Thermodynamic temperature and exchange energy in collisions. "Figure 1" below shows translational motion in gases; "" below shows translational motion in solids. Thermodynamic temperature's null point, absolute zero, is the temperature at which the particle constituents of matter are as close as possible to complete rest; that is, they have minimal motion, retaining only quantum mechanical motion. Zero kinetic energy remains in a substance at absolute zero (see "Thermal energy at absolute zero", below). Throughout the scientific world where measurements are made in SI units, thermodynamic temperature is measured in kelvins (symbol: K). Many engineering fields in the U.S. however, measure thermodynamic
Scale of temperature below as M. Assume the set M has the cardinality of c, then one can construct an injective function ƒ: M → R , by which every thermal system will have a number associated with it such that when and only when two thermal systems have the same such value, they will be in thermal equilibrium. This is clearly the property of temperature, and the specific way of assigning numerical values as temperature is called a "scale of temperature". In practical terms, a temperature scale is always based on usually a single physical property of a simple thermodynamic system, called