Three ways heat flows
Heat always flows from a hotter place to a cooler place. It can travel in three ways:
- Conduction: heat passes through a solid as particles vibrate and pass energy to their neighbours. Metals are good conductors; wood and plastic are insulators.
- Convection: heat moves through liquids and gases as warm fluid rises and cool fluid sinks, forming a current.
- Radiation: heat travels as invisible waves and needs no material, which is how the Sun's heat reaches Earth.
Key idea
Conduction needs a solid. Convection needs a liquid or gas. Radiation needs no medium and can travel through empty space.
Thermal equilibrium
When a hot object and a cold object touch, heat flows from the hot one to the cold one. The hot object cools down and the cold object warms up. Eventually both reach the same temperature and no more net heat flows. This state is called thermal equilibrium.
Example
A cold spoon placed in hot soup slowly warms up while the soup cools slightly, until the spoon and soup reach the same temperature.
Remember
- Heat flows from hot to cold.
- Conduction in solids, convection in fluids, radiation through space.
- At thermal equilibrium both objects are at the same temperature.