Q1.
Why does ice float on water?
Answer
Because ice is less dense than liquid water — the same mass of water takes up more space after it freezes.
The steps are these:
- Water is densest at 4 °C. Cool it below that and it starts behaving unusually.
- At 0 °C it turns into ice, and its structure changes — the particles arrange themselves in a pattern that takes up more space. This is called expansion.
- The mass has not changed, but the volume has increased. Since Density = Mass/Volume, the density falls.
- Being lighter for the same volume, ice floats on the water below it.
Why it happens: In almost every other substance, cooling brings the particles closer and freezing makes the solid denser than its liquid, so the solid sinks. Water is the exception: when it freezes, its particles lock into an open, roomy arrangement with gaps built into it, so the solid ends up bulkier than the liquid it came from.
Did you know? Life in cold lakes depends on this exception. Because ice floats, it forms a lid on the surface and keeps the water beneath warm enough for fish and other creatures to survive the winter. If ice sank, lakes would freeze solid from the bottom up.