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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Glossary of physics | 4/13 | https://en.wikipedia.org/wiki/Glossary_of_physics | reference | science, encyclopedia | 2026-05-05T07:51:11.278375+00:00 | kb-cron |
baryon A class of composite subatomic particle in the hadron family, such as a proton or a neutron, each of which is made of (usually) three quarks. Nearly all matter humans are likely to encounter is baryonic matter. Baryons are also considered fermions.
battery A combination of two or more electrical cells which produces electricity.
beam A structural element that is capable of withstanding a load primarily by resisting bending. Beams are traditionally descriptions of building or civil engineering structural elements, but smaller structures such as truck or automobile frames, machine frames, and other mechanical or structural systems contain beam structures that are designed and analyzed in a similar fashion.
bending Also known as flexure. The behavior of a slender structural element (e.g. a beam) which is subjected to an external load applied perpendicularly to a longitudinal axis of the element.
bending moment The reaction induced in a structural element when an external force or moment is applied to the element, causing the element to bend. The simplest structural element subjected to bending moments is the beam.
Bernoulli equation
Bernoulli's principle In fluid dynamics, a principle which states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy.
Bessel function A canonical solution y(x) of Friedrich Bessel's differential equation
x
2
d
2
y
d
x
2
+
x
d
y
d
x
+
(
x
2
−
α
2
)
y
=
0
{\displaystyle x^{2}{\frac {d^{2}y}{dx^{2}}}+x{\frac {dy}{dx}}+\left(x^{2}-\alpha ^{2}\right)y=0}
for an arbitrary complex number α, the order of the Bessel function. Although α and −α produce the same differential equation, it is conventional to define different Bessel functions for these two values in such a way that the Bessel functions are mostly smooth functions of α. The most important cases are when α is an integer or half-integer. Bessel functions for integer α are also known as cylinder functions or the cylindrical harmonics because they appear in the solution to Laplace's equation in cylindrical coordinates. Spherical Bessel functions with half-integer α are obtained when the Helmholtz equation is solved in spherical coordinates.
beta decay Also β-decay. In nuclear physics, a type of radioactive decay in which a beta particle is emitted from an atomic nucleus, transforming the original nuclide to its isobar.
beta particle A high-energy, high-speed electron or positron emitted by certain types of radioactive atomic nuclei.
Big Bang The prevailing cosmological model that describes the early development of the Universe.
binding energy The mechanical energy required to disassemble a whole into separate parts. A bound system typically has a lower potential energy than the sum of its constituent parts.
binomial random variable
biocatalysis
biophysics An interdisciplinary science using methods of and theories from physics to study biological systems.
black body A hypothetical idealized physical body that completely absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. Perfect black bodies are imagined as substitutes for actual physical bodies in many theoretical discussions of thermodynamics, and the construction of nearly perfect black bodies in the real world remains a topic of interest for materials engineers. Contrast white body.
black-body radiation The type of electromagnetic radiation within or surrounding a body in thermodynamic equilibrium with its environment, or emitted by a black body (an opaque and non-reflective body) held at constant, uniform temperature. The radiation has a specific spectrum and intensity that depends only on the temperature of the body.
block and tackle A system of two or more pulleys with a rope or cable threaded between them, usually used to lift or pull heavy loads.
Bohr model
boiling point The temperature at which a liquid undergoes a phase change into a gas; the vapour pressure of liquid and gas are equal at this temperature.
boiling point elevation The phenomenon by which the boiling point of a liquid (a solvent) increases when another compound is added, meaning that the resulting solution has a higher boiling point than the pure solvent. This happens whenever a non-volatile solute, such as a salt, is added to a pure solvent, such as water. The boiling point can be measured accurately using an ebullioscope.
Boltzmann constant A physical constant relating the average kinetic energy of the particles in a gas with the temperature of the gas. It is the gas constant R divided by the Avogadro constant NA.
Bose–Einstein condensate (BEC)
boson A type of subatomic particle that behaves according to Bose–Einstein statistics and possesses integer spin. Bosons include elementary particles such as photons, gluons, W and Z bosons, Higgs bosons, and the hypothetical graviton, as well as certain composite particles such as mesons and stable nuclides of even mass number. Bosons constitute one of two main classes of particles, the other being fermions. Unlike fermions, there is no limit to the number of bosons that can occupy the same quantum state.
Boyle's law A chemical law which states that the volume of a given mass of a gas at constant temperature is inversely proportional to its pressure.
Bra–ket notation
Bragg's law
bremsstrahlung Radiation emitted by the acceleration of unbound charged particles.
Brewster's angle Also polarization angle. The angle of incidence at which light with a particular polarization is completely transmitted through a transparent dielectric surface, with no reflection. When unpolarized light is incident at this angle, the light that is reflected is consequently perfectly polarized.
british thermal unit (btu) An Imperial unit of energy defined as the amount of energy needed to heat one pound of water by one degree Fahrenheit; 1 btu is equal to about 1,055 joules. In scientific contexts the btu has largely been replaced by the SI unit of energy, the joule.
brittleness The tendency of a material to break without significant plastic deformation when subjected to stress. Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Breaking is often accompanied by a snapping sound.