I'm learing a lot from your series of videos, they are well thought out and presented. I do have a minor concern with the contention that mercury was not suitable for this experement though. The rate of evaporation of mercury at room temperature is quite low. In fact one type of high vacuum gauge, I think called a Pirani gauge, exposes the surface of molten mercury to the vacuum. I used one for years measuring below 50 microns and never needed to top up the mercury.
atmospheric pressure, considering they can support large bubbles of air which has no tensile strength.
So a siphon can function under the tensile strength of the liquid, for instance as in this video, or it can function due to (positive) pressure gradients caused by air pressure (and also affected by flow velocity and height of liquid). Although water does have tensile strength it doesn’t make sense that a column of liquid can be under tension (molecules attracting each other) at the same time..
well even if the atm pressure acted on the first (higher) beaker, then it would ALSO act on the lower beaker, canceling any affect. - or am I mistaken?
wow they need a vaccuum machine to show people that all there is to it is gravity? Waste of time and money to educate morons. Ive understood this effect when I was about 8 on my own and im an average person.
@KrutoyPostowoy Looking at something when you're 8 and satisfying yourself you've understood how it works, and never challenging that, is why you're now an average person who isn't a scientist.
@skoockum Could you provide a quote like last time? Sometimes it's difficult to know what you're talking about.
In your chain example you missed Tension: it's important for the chain goes up bit.
Why ask stupid questions like "What the hell is "potential difference"?"? Have you heard of google? How much free education are you after on yt? If you want schooling tone down the arrogance, you'll learn more.
@lfo98 "it's difficult to know what you're talking about."
That's because you're an idiot.
"Why ask stupid questions like "What the hell is "potential difference"?"? Have you heard of google?"
I ask because potential difference applies specifically to voltage, and so far I wouldn't guess that you're quite stupid enough to think that electricity is involved ...are you?
You'll have much better luck grasping why air pressure doesn't drive siphoning if you tone down the stupidity.
HI Adrian, have posted a link to your video in Naked Scientists Forum under title: How does a siphon work? Comment: I thought it was interesting. But, not surprising. However, they obviously did not have a perfect vacuum either.
i have a question, is there a liquid that if used in the same experiment, would not siphon and instead form a vacuum inside the tube if raised above the level of the liquid. That would be awesome to see
i dont get how anyone could think that atmospheric pressure pushes the liquid down up the tube and into the other cup... the same pressure exists at the end of the nozzle thus equilizing the forces.. clearly its gravity doing all the work and the atmospheric pressure pushes at both ends of the hose and keeps the liquid together, and from forming a vacuum in the hose.. I'm talking about water generally.. i wonder if the surface tension of water alone is enough to hold it together
@ricktbdgc "clearly its gravity doing all the work". Yes, the only net energy transfer is from gravitational potential of the liquid to heat within the liquid and apparatus (which is insignificant). Energy transfered into the liquid by air pressure as the top reservior lowers is eventually given back to the atmosphere when the liquid leaves the siphon (via the same principle:work done=pressure x volume displaced). For the liquid to go up the tube this intermediate energy is required..
@lfo98 thanks for the reply, you mean the initial energy require to make the liquid rise up and over the "hill"... yeah this is done manually, before the experiment can begin. what were talking about here is the siphon effect which happen after the tube is completely filled, and the stopper is release from the bottom end of the hose.. check out a video made by science teacher steve spangler called "newtons beads" he has about 100 feet of beads chained together, and placed in a cup.
@lfo98 the cup is raised high, and the end of the beads are thrown out of the cup, and gravity pulls the beads out in a long chain for like 30 seconds until the entire chain is out of the cup. This has to be the same forces involved as in a siphon.. and I guarantee you atmospheric pressure has nothing to do with it.
@ricktbdgc A chain of beads is a good analogy for the liquid used in the video because it's molecular structure is essentially a long chain of particles, water's isn't. Also @andrynor: Google siphon theory, jump to the theory link for the first result (wikipedia) and refer to the diagram, this looks fairly repeatable (not sure I'll try myself though) and proves that no cohesion/surface tension is required.
It is a truly spectacular experiment, and proves conclusively that a siphon can work in a vacuum. My question is , what about hydrostatuic pressure, you haven't mentioned that at all and surely hydrostatic pressure must have something to do with what is going on in a siphon. Does hydrostatic pressure vary with gravity ? Or is it an inherent property of matter like mass is for a solid? Sorry for complicating things.
I wasn't trying to say gravity isn't required. You need some kind of (usually gravitational) potential difference between the top and bottom reservoir, but you also need something to push the liquid up the tube (air pressure acting on the top reservoir) or to pull it (surface tension/molecular attratcion from the liquid flowing downwards).
Are you the person who wrote to me about my experiment at Brixham where water was observed to circulate to 24 meters vertically in an open ended inverted u tube measuring 6mm inside diameter? I would love to present this experiment at your university, would this be ok with you? Best wishes Andrew
@AndrewKFletcher Hi Andrew, Yes I did try to reply via the you-tube reply but I seemed to have failed. Apologies, I have been away for x-mass and on conference last week so I have not made any more attempts to get in contact. I am happy for you to contact me directly via email ab582@le.ac.uk.
Molecular drag is the correct term. This can be demonstrated in a closed loop of tubing with a little coloured salt / sugar solution added at one point, which is then raised vertical, result salt flowing down generates a return flow = zero atmospheric influence. Density can be altered with heat and cold to generate circulation.
@AndrewKFletcher Surprised this experiment suggestion was ignored. Think about it, A closed Loop of tubing filled with water with a little coloured salt solution added before the two ends of the tube are joined together, with no air bubbles evident. Raise the part of the tube with salt in vertically and the salt is dragged down by gravity, this causes water inside the loop of tube to circulate density induced circulation without any influence from the atmosphere. Just gravity!
@AndrewKFletcher Sorry, but what is the point you are trying to make with the tube of water? Changing the density at one point will also upset the balance of pressure (and gravitational potential) along the tube and a flow is induced to correct this.
@lfo98 The point I am making here is that a flow will occur in a closed loop of tubing, eliminating any atmospheric interference which supports your experiment, also the gravitational pull on the solutes alters the pressures inside the tube inducing a positive pressure in one side and a reduction in pressure in the return flow side. As you state the pressures are changed and implications for this simple experiment in relation to our own circulation are being overlooked.
@AndrewKFletcher Ok, I see what you're saying now. I have very little knowledge of the circulatory system, but if I was going to guess I'd say variations in density of blood will probably be insignificant. No offence, like I said I'm not really qualified to comment. How many trials have you run on people with circulation problems?
A variant you might try would be to repeat the experiment under ordinary atmospheric pressure but set the maximum height of the tube above the reservoir surfaces greater than that which would normally create a Torricellian vacuum (about 76cm for mercury, 10m for water). The question, presumably per liquid, becomes how much greater can that maximum height be?
Isnt the conclusion that the traditional theory on siphons relying on air pressure is incorrect misleading? What you've done is shown surface tension can be responsible, what you need to show is that a siphon wont work with a liquid with extremely low surface tension under air pressure (which I suspect is impossible). Or change your conclusion to both factors have an effect. I may be wrong but I think air pressure will be the dominant factor in a siphon of water at room temperature and pressure.
@lfo98 yes you are correct at your last statement but, the problem with any pressure especially air pressure is that any dissolved air in the liquid can break the molecular bonds and break the siphon, the will soon be a paper coming by this scientist on more of what you are talking about.
