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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Glossary of physics | 3/13 | https://en.wikipedia.org/wiki/Glossary_of_physics | reference | science, encyclopedia | 2026-05-05T07:51:11.278375+00:00 | kb-cron |
anode The electrode through which a conventional electric current flows into a polarized electrical device; the direction of current flow is, by convention, opposite to the direction of electron flow, and so electrons flow out of the anode. In a galvanic cell, the anode is the negative terminal or pole which emits electrons toward the external part of an electrical circuit. However, in an electrolytic cell, the anode is the wire or plate having excess positive charge, so named because negatively charged anions tend to move towards it. Contrast cathode.
anti-gravity A theory of creating a place or object that is free from the force of gravity. It does not refer to the lack of weight under gravity experienced in free fall or orbit, or to balancing the force of gravity with some other force, such as electromagnetism or aerodynamic lift.
antimatter
antineutron The antiparticle of the neutron, with symbol n. It differs from the neutron only in that some of its properties have equal magnitude but opposite sign. It has the same mass as the neutron, and no net electric charge, but has opposite baryon number (+1 for the neutron, −1 for the antineutron). This is because the antineutron is composed of antiquarks, while neutrons are composed of ordinary quarks. The antineutron consists of one up antiquark and two down antiquarks.
antiparticle In particle physics, every type of particle has an associated antiparticle with the same mass but with opposite physical charges such as electric charge. For example, the antiparticle of the electron is the antielectron (often referred to as the positron). While the electron has a negative electric charge, the positron has a positive electric charge, and is produced naturally in certain types of radioactive decay. Some particles, such as the photon, are their own antiparticle. Otherwise, for each pair of antiparticle partners, one is designated as "normal" matter (the kind comprising all matter with which humans usually interact), and the other (usually given the prefix "anti-") as antimatter.
antiproton The antiparticle of the proton, having the same mass but a negative electric charge and an oppositely directed magnetic moment.
antiquark For every quark flavor there is a corresponding type of antiparticle known as an antiquark that differs from the quark only in that some of its properties (such as the electric charge) have equal magnitude but opposite sign.
arc length
Archimedes' principle A physical principle which states that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces and acts in the upward direction at the center of mass of the displaced fluid.
area moment of inertia
astrophysics The branch of astronomy that deals with the physics of the Universe, especially with the compositional nature of celestial bodies rather than their positions or motions in space.
attenuation coefficient The measure of how much the incident energy beam (e.g. ultrasound or x-rays) is weakened by the material it is passing through.
atom A basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons.
atomic line filter
atomic mass
atomic mass unit A deprecated term, usually referring to the unified atomic mass unit, a carbon-based standard, but historically referring to an oxygen-based standard.
atomic number (Z) The number of protons found in the nucleus of an atom. It is most often used to classify elements within the periodic table.
atomic orbital
atomic packing factor
atomic physics A branch of physics that studies atoms as isolated systems of electrons and an atomic nucleus. Compare nuclear physics.
atomic structure
atomic weight (A) The sum total of protons (or electrons) and neutrons within an atom.
audio frequency Also known as audible frequency (AF). A periodic vibration whose frequency is in the band audible to the average human, i.e. within the standard human hearing range (generally accepted as 20 to 20,000 Hz). It is the property of sound that most determines pitch.
Avogadro constant The ratio of the number of constituent particles in a substance, usually atoms or molecules, to the amount of substance, of which the SI unit is the mole. It is defined as exactly 6.02214076×1023 mol−1.
Avogadro number The total number of individual particles, molecules, or other indivisible units in one mole of a substance, or exactly 6.02214076×1023 by definition.
Avogadro's law A physical law which states that volumes of gases which are equal to each other at the same temperature and pressure will contain equal numbers of molecules.
axion A hypothetical subatomic particle postulated to account for the rarity of processes that break charge-parity symmetry. It is very light, electrically neutral, and pseudoscalar.
azimuthal quantum number A quantum number for an atomic orbital that determines its orbital angular momentum and describes the shape of the orbital.
== B ==
Babinet's principle A theorem concerning diffraction which states that the diffraction pattern from an opaque body is identical to that from a hole of the same size and shape except for the overall forward beam intensity.
background radiation The ubiquitous ionizing radiation to which the general human population is exposed.
balanced forces When all the forces acting upon an object balance each other, the object will be at equilibrium; it will not accelerate.
ballistics
Balmer series Also Balmer lines. In atomic physics, one of a set of six named series describing the spectral line emissions of the hydrogen atom. The Balmer series is calculated using the Balmer formula, an empirical equation discovered by Johann Balmer in 1885.
barometer A scientific instrument used in meteorology to measure atmospheric pressure. Pressure tendency can forecast short-term changes in the weather.