Just like all substances, water takes up the most space as a gas, and as it cools, it contracts. It becomes a liquid, and continues contracting as it cools, becoming more and more dense. But then a strange thing happens! At 4°C (39°F), it is at its densest point. As you continue cooling it from there, it starts expanding again! And when you get to the freezing point of 0°C (32°F), if it is still cooling, it freezes. So what, you say? Well, the strange thing is that when water freezes, it expands greatly! Ice is much less dense than water.This has huge significance. It is why ice cubes float. It is why road builders, especially in the north, are careful to build a gravel roadbed with good drainage under the road. If water is in or right under the pavement, and it freezes, it causes cracks and “frost heaves” in the road. Those of you who live in northern climates are familiar with these. The expansion of freezing water is a major force in weathering. A small amount of water in a crack in a rock can freeze and cause the whole rock to split open. If you have water pipes that freeze during a very cold winter, you have to worry about them breaking because of the expansion of the freezing water.
Water Density
Why do ice cubes float in water?
Ice cubes float because the molecules in solid ice are more ordered than liquid water. Hence, ice cubes are less dense than liquid water so they float.
