Glossary of physics

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.

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A

{{defn|A mathematical model which seeks to describe {{gli|nucleus|atomic nuclei}} by solving the non-relativistic {{gli|Schrödinger equation}} for all constituent {{gli|nucleon|nucleons}} and the {{gli|nuclear force|forces}} that exist between them. Such methods yield precise results for very light nuclei but become more approximate for heavier nuclei.}}

{{defn|In {{gli|optics}} and lens design, a measure of a transparent material's {{gli|dispersion}} (a variation of {{gli|refractive index}} versus {{gli|wavelength}}). High values of V indicate low dispersion.}}

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

{{defn|The ratio of the water vapor in a sample of air to the {{gli|volume}} of the sample.}}

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

{{defn|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.}}

{{defn|The theoretical lowest possible {{gli|temperature}}, understood by international agreement as equivalent to 0 {{gli|Kelvin}} or {{convert|-273.15|C|F}}. More formally, it is the theoretical lower limit of the {{gli|thermodynamic temperature}} scale, at which {{gli|enthalpy}} and {{gli|entropy}} of a cooled ideal gas reach their minimum values and the fundamental particles of nature have minimal vibrational motion.}}

{{defn|Any of various {{gli|spectroscopy|spectroscopic}} techniques that measure the {{gli|absorption}} of {{gli|electromagnetic radiation}} due to its interaction with a sample. The sample absorbs {{gli|energy}}, i.e. {{gli|photon|photons}}, from the radiating field. The intensity of the absorption varies as a function of {{gli|frequency}} or {{gli|wavelength}}, and this variation is the absorption spectrum. Absorption spectroscopy is performed across the {{gli|electromagnetic spectrum}}.}}

{{defn|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.{{cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |title=Cosmos Controversy: The Universe Is Expanding, but How Fast? |url=https://www.nytimes.com/2017/02/20/science/hubble-constant-universe-expanding-speed.html |date=20 February 2017 |work=The New York Times |access-date=21 February 2017 }}{{cite web |last=Scharping |first=Nathaniel |title=Gravitational Waves Show How Fast The Universe is Expanding |url=http://www.astronomy.com/news/2017/10/gravitational-waves-show-how-fast-the-universe-is-expanding |date=18 October 2017 |website=Astronomy |access-date=18 October 2017 }}{{cite web |last1=Weaver |first1=Donna |last2=Villard |first2=Ray |title=Measuring universe expansion reveals mystery – Is something unpredicted going on in the depths of space? |url=http://earthsky.org/space/measuring-universe-expansion-reveals-mystery |date=11 March 2018 |website=Earth & Sky |access-date=11 March 2018 }}{{cite web|url=http://curious.astro.cornell.edu/the-universe/cosmology-and-the-big-bang/104-the-universe/cosmology-and-the-big-bang/expansion-of-the-universe/616-is-the-universe-expanding-faster-than-the-speed-of-light-intermediate|title=Is the universe expanding faster than the speed of light?}}}}

{{defn|The rate at which the {{gli|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.}}

{{defn|The {{gli|acceleration}} on an object caused by the force of {{gli|gravitation}}.}}

{{defn|An instrument used to measure the proper {{gli|acceleration}} of a body irrespective of other forces.}}

{{defn|The branch of physics dealing with the production, transmission, and effects of {{gli|sound}}.}}

{{defn|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 {{gli|cohesion}}.}}

{{defn|A process which occurs without transfer of {{gli|heat}} or {{gli|mass}} of substances between a {{gli|thermodynamic system}} and its surroundings. In an adiabatic process, energy is transferred to the surroundings only as {{gli|work}}.{{cite journal|author-link=Constantin Carathéodory|last=Carathéodory |first=C. |date=1909 |title=Untersuchungen über die Grundlagen der Thermodynamik |journal=Mathematische Annalen |volume=67 |issue=3 |pages=355–386 |doi=10.1007/BF01450409|s2cid=118230148 |url=https://zenodo.org/record/1428268 }}. A translation may be found [http://neo-classical-physics.info/uploads/3/0/6/5/3065888/caratheodory_-_thermodynamics.pdf here]. Also a mostly reliable [https://books.google.com/books?id=xwBRAAAAMAAJ&q=Investigation+into+the+foundations translation is to be found] in {{cite book|last=Kestin |first=J. |date=1976 |title=The Second Law of Thermodynamics |publisher=Dowden, Hutchinson & Ross |location=Stroudsburg, PA }}{{cite book|last=Bailyn |first=M. |date=1994 |title=A Survey of Thermodynamics |publisher=American Institute of Physics Press |location=New York, NY|isbn=0-88318-797-3 |page=21}} 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 {{gli|thermodynamics}}.}}

{{defn|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 {{gli|fluid dynamics}} and gas dynamics, and many aspects of aerodynamics theory are common to these fields.}}

{{defn|the study of air and the design, construction, and operation of devices that move rapidly through the air, such as aircraft, missiles and rockets.}}

{{defn|An {{gli|optics|optical}} system that produces no net convergence or divergence of the beam, i.e. has an infinite effective focal length.[https://books.google.com/books?id=4nxMduNT8-gC&dq=afocal&pg=PA379 Daniel Malacara, Zacarias Malacara, Handbook of optical design. Page 379] 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 ( $d = f_1 + f_2$ ).}}

{{defn|no=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.}}

{{defn|no=2|In astronomy, the "amount of air that one is looking through"Green, Daniel W. E. 1992. Magnitude Corrections for Atmospheric Extinction. International Comet Quarterly 14, July 1992, 55–59. 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 {{gli|ray}}.}}

{{defn|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.}}

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

{{defn|A chemical mixture of a metal with one or more other metals or other elements.}}

{{defn|A type of {{gli|radioactive decay}} in which an {{gli|atomic nucleus}} emits an {{gli|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.}}

{{ghat|Also symbolized by α²⁺, {{chem|He|2+}}, and {{nuclide|helium|4|charge=2+}}.}}

{{defn|A type of {{gli|subatomic particle}} consisting of two {{gli|proton|protons}} and two {{gli|neutron|neutrons}} bound together into a particle identical to the {{gli|atomic nucleus|nucleus}} of a helium-4 {{gli|ion}}. It has a charge of {{val|+2|ul=e}} and a mass of {{val|4|ul=u}}. Alpha particles are classically produced in the process of {{gli|radioactive decay|radioactive}} {{gli|alpha decay}}, but may also be produced in other ways and given the same name.}}

{{defn|A form of {{gli|electric current}} in which the movement of {{gli|electric charge}} periodically reverses direction. Contrast {{gli|direct current}}.}}

{{defn|An instrument that is used to measure {{gli|electric current}}.}}

{{defn|A type of solid which does not have a definite geometric shape.}}

{{defn|The {{gli|SI}} base unit of {{gli|electric current}}, defined as one {{gli|coulomb}} of {{gli|electric charge}} per second.}}

{{defn|An electronic device that can increase the {{gli|power}} of a {{gli|signal}} (a time-varying {{gli|voltage}} or {{gli|electric current|current}}). It is a two-port electronic circuit that uses electric power from a power supply to increase the {{gli|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 {{gli|gain}}: the ratio of output voltage, current, or power to input. An amplifier is a circuit that has a power gain greater than one.{{cite book| last1 = Crecraft| first1 = David| last2 = Gorham| first2 = David| title = Electronics, 2nd Ed.| publisher = CRC Press| date = 2003| pages = 168| url = https://books.google.com/books?id=Yq66DDW4f8IC&dq=amplifier+power&pg=PA168| isbn = 978-0748770366}}{{cite book | last1 = Agarwal| first1 = Anant | last2 = Lang | first2 = Jeffrey | title = Foundations of Analog and Digital Electronic Circuits| publisher = Morgan Kaufmann| date = 2005| pages = 331| url = https://books.google.com/books?id=lGgP7FDEv3AC&dq=amplifier+power&pg=PA331| isbn = 978-0080506814}}{{cite book | last1 = Glisson | first1 = Tildon H. | title = Introduction to Circuit Analysis and Design | publisher = Springer Science and Business Media | date = 2011 | url = https://books.google.com/books?id=7nNjaH9B0_0C&dq=amplifier+power&pg=PA197 | isbn = 978-9048194438}}}}

{{defn|The height of a {{gli|wave}} as measured from its center (normal) position.}}

