Gravity's Effect on Water Pressure in Orbit

[haiha]

We all know that pressure inside a liquid is caused by its gravity and it is the product of the depth and weight density. So I just immagine if we have a sealed bottle full of water in the orbit, where the gravity is gone, is there any pressure of the water onto the bottle wall?

 

[mybsaccownt]

I'm not a chemistry wiz but I think pressure also comes from the collisions of the particles.

(Maybe this is only the case for gases?)

So there would be pressure inside the bottle, not very much since the temperatures would be pretty low but not quite absolute zero.

 

[vivesdn]

Just a guess, but I would say that water will produce a slight internal pressure as it will have a surface, an spherical or nearly spherical one. The surface molecules are subject to attraction forces only towards the center of the shphere, the surface tension. This, of course, if the bottle is inside a spaceship where temperature is above freezing point, and there is a non-zero total pressure to prevent boiling.

 

[russ_watters]

Is pressue in a balloon caused by gravity, haiha? How about the pressure on the discharge side of a pump?

 

[haiha]

Is pressue in a balloon caused by gravity, haiha? How about the pressure on the discharge side of a pump?

Yes, the pressure in a baaloon (of gas) is caused by molecule impacts onto the wall, and still there's some small part contributed by gravity. But this situation is liquid, and a liquid will have constant volume (almost) not depending the pressure.
Here i have a dilemma : if we consider the bottle full of water in space has some internal pressure, then if we calculate the pressure under the deep water on earth, we have to add that amount in. On other hand, if there is no pressure, then all the water molecules stop beating the wall at ambient temperature.
May be my mind is some kind of vagueness now. Please discuss it out. Thanks

 

[nrqed]

Yes, the pressure in a baaloon (of gas) is caused by molecule impacts onto the wall, and still there's some small part contributed by gravity. But this situation is liquid, and a liquid will have constant volume (almost) not depending the pressure.
Here i have a dilemma : if we consider the bottle full of water in space has some internal pressure, then if we calculate the pressure under the deep water on earth, we have to add that amount in. On other hand, if there is no pressure, then all the water molecules stop beating the wall at ambient temperature.
May be my mind is some kind of vagueness now. Please discuss it out. Thanks

If the bottle is open or if it's closed and has a volume larger than the volume occupied by the water, there will be no pressure (the water will be floating inside the bottle, forming bubbles held by surface tension). Of course, if the bottle is closed and its volume is shrunk, eventually there will be pressure exerted by the water but this has nothing to do with gravity.

 

[russ_watters]

But this situation is liquid, and a liquid will have constant volume (almost) not depending the pressure.

You said it correctly there, but it doesn't seem like you are thinking it correctly. Being incompressible means you generate very high pressures with only a little bit of compression.

And remember, it takes about 35 feet of depth to equal 1 atmosphere, so the [absolute] pressure at the bottom of a glass of water is about 98% due to the pressure of the atmosphere pushing down on it.

Here i have a dilemma : if we consider the bottle full of water in space has some internal pressure, then if we calculate the pressure under the deep water on earth, we have to add that amount in.

IIRC, the Space Shuttle is pressurized to 5psi. So if you take a rigid container, fill it completely with water, and send it out the airlock, it will be pressurized at 5psi. But there is no reason why you couldn't also pressurize it to 14.7 psi - or 1400 psi if you wanted to and had the right equipment.

On other hand, if there is no pressure, then all the water molecules stop beating the wall at ambient temperature.

Correct. And as a result, if you attempt to release the pressure, the water will boil an pressurize the container with some mixutre of water an water vapor, depending on its temperature.

 

[haiha]

Thanks Russ Watter for your explanation. Now I think it is a little bit clearer. However it would be so nice if you tell me what would happens:
Suppose we have a special liquid which does not boil under vacuum at ambient temp. So if we put it in space in a bottle whose volume is exactly the liquid volume, and the liquid temperature is such that the brownian motion exists. Would it impose some pressure onto the wall of the bottle?

 

[russ_watters]

What distinguishes a liquid from a gas is a cohesive chemical force that keeps the molecules stuck together. So aside from whatever initial motion might make the globs splash around inside the container, there would be no pressure.