Why Does Ice Float?

A True Book

Tim drops an ice cube into his glass. It does not sink. It floats on top of the water.

That seems strange. Most things that freeze get heavier and sink. Water is different.

Water is made of tiny, tiny bits. When water freezes, the bits line up in a pattern. The pattern leaves little gaps.

The gaps spread the bits apart. So ice is a little lighter than water. And lighter things float.

Tim looks closely. About a tenth of the cube sticks out. The rest hides below.

Now think of a pond in winter. The weather turns very cold. Ice begins to form on top of the water.

The ice floats there like a lid. It stops the pond from freezing from the bottom up.

Under the lid, fish live all winter. They swim slowly, and they do not eat much. The water under the lid stays liquid.

Tim taps his glass and grins. "My ice cube is a little lid!"

Here is a question for dinner. What would happen to a pond if ice sank?