On screen chemistry with Jonathan Hare

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In the cartoon, Up, 78-year old Carl Fredicksen is about to be taken away by social services to a rather depressing old folks’ home but he escapes by attaching thousands of helium balloons to his house and floating away. Could you do this in real life?

Amazing as it sounds, in July 2007, Fox News in the US reported that ‘gas station owner’ Kent Couch tied 105 very large helium balloons to a chair and took to the skies for nine hours, flying 193 miles. According to the news report, Couch was the latest American to emulate Larry Walters who, in 1982, rose three miles above Los Angeles in a chair lifted by helium balloons. So, on a small scale it looks feasible but how many helium balloons would you need to pick up a house?

Helium is far less dense than air which is why a He balloon rises, the difference in density (Δρ) gives us the lift:

ρ(dry air) = 1.28 kg m-3 = 1.28 g l-1

ρ(He) = 0.18 kg m-3 = 0.18 g l-1

So Δρ = 1.28 – 0.18 = 1.10, ie about 1 g of lift for each litre of He. For a standard (30 cm diameter) party balloon which holds ca 15 litres this amounts to roughly 10 g of lift once you take the weight of the balloon (ca 5 g) into consideration. So a 50 kg person would need about 50 000/10 = 5000 party balloons to start to float!

American houses are often made of wood rather than brick. A typical three-bedroom wooden house shown in the cartoon would weigh 10 000–25 000 kg. Since each helium balloon creates about 10 g of lift you would need at least 10 000 000/10 balloons – ie about a million balloons to lift the house!

In the film we see an enormous collection of balloons above the house, perhaps 10 times the volume of the house. If the house is 5 m × 5 m × 6 m = 150 m3 in volume this gives us a He balloon volume estimate of 10 × 150 = 1500 m3 = 1 500 000 litres, which would mean in the cartoon there would need to be about 1 500 000/15, ie about 100 000 balloons above the house. This is about a 1/10th of what would be required.

So, according to our simple calculations the thousands of balloons we see in the cartoon would be enough to lift a large garden shed but not, unfortunately, enough to lift a full-sized house…

Originally published in InfoChem