# Can a helium tank float away?

Ok, I know a regular tank can't float away, but what if it was a really light aluminum?

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Let's take the density of air at 1.26 kg/m³ and helium at 0.179 kg/m³. Then per cubic meter of air displaced by helium, the net mass displacement is 1.11 kg.

Imagine a cubic tank of aluminum 1 mm thick, density 2700 kg/m³. For a cube of side x, the mass of the tank would be

M = 6x²*0.001m * 2700kg/m³ = 16.2kg/m² * x²

For what x is the net mass displacement equal to the tank's mass?

1.11kg * x³ = 16.2kg/m² * x²

x = 14.6 m

So, IF you could construct an aluminum tank of 1 mm thickness and sides of 14.6 m or more and not have it collapse, and fill it with helium, it could float away.

Double the thickness, you'd need to double the edge dimension.

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• yes if the mass of tank is less than the helium gas

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• Anonymous
2 months ago

If the Al tank was sufficiently thin, yes.

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• No. Only if the tank was made of thin rubber. That would be a balloon.

Source(s): Snoopy, at the Thanksgiving Day parade
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• You would need either a very thin-walled tank to have less mass than the mass difference between helium and air for the volume, or a very large volume.  The extreme case would be a tank with nothing in it, a vacuum, and even that generally has more mass in the tank itself than its total volume would give if air.

Things only float because they have less mass than the equivalent volume of whatever matrix they are in.  Air has such a low density that it is difficult to use a high-density material such as metal to create a large enough volume that the air of that volume would have more mass than the tank and its contents (even if the contents were nothing, a vacuum).

The problem is really that air has such a small density that even very large volumes have only small masses.

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• do you mean a compressed gas tank?

compressed helium is dense and even without the tank will not float. Helium has buoyancy only if not compressed.

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• If you define an airship or blimp as "helium tank", then sure.

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• Anonymous
2 months ago

aluminum foil will help

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