at a >> forest. >> >> > > Well, no. You can point to many examples of water being pumped over heights > greater than 10 metres. You have not proved that for the respiration of > trees the mechanism is based on water having some form of structural > strength (resisting tension) or even what that mechanism really is or means. > > In the world of engineering, where we know exactly how thing work, we have > lots of examples of water being pumped up greater than 10 metres - in dams > used for storage of hydroelectricity, mining, and elsewhere. These always > have the pumps at the bottom (if the height to be pumped is greater than 10 > metres), and none of them as far as I know are based upon water having any > tensile strength. They "push" liquid through the pipe, either from air > pressure or a pump increasing the pressure at the bottom, not pull it using > water's intrinsic "tensile strength". > > How trees suck up water is not known exactly. There's been quite a bit of progress on this since the 60's. It's clear that in the giant pines that there are no valves or pumps along the xylem paths. There have been some direct and some indirect measurements of the tension of the water in situ. Regardless of the mechanism that is creating the tension from the top of the tree, the tension exists along the stem. http://www.springerlink.com/content/b69pvaywhddnjmu8/ Proceedings of the Physical Society, Volume 58, Number 4: <http://iopscience.iop.org/0959-5309/58/4/310> "The behaviour of water under hydrostatic tension" "It is concluded that if tension is applied statically, ordinary water can stand tensions of the order of 40 atmospheres, even if it is not perfectly air-free. Water nearly saturated with air has been shown to stand tension up to 6 atmospheres." > > However, if you believe that water can be pulled through tubes using its > tensile strength, then this would have a bazillion practical uses, the most > immediate and obvious being that you could pump water up heights excluding > 10 metres by putting the pumps at the top, filling the pipes with water, and > then sucking the water up more than 10 metres using its tensile strength. I > have never seen this at a dam or heard about it in a mine. Trees do it. Nature is a clever engineer. > > Have you a single human engineering example where the supposed tensile > strength of water is used to make siphons or pumps which will lift water > more than 10 metres by "pulling" at one end (using tension) rather than > pushing at the other end (using incompressibility) ? I think that nature has figured out how to do this, it requiring very small cross sections for the "pipes", and molecular level evaporation "pumping". Not exactly practical for current human-scale engineering. There's probablyu also a need to manage the dissolved gases in the water. I think, though, that it may be possible in the future to do something with nanotube bundles. Whatever the practicalities, I don't think that it is possible to continue to argue that water does not support tension.
From: Peter Webb on 18 May 2010 12:05 "Greg Neill" <gneillRE(a)MOVEsympatico.ca> wrote in message news:FiaIn.220667$Ma3.160257(a)unlimited.newshosting.com... > Peter Webb wrote: >> I am treating tension as meaning the ability of the material to resist >> materials being pulled apart. Liquids are easily "pulled apart". > > Liquids are easy to pull apart only if they are pemitted to > "neck", that is, they can deform into a narrow enough cross > section whereby the tension on the corss section can be > overcome. There's plenty of examples in the literature of > experimental measurements of liquid tensions. > This whole thing sounds closer to bullshit the more you explain it. A thought experiment. A piston entirely filled with water. You claim it has huge tensilke strength. Introduce one micrscopic bubble of H2O vapour. Suddenly, the resistance (the tensile strength) drops to as close to zero as as the vusicius flow of water will allow, as the liquid H2O will boil at it partial pressure at that temperature. So the whole thing boils as the volume expands. Any arrangement trying to show the tensile strength of water is inherently unstable, as the most minute bubble of water gas will allow it to behave just like a cylinder containg gas and water, which has no tensile strength at all. .. > of mines. > > There are other factors at work there, in that the > materials comprising water contact surfaces of the > pumping mechanisms etc. are not exactly perfect at > "gripping" water at the interface. > There may be other factors at work here, but the simple fact is that pumps cannot pump any higher than atmospheric pressure. Unless you can produce one which does. The claim is made (in one case) that water has tensile strength equal to 11,000 atmosphere, which suggets that it should be able