@lfo98 I agree. They could reach this conclusion lifting more and more the hose, until the point where the liquid will break apart inside the hose of siphon. With air pressure, the hight at wich the liquid will separate in two columns will be much higher than that in the case without air pressure. In one thing they are right, however. It is not the air pressure that causes the motion of the liquid, because there is the same air pressure in both exposed liquid surfaces, above and bellow.
@lfo98 I disagree, because there need to be something that drives the sippon effect, and that is gravity. To prove this you could do the experiment in space without gravity, with and without vacum.
@lfo98 "air pressure will be the dominant factor in a siphon of water at room temperature and pressure."
Really? Because when you think it thru, you realize that the air pressure on the lower fluid surface is higher than the air pressure on the higher fluid surface. Granted the difference is probably insignificant, but it's clear that if air pressure has any effect at all, it is negative, or resistant to the siphon action.
@skoockum Yes the air pressure will be greater on the lower fluid. However, given that the density of water (or any siphoned liquid) is much greater than the density of air the hydrostatic pressure will mean there is a larger discrepancy at the bottom reservoir between air and liquid pressure and so the liquid starts to flow that way. Its not that clear, especially once its moving, however pressure conciderations explain a siphon without the need of surface tension regardless of its effects.
@skoockum Google siphon explained Bernoulli's equation, Jump to Explanation using Bernoulli's equation on wiki. This clearly shows that if atmospheric pressure over density of liquid is less than the product of the acceleration due to gravity and height between reservoirs then the maximum flow velocity has no real roots. So with no air pressure there will be no velocity. This is of course the theoretical prediction not concidering surface tension, hence "I may be wrong" which you didn't quote.
@lfo98 You said "I may be wrong but I think air pressure will be the dominant factor in a siphon of water at room temperature and pressure."
And clearly you are wrong based on the obvious fact that the air pressure is slightly (if insignificantly) higher at the bottom liquid surface -- as I said in my first reply to you.
So far you seem to miss this point entirely, and for no apparent reason, respond with irrelevancy after irrelevancy.
@skoockum You're funny: "bonehead troll", quite. Did you read through the derivation for maximum flow velocity on wikipedia? More importantly did you understand it? Sorry stupid question, you cant even comprehend how its relevant. Lets agree to disagree.
@lfo98 Don't look at me. It's you who said - despite this video - that atmospheric pressure has a major role in siphoning, and that the conclusion of this exp. was "the traditional theory on siphons relying on air pressure is incorrect misleading".
All you've done by introducing flow velocity and Bernoulli's eqn is to show that, at best, you can't yet separate 'related' from 'relevant'. That and your ghost account make it hard to believe that you're anything but a walking, talking prod.
@skoockum Please clear this up for me, how is it related, yet not relevant? Surely a derivation for the flow velocity of a siphon is relevant if you accept its related. And what exactly do you suppose I have been doing with my ghost account?
Wrong question. You need to be asking 'what is the difference between relevant and related?' If you're smart enough to get that one under control, I am confident that everything else will eventually fall into place for you.
"what ... have I been doing with my ghost account"
The same thing that all the other ghost accounts are doing: trolling.
Actually, while atmospheric pressure certainly doesn't provide the potential difference that drives the movement of fluid, I think his point is correct in that it does serve the exact same purpose as surface tension in this situation - i.e. the "suction."
Remember, the key aspect of a siphon is that the water goes first over a potential "hill" before dropping down to the energetically favorable state. Gravity does not provide the force that makes this motion possible.
@oooooooooorly What the hell is "potential difference"? Difference isn't like energy where sometimes it's kinetic and sometimes it's potential... either there is a difference, or there isn't.
BTW what difference are you talking about, air pressure? potential energy? ability to articulate simple ideas regarding the physical interaction of matter and energy?
Gravity: hang a 12' chain on a pulley, 9' on 1 side, 3' on the other. The 3' goes uphill before it follows the 9' part down
You don't know what a potential difference is? That's freshman physics material. If you want a full explanation, PM me - hard to explain given the character limit on youtube comments.
Suffice to say that the fact that it's energetically favorable for all the liquid to be in the lower beaker does not mean that it can necessarily get there.
You can drop the overly-defensive, self-righteous attitude, too - believe it or not, I likely know a fair bit more physics than you.
@oooooooooorly "I likely know a fair bit more physics than you."
Not if you can't see how gravity and molecular cohesion (and not air pressure) are what drive siphons. Not to mention that "suction" is actually just a pressure differential from the low side.
"drop the overly-defensive, self-righteous attitude"
Well that's just the kettle calling the lawnmower a cooking implement
Glad to see you're so interested in civil discussion. I don't think I'll bother arguing here further - if you're interested in learning something, again, PM me - I'll be more than glad to explain why, in a liquid which cannot sustain negative pressure, air pressure is crucial to the functioning of a siphon. If not, feel free to keep up the needless hostility - it doesn't do you much credit in terms of gaining knowledge, but I'm sure it makes you feel good about yourself.
@oooooooooorly "Glad to see you're so interested in civil discussion."
Don't you think it's a little too late whine about "civil discussion" considering that I've already called you out for criticizing me for something that you've done, but which I haven't? (ie being "overly-defensive" and "self righteous")
"if you're interested in learning something, again, PM me - I'll be more than glad to explain"
That sounds more than a little like passive-aggressive hostility to me.
Actually, I was originally trying to be genuinely helpful, until you started spitting venom. I'm still perfectly willing to teach you about gravitational potentials if you want.
@oooooooooorly Still going with the passive aggressive thing, eh? There was always a guy or two in every one of my math and science classes who, despite not getting that he wasn't getting it, was willing to set me straight. And they could never figure out why I had the highest grade in the class.
You misunderstand me completely - I'm not being passive-aggressive at all, I'm legitimately offering to teach you some physics which would help you understand how, precisely, a siphon works. It's unfortunate that you feel the need to be unnecessarily nasty and flaunt anecdotes about how you get good grades in "math and science" classes when you clearly don't really know physics particularly well. Again, if you want to fix this, send me a message.
@oooooooooorly You said "Remember, the key aspect of a siphon is that the water goes first over a potential "hill" before dropping down to the energetically favorable state. Gravity does not provide the force that makes this motion possible."
This is blatantly wrong, completely without an intuitive grasp of physics.
Also, you spoke of surface tension being "suction" - and you think that the "hill" is a key aspect of the siphon, both entirely incorrect.
Actually, it's not wrong at all - the same forces (molecular cohesion) are responsible for surface tension and for liquids being able to sustain a negative pressure ("suction").
Your initial response ("what the hell is a potential difference") indicates you haven't had much physics education. I'm still willing to teach you some rudiments, but you have to drop the nasty, aggressive attitude and be willing to listen - send me a message if you're interested.
@oooooooooorly You've been stealing terms from my and other's posts to use in your own at almost exactly the same rate as Ifo98 has. If I didn't know better, I'd say that you and he are the same troll, baiting folk with a studied display of idiocy, but I do, so I wouldn't.
"Stealing terms?" Did it not occur to you that the reason the same language is used by multiple people is because they're the proper nomenclature to describe the physical system?
Really, there's no need to be so hostile. Lashing out and calling people "trolls" when they offer to teach you physics isn't exactly conducive to constructive discussion. Everyone else here has been completely civil - why can't you?
@skoockum IMO your trolling peaked with "they could never figure out why I had the highest grade in the class". I'd like to hear more imaginative stories regarding your education. Claiming you can't see how the term "hill" can be applied in describing a siphon is a bit weak.
@lfo98 I didn't hear me say I "can't see how the term "hill" can be applied in describing a siphon" ...you may want to reread my post to see what I really did say. Very weak attempt at trolling, BTW, putting words in my mouth ...very weak.
