[ INTRO ].

I’m so glad you’re still having fun with that balloon, Squeaks! [Squeaks thanks her for saving it]. Oh right!

We did almost lose it earlier today. We were in the pizza store getting some lunch, and the balloon slipped out of Squeaks’ paw! It went up to the ceiling, but the string was hanging down far enough that I could grab it back.

Then we tied it to a water bottle from my backpack so it wouldn’t get away again. It’s a good thing it didn’t escape while we were outside! [Squeaks asks what would have happened]. Well, a couple of different things can happen to a balloon that escapes into the sky — the regular type of balloon, I mean, that’s made out of the stretchy rubber stuff.

First, the balloon starts to rise higher and higher into the air. That’s because balloons aren’t filled with regular air, like the kind we breathe. They’re filled with something called helium, and it makes the balloon lighter for its size than the air around it.

So it starts to float on the air, just like certain things float on water. If you try to push a plastic spoon to the bottom of a bowl of water, the spoon will just float to the top again. If someone lets go of a helium balloon outside, it starts to rise through the air like the spoon at the bottom of the bowl rises through the water.

But unlike the small amount of water in the bowl, there’s lots of air all around us, and it stretches up really high in the sky. So the balloon keeps floating higher and higher and higher. And as it goes higher, the air around it starts to change.

The higher into the sky you go, the less air there is. There’s still some air, but it becomes more spread out. And as the air outside the balloon spreads out, the helium inside the balloon starts to spread out, too, pushing out on the inside of the balloon.

What happens next depends on the strength of the stuff the balloon is made of. If the balloon isn’t very strong, the helium pushing on it will pop the balloon before it gets too high up. Then the pieces just fall back down to the ground.

That’s why it’s usually not a good idea to send balloons into the sky on purpose. When they come back down in those big pieces, they can hurt animals that think they’re food and try to swallow them. But if the balloon is stronger, something different will happen.

It will keep floating higher and higher up into the air — sometimes even as high as an airplane! But the air very high up in the sky isn’t just more spread out — it’s also much colder. When you’re as high up as airplanes go, it’s freeeeezing.

And when rubber gets cold, it becomes stiffer and less stretchy. So eventually, with the cold combined with the helium pushing on it from the inside, the balloon can actually /shatter/, breaking into super tiny little pieces. Those also fall back down to the ground, but since they’re so small you probably wouldn’t be able to see them.

Whether it pops or shatters, the balloon always does two things: it goes up very high, as far as it can go! And then it comes back down. That’s actually what happened to your balloon too, Squeaks!

Except, since we were inside, it could only go as high as the ceiling, and then we were able to pull it back down. Have you ever lost a balloon? What do you think happened to it?

Ask a grownup to help you leave a comment below, or send us your questions through our website at patreon.com/scishowkids. We’ll see you next time here at the Fort! [ OUTRO ].