to suction pump 333,000 feet or about 600 miles into space. But funnily enough know of no siphons that operate over 30 feet which by an amazing co-incidence is 1 atmosphere. >> >> >> >>> One can point to many examples of water tension operating >>> over more than 10m height differential -- just look at a >>> forest. >>> >>> >> >> Well, no. You can point to many examples of water being pumped over > heights >> greater than 10 metres. You have not proved that for the respiration of >> trees the mechanism is based on water having some form of structural >> strength (resisting tension) or even what that mechanism really is or > means. >> >> In the world of engineering, where we know exactly how thing work, we >> have >> lots of examples of water being pumped up greater than 10 metres - in >> dams >> used for storage of hydroelectricity, mining, and elsewhere. These always >> have the pumps at the bottom (if the height to be pumped is greater than > 10 >> metres), and none of them as far as I know are based upon water having >> any >> tensile strength. They "push" liquid through the pipe, either from air >> pressure or a pump increasing the pressure at the bottom, not pull it > using >> water's intrinsic "tensile strength". >> >> How trees suck up water is not known exactly. > > There's been quite a bit of progress on this since the 60's. > It's clear that in the giant pines that there are no valves > or pumps along the xylem paths. There have been some direct > and some indirect measurements of the tension of the water > in situ. Regardless of the mechanism that is creating the > tension from the top of the tree, the tension exists along > the stem. > No, water is being moved up stem. > http://www.springerlink.com/content/b69pvaywhddnjmu8/ > > > Proceedings of the Physical Society, Volume 58, Number 4: > <http://iopscience.iop.org/0959-5309/58/4/310> > "The behaviour of water under hydrostatic tension" > > "It is concluded that if tension is applied statically, > ordinary water can stand tensions of the order of 40 > atmospheres, even if it is not perfectly air-free. > Water nearly saturated with air has been shown to stand > tension up to 6 atmospheres." Gee, and have you got a single example of a pump which can pull water up more than atmosphere (30 feet), let alone the 1,200 feet given in this argument? And how come this guy says 40 atmosphere, when the previous quite was 11,000 atmospheres? >> >> However, if you believe that water can be pulled through tubes using its >> tensile strength, then this would have a bazillion practical uses, the > most >> immediate and obvious being that you could pump water up heights >> excluding >> 10 metres by putting the pumps at the top, filling the pipes with water, > and >> then sucking the water up more than 10 metres using its tensile strength. > I >> have never seen this at a dam or heard about it in a mine. > > Trees do it. Nature is a clever engineer. > No, they don't, and no link you have provided suggests that it is somehow because water isn't easily pulled apart (which is what tensile strength is). It also has absolutely nothing to do with how siphons work because they clearly aren't "just" siphons. If you have an example of where the tensile strength of water means something which isn't just speculation about some biological system, but is something which could be built in a lab or factory to siphon water over 30 feet, let me know about it. >> >> Have you a single human engineering example where the supposed tensile >> strength of water is used to make siphons or pumps which will lift water >> more than 10 metres by "pulling" at one end (using tension) rather than >> pushing at the other end (using incompressibility) ? > > I think that nature has figured out how to do this, it > requiring very small cross sections for the "pipes", and > molecular level evaporation "pumping". Not exactly > practical for current human-scale engineering. There's > probablyu also a need to manage the dissolved gases in the > water. I think, though, that it may be possible in the > future to do something with nanotube bundles. > And the molecular level pumping occurs all along the trunk, and its not an example of tensile strength, its an argument that lots of little pumps keep moving it up. Nor is it even a siphon. So its hardly a counter-example of the dictionary definition of a siphon or proof of tensile strength. > Whatever the practicalities, I don't think that it is > possible to continue to argue that water does not > support tension. > > I'm good at spotting bullshit. This water-tension stuff largely seems confined to biological sciences, where I suspect it is being conflated with (a) surface tension and (b) the fact that if a liquid is moving through a pipe its pressure is less than if it is stationary. Siphons work by air pressure.
