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Author Topic: why does water form a ball shape on the international space station?  (Read 7063 times)

Offline gazza711

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Water creates itself into a ball shape on iss?why?
« Last Edit: 08/07/2015 08:33:01 by chris »


 

Offline PmbPhy

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Re: why does water form a ball shape on iss?
« Reply #1 on: 05/07/2015 17:10:57 »
Quote from: gazza711
Water creates itself into a ball shape on iss?why?
This is a minimization of problem. See: https://en.wikipedia.org/wiki/Sphere
Quote
The sphere has the smallest surface area of all surfaces that enclose a given volume, and it encloses the largest volume among all closed surfaces with a given surface area. The sphere therefore appears in nature: for example, bubbles and small water drops are roughly spherical because the surface tension locally minimizes surface area.
So a blob of water with a given volume will naturally form a sphere in zero gravity. If gravity was there it wouldn't be able to form a sphere because other forces, such as gravity, would be acting on it.
« Last Edit: 05/07/2015 18:00:14 by PmbPhy »
 

Offline gazza711

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Re: why does water form a ball shape on iss?
« Reply #2 on: 05/07/2015 18:08:20 »
Quote from: gazza711
Water creates itself into a ball shape on iss?why?
It has to do with a minimization of problem, i.e. see: https://en.wikipedia.org/wiki/Sphere
Quote
The sphere has the smallest surface area of all surfaces that enclose a given volume, and it encloses the largest volume among all closed surfaces with a given surface area. The sphere therefore appears in nature: for example, bubbles and small water drops are roughly spherical because the surface tension locally minimizes surface area.
So a blob of water with a given volume will naturally form a sphere in zero gravity. If gravity was there it wouldn't be able to form a sphere because other forces, such as gravity, would be acting on it.
Great.why doesnt the water disapate into 1000s of droplets.when we blow bubbles on earth,theyre round due to equal pressures in every direction from inside and out.so this would too cause surface tension?i thought surface tension was a pond skater on water or spiders  for example.could the water is forced into a blob on iss from the exterior pressures of iss?
As u can tell,im trying to think before i assume!
 

Offline Colin2B

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Re: why does water form a ball shape on iss?
« Reply #3 on: 05/07/2015 18:28:17 »
i thought surface tension was a pond skater on water or spiders
You are right, it is exactly the same thing. The water molecules pull towards each other, just like the rubber molecules in a balloon skin. It's that tension that keeps the shape of a sphere in the absence of gravity pulling the water into a flatter shape.
That attraction between the molecules is not just at the surface, all the molecules inside the ball of water are pulling together stopping it drifting apart. I say drifting because it can't fall apart as there is nothing to make it fall, but it could drift due to air currents etc.

could the water is forced into a blob on iss from the exterior pressures of iss?
Don't understand the question. Do you mean the exterior pressure on ISS? There is no pressure on the exterior of ISS.
 

Offline alancalverd

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Re: why does water form a ball shape on iss?
« Reply #4 on: 05/07/2015 18:48:00 »
Quote
Great.why doesnt the water disapate into 1000s of droplets.

If you break the blob, it does. But you will have noticed that when droplets of water meet they coalesce into a larger drop, and bubbles do the same - the smaller one is apparently absorbed by the larger. That is the calculable effect of surface tension.
 

Offline RD

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Re: why does water form a ball shape on iss?
« Reply #5 on: 06/07/2015 01:08:38 »
... it can't fall apart as there is nothing to make it fall, but it could drift due to air currents etc.

a puff of compressed air ...

or due to pushing a GoPro camera in it ...
« Last Edit: 06/07/2015 01:12:36 by RD »
 

Offline evan_au

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Re: why does water form a ball shape on iss?
« Reply #6 on: 06/07/2015 14:33:44 »
Quote from: Gazza711
could the water is forced into a blob on iss from the exterior pressures of iss?
Water (or other liquids with high surface tension) still tend to form a ball even in the absence of an atmosphere.

However, with zero atmospheric pressure, water will also tend to boil away into the vacuum, disrupting the nice spherical shape.

You could try the experiment with something like mercury (but NASA & colleagues wouldn't let liquid mercury onto the space station - the fumes are toxic, the liquid would short out electronics, and it disrupts some metal alloys).

Conclusion: Surface tension is a localised effect of the electric field of an atom's electrons affecting adjacent atoms. It is not due to atmospheric pressure.
 

Offline wolfekeeper

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Re: why does water form a ball shape on iss?
« Reply #7 on: 07/07/2015 23:38:46 »
Water creates itself into a ball shape on iss?why?
It's actually the same reason that bubbles do.

The surface of the ball has surface tension, and that compresses the ball; the trick is; it turns out that the smaller the ball, the sharper the curvature, and so the higher the pressure inside it caused by surface tension.

So let's take an example, suppose you break the ball into two, with one bigger than the other.

Now touch them into each other, what's going to happen? The smaller ball is higher pressure, so it will decant itself, really quickly, into the bigger one, and the smaller one will shrink and the bigger one will grow until it's just one big ball.

