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1. Search engineering dictionary: Browse by letter: A; B; C; D; E; F; G; H; I; J; K; L; M; N; O; P; Q; R; S; T; U; V; W; X; Y; Z.
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This glossary of engineering terms is a list of definitions about the major concepts of engineering. Please see the bottom of the page for glossaries of specific fields of engineering.

Engineering

A[edit]

Absolute electrode potential

In electrochemistry, according to an IUPAC definition,^[1] is the electrode potential of a metal measured with respect to a universal reference system (without any additional metal–solution interface).

Absolute pressure

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

Absolute zero

Is the lower limit of the thermodynamic temperature scale, a state at which the enthalpy and entropy of a cooled ideal gas reach their minimum value, taken as 0. Absolute zero is the point at which the fundamental particles of nature have minimal vibrational motion, retaining only quantum mechanical, zero-point energy-induced particle motion. The theoretical temperature is determined by extrapolating the ideal gas law; by international agreement, absolute zero is taken as −273.15° on the Celsius scale (International System of Units),^[2][3] which equals −459.67° on the Fahrenheit scale (United States customary units or Imperial units).^[4] The corresponding Kelvin and Rankine temperature scales set their zero points at absolute zero by definition.

Absorbance

Absorbance or decadic absorbance is the common logarithm of the ratio of incident to transmittedradiant power through a material, and spectral absorbance or spectral decadic absorbance is the common logarithm of the ratio of incident to transmittedspectral radiant power through a material.^[5]

AC power

Electric power delivered by alternating current; common household power is AC.

Acceleration

The rate at which the velocity of a body changes with time, and the direction in which that change is acting.

Acid

A molecule or ion capable of donating a hydron (proton or hydrogen ion H⁺), or, alternatively, capable of forming a covalent bond with an electron pair (a Lewis acid).^[6]

Acid-base reaction

A chemical reaction that occurs between an acid and a base, which can be used to determine pH.

Acid strength

In strong acids, most of the molecules give up a hydrogen ion and become ionized.

Acoustics

The scientific study of sound.

Activated sludge

A type of wastewater treatment process for treating sewage or industrial wastewaters using aeration and a biological floc composed of bacteria and protozoa.

Activated sludge model

A generic name for a group of mathematical methods to model activated sludge systems.

Active transport

In cellular biology, active transport is the movement of molecules across a membrane from a region of their lower concentration to a region of their higher concentration—against the concentration gradient. Active transport requires cellular energy to achieve this movement. There are two types of active transport: primary active transport that uses ATP, and secondary active transport that uses an electrochemical gradient. An example of active transport in human physiology is the uptake of glucose in the intestines.

Actuator

The final element of a control loop, that translates control signals into a physical output movement.

Adenosine triphosphate

A complex organic chemical that provides energy to drive many processes in living cells, e.g. muscle contraction, nerve impulse propagation, chemical synthesis. Found in all forms of life, ATP is often referred to as the 'molecular unit of currency' of intracellular energy transfer.^[7]

Adhesion

The tendency of dissimilar particles or surfaces to cling to one another (cohesion refers to the tendency of similar or identical particles/surfaces to cling to one another).

Adiabatic process

A process where no heat energy is lost to outside space.

Adiabatic wall

A barrier through which heat energy cannot pass.

Aerobic digestion

A process in sewage treatment designed to reduce the volume of sewage sludge and make it suitable^[8] for subsequent use.^[9]

Aerodynamics

The study of the motion of air, particularly its interaction with a solid object, such as an airplane wing. It is a sub-field of fluid dynamics and gas dynamics, and many aspects of aerodynamics theory are common to these fields..

Aerospace engineering

Aerospace engineering Is the primary field of engineering concerned with the development of aircraft and spacecraft.^[10] It has two major and overlapping branches: Aeronautical engineering and Astronautical Engineering. Avionics engineering is similar, but deals with the electronics side of aerospace engineering.

Afocal system

An optical system that produces no net convergence or divergence of the beam, i.e. has an infinite effective focal length.^[11]

Agricultural engineering

The profession of designing machinery, processes, and systems for use in agriculture.

Albedo

A measure of the fraction of light reflected from an astronomical body or other object.

Alkane

An alkane, or paraffin (a historical name that also has other meanings), is an acyclicsaturatedhydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in which all the carbon–carbon bonds are single.^[12]

Alkene

An unsaturated hydrocarbon that contains at least one carbon–carbon double bond.^[13] The words alkene and olefin are often used interchangeably.

Alkyne

Is an unsaturatedhydrocarbon containing at least one carbon—carbon triple bond.^[14] The simplest acyclic alkynes with only one triple bond and no other functional groups form a homologous series with the general chemical formula C_nH_2n−2.

Alloy

is a combination of metals or of a metal and another element. Alloys are defined by a metallic bonding character.^[15]

Alpha particle

Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium-4nucleus. They are generally produced in the process of alpha decay, but may also be produced in other ways. Alpha particles are named after the first letter in the Greek alphabet, α.

Alternating current

Electrical current that regularly reverses direction.

Alternative hypothesis

In statistical hypothesis testing,the alternative hypothesis (or maintained hypothesis or research hypothesis) and the null hypothesis are the two rival hypotheses which are compared by a statistical hypothesis test. In the domain of science two rival hypotheses can be compared by explanatory power and predictive power..

Ammeter

An instrument that measures current.

Amino acids

Are organic compounds containing amine (-NH₂) and carboxyl (-COOH) functional groups, along with a side chain (R group) specific to each amino acid.^[16][17][18] The key elements of an amino acid are carbon (C), hydrogen (H), oxygen (O), and nitrogen (N), although other elements are found in the side chains of certain amino acids. About 500 naturally occurring amino acids are known (though only 20 appear in the genetic code) and can be classified in many ways.^[19]

Amorphous solid

An amorphous (from the Greek a, without, morphé, shape, form) or non-crystalline solid is a solid that lacks the long-range order that is characteristic of a crystal.

Ampere

The SI unit of current flow, one coulomb per second.

