Understand Physical Changes of State

Look at this diagram carefully.  It shows how materials change between, solids, liquids and gases:

	melting		evaporation
SOLID		LIQUID		GAS
	freezing		condensation

Now look at it again. 

What's happening to change a solid to a liquid to a gas?  It's being heated.

What's happening to change a gas to a liquid to a solid?  It's being cooled.

These are physical changes and they can be reversed, which means they go back to what they were before.  When materials change in this way, it's called changing state.  Do you notice each special word as the state changes (melting, condensing, etc.)?

Water is the most obvious example to demonstrate how it changes state.  

Solid = Ice

Liquid = Water

Gas = Steam (or, better, water vapour).

Of course, many substances you come across will change like this - water's just an obvious example.

OK, to be able to talk about and describe these changes, we must understand the science vocabulary associated with each of the physical changes, so that's what we're going to be looking at in this activity.