Where did the ice go?

About this video

Drop ice cubes into a glass of water on a hot afternoon, and half an hour later they are gone and there is a little more water in the glass. The ice did not disappear: it became water. Ice and liquid water are the same stuff, water, in two different states.

A solid turning into a liquid is called melting, and a liquid turning into a solid is called freezing. Ice melts when heat goes into it, from the warm air and the warm drink around it. People often say that "the cold comes out of the ice", but cold is not a thing that moves: heat moves, from warmer things into colder things. In a freezer it is the other way round: heat leaves the water until it becomes ice.

Pure water freezes at 0 °C (32 °F), and ice melts at the same temperature. The temperature where a solid melts is its melting point, and where a liquid freezes is its freezing point; for one kind of stuff they are the same. Other stuff melts at other temperatures: chocolate at about 34 °C, a little below the inside of your mouth, which is why it melts on your tongue, and iron only at about 1,500 °C, which is why melted iron glows bright orange.

Water does one strange thing when it freezes: it takes up a bit more space. Ice is about a tenth bigger than the water it came from. That is why ice cubes float, and why a full glass bottle of water can crack in a freezer.

Transcript

1. 0:00Ice cubes vanish into a drink. Where did the ice go? It became water.
2. 0:09Cold does not come out of the ice. Heat goes in, and it melts. In a freezer, heat comes out, and water freezes.
3. 0:18Water melts and freezes at the same temperature, zero degrees Celsius.
4. 0:28Each kind of stuff has its own melting point. Chocolate about thirty-four degrees. Iron about fifteen hundred.
5. 0:37Ice is about a tenth bigger than its water. So it floats.
6. 0:45Ice or water, it is the same stuff.