temperatureas

Temperature is a physical quantity that expresses the degree of hotness or coldness of a system. In thermodynamics, it governs the direction of heat transfer: heat flows from bodies at higher temperature to those at lower temperature until thermal equilibrium is reached.

Common scales are Celsius, Fahrenheit, and Kelvin. Celsius and Fahrenheit are convenient for everyday use; Kelvin is the SI base unit for thermodynamic temperature, with 0 K defined as absolute zero, the point at which molecular motion is minimal. The relationships between scales are: K = C + 273.15, and F = (9/5)C + 32.

Measurement is performed with thermometers and sensors. Traditional liquid-in-glass thermometers use a liquid expansion; modern digital probes use resistance temperature detectors (RTDs), thermistors, or thermocouples; infrared sensors infer surface temperature without contact.

Thermodynamics links temperature to energy. The zeroth law defines temperature through thermal equilibrium; in statistical mechanics, temperature relates to the distribution of microscopic states (Boltzmann factor) and is a parameter in the ideal gas law: PV = nRT, where R is the gas constant.

Applications span meteorology, engineering, medicine, and daily life, including climate modeling, industrial process control, cryogenics, and cooking.