{{defn|In geometric optics, the angle between a ray incident on a surface and the line perpendicular to the surface at the point of incidence, called the normal. The ray can be formed by any wave: {{gli|light wave|optical}}, {{gli|sound wave|acoustic}}, {{gli|microwave}}, {{gli|X-ray}}, etc.}}

{{defn|The change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. Common examples include the reflection of {{gli|light}}, {{gli|sound}}, and water waves. The law of reflection says that for specular reflection the angle at which the wave is incident on the surface equals the angle at which it is reflected. Mirrors exhibit specular reflection.}}

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

{{defn|The time rate of change of {{gli|angular velocity}}. In three dimensions, it is a pseudovector. In SI units, it is measured in radians per second squared (rad/s{{sup|2}}), and is usually denoted by the Greek letter alpha (α).{{cite web |url=http://theory.uwinnipeg.ca/physics/circ/node3.html |title=Angular Velocity and Acceleration |publisher=Theory.uwinnipeg.ca |access-date=2015-04-13 |archive-url=https://web.archive.org/web/20120222015414/http://theory.uwinnipeg.ca/physics/circ/node3.html |archive-date=2012-02-22 |url-status=dead }} 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 {{gli|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.}}

{{defn|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.}}

{{ghat|Also angular speed, radial frequency, circular frequency, orbital frequency, radian frequency, and pulsatance.}}

{{defn|A scalar measure of rotation rate. It refers to the {{gli|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 {{gli|angular velocity}}. The term angular frequency vector $\vec{\omega}$ is sometimes used as a synonym for the vector quantity angular velocity.{{cite book

| last = Cummings

| first = Karen

|author2=Halliday, David

| title = Understanding physics

| publisher = John Wiley & Sons Inc., authorized reprint to Wiley - India

| date = 2007

| location = New Delhi

| pages = 449, 484, 485, 487

| url = https://books.google.com/books?id=rAfF_X9cE0EC

| isbn =978-81-265-0882-2 }}(UP1)

One revolution is equal to 2π radians, hence{{cite book

| last = Holzner

| first = Steven

| title = Physics for Dummies

| publisher = Wiley Publishing Inc

| year = 2006

| location = Hoboken, New Jersey

| pages = [https://archive.org/details/physicsfordummie00holz/page/201 201]

| url = https://archive.org/details/physicsfordummie00holz

| url-access = registration

| quote = angular frequency.

| isbn =978-0-7645-5433-9 }}

: $\omega = {{2 \pi} \over T} = {2 \pi f} ,$

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).}}

{{ghat|Also (rarely) moment of momentum or rotational momentum.}}

{{defn|The rotational equivalent of {{gli|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.}}

{{defn|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.}}

{{defn|A negatively charged {{gli|ion}}. Contrast {{gli|cation}}.}}

{{defn|In {{gli|particle physics}}, the process that occurs when a {{gli|subatomic particle}} collides with its respective antiparticle to produce other particles, such as an {{gli|electron}} colliding with a {{gli|positron}} to produce two {{gli|photon|photons}}.

{{cite web |title=Antimatter |url=http://www.lbl.gov/abc/Antimatter.html |publisher=Lawrence Berkeley National Laboratory |access-date=3 September 2008

|archive-url=https://web.archive.org/web/20080823180515/http://www.lbl.gov/abc/Antimatter.html

|archive-date=23 August 2008 |url-status=live}} The total {{gli|energy}} and {{gli|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.{{cite web |title=The Standard Model – Particle decays and annihilations |url=http://particleadventure.org/eedd.html |work=The Particle Adventure: The Fundamentals of Matter and Force |publisher=Lawrence Berkeley National Laboratory |access-date=17 October 2011}}}}

{{defn|The electrode through which a conventional {{gli|current|electric current}} flows into a polarized electrical device; the direction of current flow is, by convention, opposite to the direction of {{gli|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 {{gli|electrical circuit}}. However, in an {{gli|electrolytic cell}}, the anode is the wire or plate having excess positive charge, so named because negatively charged {{gli|anion|anions}} tend to move towards it. Contrast {{gli|cathode}}.}}

{{defn|A theory of creating a place or object that is free from the force of {{gli|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.}}

{{defn|The antiparticle of the {{gli|neutron}}, with symbol {{SubatomicParticle|Antineutron}}. It differs from the neutron only in that some of its properties have equal magnitude but opposite sign. It has the same {{gli|mass}} as the neutron, and no net {{gli|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 {{gli|quark|quarks}}. The antineutron consists of one up antiquark and two down antiquarks.}}

{{defn|In {{gli|particle physics}}, every type of {{gli|particle}} has an associated antiparticle with the same {{gli|mass}} but with opposite {{gli|charge|physical charges}} such as {{gli|electric charge}}. For example, the antiparticle of the {{gli|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 {{gli|radioactive decay}}. Some particles, such as the {{gli|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 {{gli|antimatter}}.}}

{{defn| It is a subatomic particle of the same mass as a proton but having a negative electric charge and oppositely directed magnetic moment. It is the proton’s antiparticle. Antiprotons were first produced and identified in 1955 by Emilio Segrè, Owen Chamberlain{{cite web | url=https://www.britannica.com/science/antiproton | title=Antiproton | Elementary Particles, Antimatter & CERN | Britannica | date=27 August 2024 }}}}

{{defn|For every {{gli|quark}} flavor there is a corresponding type of {{gli|antiparticle}} known as an antiquark that differs from the quark only in that some of its properties (such as the {{gli|electric charge}}) have equal magnitude but opposite sign.}}

{{defn|A physical principle which states that the upward {{gli|buoyancy|buoyant force}} that is exerted on a body immersed in a {{gli|fluid}}, whether fully or partially submerged, is equal to the {{gli|weight}} of the fluid that the body {{gli|displacement|displaces}} and acts in the upward direction at the center of mass of the displaced fluid.{{cite web|url=https://www.khanacademy.org/science/physics/fluids/buoyant-force-and-archimedes-principle/a/buoyant-force-and-archimedes-principle-article|title=What is buoyant force?|website=Khan Academy}}}}

{{defn|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.}}

{{defn|The measure of how much the incident energy beam (e.g. ultrasound or x-rays) is weakened by the material it is passing through.{{Cite web | title=Attenuation coefficient {{!}} Radiology Reference Article {{!}} Radiopaedia.org | url=https://radiopaedia.org/articles/attenuation-coefficient?lang=us | archive-url=https://web.archive.org/web/20210301160035/https://radiopaedia.org/articles/attenuation-coefficient?lang=us | access-date=2025-03-27 | archive-date=2021-03-01}}}}

{{defn|A basic unit of {{gli|matter}} that consists of a dense central nucleus surrounded by a cloud of negatively charged {{gli|electron|electrons}}. The atomic nucleus contains a mix of positively charged {{gli|proton|protons}} and electrically neutral {{gli|neutron|neutrons}}.}}

{{defn|A deprecated term, usually referring to the {{gli|unified atomic mass unit}}, a carbon-based standard, but historically referring to an oxygen-based standard.}}

{{defn|The number of {{gli|proton|protons}} found in the {{gli|atomic nucleus|nucleus}} of an {{gli|atom}}. It is most often used to classify elements within the periodic table.}}

{{defn|A branch of physics that studies {{gli|atom|atoms}} as isolated systems of {{gli|electron|electrons}} and an {{gli|nucleus|atomic nucleus}}. Compare {{gli|nuclear physics}}.}}

{{defn|The sum total of {{gli|proton|protons}} (or {{gli|electron|electrons}}) and {{gli|neutron|neutrons}} within an {{gli|atom}}.}}

{{defn|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)}}

{{defn|The ratio of the number of constituent {{gli|particle|particles}} in a substance, usually {{gli|atom|atoms}} or {{gli|molecule|molecules}}, to the amount of substance, of which the {{gli|SI}} unit is the mole. It is defined as exactly {{val|6.02214076|e=23|u=mol-1}}.}}

{{defn|The total number of individual molecules in one mole of a substance, by definition equaling exactly {{val|6.02214076|e=23}}.}}

{{defn|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.}}

{{defn|A hypothetical {{gli|subatomic particle}} postulated to account for the rarity of processes that break charge-parity symmetry. It is very light, electrically neutral, and pseudoscalar.}}

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

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B

{{defn|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.}}

{{defn|The ubiquitous {{gli|ionizing radiation}} to which the general human population is exposed.}}

