Effects of Temperature
- Physical properties of materials are influenced by temperature, including phase, density, solubility, vapor pressure, electrical conductivity, hardness, wear resistance, thermal conductivity, corrosion resistance, and strength.
- Chemical reactions are affected by temperature, including the rate and extent of reactions.
- Thermal radiation emitted from an object's surface is dependent on temperature.
- Air temperature has an impact on all living organisms.
- The speed of sound in a gas is proportional to the square root of the absolute temperature.

Temperature Scales
- The Celsius scale (°C) is commonly used worldwide and is based on the freezing and boiling points of water at sea level.
- The Kelvin scale (K) is an absolute scale used in scientific applications, with its zero point at absolute zero.
- The Fahrenheit scale (°F) is primarily used in the United States, with water freezing at 32°F and boiling at 212°F.

Absolute Zero and Absolute Scales
- Absolute zero is the lowest possible temperature, where no energy can be extracted as heat.
- Matter at absolute zero contains no macroscopic thermal energy but still possesses quantum-mechanical zero-point energy.
- Absolute zero is defined as 0K, which is equal to -273.15°C or -459.67°F.
- The Kelvin scale is an absolute temperature scale that is independent of specific thermometric substances and thermometer mechanisms.
- The temperature of a body in thermodynamic equilibrium is always positive relative to absolute zero.
- The Kelvin scale is widely used in science and technology.
- Lord Kelvin also developed a thermodynamic temperature scale that relates to macroscopic thermodynamic concepts, including entropy.
- This scale has a reference temperature at the triple point of water.

Empirically based thermometers
- Length of a column of mercury in a glass-walled capillary tube is dependent on temperature.
- Mercury-in-glass thermometer is valid only within convenient temperature ranges.
- Some materials, like water, contract with temperature increase over a specific range.
- Materials near their phase-change temperatures are not useful as thermometric materials.
- Empirically based thermometers can be re-calibrated using theoretical physical reasoning.

Measurement and Theory of Temperature
- The spectrum of black-body radiation provides an accurate temperature measurement.
- Wiens displacement law relates the frequency of maximum spectral radiance to temperature.
- The spectrum of noise-power produced by an electrical resistor can measure temperature.
- Johnson noise is directly proportional to temperature, resistance, and noise bandwidth.
- Accurate temperature measurement can be achieved using known values of resistance.
- Classical mechanics explains macroscopic phenomena through microscopic particles.
- The equipartition theorem of kinetic theory states that each degree of freedom of a particle has an average kinetic energy of /2.
- The speed of sound in a gas can be calculated from the molecular character, temperature, pressure, and Boltzmann constant.
- The average kinetic energy of microscopic particles can be measured by allowing them to escape from the system through a small hole.
- Temperature is a principal quantity in the study of thermodynamics.
- Temperature is an intensive variable in thermodynamics.
- Real-world bodies are often not in thermodynamic equilibrium and not homogeneous.
- Thermodynamics has conjugate variables such as pressure, volume, temperature, entropy, chemical potential, and particle number.
- Hotness means that suitably given empirical thermometers with numerical scale readings will agree on which body is hotter or if they have the same temperature.
- The relation between numerical scale readings of thermometers must be strictly monotonic.

Temperature (Wikipedia)

This article is about the physical quantity. For other uses, see Temperature (disambiguation).

Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measured with a thermometer. It reflects the kinetic energy of the vibrating and colliding atoms making up a substance.

Temperature
Thermal vibration of a segment of protein alpha helix. Its amplitude increases with temperature
Common symbols	T
SI unit	K
Other units	°C, °F, °R, °Rø, °Ré, °N, °D, °L, °W
Intensive?	Yes
Derivations from other quantities	${\displaystyle {\frac {pV}{nR}}}$, ${\displaystyle {\frac {dq_{\text{rev}}}{dS}}}$
Dimension	${\displaystyle {\mathsf {\Theta }}}$

Thermometers are calibrated in various temperature scales that historically have relied on various reference points and thermometric substances for definition. The most common scales are the Celsius scale with the unit symbol °C (formerly called centigrade), the Fahrenheit scale (°F), and the Kelvin scale (K), the latter being used predominantly for scientific purposes. The kelvin is one of the seven base units in the International System of Units (SI).

Absolute zero, i.e., zero kelvin or −273.15 °C, is the lowest point in the thermodynamic temperature scale. Experimentally, it can be approached very closely but not actually reached, as recognized in the third law of thermodynamics. It would be impossible to extract energy as heat from a body at that temperature.

Temperature is important in all fields of natural science, including physics, chemistry, Earth science, astronomy, medicine, biology, ecology, material science, metallurgy, mechanical engineering and geography as well as most aspects of daily life.