1 Convection occurs in fluids. Fluids are liquids and gases.
2 When a fluid is heated it expands. The fluid
becomes less dense and rises.
3 The warm fluid is replaced by cooler,
denser fluid. The resulting convection current
transfers energy throughout the fluid.
4 Convection currents can be on a very small scale, such as heating
water in a beaker or on a very large scale, such as heating the air
above land and sea. Convection currents are responsible for onshore
and offshore breezes.