Temperature (sometimes called thermodynamic temperature) is a measure of the average kinetic energy of the particles in a system. Adding heat to a system causes its temperature to rise. While there is no maximum theoretically reachable temperature, there is a minimum temperature, known as absolute zero, at which all molecular motion stops. Temperatures are commonly measured in the Kelvin or Celsius scales, with Fahrenheit still in common use in the Unites States.

Temperature is an important quantity in thermodynamics and kinetic theory, appearing explicitly for example in the ideal gas law

(1)

where P is the pressure, V is the volume, n is the number of moles, and R is the universal gas constant. Thermodynamically, temperature is given by the Maxwell relation

(2)

where E is the energy, S is the entropy, and the partial derivative is taken at constant volume. The quantity , where k is Boltzmann's constant, arising frequently in thermodynamics is defined as

(3)

a quantity sometimes known as thermodynamic beta.

Absolute Temperature, Absolute Zero, Blackbody Temperature, Debye Temperature, Fahrenheit, Heat, Kelvin, Potential Temperature, Rankine, Temperature Wave