Welcome to brain Stuff from How Stuff Works. Hey, brain Stuff, I'm Lauren Vogelbaum, and today we're talking about balloons, Helium balloons that have escaped the clutches of their human captors to float far beyond the mortal realms, straight up into the infinity of the stars. Well, not really. I hate to burst your well, balloon, but that's not what balloons do when they're released. They first blame the composition of our atmosphere. Helium balloons float because they're buoyant in the air,
like a beach ball is buoyant in water. Balloons don't fly. The air around them sinks pushing them upward. That's because helium ways just zero point one eight grams per leader. Nitrogen and oxygen, which together make up about of the air we breathe, weigh one point to five grams and
one point for three grams per leader, respectively. And Okay, most helium balloons these days aren't filled with one pure helium, depending on the company selling it, about maybe regular old air to help keep costs down and preserve the global helium supply. But as long as the weight of the balloon plus the helium mixture inside of it equals less than the weight of the air around it, it'll keep on moving up. However, nitrogen and oxygen aren't distributed evenly
from sea level to outer space. Earth's gravity holds air close to the surface. The higher up you go, the thinner a k a. Less massive the air gets. Just five miles up, there are only one third as many nitrogen and oxygen atoms around you. Ten miles up there are only one tenth as many. So a helium mixture balloon wouldn't keep floating up forever because eventually it would be heavier than the air around it. It'll stop when
it hits the point of equilibrium. However, However, as evidenced by the lack of a thick layer of party balloons up in the sky, that's not how the story ends for freed balloon enter atmospheric pressure. Since the elements that make up are air supply hug the surface and thin out at increasing altitudes, the pressure that the air exerts on objects also drops, and increasing altitudes, lower atmospheric pressure outside means the gases inside a balloon will want to expand.
How much that balloon can expand depends on what the balloon is made of latex rubber is pretty common and can stretch a lot. Milar, which is a trade name for a type of stretched polyester that's strengthened with a film of evaporated metal, does not stretch, So how long the balloon lasts before bursting depends on the material and how much helium mixture is in there. A half full
balloon will last longer. Also, since latex is porous, a bit of helium mixture will constantly seep out through the balloon's walls, possibly giving it a little bit more time. And finally, how the balloon pops will depend on the temperature of the air around it. That temperature will decrease as the balloon rises through the troposphere. This is the lowest layer of Earth's atmosphere, extending four to twelve miles
above surface. At the top of the troposphere, temperatures reach negative sixty degrees fahrenheit that's about negative fifty one celsius. Latex and mile are both become brittle around negative forty degrees fahrenheit or celsius, so if they make it up that far, they'll lose their ability to expand and they won't pop. They'll shatter. So when and how balloons burst depends on three things. What the balloon is made of,
how much gases inside, and the temperature around them. Today's episode was written by me and produced by Tyler Clang. From more on this and lots of other buoyant topics, visit our home planet, how stuff works dot com