Why Ice Floats

Look at a cold glass of water. Put an ice cube inside. What happens? The ice does not sink. It floats on top.

Why does this happen? The answer is about water and temperature.

Most things get smaller when they get cold. When liquids freeze, they usually become heavy and dense. They sink in their liquid form. Water is different. Water is special.

Water is made of tiny parts called molecules. When water is warm, the molecules move around fast. They bump into each other. They stay close, but they have space between them.

When water gets very cold, it turns to ice. At zero degrees Celsius, the molecules slow down. They lock into a fixed pattern. This pattern makes a crystal shape.

The crystal shape has lots of empty space inside. Because of this empty space, ice takes up more room than liquid water. Ice is less dense than the water around it.

Things that are less dense float. Things that are denser sink. Wood floats on water because wood is less dense. Ice floats on water because ice is less dense.

This simple fact is very important for our planet. Imagine if ice sank to the bottom of lakes and oceans. In winter, lakes would freeze from the bottom up. All the fish and plants would die.

Because ice floats, it stays on top. The ice makes a blanket over the water. This blanket keeps the water underneath warm enough for fish to live through the cold winter.

Next time you see ice in your drink, remember the science. Ice floats because cold water makes a special crystal shape with lots of empty space.

What other things float in water?