Introduction: Change Is Everywhere
Look around you — change is happening all the time. Ice melts in your drink, steam rises from a hot cup of tea, and puddles disappear after rain. These are all examples of everyday changes in materials.
Changes can happen in two main ways:
- Physical changes — the substance changes its form or state, but it is still the same material (e.g. water freezing into ice)
- Chemical changes — a completely new substance is formed (e.g. burning wood)
In this subtopic, we will focus mainly on changes of state — when a substance changes between solid, liquid, and gas — and expansion, which happens when materials are heated.
Think of a gold ring. It looks solid and permanent, but heat it up enough and it melts into a shiny liquid that can be poured into a mould. The gold hasn't changed into something new — it's just changed its state. Your ring is really just 'frozen' gold!
The Three States of Matter
All materials exist in one of three main states of matter: solid, liquid, or gas. Which state a substance is in depends on its temperature and the pressure of its surroundings.
The physical form that a substance takes — solid, liquid, or gas — depending on temperature and pressure conditions.
Here is a quick summary of the three states:
| State | Shape | Volume | Particle movement |
|---|---|---|---|
| Solid | Fixed | Fixed | Vibrate in place |
| Liquid | Takes shape of container | Fixed | Flow around each other |
| Gas | Fills container | Not fixed | Move freely and fast |
The same substance can exist in all three states! Water is ice (solid), liquid water, or steam (gas) — it just depends on temperature.
Imagine people in a crowd. At a concert where everyone is packed tightly and swaying slightly — that's a solid. When the concert ends and people shuffle past each other towards the exits — that's a liquid. When everyone has left and is walking freely in the open street — that's a gas.
10 more sections in this topic
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