Conduction, convection and radiation

Last time

Before we start: last time, in Expansion, heat capacity, latent heat and evaporation, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

The spoon in the soup

Leave a metal spoon in a pan of hot soup. After a minute the handle is too hot to touch. The soup never touched your hand. Meanwhile, the soup itself is swirling, and the cooker is glowing without touching the pan. Energy is on the move in three different ways.

Three ways, one direction

Thermal energy always moves from a hotter place to a cooler place, until both are at the same temperature. There are three ways it can travel: conduction, convection and radiation.

Conduction in solids

Conduction is the transfer of thermal energy through a material, without the material itself moving. In a solid, the particles vibrate about fixed positions. The hot end vibrates more strongly. Those big vibrations shake the neighbouring particles, which shake their neighbours, and so the energy passes along.

Passing the vibration on

On the left is a hot solid, where the particles vibrate strongly. On the right is a cold solid, where the particles vibrate gently. When they touch, the strong vibrations make the gentle ones vibrate more, and the cold solid warms up.

Why metals conduct best

Metals contain free electrons. These are electrons that are not stuck to one atom, and can move through the metal. They travel through the metal and collide with other particles, giving them that energy quickly. So metals conduct by vibrations and by free electrons. Non-metals, such as glass and wood, only have vibrations, so they are poor conductors.