@lfo98 the only reason they used the ionic liquid was so that the "water" didn't boil away. you are partially right with air pressure having an effect, for you need air to move out of the way to make room for the water, otherwise it wont work. at the same time it cant work without gravity and surface cohesion. in this case both the experiment and traditional thinking wins.
@lfo98 Air pressure can't be involved because both vessels in a traditional siphons are open to the same air pressure and therefor in balance. Gravity and suction is all that is involved.
@Gunther222 Yes but suction is generally the flow of material from a area of high positive pressure to a area of lower positive pressure. The experiment is an example of negative pressure (molecules attracting each other rather than repelling), but anyway generally you need air pressure for a siphon to work, well established theory and experimental evidence support this.
@lfo98 This video has just proved air pressure does not play any part in the operation of a siphon, so your statement is incorrect and the experimental evidence therefore doubtful. That said, air pressure does have two effects. First, it stops the liquid being siphoned boiling. Second, if there is a difference in air pressure between the reservoirs it will block or even reverse the siphon action. At that point however it is no longer a siphon, it has become an air pressure pump.
The video does not show that air pressure "plays no part" in the operation of a siphon - rather, it shows that a siphon *can* function in the absence of air pressure, *given a liquid with sufficient intermolecular forces. A liquid with no surface tension would not form a functioning siphon in a vacuum, yet would work fine in sufficient air pressure.
@oooooooooorly Not quite. When a liquid cannot form a siphon without air pressure (i.e. water at room temperature) it is not a lack of intermolecular forces preventing the siphon from forming, it is the lack of intermolecular forces casuing the liquid to boil and create bubbles of vapour that breaks the siphonic action. What you won't get is the liquid breaking apart and forming a vacuum in the pipe, which is what your comments about air pressure are suggesting.
False - if you could prevent the rapid evaporation of your liquid, you would indeed find the liquid breaking apart in the pipe.
Flow is governed by pressure gradient - the reason a siphon works is liquid flows from an area of higher pressure to one of lower pressure. If a liquid cannot sustain negative pressure (lack of surface tension), this *cannot occur* without some external pressure on the whole system.
@oooooooooorly It's been shown that you can have a working water siphon under vacuum, if you're careful, use very pure water, clean equipment and boil off any gas before you start. This prevents boiling and the tensile strength of the water allows it to flow. These conditions are rather strict and apparently "mechanical shock" (causing the liquid to break at a point) will stop the flow. I imagine you would need a very large mechanical shock to stop a siphon functioning under ...
@oooooooooorly If the liquid breaks apart in the pipe it will rapidly evaporate since evaporation occurrs when the intermolecular bonds are not strong enough to hold the liquid together. Its all to do with the vapour pressure and was explained in the video, and is why they used an ionic liquid in the experiment.
Flow is indeed governed by a pressure gradient, but in a siphon that pressure is entirely within the liquid and created entirely by gravity pulling the liquid downwards.
Sure, you could (probably) never practically generate the situation of a low-cohesion liquid in a vacuum - I'm not disputing that. You could, however, create a siphon of zero surface-tension liquid which works just fine in atmospheric pressure. So, no, the pressure is not necessarily generated "entirely within the liquid" - in fact, when the whole system is at positive pressure the molecular cohesion isn't very important at all.
@oooooooooorly OK, try this. Atmospheric pressure does not take part in siphonic action. However the siphon will be broken if the liquid pressure in the liquid at the highest point of the siphon is equal to or less than the vapour pressure since the liquid will begin to form bubbles of gas. Atmospheric pressure acting on the liquid increases its base pressure and therefore the maximum height of the siphon before the vapour pressure is reach and bubbles break the siphonic action.
Essentially, yes - if your liquid cannot sustain the negative pressure in the top of the siphon, then atmospheric pressure is then important to its function. In a sense, one can think of the pressure gradient at negative pressure as the molecules "pulling" each other, and at positive pressure as "pushing." Not all liquids can do the former (the one in the experiment obviously can), but the latter is not possible without some sort of external pressure.
If you would pour this liquid from a glass into another container from a quite long distance, would it still "stick" and make a constant stream? Water will make little droplets in that situation. Just curious.
They are immense energy conduits, if you force a wave through it, it will be at the other side as it enters the vacuum.
The amount of energy required to create a 'real vacuum' the size of a golf-ball is locked away in an antimatter and matter reaction equal to 2 golfballs. Once you create a vacuum using the matter and anti-matter, you are left with an amount of energy that will tear the vacuum apart again or level an entire city block.
A neat modification to this experiment would be trying a liquid that doesn't have any molecular attraction with itself (does this exist?). Would a vacuum bubble be created inside the tube? My guess is yes.
@DemiImp I think a liquid having molecular attraction with itself is the very definition of a liquid: if molecules don't pull themselves together they would form a gas.
The interesting thing would be to do that experiment on the moon, where you have a real vacuum and gravity.
It's clear that a siphon only works when the net flow of liquid down the tube exceeds the net flow of liquid up the tube just by looking at the first demonstration. I don't get what the point of testing it in a vacuum is, especially if there is atmospheric pressure pushing against both liquids equally.
@ monkeyboy4746 You see in the video that I moved the rod relatively slowly. The reason was that the rubber vacuum seals around the rod also make it a little hard to move the rod not the air pressure. The rod won't go into the chamber as there is a stop on it. The screws are there to stop the plate falling onto my toes "again" when I let air back into the chamber.
@ frichikendz My honey doesn't like being evacuated ; )
@ frizstyler Sorry I can't answer as that is not my field of expertise. I'm not sure if Pete could answer that or if its been tested. I suspect that it may expand and contract a bit when heated or cooled even though it has almost no vapor pressure.
@KemaTheAtheist Funny you should say that but some of that equipment may have come from Kroto's lab.
@ monkeyboy4746 No this was not a mock up although the partial pressure was a little higher than the best achievable as the apparatus was moved for the video. Regarding the front plate (one inch thick perspex) it has a force of about one tonne pushing it onto the chamber why would I need any bolts? The same goes for the rod at only 0.5 cm diameter it has an effective atmospheric weight (i.e. 1kg /cm sq) of 200 grams . Yes I also used the same dye for both liquids as both are colourless.
@ElectricDoctor1 OK, I could not see the thickness of the front plate in the video, I know it would be held on without screws, I just threw that in, since no one responded to my first comment. When you say "ultra high vacuum" I noted the rod was not falling back on its own into the chamber, I got a little suspicious. Thanks for clearing it up.
I think this is a mockup of the experiment, not the actual one, his vacuum chamber's front plate is being held by only 4 screws, he can retrieve a rod from the chamber that should be held down by atmospheric pressure, the water in the previous video shot is the same color as the "ionic fluid" in the chamber in the next video shot, I want to hear from Brady on this, is what I am seeing the actual experiment or a mockup done for the channel?
1.) it would look like just the same as under normal pressure - it just would go way faster - if you would get the dry ice instantly into an high vaccum then it would most likely evaporate like an explosion
2.) in principle yes, in detail it depends on the specific phase diagram of the material
Not trying to sound like a dick or anything, but I am absolutely staggered that there was any confusion about the mechanism of something as simple as a syphon. With advancements and understanding of things as diverse and complex as virtual particles, black holes, higher dimensions, the quantum world... how come it was not obvious to these people that this is gravity plain and simple? Other than that- periodic videos rock :)
@Tossphate because it doesn't make sense that gravity would cause the liquid to go UP hill. The fact is that its suction + gravity that causes this to happen, not gravity alone, thus the confusion.
