Why do boats float, even when made of heavy steel?

Boats can float even if they're made of heavy steel because of how water pushes up on them.

Imagine you're in a bathtub full of water, and you drop a big rock into it. The rock goes all the way to the bottom, it doesn’t float. But now imagine you put a toy boat in the same tub. Even though the boat is made of plastic (which isn't as heavy as steel), it floats because water pushes up on it.

Now think about a real boat made of steel, like a big ship. It looks super heavy, but it doesn’t sink because it’s shaped like a bowl, wide at the top and deep below the water. This shape lets the boat hold a lot of water, which then pushes up with enough force to lift the whole boat.

When you get into a bath, the water level goes up, that's called displacement. A boat does something similar: it pushes water aside, and the water pushes back upwards on the boat. If the boat is light enough compared to how much water it moves out of the way, it floats!

So even though steel is heavy, a boat can still float, just like your toy boat in the bathtub!