Similar things happen with smaller distortions, basically, the ball hates sharp curvatures, because that implies higher pressure, so the sharp curvature areas rapidly get the water squeezed out of them, and they disappear until it's all the same curvature/pressure.

p.s. everything everyone else is saying in this thread is basically true as well, they're looking at it from a very high level view; what I've given is the worms-eye view of what's happening.

p.p.s. there's a table of pressures versus radius (of curvature) here:

https://en.wikipedia.org/wiki/Surface_tension#Surface_curvature_and_pressure
« Last Edit: 07/07/2015 23:52:05 by wolfekeeper »
 

Offline jccc

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Re: why does water form a ball shape on iss?
« Reply #8 on: 08/07/2015 00:05:34 »
all matter connected by gravity. the strength of the attraction force is F=Gx M1M2/R^2.

the force is equal on the surface of a sphere centered at mass center.

therefore all matter (liquid and gas) will form into sphere shape without other force involved.

all the stars and planets are sphere shape, they were gas or liquid.

 

Offline wolfekeeper

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Re: why does water form a ball shape on iss?
« Reply #9 on: 08/07/2015 00:27:37 »
While that is true, self gravity is exceptionally tenuous on a thing as small as blob of water in the ISS; it would take a long time, several hours I think, for it to become a spherical if that was the dominant force, whereas it actually happens in seconds.
 

Offline jccc

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Re: why does water form a ball shape on iss?
« Reply #10 on: 08/07/2015 01:11:07 »
2 dices 1 cm apart, may take hours to contact.

a water blob all matter is connected already, the gravity is much stronger. suck the blob into a ball quickly.
 

Offline wolfekeeper

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Re: why does water form a ball shape on iss?
« Reply #11 on: 08/07/2015 02:47:27 »
No, I'm sorry that is not correct.
 

Offline jccc

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Re: why does water form a ball shape on iss?
« Reply #12 on: 08/07/2015 03:03:13 »
do you think atoms forum into matter, chemical bounding etc are not caused by gravity?

why neutral atoms able to attract each other?
 

Offline wolfekeeper

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Re: why does water form a ball shape on iss?
« Reply #13 on: 08/07/2015 03:35:05 »
Yes, even neutral atoms can attract at close range because the positive and negative charges are not located at precisely the same locations; that's what chemical bonds and Van de Waals forces are about.

These attractions cause very strong forces, including surface tension.

Gravity is enormously weaker and will take orders of magnitude longer to make water spherical.
 

Offline jccc

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Re: why does water form a ball shape on iss?
« Reply #14 on: 08/07/2015 03:55:52 »
without gravity, where surface tension came from?
 

Offline Colin2B

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Re: why does water form a ball shape on iss?
« Reply #15 on: 08/07/2015 04:44:41 »
without gravity, where surface tension came from?
Surface tension is the attraction between molecules, it has nothing to do with gravity. If a line of people hold hands it's not gravity that holds them together!
 

Offline jccc

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Re: why does water form a ball shape on iss?
« Reply #16 on: 08/07/2015 04:55:45 »
mercury drops have no molecules but neutral atoms, what force make them attract into a ball?

what's the attraction force between molecules? em force? gravity? surface tension?
 

Offline Colin2B

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Re: why does water form a ball shape on iss?
« Reply #17 on: 08/07/2015 05:24:13 »
Did you not read #13 by Wolfkeeper, or did you not understand it?
 

Offline jccc

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Re: why does water form a ball shape on iss?
« Reply #18 on: 08/07/2015 07:31:51 »
Yes, even neutral atoms can attract at close range because the positive and negative charges are not located at precisely the same locations; that's what chemical bonds and Van de Waals forces are about.

These attractions cause very strong forces, including surface tension.

Gravity is enormously weaker and will take orders of magnitude longer to make water spherical.

what do you mean by positive and negative charges are not located at precisely same location? can you explain it using 2 oxygen atoms? 8 positive charges in the nucleus, 8 electrons around, how 2 atoms attract each other? what is the bounding between the 2 atoms? what causes van de waals force?

how could positive charges and negative charges not located in the same position? aren't they attract each other with 10^40 g force?

what magic force makes electrons away from positive charged nucleus but stay within atom radius?
 

Offline wolfekeeper

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Quantum mechanics; the electron doesn't have enough mass to be localised to a very small area- it doesn't have a short enough wavelength, so it spreads out around the nucleus in a standing wave.

Turns out these waves have lots of funky shapes, and some of these shapes can fit between each other, or even overlap each other and form a very strong chemical bond between two atoms.
 

Offline alancalverd

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Metal atoms bond by sharing electrons. Those in the middle of a blob are surrounded by other nuclei and electrons but those on the surface are not competely surrounded, so their binding force is "spread sideways". The mesoscopic result is the same whether the interatomic bonds are metallic, covalent or ionic, and in the liquid state it is described as surface tension. 
 

Offline jccc

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Quantum mechanics; the electron doesn't have enough mass to be localised to a very small area- it doesn't have a short enough wavelength, so it spreads out around the nucleus in a standing wave.

Turns out these waves have lots of funky shapes, and some of these shapes can fit between each other, or even overlap each other and form a very strong chemical bond between two atoms.

ya, very funky waves. i don't get it. do you? be honest.
 

Offline wolfekeeper

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Well, I've been trained in solving the wave equation, and studied chemistry.

Here are the funky shapes you get around a hydrogen atom:



Still, as Feynman said: "I think I can safely say that nobody understands quantum mechanics"  ;D
 

Offline jccc

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that's pretty safe science. congrats!
 

Offline wolfekeeper

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It is actually, some of the predictions of quantum mechanics have been experimentally verified to about 10 decimal places.

But the equations are incredibly difficult to solve in many cases; but that's true of Newtonian mechanics also.
 

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