This is cheating! Basically this ionic liquid is a chain of connected balls that can't be separated. Lets think of a liquid with a low vapor pressure-like water.
Lets do it at atmospheric pressure. Lets raise the tube a kilometer into the sky. What will happen?
Answer; a bubble will form and there will be no siphon. This bubble will be H2O gas.
Now. In a vacuum, the bubble will form at a much lower height.
TL;DR; A siphon at ANY pressure will not work if the vapor pressure is too low.
Clearly what is needed for a siphon is that cohesiveness + air pressure is enough to prevent prevent the formation of a cavity in the tube. For ordinary liquids the cohesiveness is not enough for more than a few mm of elevation, so air pressure is needed for the rest.
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It would be interesting to repeat this to see how high the siphon could go before the cohesion that holds the liquid together in the tube failed.
I'm guessing that a bubble of vacuum would form and the liquid would simply drop down and equalise with the level of each container.
Also what would cause such a bubble to form? Would it be a tiny imperfection, like with boiling water, or would it be when the weight of the liquid in the columns exceeds the cohesive force within the liquid?
Wait wait...what kind of idiot ever said atmospheric pressure pushed the liquid down and into the tube? That's moronic. There's the same pressure on the other side of the tube. It's obviously, OBVIOUSLY just the liquid falling down the longer side of the tube sucking the other liquid behind it.
@honeymonster147 some people need things to be proved to them by experiment if they believe the outcome could be otherwise even against the numbers. It is generally good practice to do what would be called an experiment of an 'obvious' outcome anyway as a proof of concept.
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I just wonder how someone could think that atmosphere would change the result? It's all about mass and that something what we have learned from Mr. Eistein. Thanks for the video still, maybe it will clarify someone. =)
How is it possible to withdraw the metal rod which raises the tube filled with liquid if the box is under a vacuum, would not the metal rod be held down by the atmospheric pressure in the room?
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I used this technique to clean my fish tank long ago...
Nadeeja94 3 days ago
@Nadeeja94 lol me too!
falcoperegrinus82 2 days ago
I'm learing a lot from your series of videos, they are well thought out and presented. I do have a minor concern with the contention that mercury was not suitable for this experement though. The rate of evaporation of mercury at room temperature is quite low. In fact one type of high vacuum gauge, I think called a Pirani gauge, exposes the surface of molten mercury to the vacuum. I used one for years measuring below 50 microns and never needed to top up the mercury.
f7ipper 3 days ago
"siphons really suck" lol
magnetacyde 6 days ago
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as under compression (repelling each other from physically hitting each other – a knock on effect of air pressure acting at the surface).
lfo98 6 days ago
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atmospheric pressure, considering they can support large bubbles of air which has no tensile strength.
So a siphon can function under the tensile strength of the liquid, for instance as in this video, or it can function due to (positive) pressure gradients caused by air pressure (and also affected by flow velocity and height of liquid). Although water does have tensile strength it doesn’t make sense that a column of liquid can be under tension (molecules attracting each other) at the same time..
lfo98 6 days ago
"siphons really suck".
NotEnuffMana 1 week ago
What about those vacuum/siphon coffee makers?
clodester 1 week ago
well even if the atm pressure acted on the first (higher) beaker, then it would ALSO act on the lower beaker, canceling any affect. - or am I mistaken?
InebriatedEd 1 week ago
wow they need a vaccuum machine to show people that all there is to it is gravity? Waste of time and money to educate morons. Ive understood this effect when I was about 8 on my own and im an average person.
KrutoyPostowoy 1 week ago 2
@KrutoyPostowoy Looking at something when you're 8 and satisfying yourself you've understood how it works, and never challenging that, is why you're now an average person who isn't a scientist.
lfo98 1 week ago
@lfo98 So please tell us why you are a below average person.
skoockum 1 week ago
@skoockum Could you provide a quote like last time? Sometimes it's difficult to know what you're talking about.
In your chain example you missed Tension: it's important for the chain goes up bit.
Why ask stupid questions like "What the hell is "potential difference"?"? Have you heard of google? How much free education are you after on yt? If you want schooling tone down the arrogance, you'll learn more.
lfo98 1 week ago
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@lfo98 "it's difficult to know what you're talking about."
That's because you're an idiot.
"Why ask stupid questions like "What the hell is "potential difference"?"? Have you heard of google?"
I ask because potential difference applies specifically to voltage, and so far I wouldn't guess that you're quite stupid enough to think that electricity is involved ...are you?
You'll have much better luck grasping why air pressure doesn't drive siphoning if you tone down the stupidity.
skoockum 1 week ago
I honestly never knew that people thought air pressure had anything to do with syphoning. It just seemed so obvious it was gravity doing the work.
mickenoss 2 weeks ago 8
@mickenoss Me too. Gravity and the suction at the back of the tube caused by the liquid rushing out the other end
wesmatron 2 weeks ago
HI Adrian, have posted a link to your video in Naked Scientists Forum under title: How does a siphon work? Comment: I thought it was interesting. But, not surprising. However, they obviously did not have a perfect vacuum either.
AndrewKFletcher 2 weeks ago
i have a question, is there a liquid that if used in the same experiment, would not siphon and instead form a vacuum inside the tube if raised above the level of the liquid. That would be awesome to see
ricktbdgc 2 weeks ago
if anything the atmospheric pressure at the lower hose is greater, and would resist the flow of the liquid
ricktbdgc 3 weeks ago
i dont get how anyone could think that atmospheric pressure pushes the liquid down up the tube and into the other cup... the same pressure exists at the end of the nozzle thus equilizing the forces.. clearly its gravity doing all the work and the atmospheric pressure pushes at both ends of the hose and keeps the liquid together, and from forming a vacuum in the hose.. I'm talking about water generally.. i wonder if the surface tension of water alone is enough to hold it together
ricktbdgc 3 weeks ago
@ricktbdgc "clearly its gravity doing all the work". Yes, the only net energy transfer is from gravitational potential of the liquid to heat within the liquid and apparatus (which is insignificant). Energy transfered into the liquid by air pressure as the top reservior lowers is eventually given back to the atmosphere when the liquid leaves the siphon (via the same principle:work done=pressure x volume displaced). For the liquid to go up the tube this intermediate energy is required..
lfo98 3 weeks ago
@lfo98 thanks for the reply, you mean the initial energy require to make the liquid rise up and over the "hill"... yeah this is done manually, before the experiment can begin. what were talking about here is the siphon effect which happen after the tube is completely filled, and the stopper is release from the bottom end of the hose.. check out a video made by science teacher steve spangler called "newtons beads" he has about 100 feet of beads chained together, and placed in a cup.
ricktbdgc 2 weeks ago
@lfo98 the cup is raised high, and the end of the beads are thrown out of the cup, and gravity pulls the beads out in a long chain for like 30 seconds until the entire chain is out of the cup. This has to be the same forces involved as in a siphon.. and I guarantee you atmospheric pressure has nothing to do with it.
ricktbdgc 2 weeks ago
@ricktbdgc A chain of beads is a good analogy for the liquid used in the video because it's molecular structure is essentially a long chain of particles, water's isn't. Also @andrynor: Google siphon theory, jump to the theory link for the first result (wikipedia) and refer to the diagram, this looks fairly repeatable (not sure I'll try myself though) and proves that no cohesion/surface tension is required.
lfo98 2 weeks ago
@ricktbdgc unless surface tension is sufficient to pull the liquid up the tube.
lfo98 3 weeks ago
6:00 who are in the desktop?
