16.2: Heat and Thermodynamics

Conduction Conduction occurs within a material or between materials that are touching. In conduction, collisions between particles transfer thermal energy, without any overall transfer of matter.

Metals are good thermal conductors. Air is a very good thermal insulator. Wool garments and plastic foam cups use trapped air to slow down conduction.

Convection Convection is the transfer of thermal energy when particles of a fluid move from one place to another. Convection currents are important in many natural cycles, such as ocean currents, weather systems, and movements of hot rock in Earth’s interior.

Radiation Radiation is the transfer of energy by waves moving through space. All objects radiate energy. As an object’s temperature increases, the rate at which it radiates energy increases. The sun warms you by radiation on a clear day.

16.3: Using Heat

Heat Engines There are two main types: external combustion engine—an engine that burns fuel outside the engine. steam engine internal combustion engine—heat engine in which the fuel burns inside the engine. Most cars have a four-stroke internal combustion engine

Heat Pump A heat pump is a device that reverses the normal flow of thermal energy. Heat pumps must do work on a refrigerant in order to reverse the normal flow of thermal energy. Examples: refrigerator—it transfers thermal energy from the cold food compartment to the warm room. Air conditioner