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How much helium does it take to lift a person?

Tom Scott
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⬐ cutierustSurely there's a simple formula for kg helium in a round container per kg of load without watching a video⬐ eesmith⬐ 8bitsruleThe first three words are "about 70,000 liters".He later say he weights about 70 kg.

So the simple formula is 1,000L/kg body mass.

The density of dry air is 1.29 g/L. Of helium is 0.1786 g/L. Helium can therefore lift about 1.1 g per liter.

Which is 1,000L/1.1 kg mass.

The 10% difference is likely mostly due to the hardware used to connect the helium to the person (balloon, harness, wings, etc.).

⬐ latchkeyThey do mention the issue of osmosis in the video which factors into the 10% difference as well.The floating bag gains outside air over time since it isn't really under pressure internally. This displaces the helium in the bag and therefore, it doesn't provide as much lift. There is no way to remove the air without just emptying the bag. Which they said they do yearly.

So, like a sushi restaurant, make sure you time your visit well.

⬐ credit_guyHere's a different way to get to the same result, without knowing various densities, just with some rules of thumb.The first rule of thumb is that for a given substance that has both liquid and gas phases, the density of the liquid is about 1000 times higher than the density of the gas. It's not exact; for water the density of the liquid is 1000 g/l and of the gas is 0.8 g/l, so the actual ratio is 1250, but 1000 is easier to remember.

Second rule of thumb is that our density is about the same as the density of water (it's slightly lower, since we can float, but barely).

Third rule of thumb is that the density of a gas is proportional with the (average) molecular mass of the substance that forms it. Air is made of 20% O2 and 80% N2, which have masses of 32 and 28, so it's average molecular mass is about 29. Helium is just He, with a mass of 4, so air has a density about 29/4 higher than Helium, which is 7.25. Or Helium has about 13% the density of air.

The same rule of thumb is to get the ratio of water vapor and air. Water has a molecular mass of 18, and air about 29, the ratio is 29/18 = 1.6. (By the way, this approximation is surprisingly correct, the actual ratio is about 1.605; the ratio for air/helium is also very close to 7.25; using the numbers above it comes as 7.22).

So, 1kg of human is about the same as 1kg of water, which is the same as 1 liter of liquid water, which is (rule thumb 1) about the same as 1000 liters of water vapor. 1000 liters of air will be about 1.6 times as heavy (rule thumb 3), so a balloon filled with vacuum will be able to lift about 1.6 kg (of water, or human, it doesn't matter, a kilogram is a kilogram). But the balloon is not filled with vacuum, it's filled with helium, which has about 13% the density (rule thumb 3), or about 0.2 kg. So the buoyancy of the helium-filled balloon is about 1.4 kg for each 1000 liters. (If for some reason we remember that water is actually 1250 times more dense in liquid form than in gas form, rather than 1000 times, we can divide the 1.4 by 1.25 and get the 1.1 calculated above). If we throw in some adjustment for the mass of the balloon itself plus the gear around it, and a reasonable rounding for our imprecision, we get to 1000 liters of helium for each 1 kg of mass.

⬐ cutierustHow do I even thank you for taking the time to write this?It took Lawnchair Larry 43 eight-foot weather balloons to get to 16,000 feet in 1982. Others listed here used more or less balloons. (One used '600 helium-filled party balloons'.) It's gotten more expensive since then. [https://en.wikipedia.org/wiki/Lawnchair_Larry_flight]

⬐ leobgWow this is amazing!⬐ tom-thistime⬐ gabrielsrokaYeah I'm suddenly about giving in to my wife's dream of visiting France.Actual video title is "How much helium does it take to lift a person?"