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

{{defn|In {{gli|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.}}

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

{{defn|A {{gli|subatomic particle}} such as a {{gli|proton}} or a {{gli|neutron}}, each of which is made of (usually) three {{gli|quark|quarks}}. Nearly all {{gli|matter}} humans are likely to encounter is baryonic matter.}}

{{defn|A combination of two or more electrical cells which produces {{gli|electricity}}.}}

{{defn|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.}}

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

{{defn|The reaction induced in a structural element when an external {{gli|force}} or {{gli|moment of force|moment}} is applied to the element, causing the element to bend.Gere, J.M.; Timoshenko, S.P. (1996), Mechanics of Materials:Forth edition, Nelson Engineering, {{ISBN|0534934293}}Beer, F.; Johnston, E.R. (1984), Vector mechanics for engineers: statics, McGraw Hill, pp. 62–76 The simplest structural element subjected to bending moments is the {{gli|beam}}.}}

{{defn|In fluid dynamics, a principle which states that an increase in the {{gli|speed}} of a {{gli|fluid}} occurs simultaneously with a decrease in {{gli|pressure}} or a decrease in the fluid's {{gli|potential energy}}.{{cite book |last=Clancy |first=L.J. |author-link=Laurence Joseph Clancy |title=Aerodynamics |url=https://books.google.com/books?id=zaNTAAAAMAAJ |year=1975 |publisher=Wiley |isbn=978-0-470-15837-1}}{{rp|at=Ch.3}}{{cite book |last=Batchelor |first=G.K. |author-link=George Batchelor |title=An Introduction to Fluid Dynamics |url=https://books.google.com/books?id=Rla7OihRvUgC&pg=PA156 |year=2000 |publisher=Cambridge University Press |location=Cambridge |isbn=978-0-521-66396-0}}{{rp|at= § 3.5|pp=156–164}}}}

{{defn|A canonical solution {{math|y(x)}} of Friedrich Bessel's differential equation

: $x^2 \frac{d^2 y}{dx^2} + x \frac{dy}{dx} + \left(x^2 - \alpha^2 \right)y = 0$

for an arbitrary complex number {{mvar|α}}, the order of the Bessel function. Although {{mvar|α}} and {{math|−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 {{mvar|α}}. The most important cases are when {{mvar|α}} is an integer or half-integer. Bessel functions for integer {{mvar|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 {{mvar|α}} are obtained when the Helmholtz equation is solved in spherical coordinates.}}

{{defn|In {{gli|nuclear physics}}, a type of {{gli|radioactive decay}} in which a {{gli|beta particle}} is emitted from an {{gli|atomic nucleus}}, transforming the original {{gli|nuclide}} to its {{gli|isobar}}.}}

{{defn|A high-energy, high-speed {{gli|electron}} or {{gli|positron}} emitted by certain types of {{gli|radioactivity|radioactive}} atomic nuclei.}}

{{defn|The prevailing cosmological model that describes the early development of the Universe.}}

{{defn|The mechanical energy required to disassemble a whole into separate parts. A bound system typically has a lower {{gli|potential energy}} than the sum of its constituent parts.}}

{{defn|An interdisciplinary science using methods of and theories from physics to study biological systems.}}

{{defn|A hypothetical idealized physical body that completely absorbs all incident {{gli|electromagnetic radiation}}, regardless of {{gli|frequency}} or {{gli|angle of incidence}}. Perfect black bodies are imagined as substitutes for actual physical bodies in many theoretical discussions of {{gli|thermodynamics}}, and the construction of nearly perfect black bodies in the real world remains a topic of interest for materials engineers. Contrast {{gli|white body}}.}}

{{defn|The type of {{gli|electromagnetic radiation}} within or surrounding a body in thermodynamic equilibrium with its environment, or emitted by a {{gli|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.}}

{{defn|A system of two or more {{gli|pulley|pulleys}} with a rope or cable threaded between them, usually used to lift or pull heavy loads.}}

{{defn|The {{gli|temperature}} at which a {{gli|liquid}} undergoes a phase change into a {{gli|gas}}; the vapour pressure of liquid and gas are equal at this temperature.}}

{{defn|The phenomenon by which the boiling point of a {{gli|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.}}

{{defn|A {{gli|physical constant}} relating the average {{gli|kinetic energy}} of the particles in a {{gli|gas}} with the {{gli|temperature}} of the gas. It is the gas constant R divided by the {{gli|Avogadro constant}} NA.}}

{{defn|A type of {{gli|subatomic particle}} that behaves according to Bose–Einstein statistics and possesses integer {{gli|spin}}. Bosons include {{gli|elementary particle|elementary particles}} such as {{gli|photon|photons}}, {{gli|gluon|gluons}}, {{gli|W and Z bosons}}, {{gli|Higgs boson|Higgs bosons}}, and the hypothetical {{gli|graviton}}, as well as certain {{gli|composite particle|composite particles}} such as {{gli|meson|mesons}} and {{gli|stable nuclide|stable nuclides}} of even {{gli|mass number}}. Bosons constitute one of two main classes of particles, the other being {{gli|fermion|fermions}}. Unlike fermions, there is no limit to the number of bosons that can occupy the same {{gli|quantum state}}.}}

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

{{defn|{{gli|radiation|Radiation}} emitted by the {{gli|acceleration}} of unbound charged particles.}}

{{defn|The angle of incidence at which {{gli|light}} with a particular {{gli|polarization}} is completely transmitted through a transparent {{gli|dielectric}} surface, with no {{gli|reflection}}. When unpolarized light is incident at this angle, the light that is reflected is consequently perfectly polarized.}}

{{defn|An Imperial unit of {{gli|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 {{gli|joule|joules}}. In scientific contexts the btu has largely been replaced by the SI unit of energy, the joule.}}

{{defn|The tendency of a material to break without significant {{gli|plasticity|plastic}} {{gli|deformation}} when subjected to {{gli|stress}}. Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Breaking is often accompanied by a snapping sound.}}

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

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

{{defn|An upward {{gli|force}} exerted by a fluid that opposes the weight of an immersed object.}}

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C

{{defn|A branch of {{gli|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.}}

{{defn|The ratio of the change in the {{gli|electric charge}} of a system to the corresponding change in its {{gli|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 {{gli|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).}}

{{defn|An opposition to the change of {{gli|voltage}} across an electrical circuit element. Capacitive reactance $\scriptstyle{X_C}$ is inversely proportional to the signal {{gli|frequency}} $\scriptstyle{f}$ (or {{gli|angular frequency}}, ω) and the {{gli|capacitance}} $\scriptstyle{C}$ .Irwin, D. (2002). Basic Engineering Circuit Analysis, page 274. New York: John Wiley & Sons, Inc.}}

{{defn|An {{gli|electric circuit|electrical circuit}} element consisting of two {{gli|electrical conduction|conductors}} separated by an {{gli|electrical insulation|insulator}} (also known as a {{gli|dielectric}}).}}

{{defn|A theoretical ideal {{gli|thermodynamic cycle}} proposed by French physicist Nicolas Léonard Sadi Carnot in 1824 and expanded upon by others in the 1830s and 1840s. It provides an upper limit on the efficiency that any classical thermodynamic engine can achieve during the conversion of {{gli|heat}} into {{gli|work}}, or conversely, the efficiency of a refrigeration system in creating a temperature difference by the application of work to the system. It is not an actual thermodynamic cycle but is a theoretical construct.}}

{{defn|A coordinate system that specifies each point uniquely in a plane by a set of numerical coordinates, which are the signed distances to the point from two fixed perpendicular oriented lines, measured in the same unit of length. Each reference line is called a coordinate axis or just axis (plural axes) of the system, and the point where they meet is called the origin, at ordered pair {{nowrap|(0, 0)}}. The coordinates can also be defined as the positions of the perpendicular projections of the point onto the two axes, expressed as signed distances from the origin.}}

{{defn|The electrode through which a conventional {{gli|current|electric current}} flows out of a polarized electrical device; the direction of current flow is, by convention, opposite to the direction of {{gli|electron}} flow, and so electrons flow into the cathode. In a galvanic cell, the cathode is the positive terminal or pole which accepts electrons flowing from the external part of an {{gli|electrical circuit}}. However, in an {{gli|electrolytic cell}}, the cathode is the wire or plate having excess negative charge, so named because positively charged {{gli|cation|cations}} tend to move towards it. Contrast {{gli|anode}}.}}