From: Greg Neill on 18 May 2010 12:53 Peter Webb wrote: > "Greg Neill" <gneillRE(a)MOVEsympatico.ca> wrote in message > news:FiaIn.220667$Ma3.160257(a)unlimited.newshosting.com... >> Peter Webb wrote: >>> I am treating tension as meaning the ability of the material to resist >>> materials being pulled apart. Liquids are easily "pulled apart". >> >> Liquids are easy to pull apart only if they are pemitted to >> "neck", that is, they can deform into a narrow enough cross >> section whereby the tension on the corss section can be >> overcome. There's plenty of examples in the literature of >> experimental measurements of liquid tensions. >> > > This whole thing sounds closer to bullshit the more you explain it. Have you done any independent research on the topic, or are you content to just react to what I present? > > A thought experiment. > > A piston entirely filled with water. You claim it has huge tensilke > strength. Yes, provided there is no free surface and no nucleation sites. Or, alternatively, provided you are content with a "quick" measurement before the vagaries of imperfections destroy the effect. > > Introduce one micrscopic bubble of H2O vapour. Suddenly, the resistance (the > tensile strength) drops to as close to zero as as the vusicius flow of water > will allow, as the liquid H2O will boil at it partial pressure at that > temperature. So the whole thing boils as the volume expands. > > Any arrangement trying to show the tensile strength of water is inherently > unstable, as the most minute bubble of water gas will allow it to behave > just like a cylinder containg gas and water, which has no tensile strength > at all. Well, it's not as bad as you claim. Vapor pressures for water at low temperatures (say between 0 and 25 C) are pretty low, less than a tenth of an atmosphere. You won't get a spectacular boil-off of the waer as the pressure drops. Also, it was already pointed out that water is not the ideal liquid to set up a siphon in vacuum. I think Uncle Al suggested degassed vegetable oil. > . > > >> of mines. >> >> There are other factors at work there, in that the >> materials comprising water contact surfaces of the >> pumping mechanisms etc. are not exactly perfect at >> "gripping" water at the interface. >> > > There may be other factors at work here, but the simple fact is that pumps > cannot pump any higher than atmospheric pressure. Unless you can produce one > which does. The claim is made (in one case) that water has tensile strength > equal to 11,000 atmosphere, which suggets that it should be able to suction > pump 333,000 feet or about 600 miles into space. But funnily enough know of > no siphons that operate over 30 feet which by an amazing co-incidence is 1 > atmosphere. Giant redwoods and scotch pines manage several hundred feet. Why do you keep ignoring natures clear examples? Also why do you not do a literature search on the tensile strength of water? A simple Google search will turn up lots of hits, including papers and letters to Nature and other journals. > >>> >>> >>> >>>> One can point to many examples of water tension operating >>>> over more than 10m height differential -- just look at a >>>> forest. >>>> >>>> >>> >>> Well, no. You can point to many examples of water being pumped over heights >>> greater than 10 metres. You have not proved that for the respiration of >>> trees the mechanism is based on water having some form of structural >>> strength (resisting tension) or even what that mechanism really is or means. >>> >>> In the world of engineering, where we know exactly how thing work, we >>> have >>> lots of examples of water being pumped up greater than 10 metres - in >>> dams >>> used for storage of hydroelectricity, mining, and elsewhere. These always >>> have the pumps at the bottom (if the height to be pumped is greater than 10 >>> metres), and none of them as far as I know are based upon water having >>> any >>> tensile strength. They "push" liquid through the pipe, either from air >>> pressure or a pump increasing the pressure at the bottom, not pull it using >>> water's intrinsic "tensile strength". >>> >>> How trees suck up water is not known exactly. >> >> There's been quite a bit of progress on this since the 60's. >> It's clear that in the giant pines that there are no valves >> or pumps along the xylem paths. There