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Speaker 1: Welcome to brain Stuff from How Stuff Works. Hey, brain Stuff,

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Speaker 1: I'm Lauren Vogelbaum, and today we're talking about balloons, Helium

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Speaker 1: balloons that have escaped the clutches of their human captors

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Speaker 1: to float far beyond the mortal realms, straight up into

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Speaker 1: the infinity of the stars. Well, not really. I hate

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Speaker 1: to burst your well, balloon, but that's not what balloons

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Speaker 1: do when they're released. They first blame the composition of

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Speaker 1: our atmosphere. Helium balloons float because they're buoyant in the air,

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Speaker 1: like a beach ball is buoyant in water. Balloons don't fly.

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Speaker 1: The air around them sinks pushing them upward. That's because

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Speaker 1: helium ways just zero point one eight grams per leader.

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Speaker 1: Nitrogen and oxygen, which together make up about of the

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Speaker 1: air we breathe, weigh one point to five grams and

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Speaker 1: one point for three grams per leader, respectively. And Okay,

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Speaker 1: most helium balloons these days aren't filled with one pure helium,

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Speaker 1: depending on the company selling it, about maybe regular old

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Speaker 1: air to help keep costs down and preserve the global

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Speaker 1: helium supply. But as long as the weight of the

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Speaker 1: balloon plus the helium mixture inside of it equals less

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Speaker 1: than the weight of the air around it, it'll keep

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Speaker 1: on moving up. However, nitrogen and oxygen aren't distributed evenly

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Speaker 1: from sea level to outer space. Earth's gravity holds air

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Speaker 1: close to the surface. The higher up you go, the

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Speaker 1: thinner a k a. Less massive the air gets. Just

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Speaker 1: five miles up, there are only one third as many

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Speaker 1: nitrogen and oxygen atoms around you. Ten miles up there

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Speaker 1: are only one tenth as many. So a helium mixture

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Speaker 1: balloon wouldn't keep floating up forever because eventually it would

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Speaker 1: be heavier than the air around it. It'll stop when

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Speaker 1: it hits the point of equilibrium. However, However, as evidenced

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Speaker 1: by the lack of a thick layer of party balloons

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Speaker 1: up in the sky, that's not how the story ends

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Speaker 1: for freed balloon enter atmospheric pressure. Since the elements that

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Speaker 1: make up are air supply hug the surface and thin

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Speaker 1: out at increasing altitudes, the pressure that the air exerts

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Speaker 1: on objects also drops, and increasing altitudes, lower atmospheric pressure

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Speaker 1: outside means the gases inside a balloon will want to expand.

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Speaker 1: How much that balloon can expand depends on what the

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Speaker 1: balloon is made of latex rubber is pretty common and

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Speaker 1: can stretch a lot. Milar, which is a trade name

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Speaker 1: for a type of stretched polyester that's strengthened with a

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Speaker 1: film of evaporated metal, does not stretch, So how long

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Speaker 1: the balloon lasts before bursting depends on the material and

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Speaker 1: how much helium mixture is in there. A half full

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Speaker 1: balloon will last longer. Also, since latex is porous, a

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Speaker 1: bit of helium mixture will constantly seep out through the

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Speaker 1: balloon's walls, possibly giving it a little bit more time.

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Speaker 1: And finally, how the balloon pops will depend on the

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Speaker 1: temperature of the air around it. That temperature will decrease

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Speaker 1: as the balloon rises through the troposphere. This is the

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Speaker 1: lowest layer of Earth's atmosphere, extending four to twelve miles

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Speaker 1: above surface. At the top of the troposphere, temperatures reach

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Speaker 1: negative sixty degrees fahrenheit that's about negative fifty one celsius.

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Speaker 1: Latex and mile are both become brittle around negative forty

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Speaker 1: degrees fahrenheit or celsius, so if they make it up

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Speaker 1: that far, they'll lose their ability to expand and they

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Speaker 1: won't pop. They'll shatter. So when and how balloons burst

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Speaker 1: depends on three things. What the balloon is made of,

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Speaker 1: how much gases inside, and the temperature around them. Today's

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Speaker 1: episode was written by me and produced by Tyler Clang.

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Speaker 1: From more on this and lots of other buoyant topics,

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Speaker 1: visit our home planet, how stuff works dot com