Which mechanism describes heat transfer to another body or within a body by direct contact?

• A. Conduction
• B. Convection
• C. Radiation
• D. Evaporation

Answer: (A)

Conduction is heat transfer by direct contact between bodies or within a body. Energy moves from regions at a higher temperature to regions at a lower temperature through particle interactions and, in metals, free electrons passing energy along. The rate of conduction depends on the temperature difference, the area of contact, and how well the material conducts heat (its thermal conductivity). Inside an object, heat travels from the hotter part to the cooler part, which is why a metal spoon left in hot soup becomes warm all the way to the handle. Materials that conduct well (metals) transfer heat quickly, while insulators (like wood or plastic) slow the transfer. Other ways heat moves—convection, which needs moving fluids; radiation, which travels as electromagnetic waves; and evaporation, a phase-change process—do not describe direct contact transfer.