I was interpreting “state…of the tube” as the configuration of the tube (i.e., bends in the tube) as opposed to the phase of matter of the tube (i.e., solid, liquid, or gas). In retrospect, it looks like NanoByte meant the latter rather than the former; in that case, change my comment to “silly question.”
Actually, the tube would be out of gas right after the upper container went dry… Or did I misinterpret your remark?
Anyway, I thought he meant varying between say metal plumbing, to reinforces hose, to sloppy floppy easily collapsible tubing. (No Viagra jokes, please.)
Uh, regardless of what they pay you to do, your model is flawed once you place the “force” on the upper container but don’t place that force on the lower container. At this point instead of a siphon, you have a big goofy syringe full of mercury, injecting into an open container. More importantly, you’ve got a pressurized syringe injecting into an open container under a vacuum. Under those conditions, you could expect to raise the open container above the sealed container, and still continue the flow in the same direction.
A more accurate model would be the same setup, with weighted platforms sealed around the edges with o-rings (I know how you love those) on both containers.
In closing, I’d just like to say that we all just need to admit that siphons are magic, and we are never meant to understand them, any more than we are meant to understand why women have so much stuff in their purses, or have 20 pairs of identical black shoes.
Since NanoByte was talking about siphoning liquids and gasses through a solid tube, I interpreted the “state” of the tube to be referring to whether the tube itself was solid, liquid, or gas. i.e., a joke. But who knows?
I think we are moving toward a consensus.
Regarding the “handkerchief siphon”, I still don’t think it merits the label siphon. Consider that that driver for that is the capillary action of the fabric, would that make it possible to “pump” the fluid to a higher level? Or would gravity overcome that force?
Re: the handkerchief/papertowel/toiletpaper siphon;
Haven’t had a chance to test it… Does it continue to flow after the “wick” is saturated, like a hose would, and eject fluid at the far end?
Yes, by “state” of the tube, I was referring to gaseous, liquid or solid; but, in all of that series, I was not about to tax my brain (now lazy in retirement and not instilled in the physics of fluids, but rather in electronics engineering) on what I could remember of the pertinent physics; I just thought I’d throw out the highest level of feet-off-the-ground abstraction in physics that had relevancy. . .and might confuse everybody even more. 
I think TheBrain, at one point, touched on an aspect of the muck stirred up here: Physics would normally seem pretty cut and dried beyond challenge, but the consistency of all its concepts and their interrelationships tends to fray sometimes when you try to relate them to the concepts of intuitive reality. In such cases, you run to subjective philosophical attempts at solutions which never, of course, result in agreement between experts. For one thing, I don’t think ‘push’ and ‘pull’ in this context really serve well as scientific notions. Scientifically, you only have a system under study, within which there are forces and matter moves.
I haven’t entered this discussion very seriously because 1) my brain’s presently lazy and 2) I’m not qualified, either on the scientific or engineering level, to state clearly any well-founded, coherent explications of siphons.
I really don’t think Chesnakas, THE VERY FLUID MECHANIC, USN, really clarified siphon life on the moon with his solid weight. I can’t tell whether what doesn’t register with me is due to his physical model or to a defect in his description of it. With his tubs sitting solidly on the moon’s surface, a weight placed on a solid, inflexible cover over the upper tub wouldn’t do anything, whatever sort of matter or vacuum be between the liquid in that tub and its cover. And if the space between the liquid’s surface and the cover consist merely of a vacuum, even the weight on a flexible cover wouldn’t do anything. I don’t get it.
Ray
I think the part of his model you missed was the fact that the container was not sealed by an immobile lid. The reason for the o-ring was to keep a seal while the weighted cover moved down into the container under gravity, so the fluid would only escape through the hose.
That said, I still don’t like it… 
You’re right; I missed that.
Ray
Chesnakas said:
If you’ve got a question about aerodynamics or fluids, don’t go to a Physicist. In general, they don’t deal with this stuff enough to have a feel for it. Go to an aerodynamicist or a fluid mechanic.
silly,
If you want to understand something, you always go to the physicist. A decent physicist can explain anything you ever wanted to know about siphons.
-Luckie
Dunno if this will help the discussion or not, but, played with the siphons. They’re a lot of fun. 
____
/*****\
|*|---\*\
|*| \*\ <- When kept above surface of water
|*| \*\ in this position, the water column
|*| \*\ shot back into the cup. All, on both
|*| \*\ sides of the bend.
\*****|*|*****/
\***********/
\*********/
\*******/
-------
____
/*****\
|*|---\*\
|*| \*\
|*| \*\
|*| \*\ / /
|*| \*\ / /
\*****|*|*****/ \*\ /*/ <- Water stops at level
\***********/ \*\ /*/ with container.