{{defn|A positively charged {{gli|ion}}. Contrast {{gli|anion}}.}}

{{defn|A scale and unit of measurement of {{gli|temperature}}.}}

{{defn|The point in a body around which the resultant {{gli|torque}} due to {{gli|gravity}} forces vanish. Near the surface of the earth, where gravity acts downward as a parallel force field, the center of gravity and the {{gli|center of mass}} are the same.}}

{{defn|Within a given distribution of {{gli|mass}}, the unique point in space at which the weighted relative position of the distributed mass sums to zero.}}

{{defn|See {{gli|Celsius scale}}.}}

{{defn|A classic problem in potential theory involving the determination of the motion of a particle in a single {{gli|central force|central potential field}}. The solutions to such problems are important in {{gli|classical mechanics}}, since many naturally occurring forces, such as {{gli|gravity}} and {{gli|electromagnetism}}, are central forces.}}

{{defn|The apparent outward force that draws a rotating body away from the centre of rotation. It is caused by the {{gli|inertia}} of the body as the body's path is continually redirected.}}

{{defn|A force which keeps a body moving with a uniform speed along a circular path and is directed along the radius towards the centre.}}

{{defn|Any attempt in mainstream physics to {{gli|theory of everything|unify}} existing theories of {{gli|relativity}}, {{gli|gravitation}}, and {{gli|quantum mechanics}}, particularly by envisioning the three universal constants fundamental to each field – the {{gli|speed of light}} ( $c$ ), the {{gli|gravitational constant}} ( $G$ ), and the {{gli|Planck constant}} ( $h$ ) – as the edges of a three-dimensional cube, at each corner of which is positioned a major sub-field within {{gli|theoretical physics}} according to which of the three constants are accounted for by that sub-field and which are ignored. One corner of this so-called "cube of theoretical physics", where all three constants are accounted for simultaneously, has not yet been satisfactorily described: {{gli|quantum gravity}}.}}

{{defn|A sequence of reactions in which a reactive product or byproduct causes additional similar reactions to take place.}}

{{defn|A branch of chemistry and physics that studies chemical processes from the point of view of physics by investigating physicochemical phenomena using techniques from atomic and molecular physics and {{gli|condensed matter physics}}.}}

{{defn|A sub-field of {{gli|mechanics}} concerned with the set of physical laws describing the {{gli|motion}} of bodies under the collective actions of a system of {{gli|force|forces}}.}}

{{defn|The tendency of similar particles or surfaces to cling to one another. Contrast {{gli|adhesion}}.}}

{{defn|A type of light–matter interaction in which a {{gli|photon}} is scattered by a {{gli|electric charge|charged particle}}, usually an {{gli|electron}}, which results in part of the energy of the photon being transferred to the recoiling electron; a resulting decrease in the energy of the photon is called the Compton effect. The opposite phenomenon occurs in inverse Compton scattering, when a charged particle transfers part of its energy to a photon.}}

{{defn|A branch of physics that studies the physical properties of condensed phases of matter.}}

{{defn|The transfer of {{gli|heat}} by the actual transfer of {{gli|matter}}.}}

{{defn|The {{gli|SI}} derived unit of {{gli|electric charge}}, defined as the charge transported by a constant {{gli|electric current|current}} of one {{gli|ampere}} in one second.}}

{{defn|The point on a {{gli|wave}} with the maximum value or upward displacement within a cycle.}}

{{defn|The smallest amount of fissile material needed for a sustained nuclear {{gli|chain reaction}}.}}

{{defn|See {{gli|cGh physics}}.}}

{{defn|The {{gli|motion}} of a moving particle or object that conforms to a known or fixed curve. Such motion is studied with two coordinate systems: planar motion and cylindrical motion.}}

{{defn|A type of {{gli|particle accelerator}} in which charged particles accelerate outwards from the center along a spiral path.}}

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D

{{defn|Any influence upon or within an {{gli|oscillation|oscillatory}} system that has the effect of reducing, restricting, or preventing its oscillations. Damping is a result of processes that dissipate the energy stored in the oscillation.}}

{{defn|A mechanically commutated electric motor powered by {{gli|direct current}}.}}

{{defn|The degree to which a {{gli|structural element}} is displaced under a load. It may refer to an angle or a distance.}}

{{defn|A physical property of a substance defined as its {{gli|mass}} per unit volume.}}

{{defn|For a mathematical function of a real variable, a measurement of the sensitivity to change of the function value (output) with respect to a change in its argument (input); e.g. the derivative of the position of a moving object with respect to time is the object's {{gli|velocity}} and measures how quickly the position of the object changes as time changes. Derivatives are a fundamental tool of {{gli|calculus}}.}}

{{defn|An electrical {{gli|insulator}} that can be {{gli|polarization|polarized}} by an applied {{gli|electric field}}. When a dielectric material is placed in an electric field, electric charges do not flow through the material as they would in a {{gli|conductor}} but only shift slightly from their equilibrium positions, with positive charges displaced in the direction of the field's flow and negative charges displaced in the opposite direction; this creates an internal electric field that reduces the larger field within the dielectric material.}}

{{defn|no=1|(fluid) Occurs when an object is immersed in a fluid, pushing it out of the way and taking its place. The volume of the immersed object will be exactly equal to the volume of the displaced fluid, so that the volume of the immersed object can be deduced if the volume of the displaced fluid is measured.}}

{{defn|no=2|(vector) The shortest distance from the initial to the final position of a point. Thus, it is the length of an imaginary straight path, typically distinct from the path actually travelled by.}}

{{defn|The change in {{gli|frequency}} of a {{gli|wave}} (or other periodic event) for an observer moving relative to its source. Compared to the emitted frequency, the received frequency is higher during the approach, identical at the instant of passing by, and lower during the recession.}}

{{defn|Forces which act on a solid object in the direction of the relative fluid flow velocity. Unlike other resistive forces, such as dry {{gli|friction}}, which is nearly independent of velocity, drag forces depend on velocity.}}

{{defn|A solid material's ability to {{gli|deformation|deform}} under tensile stress; this is often characterized by the material's ability to be stretched into a wire.}}

{{defn|The branch of {{gli|classical mechanics}} that studies {{gli|force|forces}} and {{gli|torque|torques}} and their effects on {{gli|motion}}, as opposed to {{gli|kinematics}}, which studies motion without reference to these forces.}}

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E

{{defn|The tendency of a material to return to its original shape after it is {{gli|deformation|deformed}}.}}

{{defn|A physical property of {{gli|matter}} that causes it to experience a {{gli|force}} when near other electrically charged matter. There are two types of electric charge: positive and negative.}}

{{defn|An {{gli|electrical network}} consisting of a closed loop, giving a return path for the {{gli|current}}.}}

{{defn|A flow of {{gli|electric charge}} through a conductive medium.}}

{{defn|The region of space surrounding electrically {{gli|electric charge|charged}} particles and time-varying {{gli|magnetic field|magnetic fields}}. The electric field represents the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding.}}

{{defn|The rate at which electric energy is transferred by an {{gli|electric circuit}}.}}

{{defn|Any material which contains movable {{gli|electric charge|electric charges}} and therefore can conduct an {{gli|electric current}} under the influence of an {{gli|electric field}}.}}

{{defn|Any material whose internal {{gli|electric charge|electric charges}} do not flow freely and which therefore does not conduct an {{gli|electric current}} under the influence of an {{gli|electric field}}.}}

{{defn|An interconnection of electrical elements such as resistors, inductors, capacitors, voltage sources, current sources, and switches.}}

{{defn|The opposition to the passage of an {{gli|electric current}} through an electrical element.}}

{{defn|The set of physical phenomena associated with the presence and flow of {{gli|electric charge|electric charges}}.}}

{{defn|A type of magnet in which the {{gli|magnetic field}} is produced by the flow of {{gli|electric current}}.}}

{{defn|A physical field produced by moving electrically charged objects.}}

{{defn|A form of {{gli|energy}} emitted and absorbed by charged particles, which exhibits wave-like behavior as it travels through space.}}

{{term|electromotive force ( $\mathcal{E}$ )}}

{{defn|The electrical intensity or "pressure" developed by a source of electrical energy such as a {{gli|battery}} or {{gli|electric generator|generator}} and measured in {{gli|volt|volts}}. Any device that converts other forms of {{gli|energy}} into electrical energy provides electromotive force as its output.}}

{{defn|A {{gli|subatomic particle}} with a negative {{gli|elementary charge|elementary}} {{gli|electric charge}}.}}

{{ghat|Also called electron spin resonance (ESR) and electron magnetic resonance (EMR).}}

