JonyC/ScienceGlossary · Datasets at Hugging Face

term stringlengths 1 63 ⌀	category stringclasses 15 values	label int64 0 1	definition stringlengths 5 3.18k ⌀
ab initio	Physics	1	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	Physics	1	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	Physics	1	In electrochemistry, the electrode potential of a metal measured with respect to a universal reference system (without any additional metal–solution interface).
absolute humidity	Physics	1	The ratio of the water vapor in a sample of air to the volume of the sample.
absolute pressure	Physics	1	Is zero-referenced against a perfect vacuum, using an absolute scale, so it is equal to gauge pressure plus atmospheric pressure.
absolute scale	Physics	1	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	Physics	1	The lowest possible temperature, equivalent to -273.15 °C. Used as the zero point of the Kelvin temperature scale.
absorption spectroscopy	Physics	1	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.
accelerating expansion of the universe	Physics	1	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	Physics	1	The rate at which an object speeds up, slows down or changes direction.
acceleration due to gravity	Physics	1	The acceleration on an object caused by the force of gravitation.
accelerometer	Physics	1	A device to measure acceleration (the rate at which an object’s velocity changes).
acoustics	Physics	1	The branch of physics dealing with the production, transmission, and effects of sound.
adhesion	Physics	1	A binding force that allows unlike particles or surfaces to cling to one another.
adiabatic process	Physics	1	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	Physics	1	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	Physics	1	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 d=f_{1}+f_{2}} ).
air mass	Physics	1	1. 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.
air mass coefficient	Physics	1	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	Physics	1	The fraction of the total light incident on a reflecting surface, especially a celestial body, which is reflected back in all directions.
alloy	Physics	1	A chemical mixture of a metal with one or more other metals or other elements.
alpha decay	Physics	1	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	Physics	1	High-energy helium nucleus emitted during certain nuclear decay processes.
α	Physics	1	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.
alternating current	Physics	1	A form of electric current in which the movement of electric charge periodically reverses direction. Contrast direct current.
ac	Physics	1	A form of electric current in which the movement of electric charge periodically reverses direction. Contrast direct current.
ammeter	Physics	1	An instrument that is used to measure electric current.
amorphous solid	Physics	1	A type of solid which does not have a definite geometric shape.
ampere	Physics	1	The SI base unit of electric current, defined as one coulomb of electric charge per second.
a	Physics	1	The sum total of protons (or electrons) and neutrons within an atom.
amplifier	Physics	1	An electronic device that can increase the power of a signal (a time-varying voltage or current). It is a two-port electronic circuit that uses electric power from a power supply to increase the amplitude of a signal applied to its input terminals, producing a proportionally greater amplitude signal at its output. The amount of amplification provided by an amplifier is measured by its gain: the ratio of output voltage, current, or power to input. An amplifier is a circuit that has a power gain greater than one.
amplitude	Physics	1	The maximum displacement from the equilibrium on an energy wave (i.e. the size of the wave).
angle of incidence	Physics	1	The angle between a light ray incident on a flat surface and an imaginary line (called the normal) perpendicular to the surface at the point of incidence.
angle of reflection	Physics	1	The angle between the reflected ray moving away from a flat surface and an imaginary line (called the normal) perpendicular to the surface at the point of reflection.
ångström	Physics	1	A unit of length primarily used to measure subatomic particles that is equal to 10−10 metres (one ten-billionth of a metre) or 0.1 nanometres.
å	Physics	1	A unit of length primarily used to measure subatomic particles that is equal to 10−10 metres (one ten-billionth of a metre) or 0.1 nanometres.
angular acceleration	Physics	1	The time rate of change of angular velocity. In three dimensions, it is a pseudovector. In SI units, it is measured in radians per second squared (rad/s2), and is usually denoted by the Greek letter alpha (α). Just like angular velocity, there are two types of angular acceleration: spin angular acceleration and orbital angular acceleration, representing the time rate of change of spin angular velocity and orbital angular velocity, respectively. Unlike linear acceleration, angular acceleration need not be caused by a net external torque. For example, a figure skater can speed up her rotation (thereby obtaining an angular acceleration) simply by contracting her arms inwards, which involves no external torque.
angular displacement	Physics	1	The angle (in radians, degrees, or revolutions) through which a point revolving around a centre or line has been rotated in a specified sense about a specified axis.