Amphoterism

In chemistry, an amphoteric compound is a molecule or ion that can react both as an acid as well as a base.^[20] Many metals (such as copper, zinc, tin, lead, aluminium, and beryllium) form amphoteric oxides or hydroxides. Amphoterism depends on the oxidation states of the oxide. Al₂O₃ is an example of an amphoteric oxide..

Amplifier

A device that replicates a signal with increased power.

Amplitude

The amplitude of a periodicvariable is a measure of its change over a single period (such as time or spatial period). There are various definitions of amplitude, which are all functions of the magnitude of the difference between the variable's extreme values. In older texts the phase is sometimes called the amplitude.^[21]

Anaerobic digestion

Is a collection of processes by which microorganisms break down biodegradable material in the absence of oxygen.^[22] The process is used for industrial or domestic purposes to manage waste or to produce fuels. Much of the fermentation used industrially to produce food and drink products, as well as home fermentation, uses anaerobic digestion.

Angular acceleration

Is the 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).^[23]

Angular momentum

In physics, angular momentum (rarely, moment of momentum or rotational momentum) is the rotational equivalent of linear momentum. It is an important quantity in physics because it is a conserved quantity—the total angular momentum of a system remains constant unless acted on by an external torque.

Angular velocity

In physics, the angular velocity of a particle is the rate at which it rotates around a chosen center point: that is, the time rate of change of its angular displacement relative to the origin (i.e. in layman's terms: how quickly an object goes around something over a period of time - e.g. how fast the earth orbits the sun). It is measured in angle per unit time, radians per second in SI units, and is usually represented by the symbol omega (ω, sometimes Ω). By convention, positive angular velocity indicates counter-clockwise rotation, while negative is clockwise.

Anion

Is an ion with more electrons than protons, giving it a net negative charge (since electrons are negatively charged and protons are positively charged).^[24]

Annealing (metallurgy)

A heat treatment process that relieves internal stresses.

Annihilation

In particle physics, annihilation is 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.^[25] 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.^[26]

Anode

The electrode at which current enters a device such as an electrochemical cell or vacuum tube.

ANSI

The American National Standards Institute is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States.^[27] The organization also coordinates U.S. standards with international standards so that American products can be used worldwide.

Anti-gravity

Anti-gravity (also known as non-gravitational field) is 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.

Applied engineering

Is the field concerned with the application of management, design, and technical skills for the design and integration of systems, the execution of new product designs, the improvement of manufacturing processes, and the management and direction of physical and/or technical functions of a firm or organization. Applied-engineering degreed programs typically include instruction in basic engineering principles, project management, industrial processes, production and operations management, systems integration and control, quality control, and statistics.^[28]

Applied mathematics

Mathematics used for solutions of practical problems, as opposed to pure mathematics.

Arc length

Determining the length of an irregular arc segment is also called rectification of a curve. Historically, many methods were used for specific curves. The advent of infinitesimal calculus led to a general formula that provides closed-form solutions in some cases.

Archimedes' principle

Archimedes' principle 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.^[29] Archimedes' principle is a law of physics fundamental to fluid mechanics. It was formulated by Archimedes of Syracuse.^[30]

Area moment of inertia

The 2nd moment of area, also known as moment of inertia of plane area, area moment of inertia, or second area moment, is a geometrical property of an area which reflects how its points are distributed with regard to an arbitrary axis. The second moment of area is typically denoted with either an ${\displaystyle I}$ for an axis that lies in the plane or with a ${\displaystyle J}$ for an axis perpendicular to the plane. In both cases, it is calculated with a multiple integral over the object in question. Its dimension is L (length) to the fourth power. Its unit of dimension when working with the International System of Units is meters to the fourth power, m⁴.

Arithmetic mean

In mathematics and statistics, the arithmetic mean or simply the mean or average when the context is clear, is the sum of a collection of numbers divided by the number of numbers in the collection.^[31]

Arithmetic progression

In mathematics, an arithmetic progression (AP) or arithmetic sequence is a sequence of numbers such that the difference between the consecutive terms is constant. Difference here means the second minus the first. For instance, the sequence 5, 7, 9, 11, 13, 15, . . . is an arithmetic progression with common difference of 2.

Aromatic hydrocarbon

An aromatic hydrocarbon or arene^[32] (or sometimes aryl hydrocarbon)^[33] is a hydrocarbon with sigma bonds and delocalized pi electrons between carbon atoms forming a circle. In contrast, aliphatic hydrocarbons lack this delocalization. The term 'aromatic' was assigned before the physical mechanism determining aromaticity was discovered; the term was coined as such simply because many of the compounds have a sweet or pleasant odour. The configuration of six carbon atoms in aromatic compounds is known as a benzene ring, after the simplest possible such hydrocarbon, benzene. Aromatic hydrocarbons can be monocyclic (MAH) or polycyclic (PAH).

Arrhenius equation

The Arrhenius equation is a formula for the temperature dependence of reaction rates. The equation was proposed by Svante Arrhenius in 1889, based on the work of Dutch chemist Jacobus Henricus van 't Hoff who had noted in 1884 that Van 't Hoff's equation for the temperature dependence of equilibrium constants suggests such a formula for the rates of both forward and reverse reactions. This equation has a vast and important application in determining rate of chemical reactions and for calculation of energy of activation. Arrhenius provided a physical justification and interpretation for the formula.^[34][35][36] Currently, it is best seen as an empirical relationship.^[37]:188 It can be used to model the temperature variation of diffusion coefficients, population of crystal vacancies, creep rates, and many other thermally-induced processes/reactions. The Eyring equation, developed in 1935, also expresses the relationship between rate and energy.

Artificial intelligence

The intelligence of machines and the branch of computer science that aims to create it..

Assembly language

A computer programming language where most statements correspond to one or a few machine op-codes.

Atomic orbital

In atomic theory and quantum mechanics, an atomic orbital is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom.^[38] This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus. The term atomic orbital may also refer to the physical region or space where the electron can be calculated to be present, as defined by the particular mathematical form of the orbital.^[39]

Atomic packing factor

The percentage of the volume filled with atomic mass in a crystal formation.