NaegFowleri 3 weeks ago
why doesnt the vacuum creator suck the sides of the container together? can anyone explain this to me?
infintiyward 3 weeks ago
gravity + surface tension. Imagine the liquid as a steel chain. Eventually the chain would run thru the tube to the lower beaker.
donperry1 3 weeks ago in playlist Uploaded videos
It is a truly spectacular experiment, and proves conclusively that a siphon can work in a vacuum. My question is , what about hydrostatuic pressure, you haven't mentioned that at all and surely hydrostatic pressure must have something to do with what is going on in a siphon. Does hydrostatic pressure vary with gravity ? Or is it an inherent property of matter like mass is for a solid? Sorry for complicating things.
bajaj394 1 month ago
What type of ionic liquid did they use that doesn't evaluate?
maakjar 1 month ago
I wasn't trying to say gravity isn't required. You need some kind of (usually gravitational) potential difference between the top and bottom reservoir, but you also need something to push the liquid up the tube (air pressure acting on the top reservoir) or to pull it (surface tension/molecular attratcion from the liquid flowing downwards).
lfo98 1 month ago
Thanks will send an email to make contact, please delete your email from your last reply :)
AndrewKFletcher 1 month ago
Are you the person who wrote to me about my experiment at Brixham where water was observed to circulate to 24 meters vertically in an open ended inverted u tube measuring 6mm inside diameter? I would love to present this experiment at your university, would this be ok with you? Best wishes Andrew
AndrewKFletcher 1 month ago
@AndrewKFletcher Hi Andrew, Yes I did try to reply via the you-tube reply but I seemed to have failed. Apologies, I have been away for x-mass and on conference last week so I have not made any more attempts to get in contact. I am happy for you to contact me directly via email ab582@le.ac.uk.
ElectricDoctor1 1 month ago
Molecular drag is the correct term. This can be demonstrated in a closed loop of tubing with a little coloured salt / sugar solution added at one point, which is then raised vertical, result salt flowing down generates a return flow = zero atmospheric influence. Density can be altered with heat and cold to generate circulation.
AndrewKFletcher 2 months ago
@AndrewKFletcher Surprised this experiment suggestion was ignored. Think about it, A closed Loop of tubing filled with water with a little coloured salt solution added before the two ends of the tube are joined together, with no air bubbles evident. Raise the part of the tube with salt in vertically and the salt is dragged down by gravity, this causes water inside the loop of tube to circulate density induced circulation without any influence from the atmosphere. Just gravity!
AndrewKFletcher 2 weeks ago
@AndrewKFletcher Sorry, but what is the point you are trying to make with the tube of water? Changing the density at one point will also upset the balance of pressure (and gravitational potential) along the tube and a flow is induced to correct this.
lfo98 2 weeks ago
@lfo98 The point I am making here is that a flow will occur in a closed loop of tubing, eliminating any atmospheric interference which supports your experiment, also the gravitational pull on the solutes alters the pressures inside the tube inducing a positive pressure in one side and a reduction in pressure in the return flow side. As you state the pressures are changed and implications for this simple experiment in relation to our own circulation are being overlooked.
AndrewKFletcher 2 weeks ago
@AndrewKFletcher Ok, I see what you're saying now. I have very little knowledge of the circulatory system, but if I was going to guess I'd say variations in density of blood will probably be insignificant. No offence, like I said I'm not really qualified to comment. How many trials have you run on people with circulation problems?
lfo98 2 weeks ago
A variant you might try would be to repeat the experiment under ordinary atmospheric pressure but set the maximum height of the tube above the reservoir surfaces greater than that which would normally create a Torricellian vacuum (about 76cm for mercury, 10m for water). The question, presumably per liquid, becomes how much greater can that maximum height be?
dajwilkinson 2 months ago
'what we can actually say here is- siphons really suck.'
EPIC PUN.
EarthDefenceInferno 2 months ago
Isnt the conclusion that the traditional theory on siphons relying on air pressure is incorrect misleading? What you've done is shown surface tension can be responsible, what you need to show is that a siphon wont work with a liquid with extremely low surface tension under air pressure (which I suspect is impossible). Or change your conclusion to both factors have an effect. I may be wrong but I think air pressure will be the dominant factor in a siphon of water at room temperature and pressure.
lfo98 3 months ago 2
@lfo98 yes you are correct at your last statement but, the problem with any pressure especially air pressure is that any dissolved air in the liquid can break the molecular bonds and break the siphon, the will soon be a paper coming by this scientist on more of what you are talking about.
olie854 2 months ago
@lfo98 I agree. They could reach this conclusion lifting more and more the hose, until the point where the liquid will break apart inside the hose of siphon. With air pressure, the hight at wich the liquid will separate in two columns will be much higher than that in the case without air pressure. In one thing they are right, however. It is not the air pressure that causes the motion of the liquid, because there is the same air pressure in both exposed liquid surfaces, above and bellow.
anonimoculto 1 month ago
@lfo98 I disagree, because there need to be something that drives the sippon effect, and that is gravity. To prove this you could do the experiment in space without gravity, with and without vacum.
fkeopfkeop 1 month ago
@lfo98 "air pressure will be the dominant factor in a siphon of water at room temperature and pressure."
Really? Because when you think it thru, you realize that the air pressure on the lower fluid surface is higher than the air pressure on the higher fluid surface. Granted the difference is probably insignificant, but it's clear that if air pressure has any effect at all, it is negative, or resistant to the siphon action.
skoockum 4 weeks ago 37
@skoockum Yes the air pressure will be greater on the lower fluid. However, given that the density of water (or any siphoned liquid) is much greater than the density of air the hydrostatic pressure will mean there is a larger discrepancy at the bottom reservoir between air and liquid pressure and so the liquid starts to flow that way. Its not that clear, especially once its moving, however pressure conciderations explain a siphon without the need of surface tension regardless of its effects.
lfo98 3 weeks ago
@lfo98 ???
The point is that air pressure clearly doesn't play a part, let alone a "dominant factor" in a siphon.
skoockum 3 weeks ago
@skoockum Google siphon explained Bernoulli's equation, Jump to Explanation using Bernoulli's equation on wiki. This clearly shows that if atmospheric pressure over density of liquid is less than the product of the acceleration due to gravity and height between reservoirs then the maximum flow velocity has no real roots. So with no air pressure there will be no velocity. This is of course the theoretical prediction not concidering surface tension, hence "I may be wrong" which you didn't quote.
lfo98 3 weeks ago
@lfo98 You said "I may be wrong but I think air pressure will be the dominant factor in a siphon of water at room temperature and pressure."
And clearly you are wrong based on the obvious fact that the air pressure is slightly (if insignificantly) higher at the bottom liquid surface -- as I said in my first reply to you.
So far you seem to miss this point entirely, and for no apparent reason, respond with irrelevancy after irrelevancy.
My guess is that you're just a bonehead troll.
skoockum 3 weeks ago
@skoockum You're funny: "bonehead troll", quite. Did you read through the derivation for maximum flow velocity on wikipedia? More importantly did you understand it? Sorry stupid question, you cant even comprehend how its relevant. Lets agree to disagree.
lfo98 3 weeks ago
@lfo98 Don't look at me. It's you who said - despite this video - that atmospheric pressure has a major role in siphoning, and that the conclusion of this exp. was "the traditional theory on siphons relying on air pressure is incorrect misleading".
