Heat moves three ways — conduction, convection and radiation — and only radiation crosses empty space. Drag the sliders below to change the temperatures, conductivity, thickness and emissivity, and compare the three transfer rates in real time.
You feel heat travel three different ways, but only one of them can cross empty space. When you touch a warm mug, conduction carries energy through the solid ceramic, particle to particle. The sim reports that rate as kAΔT/d: a bigger thermal conductivity k, a wider area A, or a larger temperature gap ΔT all speed it up, while a thicker slab d slows it down. That is exactly why a fluffy jacket, thick and barely conductive, keeps you warm. Slide the Thermal conductivity and Slab thickness controls and watch the conduction readout swing.
Now let a fluid do the work. Convection moves heat by physically carrying warm material away, so its rate hAΔT climbs with the Convection coefficient h and the temperature difference. The third path abandons matter entirely. Radiation leaves every warm surface as electromagnetic waves at rate εσAT^4, where T is the absolute temperature in kelvin. That fourth power bites hard: double the absolute temperature and radiated power jumps sixteen-fold. Push the Hot temperature slider high and the radiation figure runs away from the others.
Only radiation needs no medium at all, which is how sunlight pours across the vacuum of space to warm the Earth. Test each mode yourself, then size a real wall with the thermal conduction calculator or branch into another hands-on experiment in the physics simulation collection.
Conduction (through a solid, particle to particle), convection (carried by a moving fluid), and radiation (as electromagnetic waves). Only radiation can cross a vacuum.
On Q/t = k·A·ΔT/d — the thermal conductivity k, the area A, the temperature difference ΔT and the thickness d. Thicker or less conductive materials conduct more slowly, which is why they insulate.
Radiated power follows Stefan's law, ε·σ·A·T^4, with T the absolute temperature. Because of the fourth power, doubling the absolute temperature raises the radiated power sixteen-fold.
By radiation. Conduction and convection both need matter, but radiation travels as electromagnetic waves and crosses the vacuum of space, so sunlight can warm the Earth.