What You Need to Know
This chapter explores how thermal energy moves from hotter regions to cooler ones. You'll encounter three distinct mechanisms, understand why they work differently in different materials, and apply them to real-world situations from insulation to the greenhouse effect.
The Three Mechanisms at a Glance
Conduction
Heat transfer through solids by particle-to-particle contact. Atoms vibrate and bump into neighbours, passing energy along. No bulk movement of material.
Convection
Heat transfer through fluids (liquids and gases) via the movement of the fluid itself. Hot, less-dense fluid rises; cooler, denser fluid sinks. Creates currents.
Radiation
Heat transfer via infrared waves. The only method that works through a vacuum. Depends on surface colour and texture. No medium needed.
Conduction: Heat Through Solids
What is Conduction?
Conduction is the transfer of heat through a solid material without any movement of the material itself. Imagine a metal spoon in a cup of hot tea: the handle gets warm even though it's not touching the water. That's conduction at work.
How Does Conduction Happen? The Mechanism
1. Atomic Vibration (in all solids)
When you heat one end of a solid, the atoms at that hot end vibrate more vigorously. As they vibrate, they bump into neighbouring atoms and transfer some of their energy to them. Those atoms then vibrate faster, bump into their neighbours, and so on. Energy spreads through the material atom by atom, like a chain reaction of bumps.
2. Free Electron Movement (in metals only)
Metals are much better conductors than other solids because they contain free electrons — electrons that are not bound to a specific atom and can move freely throughout the material. When one end of a metal gets hot, these free electrons gain kinetic energy, move rapidly through the material, and collide with other electrons and atoms, transferring heat very quickly.
💡 Why Metals Are Best Conductors
Metals have lots of free electrons that zip around inside them. In non-metals, atoms are fixed in place and can only vibrate, so heat spreads much more slowly. That's why a copper pot conducts heat well but a plastic handle doesn't.
Good Conductors vs Bad Conductors (Insulators)
| Good Conductors |
Bad Conductors (Insulators) |
| Metals: Copper, aluminium, iron, steel |
Non-metals: Wool, plastic, wood, cardboard, air, water |
| Free electrons move heat quickly |
Only atom vibration; atoms are locked in place |
| Heat spreads fast (you feel it immediately) |
Heat spreads slowly (good for insulation) |
Classic Experiment: Tiles vs Rug
The Setup: Stand with one foot on a cold tile floor and one foot on a thick rug in the same room. Both are at the same temperature, but the tile feels cold and the rug feels warm.
Why?
- Tile (good conductor): Your warm foot conducts heat away rapidly into the tile. Energy leaves your foot quickly. You feel cold.
- Rug (good insulator):
⚠️ Common Mistake
fast
Conduction in Liquids and Gases
very poor in liquids and gases
What to Memorise