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I was just watching some TV and saw a scene using Sulfur Hexofluoride that, due to it's density, makes your voice go lower. That made me think about balloons and the perhaps possibility of not going empty when inflated (because of it's 'weight').

Try to understand this thought: If you inflate a balloon, with the tip upwards and a gas heavy enough that won't float up, can you theoretically fill a balloon with the gas remaining inside and the balloon staying inflated?

Pretty much the same as a bag filled with water, but it's only logical the bag remains filled this way. But how about gasses?

Please answer in laymen terms as I have a minor understanding of physics and this question is based upon fantasy, rather than actual facts.. :)

It would be more awesome the other way around though. Tip down with a gas that's light enough so it floats up and not down. However, due to it's weight the stretch of the balloon itself will press the gas out. So that's a no go.. right?

Sander Schaeffer
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  • The pressure of the stretched material would expel the gas in both cases (light or heavy gas), and balancing it can also be challenging. Can you keep a balloon full of water open, without holding its neck up? – stafusa Oct 13 '17 at 15:59

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There is no discrimination between gases and liquids here: if you find a gas with the same properties of water it will act the same in your experiment (assuming it won't mix with air creating quickly a boundary that has a layer of gas that is a mixture of these gases).

Essentially you when fill a balloon with water the weight of the water stretches the balloon larger and does work. When you fill it with air you will have to actively do work to stretch the balloon. A heavy gas might stretch it a little or not at all.

Also depends on the balloon: water balloons that are made for that purpose are strong enough to push water out too. You could manufacture a very weak balloon that could then hold heavy gases.

Communisty
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Gas filled balloons are emptied when you release the opening because the gas inside the balloon is pressurized. It's this pressure that stretches the material of the balloon, and therefore causes the balloon to expand. Water filled balloon can hold water because the weight of the water does the same, it stretches the balloon. There are no known gases dense enough at normal, or room, temperature and pressure to cause this behavior for balloons made of regular materials that we think of when balloons are discussed. If you fill a balloon with a dense gas, both the pressure and weight of the gas will have an effect on balloon stretch, but the pressure will be the most significant, which will cause the same behavior as with air filled balloons. For example, Sulfur Hexafluoride has a density of just above 6 g/L at normal conditions, which is about 5 times the density of air, but water has 166 times this density. Even this very dense gas is still much less dense than water.

Manuel Fortin
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