science question...?

Question

Those big helium balloons that they have to advertise things (usually in the shape of a blimp, and often floating above a garage) would one of those have enough lift to carry a full grown person?

Also what would happen if you tied yourself to one and cut it free, how high would it go and when would it come down?

Answer 1

Helium has a lifting capacity of approximately 1 gram per litre in normal atmospheric conditions. A balloon of 20 cubic metres (a rounded cylinder 5 metres long by 2 metres) holds 20,000 litres of helium, allowing it to lift around 20kg of weight. I would assume that the balloon itself would weigh 5-10 kilos, leaving the leftover capacity of around 10-15kg. Not nearly enough for an adult, but perhaps you could equip a 5kg cat with goggles and a scarf to become a 19th century balloon explorer?

As for how high and how long it would keep the mythical cat explorer aloft, that depends much on the material the balloon is made of. At a leak rate of 1% per hour, you could expect your intrepid Mr. Boots to land in approximately 2 days time, ready for dinner! But how high? It would need to get to a level of the atmosphere where air has a 'weight' equal to lift capacity minus load... at the above figures that would be approximately 4000 meters. But that's just a guestimate!

However - get yourself a larger balloon - perhaps 12 metres long by 4 metres across - NOW we're cooking with, pardon the pun, gas! This balloon would be able to lift 185 kilos - with a balloon weight of say 40kg you would be able to leave the cat at home!

Answer 2

The density of helium is 0.1786 kg/m^3 and that of air is 1.292 (both at STP). The difference is ~1.11 kg/m^3

Therefore, to lift a 100 kg load, a helium balloon would have to be 100 kg / 1.11 kg/m^3 = 90 m^3.

An approximately spherical balloon would need a radius of:
r = (90 * 3/4 / Pi)^1/3 = ~2.8 m

So picture a balloon about 20 feet across.

As the balloon ascends it's volume will increase due to the decreased air pressure so make sure it's elastic.

It will continue to rise as long as the total mass of the balloon and it's load is less than mass of the atmospheric volume it displaces. So once the density of the air approaches that of the helium, it will stop ascending.

Answer 3

It takes 15.86 cubic feet of Helium to lift one pound mass.

A 200 pound grown man would need 3172 cubic feet of Helium to barely lift him off of the ground. After that, slight increases in the amount of Helium used would give him some altitude.

"Also what would happen if you tied yourself to one and cut it free, how high would it go and when would it come down?"

Now we're getting silly. Who cares. Look up Project Man High. The guy was carried into the Stratosphere to an altitude of 19 miles (102,500) above the Earth. This is about 96% of the way up in the layers of air mass collectively called our atmosphere. Hiow much higher would your ballon go? I don't suppose too much higher. If the balloon develops a leak, then it eventually comes down.

Answer 4

If you had a couple dozen of them, I bet your could do it. There was a guy back in the 70's who tied geez, how many?, a thousand balloons to a lawn chair he was sitting in and it rose off the ground. If I remember correctly it went something like a hundred feet in the air. I believe he was also given some kind of misdemeanor citation for the stunt.
Or was that an urban legend? Oh well, fun to think about in any case.

Answer 5

Yes they can lift a person. I don't remember the details but a woman paragliding (I think in Australia) was caught in the updrafts from a storm and went up about 30,000 feet. I should imagine one of those balloons would go nowhere near as high as that as the lifting capabilities of the helium would change with altitude.

Answer 6

i think modern balloons that carry people are using helium instead of the hydrogen that used to be used in the past because hydrogen is flammable so it is really dangerous to catch fire up there (the only easy thing is that if someone decides to run away it makes no difference wich direction he takes) so helium can lift people.
it will go only until a certain height because the higher you go the thinner the air becomes and in very thin air things don't fly easy.

Answer 7

Yes most could lift a person ,

but because helium is lighter than air it would continue on up until it burst .

Coming down would be fun but i don't think I'd enjoy the landing !

Answer 8

If it is a large one it could take u high enough to freeze and the air could be pretty thin. If it gets high enough to burst it would be down at the normal acceleration of gravity max for u is about 200 mph. But look out for that sudden stop.

Answer 9

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Answer 10

i remember seeing something like this on mythbusters. they used normal balloons, and if i remember correctly, they used around a thousand balloons and it only lifted him about a foot!! So you would need 1 hell of a big balloon to lift you right up!