Could a pipe from the ocean's depths create a fountain effect on the surface?

[Salvador]

Hello, the known presenter "Vsauce" on youtube had a video in which he talked about a " space straw" basically a pipe or circular enclousure the goes from a higher pressure area to a much lower one like a straw from surface of water at sea to outer space.

Now , my question is If I were to put a pipe that would go down to almoust the bottom of the ocean ,a deep place like the mariana trench for example and the other side of it would stick a few meters above water surface , would the pressure from the water combined with a sufficiently small diameter result in water flowing out of the pipe above water surface much like in a fountain?

 

[mfb]

How would the diameter influence anything?
You would just constrain the motion of water, but (neglecting water currents and so on) nothing moves anyway.

 

[russ_watters]

The pressure is the other half of the equilibrium with gravity already. Dropping a pipe into the ocean doesn't change that.

 

[Salvador]

Ok, but then why would in the space straw analogy he said that if we had a straw just a little below water and all the way up to open space , the difference in pressure would mean water would go up that straw some length , isn't this the same situation of pressure difference, just different pressures?

Since space has vacuum and here at sea level there is pressure which is more than vacuum of space such a straw can be considered a vacuum cleaner with the vacuum of space being the " motor".
I thought if this works then since there is greater pressure at the bottom of the water reservoir and less pressure up at water surface it should be the same , could you explain more please why the first one works but this one doesnt?

 

[russ_watters]

The "space straw" idea is wrong too, for the same reason.

 

[Salvador]

well in that case to not stir up any more confusion here is the link to the video



at the start he soon starts to talk about pressure difference atmosphere and the straw , please watch it and tell me would the water be pushed up a little bit (he mentions the approximate height) the straw or would nothing happen at all in which case he is wrong ?

thanks.

 

[nasu]

The water will be pushed up only if the air in the straw will be evacuated somehow.
He is a little ambiguous but he doesn't say that the water will be sucked into space. Not that is will raise in the space straw by 10 m. Just that it won't rise more than that.

 

[sophiecentaur]

The "space straw" idea is wrong too, for the same reason.

I'm afraid I couldn't handle ten whole minutes of that guy on the vid.
Isn't the point of this thought experiment that the straw has no air in it - therefore no pressure.?
Under that condition, the pressure on the water surface outside the straw would surely push water up inside until the total pressure at 'sea level' inside the straw is the same as the pressure at sea level. outside There would be a column of about 10m in the straw. This column would be producing the same pressure as the atmosphere outside the straw.
This is the same idea as that of Gasparo Berti, who was the first (?) to state the limit to the height of a syphon.
There's nothing under the Sun.

 

[nasu]

You can't mean that. Unless you play on the meaning of "under".
I suppose you forgot the "new".

 

[sophiecentaur]

New new new new new - silly old sod!

 

[Salvador]

Oh right I got the picture , I forgot the very important aspect of the difference in pressures also means they have to be isolated to stay different.

Ok so here would go a pretty wild guess, If a good vacuum can make water go about 10m above sea level , then would instead of using a straw which extends all the way up to space I could build a pipe with a shield inbetween so there would be two pipes in a pipe.have the pipe higher than those 10 meters and evacuate all air in the chamber above the pipe.(for throught purposes say achieve space vacuum) now the inner pipe would be made such that one side of it has a bigger diameter and the other one has smaller one.
If I'm correct the same level of vacuum will achieve different heights of water columns in different diameter pipes correct?

So if I have this two diameter pipe in one enclousure and a sealed vacuum chamber above where the water level ends and a small opening at the top of the smaller diameter pipe , would the sucked up water in the smaller diameter pipe flow down to the larger diameter pipe were the level of water should be lower and would this continue as long as the same vacuum is kept at the above chamber?

a little far off maybe but I'm keen on knowing the answer to this

 

[jbriggs444]

Ok so here would go a pretty wild guess, If a good vacuum can make water go about 10m above sea level , then would instead of using a straw which extends all the way up to space I could build a pipe with a shield inbetween so there would be two pipes in a pipe.have the pipe higher than those 10 meters and evacuate all air in the chamber above the pipe.(for throught purposes say achieve space vacuum) now the inner pipe would be made such that one side of it has a bigger diameter and the other one has smaller one.

You lost me on all of your pipes within pipes, some with the headspace evacuated and some not.

The device you describe is (presumably) a barometer. Mercury is traditionally used as the operating fluid because it has a lower saturated vapor pressure than water and because the required mercury column is less than one meter high.

