Thermal Physics

Conduction The transfer of thermal energy through a material without bulk motion of the material itself. Heat flows from the hotter to the colder region via molecular collisions and free electron movement. In solids, the rate depends on the material’s thermal conductivity k . For example, a metal rod feels cold at one end when the other end is heated because conduction carries energy rapidly through the metal. Convection The transfer of heat by the macroscopic movement of a fluid (liquid or gas) due to density differences. When a fluid is heated, it expands, becomes less dense, and rises; cooler fluid sinks to take its place, creating a convection current. A common example is a radiator heating a room: warm air rises, circulates, and transfers heat to the surroundings.