ELI5: How do submarines work?

Imagine a big metal bathtub that can go underwater! That's kind of like a submarine.

Submarines use science to sink and float. It's all about something called buoyancy. Think of it like this:

• If something is heavier than the water it pushes out of the way, it sinks.
• If it's lighter, it floats.

Here's how it works:

1. To sink: The submarine lets water into the ballast tanks. This makes the submarine heavier, so it sinks. Imagine adding rocks to your bathtub – it would sink lower, right?
2. To float (or surface): The submarine pumps air into the ballast tanks, pushing the water out. This makes the submarine lighter, so it floats up to the surface. Think of taking those rocks out of the bathtub – it would float higher!
3. Moving forward: The submarine has propellers that spin around and push water backward. This pushes the submarine forward, just like how a boat moves! They are powered by engines or electric motors.
4. Staying at a certain depth: The submarine can control how much water is in the ballast tanks. This way it can stay at the depth they want underwater.
5. Seeing underwater: They use sonar to "see" underwater. It sends out sound waves that bounce off objects. Then they listen for the echoes to find where things are.