You're camping. The fire is blazing 2 metres away — you feel its warmth on your face even though no air is blowing toward you and you're not touching it. Meanwhile the metal cooking pot, also 2 metres from the fire and much closer to the flames, stays at the same temperature as the rock beside it until you actually put it in the fire. Three completely different ways heat moves — which one is warming your face?
You're camping. The fire is blazing 2 metres away — you feel its warmth on your face even though no air is blowing toward you and you're not touching it. Meanwhile the metal cooking pot, also 2 metres from the fire and much closer to the flames, stays at the same temperature as the rock beside it until you actually put it in the fire. Three completely different ways heat moves — which one is warming your face?
Heat doesn't just teleport between objects — it travels by one of three mechanisms: conduction (through solid contact), convection (carried by moving fluids), or radiation (as electromagnetic waves). Each mechanism has a different speed, range, and governing equation. Understanding them lets engineers build better insulators, heating systems, and space probes.
Heat flows from hot to cold by three routes. Conduction: direct particle-to-particle energy transfer through contact — fastest in metals (electrons carry heat). Convection: bulk movement of fluid carries energy — hot air rises, cool air sinks, creating circulation cells. Radiation: all objects emit infrared waves — no medium needed (the Sun heats Earth across 150 million km of vacuum). Real systems involve all three.
The formula Q/t = kAΔT/d (Fourier's Law) governs conduction. It says: heat flows faster when ΔT is large, area is big, thickness is small, and k is high. Engineers use it to design home insulation (want low k), heat sinks (want high k), and cooking pans (want moderate k with even distribution). Convection is described by Newton's Law of Cooling: Q/t = hA(T_surface − T_fluid), where h is the convective heat transfer coefficient. Radiation follows the Stefan-Boltzmann Law: P = εσAT⁴ — where σ = 5.67×10⁻⁸ W/m²K⁴.