Heat Conduction

Conduction is the transfer of heat through a material from its hotter part to its colder part, without the material itself moving. It happens mainly in solids, as vibrating particles pass energy to their neighbours. For example, a metal spoon in hot tea gets hot at the handle by conduction.

Good conductors let heat pass through them easily: most metals, such as copper, aluminium, silver and iron. Bad conductors, or insulators, let heat pass very slowly: wood, plastic, glass, cloth, air and water. Insulators are used for pan handles, oven gloves and woollen clothes.

Stick small beads of wax along a metal rod with equal gaps, and heat one end with a burner or candle. The wax nearest the flame melts first and the beads drop off one by one, showing that heat travels along the rod from the hot end. Using rods of different metals shows which conducts heat fastest.

Thermal conductivity (k) measures how well a material conducts heat, in watts per metre per kelvin. Copper is about 400 W/(m·K), aluminium about 237, iron about 80, glass about 1 and wood about 0.12. A higher value means heat flows through more easily.

Conduction, through a material by particle contact (a hot pan handle); convection, by the movement of a liquid or gas (warm air rising, sea breezes); and radiation, by waves that need no material at all (heat from the Sun or a fire reaching you).

Both are at the same temperature, but metal is a good conductor, so it quickly carries heat away from your skin, which feels cold. Wood is an insulator, so it takes heat away slowly and feels warmer.