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On earth if you submerge an upside down bottle into a pool or some large tub of water the bottle doesn't fill with water. I believe this is because of air pressure and air has nowhere to go.

What would happen if you had a giant ball of water in space and insert an upside down bottle into it? Would air pressure stop the bottle from filling or because of a lack of gravity the upside down bottle would fill with water?

UPDATE: I mean inside of the ISS or something like that so there would be oxygen but we are in space.

sammy gerbil
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zgirod
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  • Not clear. Your explanation on Earth is air pressure not gravity. If there is air pressure in the ISS why should the explanation be different? Or why should lack of gravity become relevant in space but not on Earth? – sammy gerbil May 18 '18 at 08:39
  • I disagree, I think my question it quite clear. I don't know if air pressure has a preferred direction because of gravity or not. How in space would would the air know to try and escape in one direction vs the other? Maybe the answer is the same thing would happen because air pressure would still try and escape up. I don't know what answers to your questions; hence why I posted my question on.. wait for it; a question and answer site. – zgirod May 18 '18 at 10:43
  • Pressure has no preferred direction in fluids. See Direction of pressure in fluids. The air in the bottle is not trying to escape upwards on Earth, it is trying to escape in all directions. – sammy gerbil May 18 '18 at 10:57
  • Thank you that answers my question; so the bottle will still be full of air. If you want to post that as an answer opposed to a comment I will happily mark it as the answer. – zgirod May 18 '18 at 15:35
  • It's a buoyancy thing, quite simply..... – RaSullivan May 18 '18 at 18:19

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When you perform this experiment on the ISS, air is trapped inside the bottle as you insert the neck of the bottle into the ball of water. As you insert it further, the water pushes on the trapped air and the trapped air pushes back. This pressure is the same in all directions.

Unless there is something to prevent it from moving, the ball of water will be pushed away, because the force on it from the trapped air is greater than the force on it in the opposite direction from the ambient air in the ISS. You could prevent the water from moving by keeping it in a plastic container which is sealed around the neck of the bottle. The trapped air would then stay inside the bottle.

Without any gravity to create a pressure gradient in the water, the air in the bottle has no buoyancy, so it does not float "upwards" into the water and out of the bottle. If you plunged the bottle upwards through the membrane of the same container of water on Earth, the air would float upwards through the water; if you plunged downwards it would float up into the bottle.

sammy gerbil
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  • The air inside the bottle is at ambient pressure, exactly the same as the rest of the air in the ISS. There won't be any force exerted by the air in the bottle. – Nuclear Hoagie May 18 '18 at 16:58
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    @NuclearWang The air inside the bottle is at ambient pressure initially. If the bottle is inserted into the water, the volume of air inside the bottle will be reduced and its pressure increased. The force this air exerts on the water will increase. My answer says that, unless there is something to prevent it, the water will be pushed away. – sammy gerbil May 18 '18 at 17:06
  • But why is the volume of air reduced and the pressure increased? In zero-G, there's nothing to cause the water to push on the air inside the bottle. Is this solely due to the mechanical nature of pushing the bottle into the sphere or water? As soon as the bottle stops moving, there's nothing trying to force the water into the bottle, so no increase in pressure. – Nuclear Hoagie May 18 '18 at 18:08
  • Buoyancy is density dependant not gravity dependant...... – RaSullivan May 18 '18 at 18:21
  • @RaSullivan Buoyancy works very differently in zero-G. If you put an empty bottle underwater on Earth, it will float up to the surface. If you put an empty bottle inside a water sphere on the ISS, it will just stay there. Which way would you expect it to go? There's no "up" - all the forces are symmetric and cancel out. There's a great video of an Alka Seltzer tablet being dissolved in a water sphere in space - the bubbles just stay put, rather than floating to the surface. – Nuclear Hoagie May 18 '18 at 18:44
  • @NuclearWang Read my answer (paragraph 2), and my previous comment. – sammy gerbil May 18 '18 at 22:01
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    @RaSullivan Buoyant force depends on pressure gradient, which on Earth is usually caused by gravity. Without a pressure gradient, the difference in densities does not cause a buoyant force. – sammy gerbil May 18 '18 at 22:14
  • Try moving it..... Sammy.. – RaSullivan May 20 '18 at 18:07
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I believe no because unless you have oxygen in it already then you don't have any air there for there is no pressure.

Joey Goggin
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