Thermal energy can also be transferred when a liquid evaporates. The liquid particles with the most energy leave the liquid and enter the surroundings. This is why your skin feels cold if you lick the back of your hand and blow over it gently. Conduction and convection also need moving particles to transfer thermal energy.
Conduction
Thermal energy can move through a substance by conduction.
Substances that allow thermal energy to move easily through them are called conductors. Metals are good conductors of thermal energy.
Substances that do not allow thermal energy to move through them easily are called insulators. Air and plastics are insulators.
When a substance is heated, its particles gain energy and vibrate more vigorously. The particles bump into nearby particles and make them vibrate more. This passes the thermal energy through the substance by conduction, from the hot end to the cold end. This is why the handle of a metal spoon soon gets hot, as well as its rounded part, when the spoon is put into a hot drink.
Convection
The particles in liquids and gases can move from place to place. Convection happens when particles with a lot of thermal energy in a liquid or gas move, and take the place of particles with less thermal energy. Thermal energy is transferred from hot places to cold places by convection.
Radiation
All objects transfer thermal energy by radiation called infrared radiation. The hotter an object is, the more radiation it gives off. No particles are involved in radiation, unlike conduction and convection. This means that thermal energy transfer by radiation can even work in space, but conduction and convection cannot.
Radiation is why we can feel the heat of the Sun, even though it is millions of kilometres away in space. The police use infrared cameras to track down criminals in the dark.