{{defn|A method for studying materials with unpaired {{gli|electron|electrons}} which makes use of the {{gli|Zeeman effect}}. It shares some basic principles with nuclear magnetic resonance (NMR).}}

{{defn|A unit of {{gli|energy}} equal to approximately 1.6×10⁻¹⁹ {{gli|joule}}. By definition, it is the amount of energy gained by the charge of a single {{gli|electron}} moved across an electric potential difference of one {{gli|volt}}.}}

{{defn|A chemical property that describes the tendency of an atom or a functional group to attract electrons (or electron density) towards itself.}}

{{defn|A field that deals with {{gli|electric circuit|electrical circuits}} that involve active electrical components such as vacuum tubes, transistors, diodes, and integrated circuits as well as associated passive interconnection technologies.}}

{{defn|The ability to do {{gli|work}}.}}

{{defn|An adjective used to refer to a process or reaction in which a system absorbs {{gli|energy}} from its surroundings, usually in the form of {{gli|heat}} but also in the form of {{gli|light}}, {{gli|electricity}}, or {{gli|sound}}. Contrast {{gli|exothermic}}.}}

{{defn|A quantity which describes the randomness of a substance or system.}}

{{defn|The {{gli|velocity}} at which the {{gli|kinetic energy}} plus the gravitational {{gli|potential energy}} of an object is zero. It is the speed needed to "escape" from a gravitational field without further propulsion.}}

{{defn|An adjective used to refer to a process or reaction that releases {{gli|energy}} from a system, usually in the form of {{gli|heat}} but also in the form of {{gli|light}}, {{gli|electricity}}, or {{gli|sound}}. Contrast {{gli|endothermic}}.}}

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F

{{defn|Objects that are moving towards a body with greater gravitational influence, such as a planet.}}

{{defn|A type of {{gli|particle}} that behaves according to Fermi–Dirac statistics, obeys the {{gli|Pauli exclusion principle}}, and possesses half-integer {{gli|spin}}. Fermions include all {{gli|quark|quarks}} and {{gli|lepton|leptons}}, as well as all {{gli|composite particle|composite particles}} made of an odd number of these (such as all {{gli|baryon|baryons}} and many {{gli|atom|atoms}} and {{gli|nucleus|nuclei}}). Fermions constitute one of two main classes of particles, the other being {{gli|boson|bosons}}.}}

{{defn|Either a nuclear reaction or a radioactive decay process in which the nucleus of an atom splits into smaller parts (lighter nuclei), often producing free neutrons and photons (in the form of gamma rays) and releasing relatively large amounts of energy.}}

{{defn|A push or pull. Any interaction that, when unopposed, will change the {{gli|motion}} of a physical body. A force has both magnitude and direction, making it a {{gli|vector}} quantity. The {{gli|SI}} unit used to measure force is the {{gli|newton}}.}}

{{defn|Any motion of a body where its own {{gli|weight}} is the only force acting upon it.}}

{{defn|The temperature at which a substance changes state from {{gli|liquid}} to {{gli|solid}}.}}

{{defn|A nuclear reaction in which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus.}}

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G

{{defn|A form of {{gli|electromagnetic radiation}} of very high frequency and therefore very high energy.}}

{{defn|A natural phenomenon by which physical bodies attract each other with a {{gli|force}} proportional to their {{gli|mass|masses}}.}}

{{ghat|Also called the universal gravitational constant and Newton's constant.}}

{{defn|A physical constant involved in the calculation of {{gli|gravitation|gravitational force}} between two bodies.}}

{{defn|The {{gli|potential energy}} associated with the {{gli|gravitational field}}.}}

{{defn|A model used to explain the influence that a massive body extends into the space around itself, producing a {{gli|force}} ({{gli|gravity}}) on another massive body. Thus, a gravitational field is used to explain and represent gravitational phenomena. It is measured in {{gli|newton|newtons}} per kilogram (N/kg).}}

{{defn|The gravitational potential at a location is equal to the {{gli|work}} ({{gli|energy}} transferred) per unit {{gli|mass}} that is done by the force of {{gli|gravitation|gravity}} to move an object to a fixed reference location.}}

{{defn|A ripple in the curvature of {{gli|spacetime}} that propagates as a {{gli|wave}} and is generated in certain gravitational interactions, travelling outward from their source.}}

{{defn|See {{gli|gravitation}}.}}

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H

{{defn|A composite particle made from three quarks or three antiquarks baryon, or one quark and one antiquark meson.}}

{{defn|The time required for a quantity to fall to half its value as measured at the beginning of the time period. In physics, half-life typically refers to a property of {{gli|radioactive decay}}, but may refer to any quantity which follows an exponential decay.}}

{{defn|A form of {{gli|energy}} transferred from one body to another by thermal interaction.}}

{{defn|The {{gli|SI}} unit of {{gli|frequency}}, defined as the number of cycles per second of a periodic phenomenon.}}

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I

{{defn|A physical process that results in the phase transition of a substance from a liquid to a solid.}}

{{defn|The measure of the opposition that a circuit presents to a {{gli|electric current|current}} when a {{gli|voltage}} is applied.}}

{{defn|The change in momentum, which is equal to the average net external force multiplied by the time this force acts.}}

{{defn|The resistance of any physical object to a change in its state of {{gli|motion}} or {{gli|rest}}, or the tendency of an object to resist any change in its motion.}}

{{defn|The modern form of the metric system, comprising a system of units of measurement devised around seven base units and the convenience of the number ten.}}

{{defn|An {{gli|atom}} or {{gli|molecule}} in which the total number of {{gli|electron|electrons}} is not equal to the total number of {{gli|proton|protons}}, giving the atom a net positive or negative {{gli|electric charge}}.}}

{{defn|A type of chemical bond formed through an electrostatic attraction between two oppositely {{gli|electric charge|charged}} {{gli|ion|ions}}.}}

{{defn|The process of converting an {{gli|atom}} or {{gli|molecule}} into an {{gli|ion}} by adding or removing charged particles such as {{gli|electron|electrons}} or other ions.}}

{{defn|A variant of a particular chemical element. While all isotopes of a given element share the same number of {{gli|proton|protons}}, each isotope differs from the others in its number of {{gli|neutron|neutrons}}.}}

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J

{{defn|A derived unit of {{gli|energy}}, {{gli|work}}, or amount of {{gli|heat}} in the {{gli|International System of Units}}.}}

{{defn|The rate of change of acceleration, or the third derivative of displacement.}}

K

{{defn|A scale and unit of measurement of {{gli|temperature}}. The Kelvin scale is an absolute {{gli|thermodynamic temperature}} scale which uses {{gli|absolute zero}} as its null point.}}

{{defn|The branch of {{gli|classical mechanics}} that describes the {{gli|motion}} of points, bodies (objects), and systems of bodies (groups of objects) without consideration of the causes of motion. The study of kinematics is often referred to as the "geometry of motion".}}

{{defn|The {{gli|energy}} that a physical body possesses due to its {{gli|motion}}, defined as the {{gli|work}} needed to {{gli|acceleration|accelerate}} a body of a given {{gli|mass}} from rest to its stated {{gli|velocity}}. The body continues to maintain this kinetic energy unless its velocity changes. Contrast {{gli|potential energy}}.}}

{{ghat|Also called Kirchhoff's rules or simply Kirchhoff's laws.}}

{{defn|Two approximate equalities that deal with the {{gli|electric current|current}} and {{gli|voltage}} in {{gli|electrical circuit|electrical circuits}}. See Kirchhoff's laws for other meanings of the term.}}

{{defn|In {{gli|fluid dynamics}}, a set of equations which describe the {{gli|motion}} of a rigid body in an ideal {{gli|fluid}}.}}

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L

{{defn|Occurs when a fluid flows in parallel layers with no disruption between the layers.}}

{{defn|A {{gli|vector}} used chiefly to describe the shape and orientation of the orbit of one astronomical body around another, such as a planet revolving around a star. For two bodies interacting by Newtonian gravity, the LRL vector is a constant of motion, meaning that it is the same no matter where it is calculated on the orbit; equivalently, the LRL vector is said to be conserved.}}

{{defn|A device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation"}}

{{defn|A circuit consisting of an inductor (with inductance L) and a capacitor (with capacitance C).}}

{{defn|An elementary particle which does not undergo {{gli|strong interaction|strong interactions}} but is subject to the {{gli|Pauli exclusion principle}}. Two main classes of leptons exist: charged leptons (also known as the {{gli|electron}}-like leptons) and neutral leptons (better known as {{gli|neutrino|neutrinos}}).}}

