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Temperature
Temperature is a measure of the average energy of motion, or kinetic energy, of particles in matter. When particles of matter, whether in solids, liquids, gases, or elementary plasmas, move faster or have greater mass, they carry more kinetic energy, and the material appears warmer than a material with slower or less massive particles. Kinetic energy, a concept of mechanics, is the product of mass and the square of a particle's velocity. In the context of thermodynamics, it is also referred to as thermal energyand the transfer of thermal energy is commonly referred to as heat. Heat always flows from regions of higher temperature to regions of lower temperature.
English language speakers refer to an object of low temperature as being cold, and associate various degrees of higher temperature to terms such as luke-warm, warm, hot, and others.
Historically, two equivalent concepts of temperature have developed, the thermodynamic description and a microscopic explanation based on statistical physics. Since thermodynamics deals entirely with macroscopic measurements, the thermodynamic definition of temperature, first stated by Lord Kelvin, is stated entirely in empirical, measurable variables. Statistical physics provides a deeper understanding of thermodynamics by describing matter as a collection of a large number of particles, and derives thermodynamic (i.e. macroscopic) parameters as statistical averages of the microscopic parameters of the particles.
In statistical physics, it is shown that the thermodynamic definition of temperature can be interpreted as a measure of the average energy in each degree of freedom of the particles in the thermodynamic system. Because its temperature is seen as a statistical property, a system must contain a large number of particles for temperature to have a useful