Conduction, Convection, and Radiation

Conduction happens inside a solid without any visible motion. Atoms in the hot end of a metal bar vibrate harder and collide with their neighbors, passing kinetic energy down the chain like a relay of jostling springs. No atom travels far, but energy marches from hot to cold, fastest in metals because their loose electrons carry energy along too.

Convection moves heat by moving matter itself. Heat a pot of water from below and the bottom layer warms, expands, becomes less dense, and rises; cooler, denser water sinks to take its place, gets heated, and rises in turn. This loop keeps circulating as long as the burner runs, carrying thermal energy upward far faster than conduction through water alone could manage. A fan uses the same idea on your skin: it does not cool the air, it keeps replacing the warm, moisture-laden layer next to you with drier room-temperature air, so evaporation and heat loss both speed up.

Radiation is the odd one out: it needs no matter at all, which is why sunlight crosses empty space to reach you. Every object above absolute zero radiates electromagnetic energy constantly, with hotter objects radiating more and shifting their peak wavelength toward visible light, which is why only very hot things glow. A thermos fights all three mechanisms at once: a vacuum between its walls blocks conduction and convection, leaving only radiation, which silvered walls reflect back inward.