Imagine this. You have some object (let say barrel) and fill it with water. The water remains rather calm so it doesnt' spills out. Then we take a balloon filled with air and push it in that tank. What will happen when i release the balloon? Which side it will go? (if its in the middle) Will it direct to the open area of the barrel or to the bottom?

Same goes if somehow we form a perfect sphere of water and put the balloon inside of it. Where it will be pushed?

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    $\begingroup$ When you say "in space" do you mean "in a zero gravity environment"? Is the tank inside an enclosure that maintains atmospheric pressure? Please clarify your question. $\endgroup$
    – Floris
    Jun 8, 2014 at 11:21
  • $\begingroup$ Yes, by in space i mean in zero gravity. About the second question I am not sure how to answer it, but the answer given by Floris seems pretty good and explaining things to me. Thanks for your time ! $\endgroup$
    – XavorTM
    Jun 8, 2014 at 13:34

2 Answers 2


Most likely the balloon will not go anywhere as there is no net force acting on it. The pressure throughout the tank of water is the same (it is the pressure caused by the surface tension of the water, so rather low). Archimedes' law says the force on the submerged object equals the weight of the displaced liquid. No gravity, no weight, no force.

The answer changes the moment you add (micro) gravity - due to acceleration of the space ship, rotation, etc. in that case the balloon will move in the direction of the acceleration (opposite the direction of the "apparent gravity")


Exactly this experiment has been done by the astronauts on the International Space Station. The YouTube video I've linked shows a bubble within a sphere of water. In the absence of gravity there is no force on the bubble so it remains stationary within the water. The astronaut has carefully positioned the bubble at the centre of the sphere of water, but this is just to look nice on the video and the bubble would remain stationary regardless of where in the water it was.

Actually the astronaut then manages to create a water drop inside the bubble inside the sphere of water.


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