Audio frequency

An audio frequency (abbreviation: AF) or audible frequency is characterized as a periodicvibration whose frequency is audible to the average human. The SI unit of audio frequency is the hertz (Hz). It is the property of sound that most determines pitch.^[40]

Austenitization

Austenitization means to heat the iron, iron-based metal, or steel to a temperature at which it changes crystal structure from ferrite to austenite.^[41] The more open structure of the austenite is then able to absorb carbon from the iron-carbides in carbon steel. An incomplete initial austenitization can leave undissolved carbides in the matrix.^[42] For some irons, iron-based metals, and steels, the presence of carbides may occur during the austenitization step. The term commonly used for this is two-phase austenitization.^[43]

Automation

Is the technology by which a process or procedure is performed with minimum human assistance.^[44] Automation ^[45] or automatic control is the use of various control systems for operating equipment such as machinery, processes in factories, boilers and heat treating ovens, switching on telephone networks, steering and stabilization of ships, aircraft and other applications and vehicles with minimal or reduced human intervention. Some processes have been completely automated.

Autonomous vehicle

A vehicle capable of driving from one point to another without input from a human operator.

Azimuthal quantum number

The azimuthal quantum number is a quantum number for an atomic orbital that determines its orbital angular momentum and describes the shape of the orbital. The azimuthal quantum number is the second of a set of quantum numbers which describe the unique quantum state of an electron (the others being the principal quantum number, following spectroscopic notation, the magnetic quantum number, and the spin quantum number). It is also known as the orbital angular momentum quantum number, orbital quantum number or second quantum number, and is symbolized as ℓ.

B[edit]

Barometer

A device for measuring pressure.

Battery

Electrochemical cells that transform chemical energy into electricity..

Base

In chemistry, bases are substances that, in aqueous solution, release hydroxide (OH⁻) ions, are slippery to the touch, can taste bitter if an alkali,^[46] change the color of indicators (e.g., turn red litmus paper blue), react with acids to form salts, promote certain chemical reactions (base catalysis), accept protons from any proton donor, and/or contain completely or partially displaceable OH⁻ions.

Baud

Rate at which data is transferred in symbols/second; a symbol may represent one or more bits.

Beam

A structural element whose length is significantly greater than its width or height.

Beer–Lambert law

The Beer–Lambert law, also known as Beer's law, the Lambert–Beer law, or the Beer–Lambert–Bouguer law relates the attenuation of light to the properties of the material through which the light is travelling. The law is commonly applied to chemical analysis measurements and used in understanding attenuation in physical optics, for photons, neutrons or rarefied gases. In mathematical physics, this law arises as a solution of the BGK equation.

Belt

A closed loop of flexible material used to transmit mechancial power from one pulley to another.

Belt friction

Is a term describing the friction forces between a belt and a surface, such as a belt wrapped around a bollard. When one end of the belt is being pulled only part of this force is transmitted to the other end wrapped about a surface. The friction force increases with the amount of wrap about a surface and makes it so the tension in the belt can be different at both ends of the belt. Belt friction can be modeled by the Belt friction equation.^[47]

Bending

In applied mechanics, bending (also known as flexure) characterizes the behavior of a slender structural element subjected to an external load applied perpendicularly to a longitudinal axis of the element. The structural element is assumed to be such that at least one of its dimensions is a small fraction, typically 1/10 or less, of the other two.^[48]

Benefit–cost analysis

Cost–benefit analysis (CBA), sometimes called benefit costs analysis (BCA), is a systematic approach to estimating the strengths and weaknesses of alternatives (for example in transactions, activities, functional business requirements); it is used to determine options that provide the best approach to achieve benefits while preserving savings.^[49] It may be used to compare potential (or completed) courses of actions; or estimate (or evaluate) the value against costs of a single decision, project, or policy..

Bending moment

The product of bending force and distance, measured in units of length * distance..

Bernoulli differential equation

In mathematics, an ordinary differential equation of the form:

is called a Bernoulli differential equation where ${\displaystyle n}$ is any real number and ${\displaystyle n\ne 0}$ and ${\displaystyle n\ne 1}$.^[50] It is named after Jacob Bernoulli who discussed it in 1695. Bernoulli equations are special because they are nonlinear differential equations with known exact solutions. A famous special case of the Bernoulli equation is the logistic differential equation.

Bernoulli's equation

An equation for relating several measurements within a fluid flow, such as velocity, pressure, and potential energy.

Bernoulli's principle

In fluid dynamics, Bernoulli's principle 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.^{[51](Ch.3)[52](§ 3.5)} The principle is named after Daniel Bernoulli who published it in his book Hydrodynamica in 1738.^[53] Although Bernoulli deduced that pressure decreases when the flow speed increases, it was Leonhard Euler who derived Bernoulli's equation in its usual form in 1752.^[54][55] The principle is only applicable for isentropic flows: when the effects of irreversible processes (like turbulence) and non-adiabatic processes (e.g. heat radiation) are small and can be neglected.

Beta particle

also called beta ray or beta radiation (symbol β), is a high-energy, high-speed electron or positron emitted by the radioactive decay of an atomic nucleus during the process of beta decay. There are two forms of beta decay, β⁻ decay and β⁺ decay, which produce electrons and positrons respectively.^[56]

Binomial distribution

In probability theory and statistics, the binomial distribution with parameters n and p is the discrete probability distribution of the number of successes in a sequence of nindependentexperiments, each asking a yes–no question, and each with its own boolean-valued outcome: a random variable containing a single bit of information: success/yes/true/one (with probabilityp) or failure/no/false/zero (with probabilityq = 1 − p). A single success/failure experiment is also called a Bernoulli trial or Bernoulli experiment and a sequence of outcomes is called a Bernoulli process; for a single trial, i.e., n = 1, the binomial distribution is a Bernoulli distribution. The binomial distribution is the basis for the popular binomial test of statistical significance.

Biocatalysis

Biocatalysis refers to the use of living (biological) systems or their parts to speed up (catalyze) chemical reactions. In biocatalytic processes, natural catalysts, such as enzymes, perform chemical transformations on organic compounds. Both enzymes that have been more or less isolated and enzymes still residing inside living cells are employed for this task.^[57][58][59] The modern usage of biotechnologically produced and possibly modified enzymes for organic synthesis is termed chemoenzymatic synthesis; the reactions performed are chemoenzymatic reactions.

