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Author Topic: What happens to water in zero gee?
KayTi
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In particular, I'm wondering what would happen to a swimming pool in zero gravity. Anyone have an astrophysics background and care to help me out here?

That's your random space question for the day, back to your regularly scheduled programming.


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Rhaythe
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With no gravity to keep it confined, water will tend to pearl and float whichever way its momentum takes it. It will still splash against any surface it encounters, and likely glop up when it encounters more of itself, but as viscious as water is, the impact of two pearls of zero-G water will likely create more droplets that go spinning off from its own momentum.

With an entire swimming pool of water in zero-g, you'll likely have a very thick foggy mist of very small droplets that is moving in every direction and covering every surface it touches, depending upon how long it's floating gravity-free.


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rich
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Just passing through and I saw the question...I have no idea.

But there is this, and it looks to be a pretty interesting discussion:


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rich
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Oh, and this neat little video.
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Rhaythe
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Also, my answer was assuming a quick shift from gravity to zero-gravity to create a lot of momentum. Otherwise, if the shift is slow and the water has very little momentum, it will tend to gather in large clumps instead due to surface tension. However, any force enacted upon those clumps will quickly disperse them into smaller droplets again.
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extrinsic
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Subtle effects; without a controlling microgravity or encompassing container, the swimming pool might not contain the water for long. It would float out and flow like a superfluid seeking container equilibrium as powerful surface tension attracts it to other surfaces. The hydrogen bond property of water would pull the water toward virgin territory like spilled milk flowing across a floor seeking level; without gravity, across any surface regardless of spatial orientation. With no air movement across it's exanding surface, evaporation would be stifled beyond a misty boundary layer in gas-liquid phase equilibrium above the water's surface. Heat is light and irrespecitive of gravity. Barring heating or cooling induced convection currents, temperature equilibrium would also be maintained according to the ambient temperature.
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KayTi
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OK, interesting stuff, but I don't have an answer quite yet...can you go swimming in zero g or will the water flow in and around you and choke you? See what I'm asking?

Yes, I'm exploring recreation in space. Any other ideas? LOL This is the fun part, isn't it?


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extrinsic
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A swimming pool in the terrestrial sense is highly improbable in space. Picture an enclosed skindiving tank with a water lock entryway and the swimmer wearing a portable breathing apparatus. That's the simplest scenario.

A more intriguing scenario would be a natatorium with natural or artificial forces holding much of the water to the lining of the water vessel, with an open air bolus in the center, assuming the vessel is relatively stable in relation to inertial forces. But with inertial forces in suspension, globules of water would pass willy-nilly from every direction throughout the natatorium, like a lava lamp's globules coming and going in every direction, unless they were compelled to stay against the lining, say, by gentle, directed forced air contributing to weak centripetal forces.

Zero gravity is a scientific modeling principle for calculating multiple body orbital dynamics and not known to truly exist in the cosmos. Gravity in space does not appreciably diminish over relatively short distances or even vast distances. Though gravity conforms to the inverse square rule, at a quarter light year distance, the Outer Oort Cloud is tenuously bound to the Sun. On a larger scale, galaxies and galaxy clusters are held together by gravity. Centripetal forces counteract gravity.

The mass of water itself exerts gravitational forces. High mass concentrations of the station or vessel affecting the natatorium will cause relatively higher gravitational attraction than other areas. The water layer will thicken in some areas, thin in others.

Microgravitational and microacceleration forces changing influences from orbital and orbit-keeping maneuvers will act on the water in chaotic ways, although splashing and movement through the water will contribute the majority of undesirable forces to the water. Wthout gravity, the swimmer might still need to use, at least, a water separating breather. And a water lock entryway would still be essential.

[This message has been edited by extrinsic (edited October 10, 2008).]


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skadder
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Why not stick a micro-gravity generator in the centre of a sphere of water then you could swim on the surface.

Or you could contain the water in a container (clear) which has an airlock type thingy, so you could enter the water. It would keep all the water squashed together. You would of course need some sort of breathing apparatus.


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extrinsic
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Conversely, do away with the water altogether. The swimmer enters the natatorium wearing hand paddles and flippers sized to simulate swimming but in air. A whole lot less bother.
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philocinemas
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I could be completely wrong about what I am about to suggest, but to me this has the ring of logic.

