Where does convection primarily occur?

Convection primarily occurs in fluids, which include liquids and gases. It is the process by which heat is transferred through the movement of the fluid itself. When a fluid is heated, the warmer, less dense portions rise while the cooler, denser portions sink, creating a circulation pattern that distributes heat throughout the fluid.

In the context of your answer, convection occurs above a hot surface because the heat from that surface warms the adjacent fluid (air or liquid). As the fluid near the hot surface becomes heated, it expands and rises, while cooler fluid moves in to take its place. This movement forms a convection current, which efficiently transfers heat away from the source.

In contrast, convection does not primarily occur in solids because heat is conducted through the material rather than by fluid motion. Above a cold surface, convection is less effective since a cold surface would cause the fluid above it to cool and sink, creating a very different dynamic. Convection is also irrelevant within a vacuum, as there are no fluid particles to facilitate the motion required for convection to occur.