Biomedical engineering

Biomedical Engineering (BME) or Medical Engineering is the application of engineering principles and design concepts to medicine and biology for healthcare purposes (e.g. diagnostic or therapeutic). This field seeks to close the gap between engineering and medicine, combining the design and problem solving skills of engineering with medical biological sciences to advance health care treatment, including diagnosis, monitoring, and therapy.^[60]

Biomimetic

Biomimetics or biomimicry is the imitation of the models, systems, and elements of nature for the purpose of solving complex human problems.^[61]

Bionics

The application of biological methods to engineering systems.

Biophysics

Is an interdisciplinary science that applies approaches and methods traditionally used in physics to study biological phenomena.^[62][63][64] Biophysics covers all scales of biological organization, from molecular to organismic and populations. Biophysical research shares significant overlap with biochemistry, molecular biology, physical chemistry, physiology, nanotechnology, bioengineering, computational biology, biomechanics and systems biology.

Biot number

The Biot number (Bi) is a dimensionless quantity used in heat transfer calculations. It is named after the eighteenth century French physicist Jean-Baptiste Biot (1774–1862), and gives a simple index of the ratio of the heat transfer resistances inside of and at the surface of a body. This ratio determines whether or not the temperatures inside a body will vary significantly in space, while the body heats or cools over time, from a thermal gradient applied to its surface.

Block and tackle

A system of pulleys and a rope threaded between them, used to lift or pull heavy loads.

Body force

Is a force that acts throughout the volume of a body. Forces due to gravity, electric fields and magnetic fields are examples of body forces. Body forces contrast with contact forces or surface forces which are exerted to the surface of an object..

Boiler

A device whose purpose is to add heat to a working fluid to vaporise it..

Boiler (power generation)

A boiler used in a power plant for electricity or propulsion.

Boiling point

The state at which a substance becomes gaseous.

Boiling-point elevation

Boiling-point elevation describes the phenomenon that the boiling point of a liquid (a solvent) will be higher when another compound is added, meaning that a solution has a higher boiling point than a 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

The Boltzmann constant (k_B or k) is a physical constant relating the average kinetic energy of particles in a gas with the temperature of the gas^[65] and occurs in Planck's law of black-body radiation and in Boltzmann's entropy formula. It was introduced by Max Planck, but named after Ludwig Boltzmann.It is the gas constantR divided by the Avogadro constantN_A:

${\displaystyle k=\frac{R}{N_{\text{A}}}.}$.

Boson

In quantum mechanics, a boson (/ˈboʊsɒn/,^[66]/ˈboʊzɒn/^[67]) is a particle that follows Bose–Einstein statistics. Bosons make up one of the two classes of particles, the other being fermions.^[68] The name boson was coined by Paul Dirac^[69][70] to commemorate the contribution of Indian physicist and professor of physics at University of Calcutta and at University of Dhaka, Satyendra Nath Bose^[71][72] in developing, with Albert Einstein, Bose–Einstein statistics—which theorizes the characteristics of elementary particles.^[73]

Boyle's law

Boyle's law (sometimes referred to as the Boyle–Mariotte law, or Mariotte's law^[74]) is an experimental gas law that describes how the pressure of a gas tends to increase as the volume of the container decreases. A modern statement of Boyle's law is: The absolute pressure exerted by a given mass of an ideal gas is inversely proportional to the volume it occupies if the temperature and amount of gas remain unchanged within a closed system.^[75][76]

Bravais lattice

In geometry and crystallography, a Bravais lattice, named after Auguste Bravais (1850),^[77] is an infinite array (or a finite array, if we consider the edges, obviously) of discrete points generated by a set of discrete translation operations described in three dimensional space by:

${\displaystyle \mathbf{R}=n_1{\mathbf{a}}_1+n_2{\mathbf{a}}_2+n_3{\mathbf{a}}_3}$

where n_i are any integers and a_i are known as the primitive vectors which lie in different directions (not necessarily mutually perpendicular) and span the lattice. This discrete set of vectors must be closed under vector addition and subtraction. For any choice of position vector R, the lattice looks exactly the same.

Brayton cycle

A thermodynamic cycle model for an ideal heat engine, in which heat is added or removed at constant pressure; approximated by a gas turbine.

Break-even

The break-even point (BEP) in economics, business—and specifically cost accounting—is the point at which total cost and total revenue are equal, i.e. 'even'. There is no net loss or gain, and one has 'broken even', though opportunity costs have been paid and capital has received the risk-adjusted, expected return. In short, all costs that must be paid are paid, and there is neither profit nor loss.^[78][79]

Brewster's angle

Brewster's angle (also known as the polarization angle) is an angle of incidence at which light with a particular polarization is perfectly transmitted through a transparent dielectric surface, with no reflection. When unpolarized light is incident at this angle, the light that is reflected from the surface is therefore perfectly polarized. This special angle of incidence is named after the Scottish physicist Sir David Brewster (1781–1868).^[80][81]

Brittleness

A material is brittle if, when subjected to stress, it breaks without significant plastic deformation. Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Breaking is often accompanied by a snapping sound. Brittle materials include most ceramics and glasses (which do not deform plastically) and some polymers, such as PMMA and polystyrene. Many steels become brittle at low temperatures (see ductile-brittle transition temperature), depending on their composition and processing.

Bromide

Any chemical substance made up of Bromine, along with other elements.

Brønsted–Lowry acid–base theory

Is an acid–base reaction theory which was proposed independently by Johannes Nicolaus Brønsted and Thomas Martin Lowry in 1923.^[82][83] The fundamental concept of this theory is that when an acid and a base react with each other, the acid forms its conjugate base, and the base forms its conjugate acid by exchange of a proton (the hydrogen cation, or H⁺). This theory is a generalization of the Arrhenius theory..

Brownian motion

Brownian motion or pedesis is the random motion of particles suspended in a fluid (a liquid or a gas) resulting from their collision with the fast-moving molecules in the fluid.^[84]

Buckingham π theorem

A method for determining ∏ groups, or dimensionless descriptors of physical phenomena.