All you've done by introducing flow velocity and Bernoulli's eqn is to show that, at best, you can't yet separate 'related' from 'relevant'. That and your ghost account make it hard to believe that you're anything but a walking, talking prod.
skoockum 3 weeks ago
@skoockum Please clear this up for me, how is it related, yet not relevant? Surely a derivation for the flow velocity of a siphon is relevant if you accept its related. And what exactly do you suppose I have been doing with my ghost account?
lfo98 3 weeks ago
@lfo98 "how is it related, yet not relevant?"
Wrong question. You need to be asking 'what is the difference between relevant and related?' If you're smart enough to get that one under control, I am confident that everything else will eventually fall into place for you.
"what ... have I been doing with my ghost account"
The same thing that all the other ghost accounts are doing: trolling.
skoockum 3 weeks ago
@skoockum
Actually, while atmospheric pressure certainly doesn't provide the potential difference that drives the movement of fluid, I think his point is correct in that it does serve the exact same purpose as surface tension in this situation - i.e. the "suction."
Remember, the key aspect of a siphon is that the water goes first over a potential "hill" before dropping down to the energetically favorable state. Gravity does not provide the force that makes this motion possible.
oooooooooorly 1 week ago
@oooooooooorly What the hell is "potential difference"? Difference isn't like energy where sometimes it's kinetic and sometimes it's potential... either there is a difference, or there isn't.
BTW what difference are you talking about, air pressure? potential energy? ability to articulate simple ideas regarding the physical interaction of matter and energy?
Gravity: hang a 12' chain on a pulley, 9' on 1 side, 3' on the other. The 3' goes uphill before it follows the 9' part down
skoockum 1 week ago
@skoockum
You don't know what a potential difference is? That's freshman physics material. If you want a full explanation, PM me - hard to explain given the character limit on youtube comments.
Suffice to say that the fact that it's energetically favorable for all the liquid to be in the lower beaker does not mean that it can necessarily get there.
You can drop the overly-defensive, self-righteous attitude, too - believe it or not, I likely know a fair bit more physics than you.
oooooooooorly 1 week ago
@oooooooooorly "I likely know a fair bit more physics than you."
Not if you can't see how gravity and molecular cohesion (and not air pressure) are what drive siphons. Not to mention that "suction" is actually just a pressure differential from the low side.
"drop the overly-defensive, self-righteous attitude"
Well that's just the kettle calling the lawnmower a cooking implement
skoockum 1 week ago
@skoockum
Glad to see you're so interested in civil discussion. I don't think I'll bother arguing here further - if you're interested in learning something, again, PM me - I'll be more than glad to explain why, in a liquid which cannot sustain negative pressure, air pressure is crucial to the functioning of a siphon. If not, feel free to keep up the needless hostility - it doesn't do you much credit in terms of gaining knowledge, but I'm sure it makes you feel good about yourself.
oooooooooorly 1 week ago
@oooooooooorly "Glad to see you're so interested in civil discussion."
Don't you think it's a little too late whine about "civil discussion" considering that I've already called you out for criticizing me for something that you've done, but which I haven't? (ie being "overly-defensive" and "self righteous")
"if you're interested in learning something, again, PM me - I'll be more than glad to explain"
That sounds more than a little like passive-aggressive hostility to me.
skoockum 6 days ago
@skoockum
Actually, I was originally trying to be genuinely helpful, until you started spitting venom. I'm still perfectly willing to teach you about gravitational potentials if you want.
oooooooooorly 6 days ago
@oooooooooorly Good luck.
lfo98 6 days ago
@oooooooooorly Still going with the passive aggressive thing, eh? There was always a guy or two in every one of my math and science classes who, despite not getting that he wasn't getting it, was willing to set me straight. And they could never figure out why I had the highest grade in the class.
skoockum 4 days ago
@skoockum MIT? Caltech?
lfo98 4 days ago
@skoockum
You misunderstand me completely - I'm not being passive-aggressive at all, I'm legitimately offering to teach you some physics which would help you understand how, precisely, a siphon works. It's unfortunate that you feel the need to be unnecessarily nasty and flaunt anecdotes about how you get good grades in "math and science" classes when you clearly don't really know physics particularly well. Again, if you want to fix this, send me a message.
oooooooooorly 4 days ago
@oooooooooorly You said "Remember, the key aspect of a siphon is that the water goes first over a potential "hill" before dropping down to the energetically favorable state. Gravity does not provide the force that makes this motion possible."
This is blatantly wrong, completely without an intuitive grasp of physics.
Also, you spoke of surface tension being "suction" - and you think that the "hill" is a key aspect of the siphon, both entirely incorrect.
You have nothing to offer
skoockum 3 days ago
@skoockum
Actually, it's not wrong at all - the same forces (molecular cohesion) are responsible for surface tension and for liquids being able to sustain a negative pressure ("suction").
Your initial response ("what the hell is a potential difference") indicates you haven't had much physics education. I'm still willing to teach you some rudiments, but you have to drop the nasty, aggressive attitude and be willing to listen - send me a message if you're interested.
oooooooooorly 3 days ago
@oooooooooorly You've been stealing terms from my and other's posts to use in your own at almost exactly the same rate as Ifo98 has. If I didn't know better, I'd say that you and he are the same troll, baiting folk with a studied display of idiocy, but I do, so I wouldn't.
skoockum 10 hours ago
@skoockum
"Stealing terms?" Did it not occur to you that the reason the same language is used by multiple people is because they're the proper nomenclature to describe the physical system?
Really, there's no need to be so hostile. Lashing out and calling people "trolls" when they offer to teach you physics isn't exactly conducive to constructive discussion. Everyone else here has been completely civil - why can't you?
oooooooooorly 9 hours ago
@skoockum IMO your trolling peaked with "they could never figure out why I had the highest grade in the class". I'd like to hear more imaginative stories regarding your education. Claiming you can't see how the term "hill" can be applied in describing a siphon is a bit weak.
lfo98 2 days ago
@lfo98 I didn't hear me say I "can't see how the term "hill" can be applied in describing a siphon" ...you may want to reread my post to see what I really did say. Very weak attempt at trolling, BTW, putting words in my mouth ...very weak.
skoockum 11 hours ago
@skoockum Ha ha I was about to say that. :P
Seanze329 4 days ago 2
@lfo98 the only reason they used the ionic liquid was so that the "water" didn't boil away. you are partially right with air pressure having an effect, for you need air to move out of the way to make room for the water, otherwise it wont work. at the same time it cant work without gravity and surface cohesion. in this case both the experiment and traditional thinking wins.
andrynor 2 weeks ago
@lfo98 Air pressure can't be involved because both vessels in a traditional siphons are open to the same air pressure and therefor in balance. Gravity and suction is all that is involved.
Gunther222 1 week ago
@Gunther222 Yes but suction is generally the flow of material from a area of high positive pressure to a area of lower positive pressure. The experiment is an example of negative pressure (molecules attracting each other rather than repelling), but anyway generally you need air pressure for a siphon to work, well established theory and experimental evidence support this.
lfo98 1 week ago
@lfo98 This video has just proved air pressure does not play any part in the operation of a siphon, so your statement is incorrect and the experimental evidence therefore doubtful. That said, air pressure does have two effects. First, it stops the liquid being siphoned boiling. Second, if there is a difference in air pressure between the reservoirs it will block or even reverse the siphon action. At that point however it is no longer a siphon, it has become an air pressure pump.
marklandynut 1 week ago
@marklandynut
The video does not show that air pressure "plays no part" in the operation of a siphon - rather, it shows that a siphon *can* function in the absence of air pressure, *given a liquid with sufficient intermolecular forces. A liquid with no surface tension would not form a functioning siphon in a vacuum, yet would work fine in sufficient air pressure.
oooooooooorly 1 week ago
@oooooooooorly Not quite. When a liquid cannot form a siphon without air pressure (i.e. water at room temperature) it is not a lack of intermolecular forces preventing the siphon from forming, it is the lack of intermolecular forces casuing the liquid to boil and create bubbles of vapour that breaks the siphonic action. What you won't get is the liquid breaking apart and forming a vacuum in the pipe, which is what your comments about air pressure are suggesting.
marklandynut 1 week ago
@marklandynut
False - if you could prevent the rapid evaporation of your liquid, you would indeed find the liquid breaking apart in the pipe.
