Talei Cordas, of Ilam School, asks :-

Why does heat travel along metal faster than glass?

Colin Hooker, a physicist at the University of Canterbury and who specialises in thermal conduction, responded.

In metals (and minerals and crystals) the atoms are arranged in parallel rows while in glass they are all mixed up.

Atoms are constantly vibrating. When one end of a metal is heated its rows of atoms vibrate together and the heat energy is passed on by means of waves which travel along the rows of atoms. This wave is a bit like the wave which travels along a stretched rope after one end is briefly flicked sideways. So materials with the atoms arranged in rows can conduct heat energy very effectively. Diamond, which consists of rows of carbon atoms, is the best solid for conducting heat and is used to conduct the waste heat out of some semiconductor devices.

If the atoms in the solid are not arranged in rows but are in random positions it is very hard for waves to travel far along the atoms; the wave will die out after passing only one or two atoms. Hence heat travelling in glass travels about ten times slower than that travelling in waves in metals (or minerals) and about two thousand times slower than in single crystal diamond.

Good electrical conductors, such as metals, have another, more effective, method of transferring heat energy. Metals conduct electricity because some electrons become detached from atoms and are free to move throughout the metal. These free electrons can take up extra energy in the hot part of the metal and move a relatively long way through the metal before they pass on the energy to atoms. Good conductors of electricity are therefore also good conductors of heat. Copper and silver, both very good conductors of electricity, conduct heat about four hundred times better than a glass can.