Alternate designs for a water-based barometer (aka a "weather glass") allow some air to remain in the sealed head space which you would otherwise evacuate.

http://en.wikipedia.org/wiki/File:MercuryBarometer.svg

Edit: missed the following bit:

If I'm correct the same level of vacuum will achieve different heights of water columns in different diameter pipes correct?

No, not correct. That is a version of the classic "poke a hole in the bottom of the boat and have the water squirt higher than the sides fallacy"

 

[nasu]

Oh right I got the picture , I forgot the very important aspect of the difference in pressures also means they have to be isolated to stay different.

Ok so here would go a pretty wild guess, If a good vacuum can make water go about 10m above sea level , then would instead of using a straw which extends all the way up to space I could build a pipe with a shield inbetween so there would be two pipes in a pipe.have the pipe higher than those 10 meters and evacuate all air in the chamber above the pipe.(for throught purposes say achieve space vacuum) now the inner pipe would be made such that one side of it has a bigger diameter and the other one has smaller one.
If I'm correct the same level of vacuum will achieve different heights of water columns in different diameter pipes correct?

So if I have this two diameter pipe in one enclousure and a sealed vacuum chamber above where the water level ends and a small opening at the top of the smaller diameter pipe , would the sucked up water in the smaller diameter pipe flow down to the larger diameter pipe were the level of water should be lower and would this continue as long as the same vacuum is kept at the above chamber?

a little far off maybe but I'm keen on knowing the answer to this

How is this related to OP? Were you after a perpetual motion machine after all?

 

[LURCH]

Just a little side note: Something resembling perpetual motion actually is possible here, if you replace the straw with a "space elevator". Your elevator would have to extend well beyond geosynchronous orbit (say, 45,000 miles; or 75,000 km), and it would have buckets that come down one side, dip into the ocean, and climb up the other side. So long as a full bucket dumps its water at the top of the elevator every time an empty bucket fills up at the bottom (so the mass above geosynch is always greater than the mass below it), the conveyor would behave like a siphon, requiring no power source except at start-up. It would not, of course, be true perpetual motion, but it would sure look like it to anyone on the ground.

Not very helpful for understanding the vacuum-related problems of the OP perhaps, but an interesting thought experiment nonetheless.

 

[Salvador]

jbrings444, well first of all the idea was simple , two pipes each one has different diameter but their in a single enclosure , and when those pipes reach a certain height there is a vacuum chamber at the top of them sealed together with the pipes.The reason I say that the same fluid should achieve different heights in each pipe given the same vacuum which they both share is also the same logic that applies if I would puncture a hole in your boat, a smaller hole would yield a higher inrushing water column a larger hole would yield a lower inrushing water column if the weight of the boat is the same in both situations. It doesn't have to be higher than the water level around the boat but there must be difference in height with different diameters and equal pressures.
If this reasoning is wrong tell me.

yes LURCH that is an interesting idea, an there is nothing perpetual motion here , because then again solar power can be considered perpetual motion because our lifetimes are so short compared to the sun that it's almoust perpetual. :D

by the way would this space elevator bucket thing work because when the bucket of water reaches certain height the gravitational pull from the centrifugal force due to its rotation would become larger than the weigth of the bucket of water just above sea level so it would be able to pull each next one up?
If so then this device would get it's energy from the rotation of Earth itself.Ok but back to my question , is these two pipes with tha vacuum above them had different diameters and the water levels at each one of them would achieve different heigths , then if I were to take water from the smaller diameter pipe and dump it into the larger diameter lower water level pipe would the water always keep the same heigth in the first pipe , assuming the vacuum is kept ?

I apologize as this sounds a little tricky but that's the best I can explain.

 

[russ_watters]

jbrings444, well first of all the idea was simple , two pipes each one has different diameter but their in a single enclosure , and when those pipes reach a certain height there is a vacuum chamber at the top of them sealed together with the pipes.The reason I say that the same fluid should achieve different heights in each pipe given the same vacuum which they both share is also the same logic that applies if I would puncture a hole in your boat, a smaller hole would yield a higher inrushing water column a larger hole would yield a lower inrushing water column if the weight of the boat is the same in both situations. It doesn't have to be higher than the water level around the boat but there must be difference in height with different diameters and equal pressures.
If this reasoning is wrong tell me.

Yes, it is wrong. Whether static or squirted through a hole, the height of a colum of water is equal to the pressure divided by the weight density. Or the other way around: p=mgh. Period. It does not depend on the shape of the container or hole.