It seems to me there is an increased problem with density in this scenario. For example, if I am on Earth and in a room full of water vapor, I cannot propel myself by waving my arms because my density is greater than the air around me, even at 100% humidity. I can do so in and under water because now my density is nearing the density of the water.

The water molecule in "zero gravity", however, is different from the water molecule bound by gravity. Gravity causes a water molecule to coalesce with greater viscosity - thus the cumulation of water molecules have greater density - consider how density increases as one travels deeper underwater.

When I go "swimming" in zero gravity, all of the water molecules will have relatively equal density (if there is enough water to create significant gravitational forces - such as a planet - this would not be zero gravity). Therefore I think the molecules would essentially coalesce into droplets if inacted upon internally. Your body however, being a solid vessel, would retain its exterior molecular intregrity. It would be like me waving my hands in the rain and trying to move myself.

Now, if a tank was filled completely with water, without any air, the molecules still bead, but this time it would be closer to trying to swim in a container full of tiny squishy balls. Yes, I could propel myself but with considerably less proficiency than I could on Earth.

I read the link to the supposed astrophysicists, who discussed the fish and the light experiment, and it seems that the fish was able to swim, or at least orient itself, by their discription. I am curious about how this worked - it sounds a little "fishy" to me.


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rstegman
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To solve the problem, have a spinning ring, fill it with water, and you have a swimming pool held in place by centrifugal forces. Of course, someone diving it will send water into the zero G area and they might not come to rest at all.
Ways to control the splash, have the walls rotate around the central core, which is also rotating. Any water that lands on a surface will be forced back towards the pool itself. Air blowing in the direction of the pool from the central core, Panels not far from water draws the air out of the room, filtering out the water.
To get into the pool area, one enters the turning area through the central core and either climb down stairs, climb a ladder, or take an elevator, down to the pool level and enter through a door. Of course, there will be no splashing rules, and people are expected to swim, not play, lest the mess gets bad.

Several years ago, I was involved, mostly from my side, in a discussion about using modern and expected practical technology to go to another star. These were on the idea of space arks, where examples of all life on the planet is taken. The big problem, which I did not explore well, was taking sea creatures such as whales. I just figured the centrifugal spin would control the water, but this note brings up the question as to simply having spin would be enough. The spin would not effect water caught in the air unless there was a way to force the water back. to the surface or scrub the water out. It would end up being a constant fog and rain.


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TaleSpinner
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Here are some movies of experiments that NASA did with spheres of water on the ISS.

http://spaceflightsystems.grc.nasa.gov/WaterBalloon/

And here's International Space Station science officer Don Pettit, who has discovered--on the ISS--that you can make bubbles out of plain water, no soap or glycerin. Why? Because, absent the force of gravity, surface tension is effectively stronger.

http://science.nasa.gov/headlines/y2003/25feb_nosoap.htm

Here's a suggestion from the US Dept of Education that water droplets in zero G might coalesce into larger drops, under the right conditions.

http://www.newton.dep.anl.gov/askasci/gen06/gen06056.htm

So I think it's not beyond the realms of possibility that one could make large globes of water in zero G. Of course if you leapt into one, or even made some gentle swimming motions, it would splash all over the place because there'd be no gravity holding it "down" and surface tension's not that strong.

I don't see how "swimming" could exist in zero G. Water only stays in a swimming pool because of gravity. Zero gravity, zero pull "downwards". How would you fill a swimming pool? Water pouring out of a hose would bounce off the floor of the pool and go everywhere, into a mist. Perhaps, eventually, if you waited long enough, it would coalesce--but into a globe; there'd be no "down" to make it form a pool.

You could take a tank up there with you and then take the lid off, I suppose--but you'd still get problems of it going everywhere when you swim in it because there'd be no gravity to hold it in.

And why would you want to swim? Surely one of the pleasures of swimming is the low gravity sensation we feel because of bouyancy: we feel lighter. In zero G we'll feel the ultimate in lightness--weightlessness--so as extrinsic suggests, why not just wear paddles and flippers and "swim" in the air?

(And that's without going into whether you want to use water, essence of life, for recreation when your supply is limited. Would you want the expense of gathering it and recycling it?)

The question of recreation in space is an entirely different one.

If you mean "recreation" as in keeping fit, then NASA have long experience of designing exercises to counter the negative efffects of zero G, on muscle tone for example.

If "recreation" means "fun" well, just think of all the fun you could have in zero G ... and when you've exhausted that, SF stories are full of zero G games involving trampolines, wings, and so on.

