          # Temperature

• temperature two thermometers showing temperature in celsius and fahrenheit.
common symbols
t
si unitk
other units
°c, °f, °r
intensive?yes
derivations from
other quantities , dimensionΘ thermal vibration of a segment of protein alpha helix: the amplitude of the vibrations increases with temperature. average daily variation in human body temperature

temperature is a physical property of matter that quantitatively expresses hot and cold. it is the manifestation of thermal energy, present in all matter, which is the source of the occurrence of heat, a flow of energy, when a body is in contact with another that is colder.

temperature is measured with a thermometer. thermometers are calibrated in various temperature scales that historically have used various reference points and thermometric substances for definition. the most common scales are the celsius scale (formerly called centigrade), denoted °c, the fahrenheit scale (denoted °f), and the kelvin scale (denoted k), the latter of which is predominantly used for scientific purposes by conventions of the international system of units (si).

when a body has no macroscopic chemical reactions or flows of matter or energy, it is said to be in its own internal state of thermodynamic equilibrium. its temperature is uniform in space and unchanging in time. the lowest theoretical temperature is absolute zero, at which no more thermal energy can be extracted from a body. experimentally, it can only be approached very closely, but not reached, which is recognized in the third law of thermodynamics.

temperature is important in all fields of natural science, including physics, chemistry, earth science, medicine, and biology, as well as most aspects of daily life.

• effects
• scales
• classification of scales
• kinetic theory approach
• thermodynamic approach
• basic theory
• heat capacity
• measurement
• theoretical foundation
• examples
## This article is about the physical property. For other uses, see Temperature (disambiguation). Temperature Two thermometers showing temperature in Celsius and Fahrenheit.Common symbolsTSI unitKOther units°C, °F, °RIntensive?yesDerivations fromother quantities${\frac {pV}{nR}}$ , ${\frac {dq_{\text{rev}}}{dS}}$ DimensionΘ Thermal vibration of a segment of protein alpha helix: The amplitude of the vibrations increases with temperature. Thermodynamics The classical Carnot heat engine Branches Classical Statistical Chemical Quantum thermodynamics Equilibrium / Non-equilibrium Laws Zeroth First Second Third Systems State Equation of state Ideal gas Real gas State of matter Equilibrium Control volume Instruments Processes Isobaric Isochoric Isothermal Adiabatic Isentropic Isenthalpic Quasistatic Polytropic Free expansion Reversibility Irreversibility Endoreversibility Cycles Heat engines Heat pumps Thermal efficiency System propertiesNote: Conjugate variables in italics Property diagrams Intensive and extensive properties Process functions Work Heat Functions of state Temperature / Entropy (introduction) Pressure / Volume Chemical potential / Particle number Vapor quality Reduced properties Material properties Property databases Specific heat capacity  $c=$ $T$ $\partial S$ $N$ $\partial T$ Compressibility  $\beta =-$ $1$ $\partial V$ $V$ $\partial p$ Thermal expansion  $\alpha =$ $1$ $\partial V$ $V$ $\partial T$ Equations Carnot's theorem Clausius theorem Fundamental relation Ideal gas law Maxwell relations Onsager reciprocal relations Bridgman's equations Table of thermodynamic equations Potentials Free energy Free entropy Internal energy$U(S,V)$ Enthalpy$H(S,p)=U+pV$ Helmholtz free energy$A(T,V)=U-TS$ Gibbs free energy$G(T,p)=H-TS$ HistoryCulture History General Entropy Gas laws "Perpetual motion" machines Philosophy Entropy and time Entropy and life Brownian ratchet Maxwell's demon Heat death paradox Loschmidt's paradox Synergetics Theories Caloric theory Theory of heat ("living force") Mechanical equivalent of heat Motive power Key publications "An Experimental EnquiryConcerning ... Heat" "On the Equilibrium ofHeterogeneous Substances" "Reflections on theMotive Power of Fire" Timelines Thermodynamics Heat engines ArtEducation Maxwell's thermodynamic surface Entropy as energy dispersal Scientists Bernoulli Boltzmann Carnot Clapeyron Clausius Carathéodory Duhem Gibbs von Helmholtz Joule Maxwell von Mayer Onsager Rankine Smeaton Stahl Thompson Thomson van der Waals Waterston Book Categoryvt Average daily variation in human body temperature Temperature is a physical property of matter that quantitatively expresses hot and cold. It is the manifestation of thermal energy, present in all matter, which is the source of the occurrence of heat, a flow of energy, when a body is in contact with another that is colder. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have used various reference points and thermometric substances for definition. The most common scales are the Celsius scale (formerly called centigrade), denoted °C, the Fahrenheit scale (denoted °F), and the Kelvin scale (denoted K), the latter of which is predominantly used for scientific purposes by conventions of the International System of Units (SI). When a body has no macroscopic chemical reactions or flows of matter or energy, it is said to be in its own internal state of thermodynamic equilibrium. Its temperature is uniform in space and unchanging in time. The lowest theoretical temperature is absolute zero, at which no more thermal energy can be extracted from a body. Experimentally, it can only be approached very closely, but not reached, which is recognized in the third law of thermodynamics. Temperature is important in all fields of natural science, including physics, chemistry, Earth science, medicine, and biology, as well as most aspects of daily life. Contents 1 Effects 2 Scales 2.1 Commonly used scales 2.2 Absolute zero 2.3 Absolute scales 2.4 International Kelvin scale 2.5 Statistical mechanical versus thermodynamic temperature scales 3 Classification of scales 3.1 Empirical scales 3.2 Theoretical scales 3.2.1 Microscopic statistical mechanical scale 3.2.2 Macroscopic thermodynamic scale 3.2.3 Ideal gas 4 Kinetic theory approach 5 Thermodynamic approach 5.1 Intensive variability 5.2 Local thermodynamic equilibrium 6 Basic theory 6.1 Bodies in thermodynamic equilibrium 6.2 Bodies in a steady state but not in thermodynamic equilibrium 6.3 Bodies not in a steady state 6.4 Thermodynamic equilibrium axiomatics 7 Heat capacity 8 Measurement 8.1 Units 8.1.1 Conversion 8.1.2 Plasma physics 9 Theoretical foundation 9.1 Kinetic theory of gases 9.2 Zeroth law of thermodynamics 9.3 Second law of thermodynamics 9.4 Definition from statistical mechanics 9.5 Generalized temperature from single-particle statistics 9.6 Negative temperature 10 Examples 11 See also 12 Notes and references 12.1 Bibliography of cited references 13 Further reading 14 External links  