# A watertight seal that can also be penetrated by something non-water **URL:** \ **Category:** Factual Questions\ **Created:** [April 27, 2015, 5:42pm UTC](https://boards.straightdope.com/t/a-watertight-seal-that-can-also-be-penetrated-by-something-non-water/718658 "2015-04-27T17:42:05Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Mrdeals](https://avatars.discourse-cdn.com/v4/letter/m/ea666f/32.png) [@Mrdeals](https://boards.straightdope.com/u/Mrdeals)\ **Post date:** [April 27, 2015, 5:42pm UTC](https://boards.straightdope.com/t/a-watertight-seal-that-can-also-be-penetrated-by-something-non-water/718658/1 "2015-04-27T17:42:05Z")
Kind of a confusing title, Mods, feel free to clean it up if necessary. I saw this drawing of a hypothetical perpetual motion machine that I think was a joke, but seems incredibly plausible. The main issue I can see with the machine is that it requires a tank of water on one end, with a chain and string of balls running from the bottom to the top. Is it possible to have a water tight seal that can allow things to move through it, but also keep the water inside? (Or at least make leakage/spillage very small) ---
**Author:** ![Really\_Not\_All\_That\_Bright](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@Really\_Not\_All\_That\_Bright](https://boards.straightdope.com/u/Really_Not_All_That_Bright)\ **Post date:** [April 27, 2015, 5:48pm UTC](https://boards.straightdope.com/t/a-watertight-seal-that-can-also-be-penetrated-by-something-non-water/718658/2 "2015-04-27T17:48:25Z")
Do gases count? It’s fairly easy to make something impermeable to water but not air. ---
**Author:** ![AndrewL](https://avatars.discourse-cdn.com/v4/letter/a/3d9bf3/32.png) [@AndrewL](https://boards.straightdope.com/u/AndrewL)\ **Post date:** [April 27, 2015, 6:03pm UTC](https://boards.straightdope.com/t/a-watertight-seal-that-can-also-be-penetrated-by-something-non-water/718658/3 "2015-04-27T18:03:21Z")
The problem with that type of perpetual motion machine design is not the seal, but that as each ball passes through the seal into the bottom of the tank of water it will have to push a corresponding volume of water upwards out of the way. This will take exactly as much energy as you would then get back from that ball rising to the top of the tank of water. ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [April 27, 2015, 6:07pm UTC](https://boards.straightdope.com/t/a-watertight-seal-that-can-also-be-penetrated-by-something-non-water/718658/4 "2015-04-27T18:07:09Z")
> [@Mrdeals](#): > > I saw this drawing of a hypothetical perpetual motion machine that I think was a joke, but seems incredibly plausible. It occurs to me – just spitballing here – that if you supplied a link to that device, we could talk about it much more intelligently. Just sayin’. ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [April 27, 2015, 6:23pm UTC](https://boards.straightdope.com/t/a-watertight-seal-that-can-also-be-penetrated-by-something-non-water/718658/5 "2015-04-27T18:23:46Z")
First of all, as pointed out already, perpetual motion machines don’t work. There’s a picture of the device you describe in Orde-Hume’s book **Perpetual Motion** ( [http://www.amazon.com/Perpetual-Motion-The-History-Obsession/dp/1931882517](http://www.amazon.com/Perpetual-Motion-The-History-Obsession/dp/1931882517) ), along with a great many other devices. It doesn’t work – some unconsidered kink will inevitably eat up the extra force or energy you thought you had, and condemn the machine to idleness. That said, there’s a classic case of a liquid that will penetrate seals – Superfluid helium has zero viscosity and zero entropy, and will flow through barriers that block normal fluid helium. > **[Superfluid helium-4](https://en.wikipedia.org/wiki/Superfluid_helium-4)** > > Superfluid helium-4 is the superfluid form of helium-4, an isotope of the element helium. A superfluid is a state of matter in which matter behaves like a fluid with zero viscosity. The substance, which looks like a normal liquid, flows without friction past any surface, which allows it to continue to circulate over obstructions and through pores in containers which hold it, subject only to its own inertia. > The formation of the superfluid is known to be related to the formation of a Bose–Eins... One hitch is that helium is only liquid within 4 degrees or so of absolute zero, and only superfluid within about 2 degrees. The other is that, even with this advantage, you can’t build a perpetual motion machine using superfluid helium, evenutilizing the fact that heating it will convert it to normal fluid, and chilling it back down will return it to superfluid state. You can, however, use it to construct a _dilution refrigerator_ that will get you closer to absolute zero than a simple helium refrigerator will, so that’s something. > **[Dilution refrigerator](https://en.wikipedia.org/wiki/Dilution_refrigerator)** > > A 3He/4He dilution refrigerator is a cryogenic device that provides continuous cooling to temperatures as low as 2 mK, with no moving parts in the low-temperature region. The cooling power is provided by the heat of mixing of the helium-3 and helium-4 isotopes. > The dilution refrigerator was first proposed by Heinz London in the early 1950s, and was experimentally realized in 1964 in the Kamerlingh Onnes Laboratorium at Leiden University. The field of dilution refrigeration is reviewed by Zu et... ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [April 27, 2015, 6:43pm UTC](https://boards.straightdope.com/t/a-watertight-seal-that-can-also-be-penetrated-by-something-non-water/718658/6 "2015-04-27T18:43:20Z")