Games involving throwing things like balls and darts would be entirely different because trajectories would be straight, not curved. What about three-dimensional cricket, or football? Target shooting would probably be unpopular, though. There'd be new games as well--diving accurately through a distant target, for example, or wrestling in a spherical cage, or a kind of shot-put where you win on accuracy in hitting a distant target, not distance.

There'd be new kinds of dancing as well, in three dimensions. Earthly line-dancing could become sphere dancing, more reminiscent of the formation tricks of sky divers than cowboys and cowgirls. And what about dancing around a may-pole, or a may-sphere, in zero G, attached to it by coloured ribbons, something like those dancers at the Olypmic opening ceremony who seemed to defy gravity? Or, for the aesthetes, three-dimensional ballet?

Just some ideas,
Pat

[This message has been edited by TaleSpinner (edited October 11, 2008).]

[This message has been edited by TaleSpinner (edited October 11, 2008).]


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extrinsic
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At 100 kilometers altitude orbit above the Earth gravity is reduced by 3 percent. Weightless rather than gravityless, nonzero mass objects in orbit are effected by forces that might aid in controlling a contained mass of water.

"In Low Earth orbit, the force of gravity decreases by one part per million for every three meter increase in altitude. Objects which have a non-zero size will be subjected to a tidal force, or a differential pull, between the high and low ends of the object.
"In a spacecraft in orbit, the centrifugal force is greater on the side of the spacecraft furthest from the Earth. This is also a tidal force.
"Objects within a spacecraft will slowly "fall" toward the densest part of the spacecraft. When they eventually come to rest on the wall of the spacecraft, they will have weight.
"Though very thin, there is some air at the level of the Space Shuttle's orbital altitude of 185 to 1,000 km. This atmosphere causes deceleration due to friction. This has the effect of giving objects a small "weight" oriented in the direction of motion. Above 10,000 km, this effect becomes negligible compared to the effect of the solar wind." Wikipedia: Weightlessness, Microgravity.

Assuming the purpose of space recreation is encouraging enthusiastic weight-bearing excercises to diminish the deletrious effects of weightlessness, simulating weight is the key factor. Swimming places healthy stress on a body's cardiovascular systems, but swimming mostly causes torsional and tensile stresses, not much simulation of weight, but nonetheless slighty to the good for osteo health. Compression stress in space most effectively mimics weight-bearing forces. Resistance excercises involving compression stress are practiced on the International Space Station.

I imagine competive sports would encourage excercise, but as it is now the space program's excercise routines are a dreary chore best to be avoided or gotten over with as soon as possible. Pogoing sports, bouncing off the walls of a sporting arena is a common motif in fantastical fiction sporting events. Pogoing causes relatively high compression stresses. However, an ideal compression stress activity would involve constant loads, as the space program's excercises do. Push-me pull-ya stuff.

[This message has been edited by extrinsic (edited October 11, 2008).]


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TaleSpinner
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Wikipedia writers have a maddening way of being correct yet opaque.

It's possible to misinterpret this piece as saying gravity's almost as strong when you're in orbit as it is down here on the ground, which is right but misleading.

If we were in the ISS we'd believe there was zero gravity because we'd be floating around in the cabin. How to reconcile that with what Wikipedia says? The ISS is going around the Earth at quite a high speed. Its tendency to fly off at a tangent is exactly counterbalanced by Earth's gravity, so it feels like zero gravity. The pedants call it "microgravity" to distinguish it from the home-grown variety.

There are small forces acting on the ISS and its contents as extrinsic notes, but surely not strong enough to control a pool full of water in any useful fashion.

"Push-me pull-ya stuff." Arm wrestling? Tugs of war? Racing bicycles inside a wall of death?

Cheers,
Pat


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Kathleen Dalton Woodbury
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Weight may be close to zero, but mass is still the same and you still have to deal with inertia. Any exercise that involves working against inertia could help with strength training -- maybe forcing things to move in circles instead of going straight?
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KayTi
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Recreation, folks, recreation. Having fun!!! None of this exercise business, bah humbug!

There are a ton of great ideas in this thread, though - thank you to everyone for the ideas and helpful links. The sphere dancing is a particularly good lead, Pat - thanks for that!


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Lyrajean
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There is a good description of one writer's imagining of a swimming pool on an interstellar yacht going zero-g due to mishap in "Mind Changer" by James White.
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