Most substances can exist as a solid, liquid or gas. They can change state, usually when they are heated or cooled. For example, liquid water turns into water vapour when it is heated enough ...

Gases, on the other hand ... they gain energy and can move more freely, changing from a solid to a liquid, for example. This basic model is, however, just that: there are many, many more states ...

Even when liquids change their shape, they always take up the same amount of space. Their volume stays the same. Examples of gases include steam, helium and oxygen. They are often invisible.

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Students explore the attractions and motion of atoms and molecules as they experiment with and observe the heating and cooling of a solid, liquid, and gas.