What is the process called where warmer parts of a fluid rise and cooler portions sink?

The process where warmer parts of a fluid rise while cooler portions sink is known as convection. This occurs because warmer fluid is typically less dense than cooler fluid. As the fluid heats up, it expands, reducing its density and causing it to rise. When it reaches the surface, it may cool down, increase in density, and subsequently sink back down. This cycle creates a continuous movement in the fluid, effectively transferring heat throughout it. Convection is a crucial mechanism in various natural processes, such as atmospheric circulation, ocean currents, and even heating in homes.

Other processes listed, such as radiation, conduction, and evaporation, involve different mechanisms of heat transfer. Radiation involves the transfer of energy through electromagnetic waves, while conduction requires direct contact between materials, and evaporation refers to the conversion of liquid into vapor. Understanding convection helps clarify how heat is distributed in fluids and is essential in many scientific and engineering applications.