have been some direct >> and some indirect measurements of the tension of the water >> in situ. Regardless of the mechanism that is creating the >> tension from the top of the tree, the tension exists along >> the stem. >> > > No, water is being moved up stem. Oooh, it's magic is it? Do a literature search. You will find papers on the experimental measurement of the pressure differential, and the tensile strain on the water in the xylem. > >> http://www.springerlink.com/content/b69pvaywhddnjmu8/ >> >> >> Proceedings of the Physical Society, Volume 58, Number 4: >> <http://iopscience.iop.org/0959-5309/58/4/310> >> "The behaviour of water under hydrostatic tension" >> >> "It is concluded that if tension is applied statically, >> ordinary water can stand tensions of the order of 40 >> atmospheres, even if it is not perfectly air-free. >> Water nearly saturated with air has been shown to stand >> tension up to 6 atmospheres." > > Gee, and have you got a single example of a pump which can pull water up > more than atmosphere (30 feet), let alone the 1,200 feet given in this > argument? > > And how come this guy says 40 atmosphere, when the previous quite was 11,000 > atmospheres? Okay, now I think you're just trolling. If you can't sort out the meaning of "ordinary water" and "water nearly saturated with air" in the above paragraph, then you've either no hope of doing your own research or understanding the material it turns up, or you're just here as a troll. Either way, you're not worth more of my time. G'bye.
From: Peter Webb on 18 May 2010 13:50 So just to summarise, you claim it is entirely possible for a siphon to operate over more than 30 feet, and for water to have tensile strengths of from 40 to 11,000 atmospheres, but you can't provide a single example of a siphon which pulls up water more than 1.0000 atmospheres, excepting for trees where you say it isn't a siphon and its not even a pump pulling up from the top - the water is effectively pumped up as it goes along, so its not even vaguely related to a siphon. If water did have tensile strenghts of 40 to 11,000 atmospheres then it would be posible to "pull" it over heights massivle exceeding 30 feet, or up from ines more that 30 feet deep. Alas, and as far as I can tell, you have not provided a single example of a siphon which operates over more than 1.0000 atmospheres. Not 11,000 atmospheres, not 40, not even 1.01 atmospheres. Water is not pulled through a siphon by tensile strength, it is pushed through by air pressure. That is why you cannot show me a siphon which pulls water over more than one atmosphere. And no, plants are not siphons, which is what we are discussing the dictionary definition of. I do not believe that when a dictionary defines siphon it is talking about trees.
From: Greg Neill on 18 May 2010 13:56
Peter Webb wrote: > So just to summarise, you claim it is entirely possible for a siphon to > operate over more than 30 feet, and for water to have tensile strengths of > from 40 to 11,000 atmospheres, but you can't provide a single example of a > siphon which pulls up water more than 1.0000 atmospheres, excepting for > trees where you say it isn't a siphon and its not even a pump pulling up > from the top - the water is effectively pumped up as it goes along, so its > not even vaguely related to a siphon. > > If water did have tensile strenghts of 40 to 11,000 atmospheres then it > would be posible to "pull" it over heights massivle exceeding 30 feet, or up > from ines more that 30 feet deep. > > Alas, and as far as I can tell, you have not provided a single example of a > siphon which operates over more than 1.0000 atmospheres. Not 11,000 > atmospheres, not 40, not even 1.01 atmospheres. > > Water is not pulled through a siphon by tensile strength, it is pushed > through by air pressure. That is why you cannot show me a siphon which pulls > water over more than one atmosphere. And no, plants are not siphons, which > is what we are discussing the dictionary definition of. I do not believe > that when a dictionary defines siphon it is talking about trees. You can remain untutored and wallow in your stubborn refusal to admit that it has been demonstrated by experiment that normal water presents a tensile strength exceeding several atmospheres, and pure degassed water of upwards of 30,000 atmospheres. |