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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Glossary of physics | 1/13 | https://en.wikipedia.org/wiki/Glossary_of_physics | reference | science, encyclopedia | 2026-05-05T07:51:11.278375+00:00 | kb-cron |
This glossary of physics is a list of definitions of terms and concepts relevant to physics, its sub-disciplines, and related fields, including mechanics, materials science, nuclear physics, particle physics, and thermodynamics. For more inclusive glossaries concerning related fields of science and technology, see Glossary of chemistry terms, Glossary of astronomy, Glossary of areas of mathematics, and Glossary of engineering.
== A ==
ab initio A mathematical model which seeks to describe atomic nuclei by solving the non-relativistic Schrödinger equation for all constituent nucleons and the forces that exist between them. Such methods yield precise results for very light nuclei but become more approximate for heavier nuclei.
Abbe number Also called the V-number or constringence. In optics and lens design, a measure of a transparent material's dispersion (a variation of refractive index versus wavelength). High values of V indicate low dispersion.
absolute electrode potential In electrochemistry, the electrode potential of a metal measured with respect to a universal reference system (without any additional metal–solution interface).
absolute humidity The ratio of the water vapor in a sample of air to the volume of the sample.
absolute motion
absolute pressure Is zero-referenced against a perfect vacuum, using an absolute scale, so it is equal to gauge pressure plus atmospheric pressure.
absolute scale Any system of measurement that begins at a minimum, or zero point, and progresses in only one direction. The zero point of an absolute scale is a natural minimum, leaving only one direction in which to progress, whereas an arbitrary or "relative" scale begins at some point selected by a person and can progress in both directions.
absolute zero The theoretical lowest possible temperature, understood by international agreement as equivalent to 0 Kelvin or −273.15 °C (−459.67 °F). More formally, it is the theoretical lower limit of the thermodynamic temperature scale, at which enthalpy and entropy of a cooled ideal gas reach their minimum values and the fundamental particles of nature have minimal vibrational motion.
absorption spectroscopy Any of various spectroscopic techniques that measure the absorption of electromagnetic radiation due to its interaction with a sample. The sample absorbs energy, i.e. photons, from the radiating field. The intensity of the absorption varies as a function of frequency or wavelength, and this variation is the absorption spectrum. Absorption spectroscopy is performed across the electromagnetic spectrum.
absorptivity
accelerating expansion of the universe The observation that the expansion of the universe is such that the velocity at which a distant galaxy is receding from the observer is continuously increasing with time.
acceleration The rate at which the velocity of a body changes with time, also the rate of change of the rate at which the position of a body changes with time.
acceleration due to gravity The acceleration on an object caused by the force of gravitation.
accelerometer An instrument used to measure the proper acceleration of a body irrespective of other forces.
acoustics The branch of physics dealing with the production, transmission, and effects of sound.
adhesion adhesion is what makes things stick together. It's the force that allows tape to stick to a surface or glue to hold two objects together. Contrast cohesion.
adiabatic cooling
adiabatic heating
adiabatic process A process which occurs without transfer of heat or mass of substances between a thermodynamic system and its surroundings. In an adiabatic process, energy is transferred to the surroundings only as work. The adiabatic process provides a rigorous conceptual basis for the theory used to expound the first law of thermodynamics, and as such it is a key concept in thermodynamics.
aerodynamics The study of the motion of air, particularly its interaction with a solid object, such as an airplane wing. It is a sub-field of fluid dynamics and gas dynamics, and many aspects of aerodynamics theory are common to these fields.
afocal system An optical system that produces no net convergence or divergence of the beam, i.e. has an infinite effective focal length. This type of system can be created with a pair of optical elements where the distance between the elements is equal to the sum of each element's focal length (
d
=
f
1
+
f
2
{\displaystyle d=f_{1}+f_{2}}
).
air mass
- In meteorology, a volume of air that is defined by its temperature and water vapor content. Air masses may cover many hundreds or thousands of square miles and generally adapt to the characteristics of the surface below them. They are often classified according to their latitude and their source regions.
- In astronomy, the "amount of air that one is looking through" when observing a star or other celestial source from a vantage point that is within Earth's atmosphere. It is formulated as the integral of air density along the light ray.
air mass coefficient Defines the direct optical path length through the Earth's atmosphere, expressed as a ratio relative to the path length vertically upwards, i.e. at the zenith. The air mass coefficient can be used to help characterize the solar spectrum after solar radiation has traveled through the atmosphere.
albedo The fraction of the total light incident on a reflecting surface, especially a celestial body, which is reflected back in all directions.
alloy A chemical mixture of a metal with one or more other metals or other elements.
alpha decay Also α-decay. A type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms or "decays" into a different atomic nucleus, with a mass number that is reduced by four and an atomic number that is reduced by two.
alpha particle (α) Also symbolized by α2+, He2+, and 42He2+. A type of subatomic particle consisting of two protons and two neutrons bound together into a particle identical to the nucleus of a helium-4 ion. It has a charge of +2 e and a mass of 4 u. Alpha particles are classically produced in the process of radioactive alpha decay, but may also be produced in other ways and given the same name.