[ ♩ INTRO ].

Really? [Squeaks keeps talking: then the submarine got stuck under some ice!] And then what happened? [Squeaks squeaks]. That’s great!

Squeaks was just telling me about a story he was reading. It was about a submarine exploring the ocean! [Squeaks squeaks]. You want to go in a submarine, too?

That sounds like it could be a lot of fun. Maybe someday we will visit a submarine! Actually, a viewer named Sam sent us a question about submarines not too long ago.

Submarines are kind of like boats, except they go under the water. And Sam wanted to know more about how they can do that! [Squeaks squeaks]. Well, submarines work because of the way things float and sink, and some really smart thinking.

You probably know that when you put things in water, some of them float at the top, and some of them sink to the bottom. we did an experiment to learn why things float or sink with our friends Bill and Webb, remember,. Squeaks? We learned that whether something floats depends on its density, or how heavy it is for its size.

If it’s heavier for its size than water, it sinks. If it’s lighter, it floats. For example, a plastic spoon isn’t very heavy for its size, so it floats.

But a metal spoon is pretty heavy for its size, so it sinks. That’s how boats float, too. They’re really heavy — you wouldn’t be able to just pick one up!

But they’re not actually very heavy compared to how big they are. They’re not very dense, so they float! And submarines can float on top of the water for the same reason.

But for a submarine to be able to go /under/ the water, it needs some of that really smart thinking I mentioned earlier. To dive into the water, a submarine needs to become heavier for its size — it needs to be more dense. But it’s not so easy to make something heavier when you’re in the middle of the ocean!

That’s why submarines have big tanks, called ballast tanks. When it’s time for the submarine to dive down, the ballast tanks open so they fill up with water. Adding the weight of the water to the submarine makes it dense enough to sink.

You can see how this works if you have an empty plastic bottle and a bowl of water. At first, if you put the bottle in the water, it will float because the only thing inside it is air. It’s very light for its size, so it’s not very dense.

But if you take the cap off the bottle and let the water in from the bowl, it will sink! The water makes it heavier for its size, just like putting water in the ballast tanks on a submarine does. The rest of the submarine is very strong and sealed up tight, so water can’t get in, and so that if there are people on the submarine, they can breathe.

To make sure they don’t run out of air, they bring along extra air that’s all squeezed together inside a bottle, like how you squeeze air into a bicycle tire when you pump it up. And then they can go exploring under the water, just like the people in the story Squeaks was reading! [Squeaks thinks this is cool]. In real life, we use submarines for all kinds of things, including learning more about the oceans.

When scientists send submarines under the water, they find so many cool animals. There are jellyfish, octopuses, crabs, fish, and tons of animals we’ve never even seen before! But after the submarine is done exploring under the water, there’s one more thing it needs to be able to do.

Maybe you’ve already guessed what it is. We know how submarines dive under the water … but how do they get back up? Well, remember how submarines bring along extra air?

If there are people on the submarine, they can use it to breathe, but it’s not only for breathing. When it’s time for the submarine to go back up to the surface, it pushes air into the ballast tanks, and water out. That makes the submarine lighter for its size, so it can float up to the top of the water! [Squeaks is impressed].

It really is a very smart way of using science to explore the world. Thanks for joining us! If you have more questions about submarines, or exploring the oceans, or anything at all, we have a website where you can send them to us!

Just ask a grown-up to help you go to patreon.com/scishowkids to check it out. And if you are a grown-up, our Patreon page is also a place where you can support this show and help us making fun, educational videos like this one. We’ll see you next time, here at the Fort! [ OUTRO ♩ ].