Buffer solution

A buffer solution (more precisely, pH buffer or hydrogen ion buffer) is an aqueous solution consisting of a mixture of a weak acid and its conjugate base, or vice versa. Its pH changes very little when a small amount of strong acid or base is added to it. Buffer solutions are used as a means of keeping pH at a nearly constant value in a wide variety of chemical applications. In nature, there are many systems that use buffering for pH regulation.

Bulk modulus

The bulk modulus (${\displaystyle K}$ or ${\displaystyle B}$) of a substance is a measure of how resistant to compression that substance is. It is defined as the ratio of the infinitesimalpressure increase to the resulting relative decrease of the volume.^[85] Other moduli describe the material's response (strain) to other kinds of stress: the shear modulus describes the response to shear, and Young's modulus describes the response to linear stress. For a fluid, only the bulk modulus is meaningful. For a complex anisotropic solid such as wood or paper, these three moduli do not contain enough information to describe its behaviour, and one must use the full generalized Hooke's law..

Buoyancy

A force caused by displacement in a fluid by an object of different density than the fluid.

C[edit]

Calculus

The mathematics of change.

Capacitance

The ability of a body to store electrical charge.

Capacitive reactance

The impedance of a capacitor in an alternating current circuit, the opposition to current flow.

Capacitor

An electrical component that stores energy in an electric field.

Capillary action

Capillary action (sometimes capillarity, capillary motion, capillary effect, or wicking) is the ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity. The effect can be seen in the drawing up of liquids between the hairs of a paint-brush, in a thin tube, in porous materials such as paper and plaster, in some non-porous materials such as sand and liquefied carbon fiber, or in a cell. It occurs because of intermolecular forces between the liquid and surrounding solid surfaces. If the diameter of the tube is sufficiently small, then the combination of surface tension (which is caused by cohesion within the liquid) and adhesive forces between the liquid and container wall act to propel the liquid.^[86]

Carbonate

Any mineral with bound carbon dioxide.

Carnot cycle

A hypothetical thermodynamic cycle for a heat engine; no thermodynamic cycle can be more efficient than a Carnot cycle operating between the same two temperature limits.

Cartesian coordinates

Coordinates within a rectangular Cartesian plane.

Castigliano's method

Named for Carlo Alberto Castigliano, is a method for determining the displacements of a linear-elastic system based on the partial derivatives of the energy. He is known for his two theorems. The basic concept may be easy to understand by recalling that a change in energy is equal to the causing force times the resulting displacement. Therefore, the causing force is equal to the change in energy divided by the resulting displacement. Alternatively, the resulting displacement is equal to the change in energy divided by the causing force. Partial derivatives are needed to relate causing forces and resulting displacements to the change in energy.

Casting

Forming of an object by pouring molten metal (or other substances) into a mold.

Cathode

The terminal of a device by which current exits.

Cathode ray

The stream of electrons emitted from a heated negative electrode and attracted to a positive electrode.

Cell membrane

The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates the interior of all cells from the outside environment (the extracellular space) which protects the cell from its environment^[87][88] consisting of a lipid bilayer with embedded proteins.

Cell nucleus

In cell biology, the nucleus (pl. nuclei; from Latinnucleus or nuculeus, meaning kernel or seed) is a membrane-enclosed organelle found in eukaryoticcells. Eukaryotes usually have a single nucleus, but a few cell types, such as mammalian red blood cells, have no nuclei, and a few others including osteoclasts have many.

Cell theory

In biology, cell theory is the historic scientific theory, now universally accepted, that living organisms are made up of cells, that they are the basic structural/organizational unit of all organisms, and that all cells come from pre-existing cells. Cells are the basic unit of structure in all organisms and also the basic unit of reproduction.

Center of gravity

The center of mas of an object, its balance point.

Center of mass

The weighted center of an object; a force applied through the center of mass will not cause rotation of the object.

Center of pressure

Is the point where the total sum of a pressure field acts on a body, causing a force to act through that point. The total force vector acting at the center of pressure is the value of the integrated vectorial pressure field. The resultant force and center of pressure location produce equivalent force and moment on the body as the original pressure field.

Central force motion

.

Central limit theorem

In probability theory, the central limit theorem (CLT) establishes that, in some situations, when independent random variables are added, their properly normalized sum tends toward a normal distribution (informally a 'bell curve') even if the original variables themselves are not normally distributed. The theorem is a key concept in probability theory because it implies that probabilistic and statistical methods that work for normal distributions can be applicable to many problems involving other types of distributions.

Central processing unit

A central processing unit (CPU) is the electronic circuitry within a computer that carries out the instructions of a computer program by performing the basic arithmetic, logic, controlling and input/output (I/O) operations specified by the instructions. The computer industry has used the term 'central processing unit' at least since the early 1960s.^[89] Traditionally, the term 'CPU' refers to a processor, more specifically to its processing unit and control unit (CU), distinguishing these core elements of a computer from external components such as main memory and I/O circuitry.^[90]

Centripetal acceleration

.

Centripetal force

A force acting against rotational acceleration.

Centroid

The average point of volume for an object.

Centrosome

In cell biology, the centrosome is an organelle that serves as the main microtubule organizing center (MTOC) of the animal cell as well as a regulator of cell-cycle progression. The centrosome is thought to have evolved only in the metazoan lineage of eukaryotic cells.^[91]Fungi and plants lack centrosomes and therefore use structures other than MTOCs to organize their microtubules.^[92][93]

Chain reaction

Is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. In a chain reaction, positive feedback leads to a self-amplifying chain of events.

Change of base rule

.

Charles's law

Charles's law (also known as the law of volumes) is an experimental gas law that describes how gasestend to expand when heated. A modern statement of Charles's law is: When the pressure on a sample of a dry gas is held constant, the Kelvin temperature and the volume will be in direct proportion.^[94]

Chemical bond

Is a lasting attraction between atoms, ions or molecules that enables the formation of chemical compounds. The bond may result from the electrostatic force of attraction between oppositely charged ions as in ionic bonds or through the sharing of electrons as in covalent bonds. The strength of chemical bonds varies considerably; there are 'strong bonds' or 'primary bonds' such as covalent, ionic and metallic bonds, and 'weak bonds' or 'secondary bonds' such as dipole–dipole interactions, the London dispersion force and hydrogen bonding.

