Fishtie said:
Think about this. (nerd science incoming)
All materials condense when they get colder, becoming more dense and sinking. This is especially true when they change state, say from liquid to solid.
EXCEPT WATER! Ice is the ONLY thing that actually expands and floats when it freezes.
The really freaky part? If this wasn't true then life as we know it would not exist! (water frozen in winter would sink and not be thawed by the summer sun, eventually causing all water to freeze)
So just remember: you wouldn't be alive except for one tiny little middle finger to thermal dynamics.
Water expands only once it starts to solidify, and can be kept a liquid far below it's freezing point if it is not allowed to expand. There are forms of ice that do not expand the normal 9% you see in your freezer as well. Ice can form with pressure. It's not the only thing that expands when it freezes either. Gallium, Bismuth, Antimony, and Silicon also expand when they freeze.
It is true that if ice sank in water rather then floating life as we know it wouldn't exist.