angular frequency	Physics	1	A scalar measure of rotation rate. It refers to the angular displacement per unit time (e.g. in rotation) or the rate of change of the phase of a sinusoidal waveform (e.g. in oscillations and waves), or as the rate of change of the argument of the sine function. Angular frequency (or angular speed) is the magnitude of the vector quantity that is angular velocity. The term angular frequency vector ω → {\vec {\omega }}} is sometimes used as a synonym for the vector quantity angular velocity. One revolution is equal to 2π radians, hence ω = 2 π T = 2 π f , \omega ={{2\pi } \over T}={2\pi f},} where: ω is the angular frequency or angular speed (measured in radians per second), T is the period (measured in seconds), f is the ordinary frequency (measured in hertz) (sometimes symbolised with ν).
angular momentum	Physics	1	The rotational equivalent of linear momentum. It is an important quantity in physics because it is a conserved quantity–that is, the total angular momentum of a closed system remains constant.
angular velocity	Physics	1	How fast an object rotates or revolves relative to another point, i.e. how fast the angular position or orientation of an object changes with time. There are two types of angular velocity: orbital angular velocity and spin angular velocity. Spin angular velocity refers to how fast a rigid body rotates with respect to its centre of rotation. Orbital angular velocity refers to how fast a rigid body's centre of rotation revolves about a fixed origin, i.e. the time rate of change of its angular position relative to the origin. In general, angular velocity is measured in angle per unit time, e.g. radians per second. The SI unit of angular velocity is expressed as radians/sec with the radian having a dimensionless value of unity, thus the SI units of angular velocity are listed as 1/sec. Angular velocity is usually represented by the Greek letter omega (ω, sometimes Ω). By convention, positive angular velocity indicates counter-clockwise rotation, while negative is clockwise.
anion	Physics	1	A negatively charged ion. Contrast cation.
annihilation	Physics	1	In particle physics, the process that occurs when a subatomic particle collides with its respective antiparticle to produce other particles, such as an electron colliding with a positron to produce two photons. The total energy and momentum of the initial pair are conserved in the process and distributed among a set of other particles in the final state. Antiparticles have exactly opposite additive quantum numbers from particles, so the sums of all quantum numbers of such an original pair are zero. Hence, any set of particles may be produced whose total quantum numbers are also zero as long as conservation of energy and conservation of momentum are obeyed.
anode	Physics	1	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	Physics	1	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.
antineutron	Physics	1	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 neutron, −1 for the antineutron). This is because the antineutron is composed of antiquarks, while neutrons are composed of quarks. The antineutron consists of one up antiquark and two down antiquarks.
antiparticle	Physics	1	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 (which is 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	Physics	1	An antiparticle corresponding in mass and properties to a proton but negatively charged and with the opposite magnetic moment. When an elementary particle (such as an electron, proton or neutron) and its antiparticle (such as a positron, antiproton or antineutron) collide, they destroy each other in a process known as annihilation, usually creating photons (light).
antiquark	Physics	1	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.
archimedes' principle	Physics	1	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.
astrophysics	Physics	1	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	Physics	1	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	Physics	1	The smallest possible unit of matter that still maintains an element’s identity during chemical reactions. Atoms contain one or more protons and neutrons (except hydrogen (H), which normally contains no neutrons) in a nucleus around which one or more electrons move.
atomic mass unit	Physics	1	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	Physics	1	The number of protons in the nucleus of an atom. This determines an element’s properties and location on the periodic table of elements.
z	Physics	1	The number of protons found in the nucleus of an atom. It is most often used to classify elements within the periodic table.
atomic physics	Physics	1	A branch of physics that studies atoms as isolated systems of electrons and an atomic nucleus. Compare nuclear physics.
atomic weight	Physics	1	The sum total of protons (or electrons) and neutrons within an atom.
audio frequency	Physics	1	A periodic vibration whose frequency is in the band audible to the average human, the human hearing range. It is the property of sound that most determines pitch, with a generally accepted standard hearing range for humans is 20 to 20,000 Hz. Also known as audible frequency (AF)