{{defn|A type of {{gli|machine}} consisting of a beam or rigid rod pivoted at a fixed hinge or fulcrum; one of six classical {{gli|simple machine|simple machines}}.}}

{{defn|A form of {{gli|electromagnetic radiation}} that occupies a certain range of {{gli|wavelength|wavelengths}} within the {{gli|electromagnetic spectrum}}. In physics, the term sometimes refers collectively to electromagnetic radiation of any wavelength, in which case light includes {{gli|gamma ray|gamma rays}}, {{gli|X-ray|X-rays}}, {{gli|microwave|microwaves}}, and {{gli|radio wave|radio waves}}, but in common usage "light" more often refers specifically to {{gli|visible light}}.}}

{{defn|A form of motor that generates a linear movement directly.}}

{{defn|The branch of {{gli|mathematics}} concerning {{gli|vector space|vector spaces}}, often finite or countably infinite dimensional, as well as linear mappings between such spaces.}}

{{defn|The mathematical study of how solid objects deform and become internally stressed due to prescribed loading conditions. Linear elasticity is a simplification of the more general nonlinear theory of elasticity and is a branch of {{gli|continuum mechanics}}.}}

{{defn|One of four classical {{gli|state of matter|states of matter}} having a definite {{gli|volume}} but no fixed shape.}}

{{defn|A {{gli|state of matter}} which has properties between those of a conventional liquid and those of a solid crystal. For instance, an LC may flow like a liquid, but its {{gli|molecule|molecules}} may be oriented in a crystal-like way.}}

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M

{{defn|An extension of {{gli|string theory}} that attempts to unify seemingly contradictory mathematical formulations and which identifies 11 dimensions.}}

{{defn|A dimensionless quantity representing the ratio of the {{gli|speed}} of an object moving through a fluid to the local {{gli|speed of sound}}.}}

{{defn|The proposition that the existence of absolute rotation (the distinction of local inertial frames vs. rotating reference frames) is determined by the large-scale distribution of matter.}}

{{defn|Any powered tool consisting of one or more parts that is constructed to achieve a particular goal. Machines are usually powered by mechanical, chemical, thermal or electrical means, and are frequently motorised.}}

{{defn|An elementary component of a {{gli|machine}}. There are three basic types: structural components, mechanisms, and control components.}}

{{defn|A representation of a function as an infinite sum of terms that are calculated from the values of the function's derivatives at a single point.}}

{{defn|A mathematical description of the {{gli|magnetism|magnetic}} influence of {{gli|electric current|electric currents}} and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude (or strength); as such it is a {{gli|vector}} field.}}

{{defn|A property of materials that respond to an applied {{gli|magnetic field}}.}}

{{defn|An application of the law of {{gli|conservation of mass}} to the analysis of physical systems.}}

{{defn|See {{gli|density}}.}}

{{defn|The rate of mass flow per unit area. The common symbols are j, J, φ, or Φ, sometimes with subscript m to indicate mass is the flowing quantity. Its SI units are kg s−1 m−2.}}

{{defn|A property of a distribution of mass in space that measures its {{gli|inertia|resistance}} to rotational acceleration about an axis.}}

{{ghat|Also called atomic mass number or nucleon number.}}

{{defn|The total number of {{gli|proton|protons}} and {{gli|neutron|neutrons}} (together known as {{gli|nucleon|nucleons}}) in an atomic nucleus.}}

{{defn|An interdisciplinary field incorporating elements of physics, chemistry, and engineering that is concerned with the design and discovery of new materials, particularly {{gli|solid|solids}}.}}

{{defn|The application of {{gli|mathematics}} to problems in physics and the development of mathematical methods suitable for such applications and for the formulation of physical theories.}}

{{defn|The abstract study of topics encompassing quantity, structure, space, change, and other properties.}}

{{defn|A rectangular array of numbers, symbols, or expressions arranged in rows and columns. The individual items in a matrix are called its elements or entries.}}

{{defn|Any substance (often a particle) that has {{gli|rest}} {{gli|mass}} and (usually) also {{gli|volume}}.}}

{{defn|A set of partial differential equations that, together with the Lorentz force law, form the foundation of classical electrodynamics, classical optics, and electric circuits. Maxwell's equations describe how {{gli|electric field|electric}} and {{gli|magnetic field|magnetic fields}} are generated and altered by each other and by {{gli|electric charge|charges}} and {{gli|electric current|currents}}.}}

{{defn|A term which relates to the way in which quantitative data tend to cluster around some value. A measure of central tendency is any of a number of ways of specifying this "central value".}}

{{defn|The branch of science concerned with the behaviour of physical bodies when subjected to {{gli|force|forces}} or displacements and the subsequent effects of the bodies on their environment.}}

{{defn|A physical process that results in the phase transition of a substance from a solid to a liquid.}}

{{defn|A type of {{gli|hadron|hadronic}} {{gli|subatomic particle}} composed of one {{gli|quark}} and one {{gli|antiquark}} bound together by the {{gli|strong interaction}}. All mesons are unstable, with the longest-lived lasting for only a few hundredths of a microsecond.}}

{{defn|The mathematical description of an object's or substance's tendency to be {{gli|deformation|deformed}} elastically (i.e. non-permanently) when a force is applied to it. The elastic modulus of an object is defined as the slope of its {{gli|stress–strain curve}} in the elastic deformation region. As such, a {{gli|stiffness|stiffer}} material will have a higher elastic modulus.}}

{{defn|A physical property of {{gli|matter}} defined as the {{gli|mass}} of a given substance divided by the amount of substance and expressed in grams per mole.}}

{{defn|An electrically neutral group of two or more {{gli|atom|atoms}} held together by covalent chemical bonds. Molecules are distinguished from {{gli|ion|ions}} by having a net {{gli|electric charge}} equal to zero.}}

{{defn|A branch of physics that studies the physical properties of {{gli|molecule|molecules}} and the chemical bonds between {{gli|atom|atoms}} as well as their molecular dynamics. It is closely related to atomic physics and overlaps greatly with theoretical chemistry, {{gli|physical chemistry}} and {{gli|chemical physics}}.}}

{{defn|A property of a distribution of {{gli|mass}} in space that measures its {{gli|inertia|resistance}} to rotational acceleration about an axis.}}

{{defn|A vector quantity consisting of the product of the mass and velocity of an object.}}

{{defn|Any change in the position of an object over {{gli|time}}. Motion can be mathematically described in terms of {{gli|displacement (vector)|displacement}}, {{gli|distance}}, {{gli|velocity}}, {{gli|speed}}, {{gli|acceleration}}, and {{gli|momentum}}, and is observed by attaching a {{gli|frame of reference}} to an observer and measuring the change in an object's position relative to that frame. An object's motion cannot change unless it is acted upon by a {{gli|force}}.}}

{{defn|An elementary particle, technically classified as a {{gli|lepton}}, that is similar to the {{gli|electron}}, with unitary negative electric charge (−1) and a spin of 1⁄2. Muons are not believed to have any sub-structure.}}

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N

{{defn|The practice of engineering on the nanoscale. Nanoengineering is largely a synonym for {{gli|nanotechnology}}, but emphasizes the applied rather the field.}}

{{defn|The manipulation of matter on an {{gli|atom|atomic}} and {{gli|molecule|molecular}} scale; a more generalized description by the National Nanotechnology Initiative is "the manipulation of matter with at least one dimension sized from 1 to 100 nanometres".}}

{{defn|A type of electrically neutral {{gli|subatomic particle}} denoted by the Greek letter ν (nu). All evidence suggests that neutrinos have {{gli|mass}} but that their mass is tiny even by the standards of subatomic particles. Their mass has never been measured accurately.}}

{{term|prompt neutron}}

: {{defn|Immediate emission of neutrons after a nuclear fission event}}

{{term|delayed neutron}}

: {{defn|Delayed emission of neutrons after a nuclear fission event, by one of the fission products (actually, a fission product daughter after beta decay)}}

{{defn|A set of three physical laws which describe the relationship between the {{gli|force|forces}} acting on a body and its motion due to those forces. Together they form the basis for {{gli|classical mechanics|classical or Newtonian mechanics}}.}}

{{defn|The branch of physics that studies the constituents and interactions of {{gli|nucleus|atomic nuclei}}.}}

