What is heat conduction?
Heat conduction is the way energy travels through a material by the vibration of its own particles, without the material moving at all. Heat a metal bar at one end and the other end eventually warms up — yet no metal has flowed from one end to the other. Only energy has.
Reading the diagram
The bar is coloured from orange at the hot end through to blue at the cold end, showing how the temperature falls along it. Inside, a row of atoms is joined by bonds; the ones nearest the flame jiggle hard, the ones at the far end barely move. The dashed orange arrows show the direction the energy is passed, always from hot towards cold, and the temperature scale underneath reads the same story.
Why it matters
Conduction is everywhere around us: cooking pans, heatsinks in electronics, the walls of a house. Understanding it explains why metal handles get hot when you stir, why a well-insulated wall slows heat loss, and why a computer needs a fan — all of them are about controlling how quickly energy conducts away.
1. Energy enters at the hot end
The flame delivers energy to the left end of the bar. That energy goes into making the atoms there vibrate harder, which is exactly what a higher temperature means.
2. The atoms pick up the vibration
An atom cannot leave its place in the lattice, but it never sits still: it shakes about a fixed point. A warmer atom shakes with a bigger swing than a cooler one.
3. Energy is handed to the next atom
A strongly vibrating atom pushes against its neighbour and passes some of its energy on. That neighbour now vibrates harder and pushes the next one, and so the energy travels along the bar — passed by the material, not carried by it.
4. The temperature falls along the bar
Energy is always passed from hotter to cooler, and as it moves it spreads out along the bar. The result is a smooth drop in temperature from the hot end to the cold end — the colour gradient you see running along the metal.
5. Energy leaves at the cold end
At the far end, the finned heat sink hands energy on to the surrounding air. Energy arriving by conduction is balanced by energy leaving through the sink, so that end stays at a steady, low temperature while heat keeps flowing.
What is heat conduction?
It is the transfer of energy through a material by the vibration of its particles, without the material itself moving. A hot, strongly vibrating atom nudges its neighbour, which nudges the next, and energy works its way from the hot end to the cold end.
If the atoms do not move, how does the energy travel?
The atoms stay in place but they do not stay still — each one vibrates about a fixed point. A fast-vibrating atom pushes on its neighbour and speeds up that neighbour's vibration, handing the energy along like a row of people passing a message.
Why do metals conduct heat so well?
Metals contain free electrons that can travel through the metal, not just atoms fixed in a lattice. These free electrons carry energy quickly, which is why a metal spoon heats up much faster than a wooden one.
Does heat flow from cold to hot ever happen by conduction?
No, not on its own. Conduction always runs from the hotter region to the cooler one, and it stops once both ends are the same temperature. Forcing heat the other way takes outside work, as a refrigerator does.
What decides how fast energy moves along the bar?
Three things: the material's conductivity, the cross-sectional area of the bar, and how steep the temperature difference is along it. A wider bar, a better conductor or a bigger drop from end to end all let energy move faster.
Why does one end stay cold even though heat keeps arriving?
Because the heat sink at that end keeps carrying energy away into the air. Energy arriving by conduction is balanced by energy leaving through the sink, so that end settles at a steady, low temperature.