avogadro constant	Physics	1	A fundamental physical quantity (symbolNAorL) representing the molar number of entities. It has the value 6.022 141 5 x 1023mol-1.
avogadro number	Physics	1	The total number of individual molecules in one mole of a substance, by definition equaling exactly 6.02214076×1023.
avogadro's law	Physics	1	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	Physics	1	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	Physics	1	A quantum number for an atomic orbital that determines its orbital angular momentum and describes the shape of the orbital.
babinet's principle	Physics	1	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	Physics	1	The ubiquitous ionizing radiation to which the general human population is exposed.
balanced forces	Physics	1	When all the forces acting upon an object balance each other, the object will be at equilibrium; it will not accelerate.
balmer series	Physics	1	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	Physics	1	A scientific instrument used in meteorology to measure atmospheric pressure. Pressure tendency can forecast short-term changes in the weather.
baryon	Physics	1	A subatomic particle 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.
battery	Physics	1	A combination of two or more electrical cells which produces electricity.
beam	Physics	1	A structural element that is capable of withstanding 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	Physics	1	The behavior of a slender structural element subjected to an external load applied perpendicularly to a longitudinal axis of the element.
bending moment	Physics	1	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's principle	Physics	1	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.: Ch.3 : 156–164, § 3.5
bessel function	Physics	1	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 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	Physics	1	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	Physics	1	High-energy electron emitted during certain nuclear decay processes.
big bang	Physics	1	This theory describes that the universe originated approximately 14 billion years ago from a violent explosion of a very small concentration of matter of extremely high density and temperature.
binding energy	Physics	1	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.
biophysics	Physics	1	An interdisciplinary science using methods of and theories from physics to study biological systems.
black body	Physics	1	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	Physics	1	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	Physics	1	A system of two or more pulleys with a rope or cable threaded between them, usually used to lift or pull heavy loads.
boiling point	Physics	1	The temperature at which a substance changes state from a liquid to a vapour.
boiling point elevation	Physics	1	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	Physics	1	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.
boson	Physics	1	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	Physics	1	A chemical law which states that the volume of a given mass of a gas at constant temperature is inversely proportional to its pressure.
bremsstrahlung	Physics	1	Radiation emitted by the acceleration of unbound charged particles.
brewster's angle	Physics	1	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	Physics	1	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.
btu	Physics	1	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	Physics	1	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.
brownian motion	Physics	1	The presumably random movement of particles suspended in a fluid (liquid or gas) resulting from their bombardment by fast-moving atoms or molecules in the gas or liquid.
bubble	Physics	1	A measure of a substance's resistance to uniform compression defined as the ratio of the infinitesimal pressure increase to the resulting relative decrease of the volume. Its base unit is the pascal.
bulk modulus	Physics	1	A measure of a substance's resistance to uniform compression defined as the ratio of the infinitesimal pressure increase to the resulting relative decrease of the volume. Its base unit is the pascal.
buoyancy	Physics	1	The upward force of a fluid on an object that is immersed in it. The morebuoyant an object is, the more likely it is to float in a fluid.
calculus	Physics	1	A branch of mathematics that studies change and has two major sub-fields: differential calculus (concerning rates of change and slopes of curves), and integral calculus (concerning accumulation of quantities and the areas under and between curves). These two branches are related to each other by the fundamental theorem of calculus.
capacitance	Physics	1	The ratio of the change in the electric charge of a system to the corresponding change in its electric potential. There are two closely related notions of capacitance: self capacitance and mutual capacitance. Any object that can be electrically charged exhibits self capacitance. A material with a large self capacitance holds more electric charge at a given voltage than one with low capacitance. The notion of mutual capacitance is particularly important for understanding the operations of the capacitor, one of the three elementary linear electronic components (along with resistors and inductors).

