I came up with this argument: it’s possible that in the right circumstance helium would weigh more than the empty bottle. If I were to fill empty bottle full of helium can it lift the bottle in the air?
Any idea would be greatly appreciated.
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6$\begingroup$ Sure, you made a helium ballon! :) $\endgroup$– fra_peroCommented Oct 22, 2020 at 9:32
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3 Answers
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Substituting helium for air inside a bottle will make the bottle lighter, but unless the combination of helium plus bottle is lighter than an equal volume of air, the helium-filled bottle will NOT float.
Putting helium inside a bottle that is initially totally empty (that is, it initially contains a vacuum) simply increases the total weight of the bottle plus contents. A bottle that is large enough, stiff enough, and strong enough can support a vacuum in a volume which, if filled with air at normal pressure, would weigh more than the bottle. In that case, the vacuum-filled bottle will float in air. Adding helium could prevent it from floating.
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Yes. If something has a net density lower than air, it will float. If the circumstances result in a bottle with helium having a net density lower than air, it will float.
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$\begingroup$ Many thanks for the illuminative responses and comments. Likewise, will the water vapor does the same effect in lifting the empty bottle in the air? In both cases when using helium or water vapor, I guess that the bottle must weigh equal to balloon. $\endgroup$ Commented Oct 27, 2020 at 16:49
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$\begingroup$ It would not matter what is being used, as long as the density of the container and its contents are less than air, it will float. $\endgroup$ Commented Oct 28, 2020 at 17:40
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It is not the weight of the He gas that determines the buoyancy but the difference of Helium and air. When He is in a bottle it is usually a very heavy steel one and it is either a liquid at very low temperature or a compressed gas a room temperature. In both cases the Helium weighs more that the air it replaces and in any case even the evacuated bottle will make quite a dent in your carpet.
