Conduction occurs anywhere two objects or particles at different temperatures are in direct contact. In physics, it happens in solids, liquids, and gases as energy transfers from faster-moving particles to slower ones. In biology, conduction describes how electrical signals travel through your heart and nerves. The underlying principle is always the same: energy moves through a material without the material itself moving.
How Conduction Works in Solids
Solids are where thermal conduction is most effective because their molecules are tightly packed together. Energy transfers through two main mechanisms: vibrations in the material’s atomic structure and the movement of free electrons. Which mechanism dominates depends on the type of solid.
In metals like copper and aluminum, free electrons do most of the work. These electrons move easily through the metal’s structure, colliding with atoms and transferring kinetic energy as they go. That’s why metals feel cold to the touch: they’re pulling heat away from your skin efficiently. Copper conducts heat at roughly 400 watts per meter-kelvin (W/mK), making it one of the best natural conductors available. Silver edges it out slightly, and diamond, despite not being a metal, reaches even higher values because of its extremely rigid atomic lattice, which transmits vibrations with very little energy loss.
In non-metals like glass, ceramic, and rubber, there are few or no free electrons. Heat instead moves through vibrations in the atomic lattice, which is a slower process. This is why a wooden spoon stays cool in a hot pot while a metal one burns your hand.
Conduction in Liquids and Gases
Conduction also occurs in liquids and gases, but far less efficiently. In these states, molecules are spaced farther apart and move randomly. Energy transfers when molecules collide and through diffusion, but because the gaps between molecules are larger, collisions happen less frequently. Air, for example, is such a poor conductor that it’s used as insulation in double-pane windows and down jackets. The air itself barely moves heat at all; it’s convection (the bulk movement of the fluid) that typically dominates heat transfer in liquids and gases.
Conduction in Your Kitchen
Every time you cook on a stovetop, conduction is the first step. Heat moves from the burner into the pan, then from the pan’s inner surface into your food. The pan material makes a real difference. Relative thermal conductivities of common cookware materials, using stainless steel as a baseline of 1, are roughly: aluminum at 200, copper at 333, and glass (Pyrex) at 25.
This is why high-end cookware uses copper-clad bottoms on stainless steel pots. Even if a gas flame heats the bottom unevenly, copper spreads that heat across the entire surface so food cooks uniformly. Aluminum pans are a solid middle ground, conducting heat well at a lower cost. Glass and ceramic bakeware conduct heat poorly, which is actually useful for casseroles and slow baking, where you want gentle, even heating and less evaporation. Some brownie recipes even specify different baking times depending on whether you use a glass or metal pan.
Conduction in Electronics
Inside your computer, conduction is what keeps processors from overheating. A chip generates heat, and that heat must travel by conduction into a metal heat sink sitting on top of it. The problem is that even two flat metal surfaces have microscopic air gaps between them, and air conducts heat terribly. Thermal paste fills those gaps, creating a continuous conductive path between the chip and the heat sink. From there, a fan blows air across the heat sink’s fins to carry the heat away by convection, but the critical first transfer is pure conduction.
Electrical Conduction in Your Heart
In biology, conduction refers to how electrical signals travel through tissue. Your heart has a built-in conduction system: a network of specialized cells that generate and carry electrical impulses to make each chamber contract in the right order.
The signal starts at the sinoatrial (SA) node, a small cluster of cells in the upper right chamber. The SA node fires an electrical impulse that spreads across both upper chambers, causing them to contract and push blood downward. The signal then reaches the atrioventricular (AV) node, located near the center of the heart, which briefly delays the impulse. That delay gives the upper chambers time to finish emptying before the lower chambers fire. From the AV node, the signal travels down a bundle of nerve fibers running along the wall between the two lower chambers, then fans out through a network called the Purkinje fibers, which triggers the powerful contraction that sends blood to your lungs and body.
When any part of this conduction pathway malfunctions, the result is an arrhythmia, a heartbeat that’s too fast, too slow, or irregular.
Nerve Impulse Conduction
Your nerves also rely on conduction to send signals between your brain and body. An electrical impulse travels along a nerve fiber (axon) as charged particles flow in and out of the cell membrane. In unmyelinated nerves, this signal moves continuously along the entire length of the fiber, which is relatively slow.
Most nerves in your body speed things up with a fatty coating called myelin, which acts as electrical insulation. The myelin wraps around the axon in segments, leaving tiny exposed gaps called nodes of Ranvier. The electrical signal jumps from one gap to the next, skipping over the insulated sections entirely. This “saltatory conduction” dramatically increases signal speed. Healthy motor nerves in your arms conduct signals at 49 to 53 meters per second or faster, while sensory nerves typically conduct at 40 to 50 m/s. Damage to the myelin coating, as occurs in conditions like multiple sclerosis, slows or blocks these signals and can cause numbness, weakness, or loss of coordination.
Conduction Deep Inside the Earth
Conduction also operates on a planetary scale. At the boundary between Earth’s core and its mantle, roughly 2,900 kilometers below the surface, temperatures reach 2,000 to 4,000 Kelvin. Heat from the molten outer core transfers into the base of the mantle primarily by conduction, since the two layers don’t mix chemically. The minerals at this boundary conduct heat at roughly 8.5 to 12 W/mK under extreme pressure, far less than metals at the surface. This slow conduction rate controls how quickly the core cools and influences both plate tectonics above and the churning of liquid iron below that generates Earth’s magnetic field.