ab initio

Physics

1

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

Physics

1

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

Physics

1

In electrochemistry, the electrode potential of a metal measured with respect to a universal reference system (without any additional metal–solution interface).

absolute humidity

Physics

1

The ratio of the water vapor in a sample of air to the volume of the sample.

absolute pressure

Physics

1

Is zero-referenced against a perfect vacuum, using an absolute scale, so it is equal to gauge pressure plus atmospheric pressure.

absolute scale

Physics

1

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

Physics

1

The lowest possible temperature, equivalent to -273.15 °C. Used as the zero point of the Kelvin temperature scale.

absorption spectroscopy

Physics

1

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.

accelerating expansion of the universe

Physics

1

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

Physics

1

The rate at which an object speeds up, slows down or changes direction.

acceleration due to gravity

Physics

1

The acceleration on an object caused by the force of gravitation.

accelerometer

Physics

1

A device to measure acceleration (the rate at which an object’s velocity changes).

acoustics

Physics

1

The branch of physics dealing with the production, transmission, and effects of sound.

adhesion

Physics

1

A binding force that allows unlike particles or surfaces to cling to one another.

adiabatic process

Physics

1

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

Physics

1

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

Physics

1

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 d=f_{1}+f_{2}} ).

air mass

Physics

1

1. 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.

air mass coefficient

Physics

1

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

Physics

1

The fraction of the total light incident on a reflecting surface, especially a celestial body, which is reflected back in all directions.

alloy

Physics

1

A chemical mixture of a metal with one or more other metals or other elements.

alpha decay

Physics

1

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

Physics

1

High-energy helium nucleus emitted during certain nuclear decay processes.

α

Physics

1

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.

alternating current

Physics

1

A form of electric current in which the movement of electric charge periodically reverses direction. Contrast direct current.

ac

Physics

1

A form of electric current in which the movement of electric charge periodically reverses direction. Contrast direct current.

ammeter

Physics

1

An instrument that is used to measure electric current.

amorphous solid

Physics

1

A type of solid which does not have a definite geometric shape.

ampere

Physics

1

The SI base unit of electric current, defined as one coulomb of electric charge per second.

a

Physics

1

The sum total of protons (or electrons) and neutrons within an atom.

amplifier

Physics

1

An electronic device that can increase the power of a signal (a time-varying voltage or current). It is a two-port electronic circuit that uses electric power from a power supply to increase the amplitude of a signal applied to its input terminals, producing a proportionally greater amplitude signal at its output. The amount of amplification provided by an amplifier is measured by its gain: the ratio of output voltage, current, or power to input. An amplifier is a circuit that has a power gain greater than one.

amplitude

Physics

1

The maximum displacement from the equilibrium on an energy wave (i.e. the size of the wave).

angle of incidence

Physics

1

The angle between a light ray incident on a flat surface and an imaginary line (called the normal) perpendicular to the surface at the point of incidence.

angle of reflection

Physics

1

The angle between the reflected ray moving away from a flat surface and an imaginary line (called the normal) perpendicular to the surface at the point of reflection.

ångström

Physics

1

A unit of length primarily used to measure subatomic particles that is equal to 10−10 metres (one ten-billionth of a metre) or 0.1 nanometres.

å

Physics

1

A unit of length primarily used to measure subatomic particles that is equal to 10−10 metres (one ten-billionth of a metre) or 0.1 nanometres.

angular acceleration

Physics

1

The time rate of change of angular velocity. In three dimensions, it is a pseudovector. In SI units, it is measured in radians per second squared (rad/s2), and is usually denoted by the Greek letter alpha (α). Just like angular velocity, there are two types of angular acceleration: spin angular acceleration and orbital angular acceleration, representing the time rate of change of spin angular velocity and orbital angular velocity, respectively. Unlike linear acceleration, angular acceleration need not be caused by a net external torque. For example, a figure skater can speed up her rotation (thereby obtaining an angular acceleration) simply by contracting her arms inwards, which involves no external torque.

