Convection
Convection is the transfer of thermal energy when particles of a fluid move from one place to another.
Examples of convection currents in nature
Temperature in an oven
Why is temperature higher at the bottom of an oven? When air at the bottom of the oven heats up, it expands and become less dense than the surrounding air. When a fluid circulates in a loop as it alternately heats up and cools down, a Convection Current occurs.