Flow is governed by pressure gradient - the reason a siphon works is liquid flows from an area of higher pressure to one of lower pressure. If a liquid cannot sustain negative pressure (lack of surface tension), this *cannot occur* without some external pressure on the whole system.
oooooooooorly 1 week ago
This has been flagged as spam show
@oooooooooorly It's been shown that you can have a working water siphon under vacuum, if you're careful, use very pure water, clean equipment and boil off any gas before you start. This prevents boiling and the tensile strength of the water allows it to flow. These conditions are rather strict and apparently "mechanical shock" (causing the liquid to break at a point) will stop the flow. I imagine you would need a very large mechanical shock to stop a siphon functioning under ...
lfo98 6 days ago
@oooooooooorly If the liquid breaks apart in the pipe it will rapidly evaporate since evaporation occurrs when the intermolecular bonds are not strong enough to hold the liquid together. Its all to do with the vapour pressure and was explained in the video, and is why they used an ionic liquid in the experiment.
Flow is indeed governed by a pressure gradient, but in a siphon that pressure is entirely within the liquid and created entirely by gravity pulling the liquid downwards.
marklandynut 6 days ago
@marklandynut
Sure, you could (probably) never practically generate the situation of a low-cohesion liquid in a vacuum - I'm not disputing that. You could, however, create a siphon of zero surface-tension liquid which works just fine in atmospheric pressure. So, no, the pressure is not necessarily generated "entirely within the liquid" - in fact, when the whole system is at positive pressure the molecular cohesion isn't very important at all.
oooooooooorly 6 days ago
@oooooooooorly OK, try this. Atmospheric pressure does not take part in siphonic action. However the siphon will be broken if the liquid pressure in the liquid at the highest point of the siphon is equal to or less than the vapour pressure since the liquid will begin to form bubbles of gas. Atmospheric pressure acting on the liquid increases its base pressure and therefore the maximum height of the siphon before the vapour pressure is reach and bubbles break the siphonic action.
marklandynut 6 days ago
@marklandynut
Essentially, yes - if your liquid cannot sustain the negative pressure in the top of the siphon, then atmospheric pressure is then important to its function. In a sense, one can think of the pressure gradient at negative pressure as the molecules "pulling" each other, and at positive pressure as "pushing." Not all liquids can do the former (the one in the experiment obviously can), but the latter is not possible without some sort of external pressure.
oooooooooorly 6 days ago
If you would pour this liquid from a glass into another container from a quite long distance, would it still "stick" and make a constant stream? Water will make little droplets in that situation. Just curious.
matthias4lupe 3 months ago
So what was that fluid composed of?
HazMatLabz 3 months ago
I'd say this was quite a risky experiment with that rather big flat glass? in the door. Next time be careful of an implosion.
oomblikkies 3 months ago
So what about turkey basters and such? Do those require atmospheric pressure?
KingCrassusII 3 months ago
Almost vacuum is not vacuum, you still have some pressure pushing the two surfaces of the liquid.
What would happen in real vacuum?
retepaskab 4 months ago
@retepaskab
A short lesson in real vacuums.
They are immense energy conduits, if you force a wave through it, it will be at the other side as it enters the vacuum.
The amount of energy required to create a 'real vacuum' the size of a golf-ball is locked away in an antimatter and matter reaction equal to 2 golfballs. Once you create a vacuum using the matter and anti-matter, you are left with an amount of energy that will tear the vacuum apart again or level an entire city block.
So no...
MarxIzalias 3 months ago
Comment removed
retepaskab 4 months ago
A neat modification to this experiment would be trying a liquid that doesn't have any molecular attraction with itself (does this exist?). Would a vacuum bubble be created inside the tube? My guess is yes.
DemiImp 4 months ago
@DemiImp I think a liquid having molecular attraction with itself is the very definition of a liquid: if molecules don't pull themselves together they would form a gas.
The interesting thing would be to do that experiment on the moon, where you have a real vacuum and gravity.
Bye.
xja85mac 4 months ago
@DemiImp that would evaporate like he said in the vid
Tob3ster97 4 months ago
Isn't this more of a sixtysymbols video? Chemists stealing credit from physicists, pfff! So typical!
SubTachyon 4 months ago
@SubTachyon lol
juanarruti 3 months ago
It's clear that a siphon only works when the net flow of liquid down the tube exceeds the net flow of liquid up the tube just by looking at the first demonstration. I don't get what the point of testing it in a vacuum is, especially if there is atmospheric pressure pushing against both liquids equally.
DogHouseRock4 4 months ago
its not air, it's gravity..... and it's not pushing up, it's sucking down
raymix1 4 months ago
No gloves?!
superscar 4 months ago
@ monkeyboy4746 You see in the video that I moved the rod relatively slowly. The reason was that the rubber vacuum seals around the rod also make it a little hard to move the rod not the air pressure. The rod won't go into the chamber as there is a stop on it. The screws are there to stop the plate falling onto my toes "again" when I let air back into the chamber.
@ frichikendz My honey doesn't like being evacuated ; )
ElectricDoctor1 4 months ago
Can you try this with honey?
frichikendz 4 months ago
@ frizstyler Sorry I can't answer as that is not my field of expertise. I'm not sure if Pete could answer that or if its been tested. I suspect that it may expand and contract a bit when heated or cooled even though it has almost no vapor pressure.
@KemaTheAtheist Funny you should say that but some of that equipment may have come from Kroto's lab.
ElectricDoctor1 4 months ago
@ monkeyboy4746 No this was not a mock up although the partial pressure was a little higher than the best achievable as the apparatus was moved for the video. Regarding the front plate (one inch thick perspex) it has a force of about one tonne pushing it onto the chamber why would I need any bolts? The same goes for the rod at only 0.5 cm diameter it has an effective atmospheric weight (i.e. 1kg /cm sq) of 200 grams . Yes I also used the same dye for both liquids as both are colourless.
ElectricDoctor1 4 months ago
@ElectricDoctor1 OK, I could not see the thickness of the front plate in the video, I know it would be held on without screws, I just threw that in, since no one responded to my first comment. When you say "ultra high vacuum" I noted the rod was not falling back on its own into the chamber, I got a little suspicious. Thanks for clearing it up.
monkeyboy4746 4 months ago
is this also the least compressible liquid there is,apart from being the least expandable??? sorry if i make orthographic mistakes
frizstyler 4 months ago
Did anyone else starting thinking about buckyballs/cubes when he was talking about the ionic liquids as bar magnets?
KemaTheAtheist 4 months ago
I think this is a mockup of the experiment, not the actual one, his vacuum chamber's front plate is being held by only 4 screws, he can retrieve a rod from the chamber that should be held down by atmospheric pressure, the water in the previous video shot is the same color as the "ionic fluid" in the chamber in the next video shot, I want to hear from Brady on this, is what I am seeing the actual experiment or a mockup done for the channel?
monkeyboy4746 4 months ago
of course it has nothing to do with atmospheric pressure! You can demonstrate the same thing with a long piece of bath-plug chain.
risvegliato 4 months ago
Well done Sherlock.
ajuk1 4 months ago
is this still called science?
