Water can be a solid, a liquid, or a gas, and at various times and seasons we can find examples of all three phases. Because it takes a relatively large amount of energy to cause a change in phase, this process plays an important role in moving energy around.

Here are some questions that we can discuss when we have studied changes of phase:

	A cup of hot coffee has a plume of steam. This is actually a cloud of tiny drops of water. Why does it happen? Why does the plume disappear as it rises?

A steam radiator. Why is steam a really good way to move energy around (especially if you don't mind that the radiator is too hot to touch)?

After a clear, cold night, fence posts and car tops are decorated with ice crystals, and the grass is frosty. Where did the water come from? How cold does it have to be for dew or frost to form?

On a cold day, some cars have great white clouds coming out of their exhaust pipes, while others do not. What's going on? How are the cars different

In the winter you sometimes get a shock from static electricity. Why does this only happen in the winter?

The unit on phase transformations