\*********/ \*\____/*/
\*******/ \******/
------- -----/
____
/*O*o*\
|o|---\*\
|*| \O\ <- When pipe reached level of water
|O| \*\ in top container, air bubble separated
|*| \O\ sections of water developed. These
|O| \*\ ____
\ |o| / \O\ /****\
\***********/ \*\ /*/---*\
\*********/ -> \O\_____/*/ \*\*\*/
\*******/ | \*******/ \***/
------- | ------- ---
stopped at lowest point.
Refilling container did not force the air bubbles up,
they stayed in the tube, under the water, unmoving.
As soon as an unbroken length of water was drawn over
the highest point, the bubbles were pushed into the lower
container, make the water bubble nicely.
Man, I had no idea what kind of bomb I dropped here. I’ve been traveling on business for two days, no intention of ignoring posts.
First, though I have three letters following my name now, I’m still quite prone to error, and I don’t walk on water (not enough surface tension to overcome the density difference, I guess). Several later posts by Irishman and freightliner helped clarify my thoughts considerably. Thanks for that.
I haven’t answered to every reply, I simply don’t have the time. I have read most of the arguments, and agree with many of the observations (and disagree with some too).
Re: Zut’s experiment–you created a vacuum inside the tube, and it pulled the water up and over, the water being held together by tensile strength. Very clever idea though.
Re: Zen Beam’s–If there are bubbles, assuming the whole cross-sectional area of the tube isn’t vapor, then there should be sufficient force to pull it over. I don’t know how high the siphon would work, less than 34 feet I would presume. We also can have pressure in a closed system without atmospheric effects
Now, here’s a wierd one. I’ve read a couple of people’s posts citing pressures less than absolute zero. My initial reaction was “Hmmm, maybe they need to think about this,” but some years ago I remember a professor skeptically quoting Dr. Ken Bell (a.k.a the god of heat exchangers, creator of the Bell-Delaware method for shell and tube heat exchanger design) about negative absolute pressures. He was doubtful, but said, “If it were anyone else, I’d say he’s full of s@#$, but he’s really smart, I won’t discount it.”
I later asked Dr. Bell, in his spectacular heat exchanger class, where negative absolute pressure could exist, and his reply was “I don’t recall the author’s name exactly, but it pertained to work measuring the tensile strength of fluids.” At the time I nodded dumbly, but these posts brought him to mind, making me think we have either a closet genius posting not giving us the whole story, or maybe they had a concept errors. I guess we will never know.
This has been a fun discussion everyone, thanks for your contributions. I’m officially signing off this thread.
Hussman
Ah, but he didn’t specify a Decent physicist, did he?
Regarding the tubs of mercury on the moon, and the weighted lids, the lids are not rigid. They float on the liquid (so there is no air gap), and slide down as the weight pushes down under gravity.
Holy Flying Monkeys! I’m sitting here describing that analogy and why it applies, and suddenly I had a revelation. It’s NOT the air pressure pushing down that’s doing anything. Think about it. You have two tanks, each one exposed to the atmosphere, and connected by a sealed, filled tube. It can be a siphon, but doesn’t have to be. It can also be a straight tube. Now put them at different levels, so that one is higher than the other. If the air pressure were driving the water through the tube, then why doesn’t the water flow to the higher tank? Think about it. The atmospheric pressure is created by the weight of all the air pushing down. Air has weight - that’s what keeps it from floating away and leaving the Earth an airless lump of rock. The compression of the air is caused by the higher molecules pushing down on the lower ones. So if that’s the case, then the lower the altitude, the higher the air pressure. We all know this - sea level pressure vs on top of Mt. Everest. Okay, so if the pressure is greater at the lower level, it should work like that syringe and push the water to the higher bucket. But it doesn’t. So what is going on?
We’re back to square one - weight. Not the weight of the air, the weight of the water. Specifically, the water in the bucket, not just the tube. That is why the hydrostatic equation simplifies to the height only. Duh! (How’d I miss this before?)
The water in the bucket between the surface and the tube inlet pushes down. We’ll use the open hose config Slug drew and Cecil refers to in the column. If the hose exit is above the water surface level, then the weight of water inside the two legs of the hose balance out and the heavier side pulls down, so the water flows back into the bucket. With the water removed, the air flows into the hose behind. Now if the hose end is below the water surface in the bucket, you have the heavier weight of water in the longest leg, the exit leg. It falls out of the tube. The water molecules behind it are sitting there, and there’s nothing pushing on that side, so they flow that way. The other side does have a pressure, the pressure from the water in the tank, given by the weight of water above the tube inlet. The atmospheric pressure above it is irrelevant. The air just follows the vacancy left by the water.
That is why when emptying the aquarium, the rate of water leaving slows - there is less height between the surface and the inlet as well as less height difference between the surface and the exit (or exit surface if into a tank), so the driving pressure difference is less.
