Conduction is the transfer of energy in the form of heat or electricity from one atom to another within an object by direct contact. Conduction occurs in solids, liquids, and gases. However, solids transfer energy most efficiently since the molecules in solids are most tightly packed, and the molecules are closer together, as shown in this figure. For liquids and gases, the density of the particles are generally lower than those of solids and the particles are farther apart, so the energy transfer is less efficient.
There are two main types of conduction:
Conduction of heat occurs when molecules increase in temperature; they vibrate, and this vibration and movement passes the heat energy to the surrounding molecules. Some examples of conduction of heat are accidentally touching a hot pot, or when a heating pad is applied to you directly and warms your muscles.
Conduction of electricity occurs due to the movement of electrically charged particles through a medium. This movement can result in an electric current, which may be carried by electrons or ions. An example of electrical conduction is when you accidentally get electrocuted when you touch a live wire because your body contains water, which is a conductor of electricity. Another example is when electricity passes through wires, which are conductors, so we can watch TV or use a computer.
The picture on the left shows what happens if you leave a metal spoon inside a cup with hot liquid. The spoon is at room temperature at first when we touch it, but as the spoon has longer contact with the hot water, the spoon becomes hot to the touch. This is because the heat from the liquid is transferred to the spoon due to conduction of heat. The picture on the right shows a light bulb that is turned on because electricity travels through the wires due to the conduction of electricity.