[![](https://i.imgur.com/4qdvX.png) ](https://i.imgur.com/4qdvX.png) The obvious flaw is the same one that affects all PM machines - friction and the law. Not to mention spelling:) ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 27, 2015, 7:37pm UTC](https://boards.straightdope.com/t/a-watertight-seal-that-can-also-be-penetrated-by-something-non-water/718658/7 "2015-04-27T19:37:33Z")
Friction is not what kills free-energy machines. If that were the only problem, then all you’d have to do would be to improve your engineering until the losses due to friction were less than your energy output. We can’t get friction all the way to zero, but we can get it arbitrarily low. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [April 27, 2015, 7:53pm UTC](https://boards.straightdope.com/t/a-watertight-seal-that-can-also-be-penetrated-by-something-non-water/718658/8 "2015-04-27T19:53:54Z")
> [@Mrdeals](#): > > Is it possible to have a water tight seal that can allow things to move through it, but also keep the water inside? (Or at least make leakage/spillage very small) fuel filters for diesel engines have a hydrophobic coating on the filter element which lets fuel through but water beads up on the element and drops into a collection bowl. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [April 27, 2015, 8:11pm UTC](https://boards.straightdope.com/t/a-watertight-seal-that-can-also-be-penetrated-by-something-non-water/718658/9 "2015-04-27T20:11:54Z")
> [@bob\_2](#): > > [I cracked free energy! Critique? - Imgur](http://i.imgur.com/4qdvX.png) > > The obvious flaw is the same one that affects all PM machines - friction and the law. > > Not to mention spelling:) As **Chronos** points out, friction isn’t the issue. The problem in this case is that when a ball enters the bottom of the tank through that seal, it’s fighting against the water pressure at the bottom of the tank; it has to lift up an entire column of water to make room for itself at the bottom of the tank, offsetting the energy that’s recovered as the ball floats up to the surface (and gradually lets the column of water settle back down at the bottom of the tank). Even if the whole device (including that amazing artificial anus at the bottom of the tank) is completely frictionless, it would grind to a halt as soon as you tried to extract any mechanical work from it. Speaking of which, that nicely answers the OP’s question: an anus is pretty good at retaining liquid while allowing the admission of solid objects from the gas side to the liquid side. ---
**Author:** ![SpyOne](https://avatars.discourse-cdn.com/v4/letter/s/82dd89/32.png) [@SpyOne](https://boards.straightdope.com/u/SpyOne)\ **Post date:** [April 28, 2015, 2:04am UTC](https://boards.straightdope.com/t/a-watertight-seal-that-can-also-be-penetrated-by-something-non-water/718658/10 "2015-04-28T02:04:27Z")
> [@Chronos](#): > > Friction is not what kills free-energy machines. If that were the only problem, then all you’d have to do would be to improve your engineering until the losses due to friction were less than your energy output. We can’t get friction all the way to zero, but we can get it arbitrarily low. But friction IS what killed perpetual motion machines. Let’s say I have an upside down bicycle. If we could reduce friction to zero, I could spin a wheel and it would keep spinning forever. But we can’t, so the wheel will eventually stop. Machines that generate more energy than they use are certainly a popular subclass of perpetual motion machine, but they aren’t the only kind, and ALL of them are impossible. ---
**Author:** ![jezzaOZ](https://avatars.discourse-cdn.com/v4/letter/j/a9a28c/32.png) [@jezzaOZ](https://boards.straightdope.com/u/jezzaOZ)\ **Post date:** [April 28, 2015, 2:06am UTC](https://boards.straightdope.com/t/a-watertight-seal-that-can-also-be-penetrated-by-something-non-water/718658/11 "2015-04-28T02:06:25Z")
I thought sexual intercourse had solved that particular problem some time ago? ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [April 28, 2015, 2:27am UTC](https://boards.straightdope.com/t/a-watertight-seal-that-can-also-be-penetrated-by-something-non-water/718658/12 "2015-04-28T02:27:04Z")
Martin Gardner once wrote about a similar machine invented by [Irving Joshua Matrix.](http://en.wikipedia.org/wiki/Irving_Joshua_Matrix) One of the clever elements to the device was the float components that were labeled “up” as they were going up, but on the down trip, “up” became “dn”. Dr. Matrix, the noted numerologist, had an aboriginal-looking sidekick named Rhee, who was missing most of his choppers. They called him “One-Tooth Rhee.” ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [April 28, 2015, 2:27am UTC](https://boards.straightdope.com/t/a-watertight-seal-that-can-also-be-penetrated-by-something-non-water/718658/13 "2015-04-28T02:27:31Z")