Using Lurch's barometer: a barometer gives the same reading (same fluid column height) regardless of the column's diameter.

yes LURCH that is an interesting idea, an there is nothing perpetual motion here , because then again solar power can be considered perpetual motion because our lifetimes are so short compared to the sun that it's almoust perpetual. :D

This thread is on shaky ground instead of already locked because I can't decide if you are really trying to find a perpetual motion machine. Part of the problem is you don't know what a perpetual motion machine even is. Despite the name, it isn't about how long a machine runs it is about whether or not the machine violates the laws of physics -- most often conservation of energy:
http://en.wikipedia.org/wiki/Perpetual_motion

 

[LURCH]

yes LURCH that is an interesting idea, an there is nothing perpetual motion here , because then again solar power can be considered perpetual motion because our lifetimes are so short compared to the sun that it's almoust perpetual. :D

by the way would this space elevator bucket thing work because when the bucket of water reaches certain height the gravitational pull from the centrifugal force due to its rotation would become larger than the weigth of the bucket of water just above sea level so it would be able to pull each next one up?
If so then this device would get it's energy from the rotation of Earth itself.

That's right. At geosynchronous orbit, gravity and centrifugal force are balanced (for any object orbiting once every 24 hrs). Anywhere above that, centrifugal force is greater. And yes, that is exactly why it's not perpetual motion, because it is being powered by Earth's rotation.

But regarding your OP, all you've got there is an extremely expensive barometer that's impossible to build with any currently known materials. Once you've evacuated the tube, you could maintain that vacuum by either extending your tube out to space, so the open end is in a naturally occurring vacuum, or you could just cap it off. Either way, the guy is correct; the water would go up about 10 meters and stop, if the straw were evacuated first (which I notice he doesn't specify) .

 

[Salvador]

Well that sounds interesting , so you are saying that if I had two pipes one with the diameter of 10cm and the other of 1km the same pressure would push the same fluid at equal heigths in both pipes?

 

[jbriggs444]

Well that sounds interesting , so you are saying that if I had two pipes one with the diameter of 10cm and the other of 1km the same pressure would push the same fluid at equal heigths in both pipes?

Yes. That is correct.

 

[russ_watters]

Yes: Hydrostatic pressure, p= ρ g h

 

[Salvador]

Just a sidenote, so if my space straw could be physically made many km's in diameter and extended all the way up to space , i could suck half the ocean up that straw and the shores would become dry.
That is very interesting indeed.

Ok but one thing still confuses me a little.For example we have a pipe of whatever diameter one side is submerged in water the other has a vacuum (space or artificial doesn't matter I guess) Now water is sucked up to a certain height.then there is a man with buckets or a small pump at the top of the water level in the pipe which continuously pumps the water down back into the water tank or sea or whatever.but as long as the vacuum is maintained at the top , water will keep coming up to replace the lost water which was pumped back down correct?

 

[A.T.]

Ok but one thing still confuses me a little.

What is confusing about pumping water in a cycle?

 

[jbriggs444]

Just a sidenote, so if my space straw could be physically made many km's in diameter and extended all the way up to space , i could suck half the ocean up that straw and the shores would become dry.

Please calculate the pipe diameter needed so that half of the ocean will fit within 10 meters of pipe length. Compare to the diameter of the Earth.

 

[mfb]

It could not even suck a relevant fraction up. Its surface area cannot exceed the total surface area of Earth for obvious reasons, and if you would distribute all water in the oceans evenly you get a layer 3 kilometers deep (or high, depending on the point of view). 10 meters are just 0.3% of that.

Also, the water level in your "straw" is 10 meters above the water level outside. As soon as you would have a significant amount of water inside, the water level outside would drop, spoiling your attempt.

 

[nasu]

Just a sidenote, so if my space straw could be physically made many km's in diameter and extended all the way up to space , i could suck half the ocean up that straw and the shores would become dry.
That is very interesting indeed.

To add to what was already said, the space does not help you at all. You still have to remove the air on top, or at least part of it, as you do when you use a regular straw.
The water won't go up by itself. It will just be harder for you to suck at the top end if you extend it to space.

 

[Salvador]

thanks for the interest, the part about sucking the oceans up was more of a joke than a real thing I thought would be possible.

the part to which only A.T. responded , the second part of my post I was more interested into.Because if you have water held up to a certain point by vacuum and then you take some of that water and pour it down back again you are doing much less of a work if you had to take the water up to that level and then pour it down , so my question was can the water level in a pipe stay there even if it is being constantly taken away but the vacuum is maintained or does the vacuum needs to be constantly kept by some vacuum pumps or something?