Copimi 4 months ago
OMG - There is nothing like reading these comments to justify the closing of all government run schools (ie public education, at least in the US)
5000loto 4 months ago
I'm kind of embarrassed that I learned something from this video.
I really should have understood how siphons worked...
:(
tybo09 4 months ago
1.) it would look like just the same as under normal pressure - it just would go way faster - if you would get the dry ice instantly into an high vaccum then it would most likely evaporate like an explosion
2.) in principle yes, in detail it depends on the specific phase diagram of the material
Hypernaut74 4 months ago
Comment removed
SluzBag1993 4 months ago
i knew that
gman9884 4 months ago
I have never even heard the explanation on pressure. I always assumed it's gravity-driven.
Does that make me a genius? :P
Surtak 4 months ago
in space there is no gavity does the fact that this experiment is conduction on earth mean that gravity is helping the siphon?
badshabz1 4 months ago
@badshabz1 Of course, you don't have "up and down", the liquids wont flow in space.
1997xander 4 months ago
The weight of the atmosphere sure does help assist me in stopping really fast when some jerk off pulls out in front of me.
stevenmorookian16 4 months ago
Lol siphons really suck
aurestest 4 months ago 64
@aurestest One end swallows, the other spits.
ba3cool 3 weeks ago
Not trying to sound like a dick or anything, but I am absolutely staggered that there was any confusion about the mechanism of something as simple as a syphon. With advancements and understanding of things as diverse and complex as virtual particles, black holes, higher dimensions, the quantum world... how come it was not obvious to these people that this is gravity plain and simple? Other than that- periodic videos rock :)
Tossphate 4 months ago
@Tossphate Probably because no one thought to do experiment, till know :)
soulvibe2007 4 months ago
@Tossphate because it doesn't make sense that gravity would cause the liquid to go UP hill. The fact is that its suction + gravity that causes this to happen, not gravity alone, thus the confusion.
optikalefxx 4 months ago
We've spent the past week on Bernoulli's equation and siphons in my chemical engineering class. This is a great timing for this video.
elementaleel 4 months ago
Thats good physics. Hey wait, your chemists!!
appletek 4 months ago
LOL Great ending
RiceWithSticks 4 months ago
"Siphons really suck" lol yes they do haha
phayz9 4 months ago
This is cheating! Basically this ionic liquid is a chain of connected balls that can't be separated. Lets think of a liquid with a low vapor pressure-like water.
Lets do it at atmospheric pressure. Lets raise the tube a kilometer into the sky. What will happen?
Answer; a bubble will form and there will be no siphon. This bubble will be H2O gas.
Now. In a vacuum, the bubble will form at a much lower height.
TL;DR; A siphon at ANY pressure will not work if the vapor pressure is too low.
kurtu5 4 months ago
@kurtu5 Of course, that was not the friggin point of the video.
1997xander 4 months ago
Wow. It's been awhile since I've seen someone use a metaphor and it actually facilitates understanding!
BuBBaGump014 4 months ago
Amazing !!! in some minutes you just destroyed one "common piece of knowledge".
Thanks :-)
lhtd 4 months ago
@lhtd in a positive way of course
lhtd 4 months ago
Siphons really suck!
raishisou 4 months ago
Clearly, this video sucks. Literally.
47f0 4 months ago
Clearly what is needed for a siphon is that cohesiveness + air pressure is enough to prevent prevent the formation of a cavity in the tube. For ordinary liquids the cohesiveness is not enough for more than a few mm of elevation, so air pressure is needed for the rest.
njimko23 4 months ago
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OwRob 4 months ago
...well done Adrian Boatwright and Pete Licence
-siphons really do suck !
=but pressure still pushes a little bit, as all energy inequality seeks a balance, always
docatomics 4 months ago
Any chance getting some of the physics guys (Moriarty) to weigh in on this, for further explanation?
twstdelf 4 months ago
And that's why you're chemists and not physicists.
525047 4 months ago
It would be interesting to repeat this to see how high the siphon could go before the cohesion that holds the liquid together in the tube failed.
I'm guessing that a bubble of vacuum would form and the liquid would simply drop down and equalise with the level of each container.
Also what would cause such a bubble to form? Would it be a tiny imperfection, like with boiling water, or would it be when the weight of the liquid in the columns exceeds the cohesive force within the liquid?
Hewpie 4 months ago
photoshop
lumina998 4 months ago
...siphons suck...
stalker7d7 4 months ago 5
its called gravity
MinfangDuan 4 months ago
so basically its really hard to siphon custard...
TheRealJoeSparrow 4 months ago
thumbs up if you found this really hard to masturbate to...but got there in the end ;)
TheRealJoeSparrow 4 months ago
Wait wait...what kind of idiot ever said atmospheric pressure pushed the liquid down and into the tube? That's moronic. There's the same pressure on the other side of the tube. It's obviously, OBVIOUSLY just the liquid falling down the longer side of the tube sucking the other liquid behind it.
aluisious 4 months ago
@aluisious True, but now we have the proof.
mcmire 4 months ago
This is so obvious - didn't need explaining - anyone who didnt realise it was intermolecular forces from the start is an idiot.
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TheBannedPoet 4 months ago
Very clever... but seriously who didnt know this?... why did they bother doing this?
honeymonster147 4 months ago
@honeymonster147 some people need things to be proved to them by experiment if they believe the outcome could be otherwise even against the numbers. It is generally good practice to do what would be called an experiment of an 'obvious' outcome anyway as a proof of concept.
ConnorXV 4 months ago
@ConnorXV 1+1=.... Wait let me get one thing and another one thing... :O Omg IT EQUALS TWO!!! (sorry i have an extreme sarcasm disorder)
honeymonster147 4 months ago
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@honeymonster147 "Very clever... but seriously who didnt know this?... why did they bother doing this?"
Quite a lot of people don't seem to know it, including Wikipedia.
chrisofnottingham 4 months ago
your hairr is well greasy ewwww
lickylickyass 4 months ago
So why not show next time water boil away in the vacuum ?
unitasetmagus 4 months ago
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OwRob 4 months ago
That's my uncle Adrian :)
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lightandbeautiful 4 months ago
I just wonder how someone could think that atmosphere would change the result? It's all about mass and that something what we have learned from Mr. Eistein. Thanks for the video still, maybe it will clarify someone. =)
qettyz 4 months ago
I learned nothing. Do people really intuitively think it is atmospheric pressure and not gravity that drives a siphon?
zunathanzu 4 months ago
How is it possible to withdraw the metal rod which raises the tube filled with liquid if the box is under a vacuum, would not the metal rod be held down by the atmospheric pressure in the room?
monkeyboy4746 4 months ago
C7H9F6N3O4S2,C11H20F6N2O4S2,C10H15F6N3O4S2,C12H15F10N3O4S2,C10H15N5,C8H15F6N2P,C9H18N2O4S,C8H15BF4N2,C9H15F3N2O3S,C10H15F3N2O2,C11H14F6N2O4S2,C16H23F6N3O4S2,C8H11F6N3O4S2,C8H11N5,C8H16N2O4S,C6H11BF4N2,C12H19F6N3O4S2,C10H19F6N2P,C10H19BF4N2 and C10H18F6N2O4S2 :P
mrblisterfist 4 months ago
@mrblisterfist Use any of the above in your demonstration ?
mrblisterfist 4 months ago
Sounds like fluid weight diff. Is pulling the rest down period
Hugoboss206 4 months ago