Chemical compound

Is a chemical substance composed of many identical molecules (or molecular entities) composed of atoms from more than one element held together by chemical bonds. A chemical element bonded to an identical chemical element is not a chemical compound since only one element, not two different elements, is involved.

Chemical equilibrium

In a chemical reaction, chemical equilibrium is the state in which both reactants and products are present in concentrations which have no further tendency to change with time, so that there is no observable change in the properties of the system.^[95] Usually, this state results when the forward reaction proceeds at the same rate as the reverse reaction. The reaction rates of the forward and backward reactions are generally not zero, but equal. Thus, there are no net changes in the concentrations of the reactant(s) and product(s). Such a state is known as dynamic equilibrium.^[96][97]

Chemical kinetics

Chemical kinetics, also known as reaction kinetics, is the study of rates of chemical processes. Chemical kinetics includes investigations of how different experimental conditions can influence the speed of a chemical reaction and yield information about the reaction's mechanism and transition states, as well as the construction of mathematical models that can describe the characteristics of a chemical reaction.

Chemical reaction

A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another.^[98] Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between atoms, with no change to the nuclei (no change to the elements present), and can often be described by a chemical equation. Nuclear chemistry is a sub-discipline of chemistry that involves the chemical reactions of unstable and radioactive elements where both electronic and nuclear changes can occur.

Chemistry

Is the scientific discipline involved with elements and compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during a reaction with other substances.^[99][100]

Chloride

Any chemical compound containing the element chlorine.

Chromate

Chromate salts contain the chromate anion, CrO²⁻
₄. Dichromate salts contain the dichromate anion, Cr
₂O²⁻
₇. They are oxoanions of chromium in the 6+ oxidation state . They are moderately strong oxidizing agents. In an aqueoussolution, chromate and dichromate ions can be interconvertible.

Circular motion

In physics, circular motion is a movement of an object along the circumference of a circle or rotation along a circular path. It can be uniform, with constant angular rate of rotation and constant speed, or non-uniform with a changing rate of rotation. The rotation around a fixed axis of a three-dimensional body involves circular motion of its parts. The equations of motion describe the movement of the center of mass of a body.

Civil engineering

The profession that deals with the design and construction of structures, or other fixed works.

Clausius–Clapeyron relation

The Clausius–Clapeyron relation, named after Rudolf Clausius^[101] and Benoît Paul Émile Clapeyron,^[102] is a way of characterizing a discontinuous phase transition between two phases of matter of a single constituent. On a pressure–temperature (P–T) diagram, the line separating the two phases is known as the coexistence curve. The Clausius–Clapeyron relation gives the slope of the tangents to this curve. Mathematically,

${\displaystyle \frac{\mathrm{d}P}{\mathrm{d}T}=\frac{L}{T\mathrm{\Delta }v}=\frac{\mathrm{\Delta }s}{\mathrm{\Delta }v},}$

where ${\displaystyle \mathrm{d}P/\mathrm{d}T}$ is the slope of the tangent to the coexistence curve at any point, ${\displaystyle L}$ is the specific latent heat, ${\displaystyle T}$ is the temperature, ${\displaystyle \mathrm{\Delta }v}$ is the specific volume change of the phase transition, and ${\displaystyle \mathrm{\Delta }s}$ is the specific entropy change of the phase transition.

Clausius inequality

.

Clausius theorem

The Clausius theorem (1855) states that a system exchanging heat with external reservoirs and undergoing a cyclic process, is one that ultimately returns a system to its original state,

${\displaystyle \text{∮}\frac{\delta Q}{T_{surr}}\le 0,}$

where ${\displaystyle \delta Q}$ is the infinitesimal amount of heat absorbed by the system from the reservoir and ${\displaystyle T_{surr}}$ is the temperature of the external reservoir (surroundings) at a particular instant in time. In the special case of a reversible process, the equality holds.^[103] The reversible case is used to introduce the entropy state function. This is because in a cyclic process the variation of a state function is zero. In words, the Clausius statement states that it is impossible to construct a device whose sole effect is the transfer of heat from a cool reservoir to a hot reservoir.^[104] Equivalently, heat spontaneously flows from a hot body to a cooler one, not the other way around.^[105] The generalized 'inequality of Clausius'^[106]

${\displaystyle dS>\frac{\delta Q}{T_{surr}}}$

for an infinitesimal change in entropy S applies not only to cyclic processes, but to any process that occurs in a closed system.

Coefficient of performance

The coefficient of performance or COP (sometimes CP or CoP) of a heat pump, refrigerator or air conditioning system is a ratio of useful heating or cooling provided to work required.^[107][108] Higher COPs equate to lower operating costs. The COP usually exceeds 1, especially in heat pumps, because, instead of just converting work to heat (which, if 100% efficient, would be a COP_hp of 1), it pumps additional heat from a heat source to where the heat is required. For complete systems, COP calculations should include energy consumption of all power consuming auxiliaries. COP is highly dependent on operating conditions, especially absolute temperature and relative temperature between sink and system, and is often graphed or averaged against expected conditions.^[109]

Coefficient of variation

In probability theory and statistics, the coefficient of variation (CV), also known as relative standard deviation (RSD), is a standardized measure of dispersion of a probability distribution or frequency distribution. It is often expressed as a percentage, and is defined as the ratio of the standard deviation${\displaystyle \sigma }$ to the mean${\displaystyle \mu }$ (or its absolute value, ${\displaystyle |\mu |}$).

Coherence

In physics, two wave sources are perfectly coherent if they have a constant phase difference and the same frequency, and the same waveform. Coherence is an ideal property of waves that enables stationary (i.e. temporally and spatially constant) interference. It contains several distinct concepts, which are limiting cases that never quite occur in reality but allow an understanding of the physics of waves, and has become a very important concept in quantum physics. More generally, coherence describes all properties of the correlation between physical quantities of a single wave, or between several waves or wave packets.

