Which form of heat transfer occurs via the movement of fluids (air or water) to transfer energy?

• A. Convection
• B. Conduction
• C. Radiation
• D. Expansion

Answer: (A)

Convection is heat transfer driven by the bulk movement of fluids. When part of a fluid is heated, it becomes less dense and rises, while cooler, denser fluid sinks, creating circulation that carries thermal energy with it. This is why you see warm air rise from a heater and hot water currents in a pot. Conduction transfers energy through direct contact between molecules (often in solids), and radiation moves energy as electromagnetic waves and can occur without a medium. Expansion isn’t a heat transfer mechanism itself, though heating can cause a fluid to expand and change density, which helps drive convection.