Convection

Convection transfers thermal energy through the bulk movement of a fluid. Fluids include liquids and gases. Heating usually causes fluid expansion and a decrease in density. Warmer fluid rises, while cooler, denser fluid moves downward. This circulation creates a **convection current**.

Heating → expansion → lower density → rise → cooler fluid sinks → circulation

**Natural convection: driven by density differences. Forced convection:** driven by fans or pumps.