{{defn|Either a {{gli|proton}} or a {{gli|neutron}} in its role as a component of an {{gli|nucleus|atomic nucleus}}.}}

{{defn|An {{gli|atomic}} species characterized by the specific composition of its {{gli|nucleus}}, i.e. by its number of {{gli|proton|protons}}, its number of {{gli|neutron|neutrons}}, and its nuclear {{gli|energy level|energy state}}.}}

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O

{{defn|The {{gli|SI}} derived unit of {{gli|resistance|electrical resistance}}.}}

{{defn|The {{gli|electric current}} through a {{gli|conductor}} between two points is directly proportional to the {{gli|electric potential|potential}} difference across the two points.}}

{{defn|An optomechanical device used for the capture, analysis, and manipulation of {{gli|dielectric}} objects or particles, which operates via the application of {{gli|force}} by the {{gli|electric field}} of light.}}

{{defn|An optical technique for the initialisation and readout of {{gli|quantum spin}} in some crystal defects.}}

{{defn|The branch of physics which involves the behaviour and properties of {{gli|light}}, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviolet, and infrared light; however, other forms of {{gli|electromagnetic radiation}} such as {{gli|X-ray|X-rays}}, microwaves, and radio waves exhibit similar properties.}}

P

{{defn|A branch of physics that studies the nature of {{gli|particle|particles}}, which are the constituents of what is usually referred to as {{gli|matter}} and {{gli|radiation}}.}}

{{defn|A principle in {{gli|fluid mechanics}} which states that {{gli|pressure}} exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid such that the initial pressure variations remain the same.}}

{{defn|A tabular display of the chemical elements organised on the basis of their {{gli|atomic number|atomic numbers}}, electron configurations, and recurring chemical properties. Elements are presented in order of increasing atomic number (number of protons).}}

{{defn|An elementary particle, the {{gli|quantum}} of {{gli|light}} and all other forms of {{gli|electromagnetic radiation}}, and the force carrier for the {{gli|electromagnetism|electromagnetic force}}.}}

{{defn|The study of macroscopic, atomic, subatomic, and particulate phenomena in chemical systems in terms of laws and concepts of physics.}}

{{defn|The natural science that involves the study of {{gli|matter}} and its motion through {{gli|space}} and {{gli|time}}, along with related concepts such as {{gli|energy}} and {{gli|force}}. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.}}

{{defn|A fundamental universal {{gli|physical constant}} that is the {{gli|quantum}} of action in {{gli|quantum mechanics}}.}}

{{defn|The study and control of mechanical force and movement generated by the application of compressed gas.}}

{{defn|The ratio of {{gli|force}} to the area over which that force is distributed.}}

{{defn|A measure of the expectation that an event will occur or that a statement is true. Probabilities are given a value between 0 (will not occur) and 1 (will occur). The higher the probability of an event, the more certain one can be that the event will occur.}}

{{defn|A {{gli|wheel and axle|wheel on an axle}} that is designed to support movement of a cable or belt along its circumference; one of six classical {{gli|simple machine|simple machines}}. Pulleys are used in a variety of ways to lift loads, apply {{gli|force|forces}}, and transmit {{gli|power}}.}}

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Q

{{defn|The {{gli|relativity|relativistic}} {{gli|quantum field theory}} of {{gli|electrodynamics}}. In essence, it describes how {{gli|light}} and {{gli|matter}} interact and is the first theory where full agreement between {{gli|quantum mechanics}} and {{gli|special relativity}} is achieved. QED mathematically describes all phenomena involving electrically charged particles interacting by means of exchange of {{gli|photon|photons}} and represents the quantum counterpart of {{gli|classical electromagnetism}}, giving a complete account of matter and light interaction.}}

{{defn|A theoretical framework for constructing quantum mechanical models of {{gli|subatomic particle|subatomic particles}} in {{gli|particle physics}} and {{gli|quasiparticle|quasiparticles}} in {{gli|condensed matter physics}}.}}

{{defn|A branch of physics dealing with physical phenomena at microscopic scales, where the action is on the order of the {{gli|Planck constant}}. Quantum mechanics departs from {{gli|classical mechanics}} at {{gli|atom|atomic}} and {{gli|subatomic particle|subatomic}} length scales, and provides a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter that occur at this scale.}}

{{defn|An elementary {{gli|particle}} and a fundamental constituent of {{gli|matter}}. Quarks combine to form composite particles called {{gli|hadron|hadrons}}, the most stable of which are {{gli|proton|protons}} and {{gli|neutron|neutrons}}, the components of {{gli|nucleus|atomic nuclei}}.}}

R

{{ghat|Also called a radioactive nuclide, radioisotope, or radioactive isotope.}}

{{defn|Any {{gli|nuclide}} possessing excess nuclear {{gli|energy}} to the point that it is unstable. Such excess energy is emitted through any of several processes of {{gli|radioactive decay}}, resulting in a {{gli|stable nuclide}} or sometimes another unstable radionuclide which can then undergo further decay. Certain radionuclides occur naturally; many others can be produced artificially in nuclear reactors, {{gli|cyclotron|cyclotrons}}, {{gli|particle accelerator|particle accelerators}}, or radionuclide generators.}}

{{defn|A phenomenon which occurs when {{gli|light}} seen coming from an object that is moving away from the observer is proportionally increased in {{gli|wavelength}} or "shifted" to the red end of the {{gli|visible light}} spectrum.}}

{{defn|The change in direction of a {{gli|wave}} as it passes from one {{gli|transmission medium}} to another or as a result of a gradual change in the medium. Though most commonly used in the context of refraction of {{gli|light}}, other waves such as {{gli|sound}} waves and fluid waves also experience refraction.}}

{{defn|An idealization of a solid body in which {{gli|deformation}} is neglected. In other words, the {{gli|distance}} between any two given points of a rigid body remains constant in time regardless of the external forces exerted on it. Even though such an object cannot physically exist due to {{gli|relativity}}, objects can normally be assumed to be perfectly rigid if they are not moving near the {{gli|speed of light}}.}}

{{defn|The {{gli|kinetic energy}} due to the rotation of an object, which forms part of its total kinetic energy.}}

{{defn|The number of complete rotations or revolutions a rotating body makes per unit time.}}

{{defn|A formula used in atomic physics to describe the wavelengths of spectral lines of many chemical elements.}}

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S

{{defn|Any simple physical quantity that can be described by a single number (as opposed to {{gli|vector|vectors}}, {{gli|tensor|tensors}}, etc., which are described by several numbers such as magnitude and direction) and is unchanged by coordinate system rotations or translations (in Newtonian mechanics) or by Lorentz transformations or central-time translations (in relativity).}}

{{defn|The general physical process by which some forms of {{gli|radiation}}, such as {{gli|light}}, {{gli|sound}}, or moving particles, are forced to deviate from a straight {{gli|trajectory}} by one or more localised non-uniformities in the medium through which they pass.}}

{{defn|A systematic enterprise that builds and organises knowledge in the form of testable explanations and predictions about the universe.}}

{{defn|A mechanism that converts rotational motion to linear motion, and a {{gli|torque}} (rotational force) to a linear force; one of six classical {{gli|simple machine|simple machines}}.}}

{{defn|{{gli|radiant energy|Radiant energy}} of the {{gli|electromagnetic spectrum}} with {{gli|wavelength|wavelengths}} in the {{gli|visible light|visible}}, near-ultraviolet, and near-infrared spectra, the broadest definition of which includes all radiation with a wavelength between 0.1 μm and 5.0 μm.}}

{{defn|A mathematical equation which describes the time evolution of wave functions in {{gli|quantum mechanics}}.}}

{{defn|A mechanical device that changes the direction or magnitude of a {{gli|force}}. In general, a set of six classical simple machines identified by Renaissance scientists drawing from Greek texts on technology are collectively defined as the simplest mechanisms that can provide mechanical advantage (also called leverage).}}

{{defn|A tube in an inverted U shape that causes a liquid to flow uphill without pumps, powered by the fall of the liquid as it flows down the tube under the pull of {{gli|gravity}}. The term may also more generally refer to a wide variety of devices involving the flow of liquids through tubes.}}

{{defn|The tendency of a {{gli|solid}}, {{gli|liquid}}, or {{gli|gas}}eous chemical substance (called a solute) to dissolve in another solid, liquid, or gaseous substance (called a solvent) to form a homogeneous solution of the solute in the solvent. The solubility of a solute fundamentally depends on the specific solvent as well as on {{gli|temperature}} and {{gli|pressure}}.}}

