Conduction: Heat Through Solids
≈ 20 minConduction is the transfer of heat through a material, or between two materials that are touching, without the material itself travelling. Heat moves along the spoon; the spoon stays in the pot.
Materials that conduct heat quickly are thermal conductors — almost all metals, with copper and aluminium among the best. Materials that conduct heat slowly are insulators: wood, plastic, rubber, glass, wool, polystyrene, and — importantly — still air.
Conduction is the main way heat travels through solids.
Worked example — an investigation you can run. Take rods of copper, aluminium, steel and glass, all the same length and thickness. Stick a drawing pin to the far end of each with a blob of candle wax, then heat all four ends equally.
As heat conducts along each rod, the wax melts and the pin drops. Typical results:
| Rod | Time for the pin to fall |
|---|---|
| copper | 12 s |
| aluminium | 20 s |
| steel | 45 s |
| glass | over 300 s |
The steel rod took seconds longer than the copper. Everything except the material was kept the same — same length, same heat source, same size blob of wax — which is what makes the comparison fair.
A metal spoon is left standing in a pot of hot pap. After a few minutes the handle is too hot to hold, even though the handle is nowhere near the food. Which process moved the heat?
What is the name for a material that does not let heat pass through it easily?
In the wax-and-pin investigation the pin fell off the copper rod after 12 seconds and off the steel rod after 45 seconds. How many seconds longer did the steel rod take?
On a cold morning a metal gate feels much colder than the wooden post next to it, although a thermometer gives both the same reading. What is the best explanation?