Why ice floats
Ice is less dense than water.
Ice in a glass
An ice cube floats in a glass of water.
Why does ice float?
What this lesson covers
The idea
Water is densest at 4 °C; when it freezes at 0 °C its particles arrange to take up more space (expansion), so ice is less dense than liquid water and floats on it.
Ice in a glass
An ice cube floats in a glass of water.
Why does ice float?
- Ice is less dense than liquid water
- Ice is heavier than water
- Ice has no mass
Freeze the water
Press Next step.
Expansion on freezing
Water's density is highest at 4 °C. On freezing at 0 °C it expands, so the density decreases. That is why ice floats. The ice layer on top keeps the water below warm enough for fish and other creatures to live in cold weather.
Water is densest at 4 °C. On freezing at 0 °C it expands, so ice is less dense than liquid water and floats.
Notes
Water is densest at 4 °C. Ice expands, is less dense, and floats.
Check yourself
At which temperature is water densest?
When water freezes at 0 °C, its particles …
Ice floats on water because ice is …
The same amount of water as ice occupies …
- 0 °C. At 0 °C water freezes and expands.
- 4 °C — correct. Yes!
- 100 °C. Water is densest at 4 °C.
- take up less space. They arrange to take up more space.
- disappear. They arrange themselves to take up more space.
- take up more space — correct. Yes!
- less dense than liquid water — correct. Yes!
- denser than liquid water. Ice is less dense, so it floats.
- hotter than water. Ice floats because it is less dense.
- a smaller volume. It takes more space, a larger volume.
- a larger volume — correct. Yes!
- no volume. It occupies a larger volume.