{{defn|A mechanical {{gli|wave}} that is an oscillation of {{gli|pressure}} transmitted through a solid, liquid, or gas and composed of frequencies within the range of human hearing.}}

{{defn|A fundamental universal {{gli|physical constant}} defined as exactly 299,792,458 metres per second, a figure that is exact because the length of the metre is defined from this constant and the international standard for time. When not otherwise qualified, the term "speed of light" usually refers to the speed of {{gli|light}} in {{gli|vacuum}}, as opposed to the speed of light through some physical medium.}}

{{defn|The relative abundances of the atomically {{gli|stable nuclide|stable}} {{gli|isotope|isotopes}} of a given element as they occur in nature or in a particular experimental context.}}

{{defn|Any {{gli|nuclide}} that is not radioactive and does not spontaneously undergo {{gli|radioactive decay}}, as opposed to a {{gli|radionuclide}}. When such nuclides are referred to in relation to specific elements, they are usually termed {{gli|stable isotope ratio|stable isotopes}}.}}

{{defn|The theory of {{gli|particle physics}} which describes three of the four known {{gli|fundamental forces}} (the {{gli|electromagnetism|electromagnetic force}}, the {{gli|weak interaction|weak force}}, and the {{gli|strong interaction|strong force}}, but not the {{gli|gravitation|gravitational force}}) and classifies all known {{gli|elementary particle|elementary particles}}.}}

{{defn|The branch of mechanics concerned with the analysis of loads ({{gli|force}} and {{gli|torque}}, or "moment") on physical systems in static equilibrium, that is, in a state where the relative positions of subsystems do not vary over time, or where components and structures are at a constant {{gli|velocity}}.}}

{{defn|The rigidity of an object, i.e. the extent to which it resists {{gli|deformation}} in response to an applied {{gli|force}}.}}

{{defn|The transformation of a body from a reference configuration to a current configuration. A configuration is a set containing the positions of all particles of the body.}}

{{defn|no=1|An applied {{gli|force}} or system of forces that tends to {{gli|strain}} or {{gli|deformation|deform}} a physical body.}}

{{defn|no=2|A measure of the internal forces acting within a deformable body.}}

{{defn|no=3|A quantitative measure of the average force per unit area of a surface within a body on which internal forces act.}}

{{defn|Any particle that is smaller than an {{gli|atom}}.}}

{{defn|The physical process by which matter is transformed directly from the solid phase to the gas phase without passing through an intermediate liquid phase. Sublimation is an {{gli|endothermic}} phase transition that occurs at temperatures and pressures below a substance's {{gli|triple point}} in its phase diagram.}}

{{defn|A phenomenon of exactly zero {{gli|resistance|electrical resistance}} and expulsion of {{gli|magnetic field|magnetic fields}} occurring in certain materials when cooled below a characteristic critical temperature.}}

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T

{{defn|A physical property of {{gli|matter}} that quantitatively expresses the common notions of hot and cold.}}

{{defn|A branch of physics that employs mathematical models and abstractions of physical objects and systems in order to rationalize, explain, and predict natural phenomena, as opposed to {{gli|experimental physics}}, which relies on data generated by experimental observations.}}

{{defn|A state in which there is no net flow of {{gli|heat|thermal energy}} between two physical systems when the systems are connected by a path permeable to heat. A system may also be said to be in thermal equilibrium with itself if the {{gli|temperature}} within the system is spatially and temporally uniform. Systems in {{gli|thermodynamic equilibrium}} are always in thermal equilibrium, but the converse is not always true.}}

{{defn|An instrument used to measure {{gli|temperature}}.}}

{{defn|The tendency of a {{gli|force}} to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist to an object.}}

{{defn|The ability of a material to absorb {{gli|energy}} and plastically {{gli|deformation|deform}} without fracturing. Material toughness is defined as the amount of energy per unit volume that a material can absorb before rupturing. It is also defined as the resistance to fracture of a material when {{gli|stress|stressed}}.}}

{{defn|The path that a moving object follows through {{gli|space}} as a function of {{gli|time}}.}}

{{defn|A branch of mathematics that studies triangles and the relationships between their sides and the angles between these sides.}}

{{defn|The {{gli|temperature}} and {{gli|pressure}} at which the three {{gli|phase (matter)|phases}} (gas, liquid, and solid) of a given substance coexist in {{gli|thermodynamic equilibrium}}.}}

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U

{{defn|When there is unbalanced force(s); and as such, the object changes its state of motion. The object is not at equilibrium and subsequently accelerates.}}

{{defn|Any of a variety of mathematical inequalities asserting a fundamental limit to the precision with which certain pairs of physical properties of a {{gli|particle}}, such as position x and momentum p, cannot be known simultaneously.}}

{{defn|One dalton: one-twelfth the mass of an isolated neutral atom of the {{gli|isotope}} {{chem|12|6|C}} in its ground state.}}

{{defn|The {{gli|frequency}} of the oscillations of {{gli|alternating current}} (AC) in an electric power grid transmitted from a power plant to the end-user.}}

V

{{defn|An area of {{gli|space}} which contains no {{gli|matter}}.}}

{{defn|An {{gli|electron}} that is associated with an {{gli|atom}} and can participate in the formation of a chemical bond.}}

{{defn|The outermost electron shell of an {{gli|atom}}.}}

{{defn|A mathematical structure formed by a collection of elements called {{gli|vector|vectors}}, which may be added together and multiplied ("scaled") by numbers called {{gli|scalar|scalars}}.}}

{{defn|A {{gli|vector}} quantity defined as the rate of change of the position of an object with respect to a given {{gli|frame of reference}}. Velocity specifies both an object's {{gli|speed}} and direction of {{gli|motion}} (e.g. 60 kilometres per hour to the north).}}

{{defn|A form of {{gli|electromagnetic radiation}} generally defined as the range of {{gli|wavelength|wavelengths}} visible to the average human eye.}}

{{defn|The {{gli|SI}} derived unit for {{gli|electric potential}}, {{gli|voltage|electric potential difference}}, and {{gli|electromotive force}}, defined as the difference in electric potential between two points of a {{gli|electrical conductor|conducting}} wire when an {{gli|electric current}} of one {{gli|ampere}} dissipates one {{gli|watt}} of {{gli|power}} between those two points.}}

{{defn|An instrument used for measuring the difference in {{gli|electric potential}} between two points in an {{gli|electric circuit}}. Analog voltmeters move a pointer across a scale in proportion to the {{gli|voltage}} of the circuit.}}

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W

{{defn|A derived unit of {{gli|power}} in the International System of Units (SI) defined as one joule per second. The watt measures the rate of energy conversion or transfer.}}

{{defn|A disturbance or oscillation that travels through {{gli|spacetime}} accompanied by a transfer of {{gli|energy}}.}}

{{defn|A measure of the distance traversed by a single spatial period of a sinusoidal {{gli|wave}}, i.e. the distance over which the wave's shape repeats.}}

{{ghat|Also called the weak force or weak nuclear force.}}

{{defn|One of the four fundamental forces of nature, along with the {{gli|strong nuclear force}}, {{gli|electromagnetism}}, and {{gli|gravitation}}. It is responsible for the {{gli|radioactive decay}} of {{gli|subatomic particle|subatomic particles}} and initiates the process known as {{gli|fusion|hydrogen fusion}} in stars.}}

{{defn|A triangular round tool in the form of a compound and portable inclined plane; one of six classical {{gli|simple machine|simple machines}}.}}

{{defn|A wheel attached to an axle in such a way that the two parts rotate together and transfer forces between them; one of six classical {{gli|simple machine|simple machines}}.}}

{{defn|A hypothetical idealized physical body that reflects all incident {{gli|electromagnetic radiation}} completely and uniformly in all directions; the opposite of a {{gli|black body}}.}}

X

{{defn|A high-energy {{gli|photon}} (between 100 {{gli|electron volt|eV}} and 100 keV) with a wavelength shorter than that of ultraviolet radiation and longer than that of gamma radiation.}}

Y

{{defn|A measure of the {{gli|stiffness}} of a solid material which defines the relationship between mechanical {{gli|stress}} and {{gli|strain}}.}}

Z

{{defn|The effect of splitting a spectral line into several components in the presence of a static magnetic field by the lifting of degeneracy in electronic states.}}

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References

Category:Glossaries of science

Category:Wikipedia glossaries using description lists

Glossary of physics

A

B

C

D

E

F

G

H

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See also

References