10.2: CONDUCTION

Conduction is the transport of thermal energy through an object by a series of collisions between atoms, molecules and electrons. Different materials transfer heat by conduction at different rates - this is measured by the material's thermal conductivity.

Conduction occurs when two object at different temperatures are in contact with each other. Heat flows from the warmer to the cooler object until they are both at the same temperature. At the place where the two object touch, the faster-moving molecules of the warmer object collide with the slower moving molecules of the cooler object. As they collide, the faster molecules give up some of their energy to the slower molecules. The slower molecules gain more thermal energy and collide with other molecules in the cooler object. This process continues until heat energy from the warmer object spreads throughout the cooler object. Some substances conduct heat more easily than others. Solids are better conductor than liquids and liquids are better conductor than gases. Metals are very good conductors of heat, while air is very poor conductor of heat. You experience heat transfer by conduction whenever you touch something that is hotter or colder than your skin e.g. when you wash your hands in warm or cold water.

If one end of a metal spoon is held in a pan or a stove, the other end soon becomes hot. This is because, the energy from the stove causes the molecules in the end of the spoon, that is in the pan, to move faster, increasing the rate and size of their vibrations. These molecules transfer some of their extra kinetic energy to neighbouring molecules and these, in turn, affect their neighbours. Therefore, the temperature of the entire spoon increases. If the pan is kept at a constant temperature, overtime, the pan and the spoon will have the same temperature. Most of us would not pick this spoon up without a potholder. The potholder is a poor conductor of heat and a good thermal insulator.

How rapidly an object transports thermal energy by conduction depends, in part, on what material the object is made of.