It takes a little science to see why this is a very good question instead of a no-brainer.
- Matter gets denser as it cools down.
- Light things float.
- Dense things sink.
This is one reason why, for instance, hot magma rises through “cold” rock from a source of molten rock deep within Earth’s mantle. The hot stuff is more buoyant than the cold stuff.
To some extent water works this way, too (though at much lower temperatures, of course). Warm ocean currents circulate in the upper parts of the sea, above cold bottom currents.
When water freezes, it should be at its most dense and drop to the bottom like a rock.
Instead, ice floats.
Here’s a BBC presenter drawing magic circles in the air to show you why this happens.
Featured Image: Niekverlaan at Pixabay. Public domain.