Touch a metal spoon left in a pot of soup and you feel heat. That heat traveled through the spoon by conduction. Conduction is the transfer of heat through direct contact, from a hotter object to a cooler one. The atoms in the hot end vibrate faster and collide with neighboring atoms, passing energy along. In metals, free electrons also carry energy, which is why metals conduct heat so well.

Conduction happens in solids, liquids, and gases, but it is most effective in solids, where particles are packed closely together. The rate of conduction depends on the material. Copper conducts heat about 400 times better than water and about 10,000 times better than air. That is why a metal handle on a hot pan burns your hand, while a wooden one does not. It is also why a down jacket keeps you warm. The feathers trap air, and air is a poor conductor. Conduction is one of three ways heat moves, along with convection and radiation. It is the only one that requires direct contact.

Conduction facts

• Definition. Heat transfer through direct contact.
• Metals. Conduct heat well because of free electrons.
• Insulators. Conduct heat poorly, like wood and air.
• Rate. Depends on material, area, and temperature difference.

Conduction is not the same as convection. Conduction transfers heat through contact. Convection transfers heat through the movement of fluids.