So I’ve just refuted myself. It is not air pressure, but water pressure, caused by the weight, i.e. purely a gravity effect. The water tension is negligible unless it’s a really narrow diameter tube. The water isn’t really pulled through like a chain, but pushed through.
Yack! I didn’t know revelations were so painful to the gray matter.
Finally! Someone else who has realized that atmospheric pressure exerted on two open containers will not drive water uphill… If that were the case, air would drive water away from the surface of the Earth, and those deep dark recesses of the ocean floor would instead be pleasantly airy canyons beneath a watery sky.
While we’re toying with the effects of reversed density/bouyancy relationships, does that mean that ice would sit at the bottom of the glass? Would submarines replace airplanes?
Well, if you do that, I’m gonna interchange gravity and levity. :mad:
Ray
I am really sorry that your revelation is a fantasy. Gravity and Air pressure are both contributing to the movement of the water (in a positive pressure environment).
Do a point force analysis of the water as it goes through the tube. You will notice that on the side of the tube that the water is going up the gravity force vector is pointed in the opposite direction of movement. It is not possible for gravity to be the force that moves the water up the tube.
Stop being so stubborn about this and release your intuitive reasoning on this. Open a fluid dynamics book and look at the chapters on fluid movement caused by pressure. You will find that faster moving fluids have a lower pressure than the same fluid in the same system going at a slower velocity. At the opening of the tube we have a certain pressure due to air pressure and the weight of the water. Gravity moves the water on the downside which causes a pressure difference. So at the opening and all the way up the climbing side of the tube, the pressure difference overcomes gravity, which is going in the OPPOSITE direction, and accelerates the fluid up the tube.
To hussman: I politely ask you to do some research on this subject before you post again. Your use of termanology and physical descriptions are inaccurate at best. First off a vacuum does not pull anything. It never has and it never will. A vacuum by definition is a volume with NO ENERGY. If you have NO ENERGY how can you get work out of it and then how can you get a force and then how can you get movement? You can’t, so stop posting fantasy misnomers like you know what you are talking about. When there is a pressure difference the resultant force vector orginates on the side with the higher pressure. I suggest you do a force analysis as well. Look at a point of water and all the forces on it as it travels through the tube. There is pushing and pulling by the resultant force vectors. Pushing by the air pressure up the tube, and pulling by gravity and pushing by air pressure on the falling side. (The resultant force vector would be the sum of the two and on the falling side the resultant would be greater causing the fluid to accelerate move faster and…)
No one post on this string again unless they understand this or they can prove me wrong with a point force analysis of the water as it travels throught the tube.
I was not specific enough about the vacuum, I can tell already.
You will say, “I am not talking about a perfect vacuum, so there is mass energy and kenetic energy on that side.”
To which I reply. You are right. However, on the side of higher pressure there is more energy by definition. Period. If you argue this you are wrong by definition. Now then I will expound on this by directing you to a Thermodynamics book again. In it you will find that energy only likes to go from higher to lower levels. I hate to use thermo after my earlier remarks, but I thought if I did you might, just might, understand.
It isn’t a fallacy to think if you can’t do teach in this country. What a shame.
Now who’s being stubborn? You insist that gravity and air pressure are the contributing factors, but you’re missing something. Regardless of tiny bubbles in the wine, the hose is still basically full of water. Only the water in the two containers is in a position to apply pressure to the contents of the hose. You could say that air applies pressure to the water in the containers, but that air is applying pressure to BOTH containers! I don’t discount that pressure is a factor in moving the water UP the short side to the top of the loop, but wouldn’t it be more accurate to say that it is a difference in WATER pressure, caused by the effect of gravity on the greater volume of water on the long downhill side? In that sense, gravity is indirectly the force moving the short side column AGAINST itself, because if has a greater amount of water on the long side, and thus gravity is the source of the pressure difference.
If atmospheric pressure on the higher container could PUSH water through the tube, you should be able to drip a straw into a cup of water and watch as the water is pushed up the straw until the cup is empty.
Again, no on reads my posts!!! ARGGGH!!!
Force causes movement. OK
The water in the siphon is moving. OK
Forces are moving the water. OK
The water is in compression on the rising side. Compression in this thread = pushing. You people don’t understand this part.
The water is in tension on the falling side. In tension the tensile strength comes into effect. In this thread tension = pulling. You people kind of get this but you don’t take into account the additional force due to the pressure difference.
If you do a really good point force analysis of the water and get every friggin force acting on the water you will see this. Then find the resultant force vector. If you can’t do this go to school somewhere that hussman doesn’t teach and learn how. If you can’t do that just realize that as far as you are concerned a siphon is magic and can not be understood. Stop trying to reason this out.