Temperature

Temperature, degree of hotness or coldness, as measured quantitatively by thermometers. The various scales used are arbitrary: the Fahrenheit scale was originally based on the values 0°F for an equal ice-salt mixture, 32°F for the freezing point of water, and 96°F for normal human body temperature. There are certain primary calibration points corresponding to the boiling, freezing, or melting points of particular substances, whose values are fixed by convention. The thermodynamic, or absolute, temperature scale, is not arbitrary; starting at absolute zero, at which there is no kinetic energy, and graduated in kelvins, it is defined with respect to an ideal reversible heat engine working on a Carnot cycle between two temperatures, T₁ and T₂. If Q₁ is the heat received at the higher temperature T₁, and Q₂, the heat lost at the lower temperature T₂, then T₁/T₂ is equal to Q₁/Q₂ Absolute temperature is independent of a body's mass or nature; it is thus only indirectly related to the heat content of the body. Heat always flows from a higher temperature to a lower. On the molecular scale, temperature may be defined in terms of the statistical distribution of the kinetic energy of the molecules.