Thermal energy transfer — Physics, 14–17 years
Thermal energy moves from hotter places to cooler ones by conduction, convection or radiation. Each process has a different physical picture, so the best insulation depends on the situation.
Three ways heat travels
Conduction passes energy through touching particles, especially in solids. Convection carries energy in moving liquids or gases, as warmer, less dense regions rise. Radiation carries energy by electromagnetic waves, so it can cross empty space, as sunlight crosses space to Earth.
Why distinguish them?
Early heat experiments showed that warmth could move through a metal rod, circulate in water or arrive from the Sun. Treating all three as one process made predictions fail. Separating the mechanisms helps explain why a metal spoon, a radiator and a blanket behave differently.
Worked example
A metal spoon rests in hot tea. After a minute, its handle becomes warm even though it is not in the tea. Vibrating particles pass energy from the immersed end to neighbouring particles along the metal: this is conduction. No bulk flow carries the energy, so it is not convection; and the main route is not radiation.
The common mistake
People often say that cold flows into a warm object. It feels right when a cold hand touches a warm mug, because the hand becomes colder. Physically, thermal energy flows from the mug to the hand; the hand loses energy, while the mug cools slightly.
Where it is used
A house loses heat through walls by conduction, with moving air by convection, and from surfaces by radiation. Loft insulation traps air, sealed windows reduce convection, and shiny foil reflects infrared radiation. Designers combine these methods rather than expecting one material to stop every transfer.
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