Cohesion

Or cohesive attraction or cohesive force is the action or property of like molecules sticking together, being mutually attractive. It is an intrinsic property of a substance that is caused by the shape and structure of its molecules, which makes the distribution of orbiting electrons irregular when molecules get close to one another, creating electrical attraction that can maintain a microscopic structure such as a water drop. In other words, cohesion allows for surface tension, creating a 'solid-like' state upon which light-weight or low-density materials can be placed.

Cold forming

Or cold working, any metal-working procedure (such as hammering, rolling, shearing, bending, milling, etc.) carried out below the metal's recrystallization temperature.

Combustion

Or burning,^[110] is a high-temperature exothermicredoxchemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke.

Compensation

Is planning for side effects or other unintended issues in a design. In a more simpler term, it's a 'counter-procedure' plan on expected side effect performed to produce more efficient and useful results. The design of an invention can itself also be to compensate for some other existing issue or exception.

Compiler

A computer program that translates a high-level language into machine language.

Compressive strength

Compressive strength or compression strength is the capacity of a material or structure to withstand loads tending to reduce size, as opposed to tensile strength, which withstands loads tending to elongate. In other words, compressive strength resists compression (being pushed together), whereas tensile strength resists tension (being pulled apart). In the study of strength of materials, tensile strength, compressive strength, and shear strength can be analyzed independently.

Computational fluid dynamics

The numerical solution of flow equations in practical problems such as aircraft design or hydraulic structures.

Computer

A computer is a device that can be instructed to carry out sequences of arithmetic or logical operations automatically via computer programming. Modern computers have the ability to follow generalized sets of operations, called programs. These programs enable computers to perform an extremely wide range of tasks.

Computer-aided design

Computer-aided design (CAD) is the use of computer systems (or workstations) to aid in the creation, modification, analysis, or optimization of a design.^[111] CAD software is used to increase the productivity of the designer, improve the quality of design, improve communications through documentation, and to create a database for manufacturing.^[112] CAD output is often in the form of electronic files for print, machining, or other manufacturing operations. The term CADD (for Computer Aided Design and Drafting) is also used.^[113]

Computer-aided engineering

Computer-aided engineering (CAE) is the broad usage of computer software to aid in engineering analysis tasks. It includes finite element analysis (FEA), computational fluid dynamics (CFD), multibody dynamics (MBD), durability and optimization.

Computer-aided manufacturing

Computer-aided manufacturing (CAM) is the use of software to control machine tools and related ones in the manufacturing of workpieces.^{[114][115][116][117][118]} This is not the only definition for CAM, but it is the most common;^[114] CAM may also refer to the use of a computer to assist in all operations of a manufacturing plant, including planning, management, transportation and storage.^[119][120]

Computer engineering

Computer engineering is a discipline that integrates several fields of computer science and electronics engineering required to develop computer hardware and software.^[121]

Computer science

Is the theory, experimentation, and engineering that form the basis for the design and use of computers. It involves the study of algorithms that process, store, and communicate digitalinformation. A computer scientist specializes in the theory of computation and the design of computational systems.^[122]

Concave lens

Lenses are classified by the curvature of the two optical surfaces. A lens is biconvex (or double convex, or just convex) if both surfaces are convex. If both surfaces have the same radius of curvature, the lens is equiconvex. A lens with two concave surfaces is biconcave (or just concave). If one of the surfaces is flat, the lens is plano-convex or plano-concave depending on the curvature of the other surface. A lens with one convex and one concave side is convex-concave or meniscus.

Condensed matter physics

Is the field of physics that deals with the macroscopic and microscopic physical properties of matter. In particular it is concerned with the 'condensed' phases that appear whenever the number of constituents in a system is extremely large and the interactions between the constituents are strong.

Confidence interval

In statistics, a confidence interval or compatibility interval (CI) is a type of interval estimate, computed from the statistics of the observed data, that might contain the true value of an unknown population parameter. The interval has an associated confidence level that, loosely speaking, quantifies the level of confidence that the parameter lies in the interval. More strictly speaking, the confidence level represents the frequency (i.e. the proportion) of possible confidence intervals that contain the true value of the unknown population parameter. In other words, if confidence intervals are constructed using a given confidence level from an infinite number of independent sample statistics, the proportion of those intervals that contain the true value of the parameter will be equal to the confidence level.^{[123][124][125]}

Conjugate acid

A conjugate acid, within the Brønsted–Lowry acid–base theory, is a species formed by the reception of a proton (H⁺) by a base—in other words, it is a base with a hydrogen ion added to it. On the other hand, a conjugate base is what is left over after an acid has donated a proton during a chemical reaction. Hence, a conjugate base is a species formed by the removal of a proton from an acid.^[126] Because some acids are capable of releasing multiple protons, the conjugate base of an acid may itself be acidic.

Conjugate base

A conjugate acid, within the Brønsted–Lowry acid–base theory, is a species formed by the reception of a proton (H⁺) by a base—in other words, it is a base with a hydrogen ion added to it. On the other hand, a conjugate base is what is left over after an acid has donated a proton during a chemical reaction. Hence, a conjugate base is a species formed by the removal of a proton from an acid.^[126] Because some acids are capable of releasing multiple protons, the conjugate base of an acid may itself be acidic..

Conservation of energy

In physics and chemistry, the law of conservation of energy states that the total energy of an isolated system remains constant; it is said to be conserved over time.^[127] This law means that energy can neither be created nor destroyed; rather, it can only be transformed or transferred from one form to another.

Conservation of mass

The law of conservation of mass or principle of mass conservation states that for any system closed to all transfers of matter and energy, the mass of the system must remain constant over time, as system's mass cannot change, so quantity cannot be added nor removed. Hence, the quantity of mass is conserved over time.

Continuity equation

A continuity equation in physics is an equation that describes the transport of some quantity. It is particularly simple and powerful when applied to a conserved quantity, but it can be generalized to apply to any extensive quantity. Since mass, energy, momentum, electric charge and other natural quantities are conserved under their respective appropriate conditions, a variety of physical phenomena may be described using continuity equations.

Continuum mechanics

Is a branch of mechanics that deals with the mechanical behavior of materials modeled as a continuous mass rather than as discrete particles. The French mathematician Augustin-Louis Cauchy was the first to formulate such models in the 19th century.

