Page 4 - Curriculum Visions Dynamic Book

1: Introduction
A material is something that people work with to make something that others need. Anything that is solid, liquid, or gas can be a material.
Most materials that we want to use have to be taken from the earth. Rocks have to be heated to release
their metals; plastics come from oil obtained by deep drilling. But water is different – it is all around us. All we have to do is collect it from rivers and the sea.
The universal presence of water has been
noted since ancient times. Some ancient Greeks (for example, Thales of Miletus) believed that water
was the only basic building block of matter and that everything else was formed from it.
2. Clouds
There is water vapour in the
air around you now, but it is so thinly spread that you cannot see it. However, high in the cold clouds moisture forms into tiny droplets, which then grow large enough to fall from the air as rain (or snow if the air is very cold).
Another Greek, Aristotle, believed water to be one
of four fundamental “elements,” the others being earth, air, and fire. It took until the 18th century to show that this was not so and that water is made from oxygen and hydrogen.
(Right) The natural water cycle. Notice that water changes from a liquid to a gas (vapor) and back to a liquid. It is never used up.
1. The oceans
More than nine-tenths of the world’s water is in the oceans. However, we can’t drink this water because it contains lots of salt.
Liquid water changes to invisible water vapour due to the warmth
of the air and the heat from the Sun. This is known as evaporation.
The water vapour that rises from the oceans contains no salt. It will form the fresh water that we can drink.
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