 

[sophiecentaur]

thanks for the interest, the part about sucking the oceans up was more of a joke than a real thing I thought would be possible.

the part to which only A.T. responded , the second part of my post I was more interested into.Because if you have water held up to a certain point by vacuum and then you take some of that water and pour it down back again you are doing much less of a work if you had to take the water up to that level and then pour it down , so my question was can the water level in a pipe stay there even if it is being constantly taken away but the vacuum is maintained or does the vacuum needs to be constantly kept by some vacuum pumps or something?

There is no end to the combinations that you can think of, in which energy is transferred here and there. The overall energy consumed by raising and lowering something (water, solids, gases etc. etc.) will always be positive. That is basic and incontrovertible Physics. So, whatever system you are proposing, you can possibly say that it will use less mechanical energy than you might have thought (because some energy is stored somewhere in the system) but you also have to realize that energy is 'lost' in the form of thermal energy. Getting more and more intricate models is not the way to establish the basic principles or to get understanding. The PM fanatics of the past (and present) always forget something that invalidates their inventions.

 

[nasu]

the part to which only A.T. responded , the second part of my post I was more interested into.Because if you have water held up to a certain point by vacuum and then you take some of that water and pour it down back again you are doing much less of a work if you had to take the water up to that level and then pour it down , so my question was can the water level in a pipe stay there even if it is being constantly taken away but the vacuum is maintained or does the vacuum needs to be constantly kept by some vacuum pumps or something?

The work done in the process is the same. Just that some of it may not be done by you.
Same as when we use hydroelectric power. The work done to rise the water up hill is the same done by the water when it goes downhill and turns the turbines.
The only reason this is a practical application is that we don't have to do the uphill work.

So theoretically there s nothing interesting or unusual in your system.
Practically, in any vacuum chamber on Earth you need to maintain vacuum by pumping at least once in while. And you want to open the chamber to remove some of the water, too. What you propose is like a hydroelectric system where you pump the water up instead of using a natural course of water. And it will be limited to a difference in height of only 10 m. Unless you have a system with several steps.

 

[Salvador]

I don't count myself as a PM fanatic , I just want to find out if something works , once i understand it doesn't I leave it and go further.
the thing I most wanted to understand here is , can the vacuum , once established, keep on sucking in water if some of the water kinda escapes from the top or is allowed to flow away or is pumped away or whatever.

 

[jbriggs444]

I don't count myself as a PM fanatic , I just want to find out if something works , once i understand it doesn't I leave it and go further.
the thing I most wanted to understand here is , can the vacuum , once established, keep on sucking in water if some of the water kinda escapes from the top or is allowed to flow away or is pumped away or whatever.

Have you ever sucked water through a straw, one mouthful at a time? Yes, you can keep sucking up as much as you like as long as you keep swallowing between sucks.

 

[nasu]

Yes, but you have to suck again after each mouthful. I think he wants to make the water go outside, form the low pressure inside to the high pressure outside without changing the pressure inside.

 

[jbriggs444]

Yes, but you have to suck again after each mouthful. I think he wants to make the water go outside, form the low pressure inside to the high pressure outside without changing the pressure inside.

Having sucked water through a straw myself, I know that it is perfectly possible to do so without ever letting the water drain out of the straw.

Edit: You are right, of course, that there is effort involved in re-inflating the mouth cavity to allow water to re-enter. There ain't no such thing as a free lunch.

 

[nasu]

Yes, you can. But try to spit some water out without without ever letting the water drain out of the straw and without having to tension your diaphragm or inter-costal muscles to reduce again the pressure afterwards.:)

I think you mean to inflate your lungs. You don't inflate the mouth to suck water.

 

[sophiecentaur]

I think this is getting a bit silly. The basics of energy conservation will always apply and making up some whacky scenario involving sucking and vacua does not alter that. It should be an exercise for the student to find the flaw in every argument that doesn't seem to involve energy conservation. It's little more than a waste of time for people who have already accepted the basic principles and proved it to themselves once or twice and found the secret source of energy in one or two of these aunt sallys.

 

[Salvador]

I think it's kinda simple , well here's my reasoning.
I think it is possible for a once established vacuum(vacuum , pumped out air and then the pumps disconnected) to keep on sucking up new water once the old has ran away from the top, the thing that would probably destroy this nice little scheme is what nasu and others here pointed out that in order for the water to escape the top to make way for new water keeping the same vacuum would imply not destroying the vacuum , but if one would make an opening in the enclousure higher surrounding pressure would inrush towards the vacuum and the column of water would collapse ,

using a pump to pump out the water from the column would probably work but then again the pump would have to use as much energy as it would use to get the water from the source up to that point anyways probably, the problem is I guess that the vacuum and water column is a satic situation and getting the water out from a low pressure area to a higher pressure area would basically mean " water climbing up a hill " work so there would need to be extra energy applied.