angular displacement

Physics

1

The angle (in radians, degrees, or revolutions) through which a point revolving around a centre or line has been rotated in a specified sense about a specified axis.

angular frequency

Physics

1

A scalar measure of rotation rate. It refers to the angular displacement per unit time (e.g. in rotation) or the rate of change of the phase of a sinusoidal waveform (e.g. in oscillations and waves), or as the rate of change of the argument of the sine function. Angular frequency (or angular speed) is the magnitude of the vector quantity that is angular velocity. The term angular frequency vector ω → {\vec {\omega }}} is sometimes used as a synonym for the vector quantity angular velocity. One revolution is equal to 2π radians, hence ω = 2 π T = 2 π f , \omega ={{2\pi } \over T}={2\pi f},} where: ω is the angular frequency or angular speed (measured in radians per second), T is the period (measured in seconds), f is the ordinary frequency (measured in hertz) (sometimes symbolised with ν).

angular momentum

Physics

1

The rotational equivalent of linear momentum. It is an important quantity in physics because it is a conserved quantity–that is, the total angular momentum of a closed system remains constant.

angular velocity

Physics

1

How fast an object rotates or revolves relative to another point, i.e. how fast the angular position or orientation of an object changes with time. There are two types of angular velocity: orbital angular velocity and spin angular velocity. Spin angular velocity refers to how fast a rigid body rotates with respect to its centre of rotation. Orbital angular velocity refers to how fast a rigid body's centre of rotation revolves about a fixed origin, i.e. the time rate of change of its angular position relative to the origin. In general, angular velocity is measured in angle per unit time, e.g. radians per second. The SI unit of angular velocity is expressed as radians/sec with the radian having a dimensionless value of unity, thus the SI units of angular velocity are listed as 1/sec. Angular velocity is usually represented by the Greek letter omega (ω, sometimes Ω). By convention, positive angular velocity indicates counter-clockwise rotation, while negative is clockwise.

anion

Physics

1

A negatively charged ion. Contrast cation.

annihilation

Physics

1

In particle physics, the process that occurs when a subatomic particle collides with its respective antiparticle to produce other particles, such as an electron colliding with a positron to produce two photons. The total energy and momentum of the initial pair are conserved in the process and distributed among a set of other particles in the final state. Antiparticles have exactly opposite additive quantum numbers from particles, so the sums of all quantum numbers of such an original pair are zero. Hence, any set of particles may be produced whose total quantum numbers are also zero as long as conservation of energy and conservation of momentum are obeyed.

anode

Physics

1

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

Physics

1

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.

antineutron

Physics

1

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 neutron, −1 for the antineutron). This is because the antineutron is composed of antiquarks, while neutrons are composed of quarks. The antineutron consists of one up antiquark and two down antiquarks.

antiparticle

Physics

1

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 (which is 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

Physics

1

An antiparticle corresponding in mass and properties to a proton but negatively charged and with the opposite magnetic moment. When an elementary particle (such as an electron, proton or neutron) and its antiparticle (such as a positron, antiproton or antineutron) collide, they destroy each other in a process known as annihilation, usually creating photons (light).

antiquark

Physics

1

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.

archimedes' principle

Physics

1

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.

astrophysics

Physics

1

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

Physics

1

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

Physics

1

The smallest possible unit of matter that still maintains an element’s identity during chemical reactions. Atoms contain one or more protons and neutrons (except hydrogen (H), which normally contains no neutrons) in a nucleus around which one or more electrons move.

atomic mass unit

Physics

1

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

Physics

1

The number of protons in the nucleus of an atom. This determines an element’s properties and location on the periodic table of elements.

z

Physics

1

The number of protons found in the nucleus of an atom. It is most often used to classify elements within the periodic table.

atomic physics

Physics

1

A branch of physics that studies atoms as isolated systems of electrons and an atomic nucleus. Compare nuclear physics.

atomic weight

Physics

1

The sum total of protons (or electrons) and neutrons within an atom.