> [@SpyOne](#): > > But friction IS what killed perpetual motion machines. > Let’s say I have an upside down bicycle. If we could reduce friction to zero, I could spin a wheel and it would keep spinning forever. But we can’t, so the wheel will eventually stop. Thought experiment: suppose you invent a frictionless bicycle wheel that spins forever. Now you attach a frictionless generator to it and connect a load to the generator. Will the wheel continue to spin? Why or why not? ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [April 28, 2015, 2:34am UTC](https://boards.straightdope.com/t/a-watertight-seal-that-can-also-be-penetrated-by-something-non-water/718658/14 "2015-04-28T02:34:43Z")
> [@friedo](#): > > Thought experiment: suppose you invent a frictionless bicycle wheel that spins forever. Now you attach a frictionless generator to it and connect a load to the generator. Will the wheel continue to spin? Why or why not? Is it a frictionless load, too? ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [April 28, 2015, 3:01am UTC](https://boards.straightdope.com/t/a-watertight-seal-that-can-also-be-penetrated-by-something-non-water/718658/15 "2015-04-28T03:01:17Z")
> [@Musicat](#): > > Is it a frictionless load, too? Let’s say it’s a resistive load. Like a light bulb. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [April 28, 2015, 6:30am UTC](https://boards.straightdope.com/t/a-watertight-seal-that-can-also-be-penetrated-by-something-non-water/718658/16 "2015-04-28T06:30:48Z")
> [@friedo](#): > > Let’s say it’s a resistive load. Like a light bulb. It will stop, because in extracting the power to run the light bulb, the generator will exert forces upon the wheel tending to slow it. A current generated by a moving magnetic field generates its own magnetic field that opposes the change that caused it. Lenz’s Law - the Sod’s Law of Physics. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [April 28, 2015, 10:29am UTC](https://boards.straightdope.com/t/a-watertight-seal-that-can-also-be-penetrated-by-something-non-water/718658/17 "2015-04-28T10:29:22Z")
> [@friedo](#): > > Thought experiment: suppose you invent a frictionless bicycle wheel that spins forever. Now you attach a frictionless generator to it and connect a load to the generator. Will the wheel continue to spin? Why or why not? no, because a generator is only around 70% efficient, even w/o friction. heat loss in the windings, eddy current losses in the armature/stator laminations, etc. Let’s say you wanted to power a 100 watt light bulb with such a setup. Your light bulb needs 100 watts from the generator to reach full brightness. but its inefficiencies mean you need about 145 watts **mechanical** power to drive it. see how fast that pipe dream bursts? ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [April 28, 2015, 10:53am UTC](https://boards.straightdope.com/t/a-watertight-seal-that-can-also-be-penetrated-by-something-non-water/718658/18 "2015-04-28T10:53:00Z")
> [@jz78817](#): > > see how fast that pipe dream bursts? You can’t win, you can’t break even, and you can’t get out of the game. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [April 28, 2015, 12:07pm UTC](https://boards.straightdope.com/t/a-watertight-seal-that-can-also-be-penetrated-by-something-non-water/718658/19 "2015-04-28T12:07:17Z")
> [@jz78817](#): > > no, because a generator is only around 70% efficient, even w/o friction. heat loss in the windings, eddy current losses in the armature/stator laminations, etc. Let’s say you wanted to power a 100 watt light bulb with such a setup. Your light bulb needs 100 watts from the generator to reach full brightness. but its inefficiencies mean you need about 145 watts **mechanical** power to drive it. > > see how fast that pipe dream bursts? You don’t even need friction to kill the proposed frictionless bicycle wheel. Wrap a rope around the rim so that the spinning of a wheel winds the rope and raises a weight. Even if the rope has no internal friction whatsoever, and there’s no aero drag on the weight as it is raised, the weight will receive mechanical work form the frictionless bicycle wheel, causing it to decelerate. ---
**Author:** ![Peter\_Morris](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/peter_morris/32/359_2.png) [@Peter\_Morris](https://boards.straightdope.com/u/Peter_Morris)\ **Post date:** [April 28, 2015, 12:26pm UTC](https://boards.straightdope.com/t/a-watertight-seal-that-can-also-be-penetrated-by-something-non-water/718658/20 "2015-04-28T12:26:10Z")
> [@CalMeacham](#): > > That said, there’s a classic case of a liquid that will penetrate seals – Superfluid helium has zero viscosity and zero entropy, and will flow through barriers that block normal fluid helium. Isn’t that the exact opposite of what the OP asked, though? I think he wants a valve that will allow the string of balls to enter, while keeping the liquid inside. [Next page](https://boards.straightdope.com/t/a-watertight-seal-that-can-also-be-penetrated-by-something-non-water/718658.md?page=2)