Thermal Expansion
Physics: Cambridge International GCSE Supplement, topic 2.2.1
Thermal Expansion
All materials expand when they are heated. This is called thermal expansion.
In solids
- The molecules in a solid are fixed. When the temperature rises, the molecules vibrate more and are pushed apart.
- Engineers leave gaps in train tracks to allow for thermal expansion. These gaps create the “clickety-click” sound that trains make.
- Engineers also allow for thermal expansion when designing buildings and bridges.
In liquids
- When heated, the molecules in a liquid move faster and are pushed apart (like in solids).
- For a 1°C rise in temperature, a liquid will expand more than a solid.
In gases
- When heated, molecules in a gas will move faster. For a 1°C rise in temperature, the volume of a gas will increase more than the volume of a liquid.
- If a gas is in a fixed container, its volume cannot change. Both the force exerted on the container walls and the pressure will rise.
Examples
- Buildings and bridges need to be safe at all temperatures. Engineers need to allow for thermal expansion and often use steel reinforcement to strengthen buildings.
- The “clickety-click” sound of trains is produced by small gaps between the train tracks. These gaps exist to allow for thermal expansion.
Test yourself on Thermal Expansion
Which of these states of matter expand when heated (experience thermal expansion)?
Why do trains make "clickety click" sounds?
A glass jar has a metal lid that is difficult to unscrew. Why does holding the jar under a hot tap make it easier to unscrew the lid?