Glossary
convection
Convection moves heat by moving the heated material itself: warm fluid or air expands, rises because it is less dense, cools, and sinks, setting up a circulating current.
Convection is heat transfer by the movement of a fluid — a liquid or a gas. Warm material expands and becomes less dense, so it rises; cooler, denser material sinks to take its place, and that circulation is a convection current. It is why a room warms from the top down, why a pot heated at the bottom warms all the way through, and why a hot-air balloon floats.
Convection is the heat engine of the planet as well as the kitchen. Uneven heating of the air drives the winds, uneven heating of the ocean drives the currents, and the same rising and sinking of hot rock in the mantle moves the tectonic plates. A sea breeze is convection on a small scale: land heats faster than water during the day, so air rises over the land and cooler air blows in off the sea.
On this subtest convection is one of the three ways heat travels, and the questions turn on telling them apart. Conduction passes heat through touching material, particle to particle, which is how a metal spoon left in soup becomes hot. Radiation carries heat as waves and needs no material at all, which is how the Sun's heat crosses empty space. Convection is the only one of the three that moves the heated material itself.
Taught in
Related terms
- radiation — Radiation is heat traveling as invisible electromagnetic waves. It needs no material to pass through, which is how the Sun's energy crosses empty space to warm the Earth.
- water cycle — The water cycle is the endless movement of water between the ocean, the air and the land — evaporation, condensation, precipitation, and runoff or infiltration back to the sea.
Source: Official ASVAB — subtest descriptions (what each subtest asks) and the CAT-ASVAB scored-question counts (accessed 2026-09)