Which mode of heat transfer relies on moving fluids to transfer heat?

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

Answer: (B)

Convection is the mode of heat transfer that relies on moving fluids to carry thermal energy from one place to another. When a fluid is heated, it becomes less dense and rises, while cooler, denser fluid moves in to take its place, creating a circulating flow that transports heat through the fluid itself. This is why warm air rising from a radiator or steam rising in a pot effectively heats a space or cooks food. By contrast, radiation transfers energy via electromagnetic waves and can occur without any fluid, while conduction moves heat through direct contact between substances, typically in solids. Absorption describes taking in energy, not the mechanism of its distribution. The key idea here is that bulk fluid movement is what enables heat to be carried from hotter to cooler regions, which is convection.