An Etymological Dictionary of Astronomy and Astrophysics
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The total energy of a → closed system is constant. This means that energy can be changed from one form to another, or transferred from one system to another, but it cannot be created or destroyed. A mathematical formulation of the first law is: δQ = δU + δW, where δQ is the heat transferred to the system, δU the change in internal energy (resulting in a rise or fall of temperature), and δW is the work done by the system.

→ first; → law; → thermodynamics.

1) Heat cannot be transferred from a colder to a hotter body without some other effect, i.e. without → work being done. Expressed in terms of → entropy: the entropy of an → isolated system tends toward a maximum and its available energy tends toward a minimum.
2) In language of → statistical physics, an isolated physical system will tend toward an equilibrium → macrostate with as large a total → entropy as possible, because then the number of → microstates is the largest. See also → Kelvin's postulate, → Clausius's postulate.

→ second; → law; → thermodynamics.

Same as → statistical mechanics.

→ statistical; → thermodynamics.

A branch of physics concerned with the relations between heat and other forms of energy and how these affect temperature, pressure, volume, mechanical action, and work.

→ thermo-; → dynamics, coined by the Scottish physicist William Thomson (Lord Kelvin, 1824-1907), in 1849.

The → entropy of an idealized state of maximum order is zero at the temperature of → absolute zero. Another version of this law: As a system approaches absolute zero, all processes cease and the entropy of the system approaches a minimum value.

→ third; → law; → thermodynamics.

Two objects that are in → thermal equilibrium with a third object will be in thermal equilibrium with each other.

→ zero; → law; → thermodynamics.