audio frequency

Physics

1

A periodic vibration whose frequency is in the band audible to the average human, the human hearing range. It is the property of sound that most determines pitch, with a generally accepted standard hearing range for humans is 20 to 20,000 Hz. Also known as audible frequency (AF)

avogadro constant

Physics

1

A fundamental physical quantity (symbolNAorL) representing the molar number of entities. It has the value 6.022 141 5 x 1023mol-1.

avogadro number

Physics

1

The total number of individual molecules in one mole of a substance, by definition equaling exactly 6.02214076×1023.

avogadro's law

Physics

1

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

Physics

1

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

Physics

1

A quantum number for an atomic orbital that determines its orbital angular momentum and describes the shape of the orbital.

babinet's principle

Physics

1

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

Physics

1

The ubiquitous ionizing radiation to which the general human population is exposed.

balanced forces

Physics

1

When all the forces acting upon an object balance each other, the object will be at equilibrium; it will not accelerate.

balmer series

Physics

1

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

Physics

1

A scientific instrument used in meteorology to measure atmospheric pressure. Pressure tendency can forecast short-term changes in the weather.

baryon

Physics

1

A subatomic particle 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.

battery

Physics

1

A combination of two or more electrical cells which produces electricity.

beam

Physics

1

A structural element that is capable of withstanding 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

Physics

1

The behavior of a slender structural element subjected to an external load applied perpendicularly to a longitudinal axis of the element.

bending moment

Physics

1

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's principle

Physics

1

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.: Ch.3 : 156–164, § 3.5

bessel function

Physics

1

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 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

Physics

1

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

Physics

1

High-energy electron emitted during certain nuclear decay processes.

big bang

Physics

1

This theory describes that the universe originated approximately 14 billion years ago from a violent explosion of a very small concentration of matter of extremely high density and temperature.

binding energy

Physics

1

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.

biophysics

Physics

1

An interdisciplinary science using methods of and theories from physics to study biological systems.

black body

Physics

1

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

Physics

1

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

Physics

1

A system of two or more pulleys with a rope or cable threaded between them, usually used to lift or pull heavy loads.

boiling point

Physics

1

The temperature at which a substance changes state from a liquid to a vapour.

boiling point elevation

Physics

1

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

Physics

1

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.

boson

Physics

1

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

Physics

1

A chemical law which states that the volume of a given mass of a gas at constant temperature is inversely proportional to its pressure.

bremsstrahlung

Physics

1

Radiation emitted by the acceleration of unbound charged particles.

brewster's angle

Physics

1

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

Physics

1

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.

btu

Physics

1

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

Physics

1

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.

brownian motion

Physics

1

The presumably random movement of particles suspended in a fluid (liquid or gas) resulting from their bombardment by fast-moving atoms or molecules in the gas or liquid.

bubble

Physics

1

A measure of a substance's resistance to uniform compression defined as the ratio of the infinitesimal pressure increase to the resulting relative decrease of the volume. Its base unit is the pascal.

bulk modulus

Physics

1

A measure of a substance's resistance to uniform compression defined as the ratio of the infinitesimal pressure increase to the resulting relative decrease of the volume. Its base unit is the pascal.

buoyancy

Physics

1

The upward force of a fluid on an object that is immersed in it. The morebuoyant an object is, the more likely it is to float in a fluid.

calculus

Physics

1

A branch of mathematics that studies change and has two major sub-fields: differential calculus (concerning rates of change and slopes of curves), and integral calculus (concerning accumulation of quantities and the areas under and between curves). These two branches are related to each other by the fundamental theorem of calculus.

capacitance

Physics

1

The ratio of the change in the electric charge of a system to the corresponding change in its electric potential. There are two closely related notions of capacitance: self capacitance and mutual capacitance. Any object that can be electrically charged exhibits self capacitance. A material with a large self capacitance holds more electric charge at a given voltage than one with low capacitance. The notion of mutual capacitance is particularly important for understanding the operations of the capacitor, one of the three elementary linear electronic components (along with resistors and inductors).