Control engineering

Control engineering or control systems engineering is an engineering discipline that applies automatic control theory to design systems with desired behaviors in control environments.^[128] The discipline of controls overlaps and is usually taught along with electrical engineering at many institutions around the world.^[128].

Convex lens

Lenses are classified by the curvature of the two optical surfaces. A lens is biconvex (or double convex, or just convex) if both surfaces are convex. If both surfaces have the same radius of curvature, the lens is equiconvex. A lens with two concave surfaces is biconcave (or just concave). If one of the surfaces is flat, the lens is plano-convex or plano-concave depending on the curvature of the other surface. A lens with one convex and one concave side is convex-concave or meniscus.

Corrosion

Is a natural process, which converts a refined metal to a more chemically-stable form, such as its oxide, hydroxide, or sulfide. It is the gradual destruction of materials (usually metals) by chemical and/or electrochemical reaction with their environment. Corrosion engineering is the field dedicated to controlling and stopping corrosion.

Cosmic rays

Cosmic rays are high-energy radiation, mainly originating outside the Solar System.^[129]

Coulomb

The coulomb (symbol: C) is the International System of Units (SI) unit of electric charge. It is the charge (symbol: Q or q) transported by a constant current of one ampere in one second:

${\displaystyle 1\text{C}=1\text{A}\cdot 1\text{s}}$

Thus, it is also the amount of excess charge on a capacitor of one farad charged to a potential difference of one volt:

${\displaystyle 1\text{C}=1\text{F}\cdot 1\text{V}}$

The coulomb is equivalent to the charge of approximately 6.242×10¹⁸ (1.036×10⁻⁵mol) protons, and −1 C is equivalent to the charge of approximately 6.242×10¹⁸electrons.A new definition, in terms of the elementary charge, will take effect on 20 May 2019.^[130] The new definition, defines the elementary charge (the charge of the proton) as exactly 1.602176634×10⁻¹⁹ coulombs. This would implicitly define the coulomb as ​¹⁄_0.1602176634×10¹⁸ elementary charges.

Coulomb's law

Coulomb's law, or Coulomb's inverse-square law, is a law of physics for quantifying Coulomb's force, or electrostatic force. Electrostatic force is the amount of force with which stationary, electrically charged particles either repel, or attract each other. This force and the law for quantifying it, represent one of the most basic forms of force used in the physical sciences, and were an essential basis to the study and development of the theory and field of classical electromagnetism. The law was first published in 1785 by French physicist Charles-Augustin de Coulomb.^[131]In its scalar form, the law is:

${\displaystyle F=k_e\frac{q_1{q}_2}{r^2}}$,

where k_e is Coulomb's constant (k_e ≈ 9×10⁹ N m² C⁻²), q₁ and q₂ are the signed magnitudes of the charges, and the scalar r is the distance between the charges. The force of the interaction between the charges is attractive if the charges have opposite signs (i.e., F is negative) and repulsive if like-signed (i.e., F is positive).Being an inverse-square law, the law is analogous to Isaac Newton's inverse-square law of universal gravitation. Coulomb's law can be used to derive Gauss's law, and vice versa.

Covalent bond

A covalent bond, also called a molecular bond, is a chemical bond that involves the sharing of electron pairs between atoms.

Crookes tube

A type of vacuum tube that demonstrates cathode rays.

Cryogenics

The science of low temperatures.

Crystallization

Crystallization is the (natural or artificial) process by which a solid forms, where the atoms or molecules are highly organized into a structure known as a crystal. Some of the ways by which crystals form are precipitating from a solution, freezing, or more rarely deposition directly from a gas. Attributes of the resulting crystal depend largely on factors such as temperature, air pressure, and in the case of liquid crystals, time of fluid evaporation.

Crystallography

The study of crystals.

Curvilinear motion

Describes the motion of a moving particle that conforms to a known or fixed curve. The study of such motion involves the use of two co-ordinate systems, the first being planar motion and the latter being cylindrical motion.

Cyclotron

A cyclotron is a type of particle accelerator invented by Ernest O. Lawrence in 1929-1930 at the University of California, Berkeley,^[132][133] and patented in 1932.^[134][135] A cyclotron accelerates charged particles outwards from the center along a spiral path.^[136][137] The particles are held to a spiral trajectory by a static magnetic field and accelerated by a rapidly varying (radio frequency) electric field. Lawrence was awarded the 1939 Nobel prize in physics for this invention.^[137][138]

D[edit]

Dalton's law

In chemistry and physics, Dalton's law (also called Dalton's law of partial pressures) states that in a mixture of non-reacting gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases.^[139]

Damped vibration

Any vibration with a force acting against it to lessen the vibration over time.

Darcy–Weisbach equation

An equation used in fluid mechanics to find the pressure change cause by friction within a pipe or conduit.

DC motor

An electrical motor driven by direct current.

Decibel

A logarithmic unit of ratios.

Definite integral

.

Deflection

Is the degree to which a structural element is displaced under a load. It may refer to an angle or a distance.

Deformation (engineering)

In materials science, deformation refers to any changes in the shape or size of an object due to

• an applied force (the deformation energy in this case is transferred through work) or
• a change in temperature (the deformation energy in this case is transferred through heat).

The first case can be a result of tensile (pulling) forces, compressive (pushing) forces, shear, bending or torsion (twisting).In the second case, the most significant factor, which is determined by the temperature, is the mobility of the structural defects such as grain boundaries, point vacancies, line and screw dislocations, stacking faults and twins in both crystalline and non-crystalline solids. The movement or displacement of such mobile defects is thermally activated, and thus limited by the rate of atomic diffusion.^[140][141]

Deformation (mechanics)

Deformation in continuum mechanics is the transformation of a body from a reference configuration to a current configuration.^[142] A configuration is a set containing the positions of all particles of the body.A deformation may be caused by external loads,^[143]body forces (such as gravity or electromagnetic forces), or changes in temperature, moisture content, or chemical reactions, etc.

Degrees of freedom

The number of parameters required to define the motion of a dynamical system.

Delta robot

A tripod linkage, used to construct fast-acting manipulators with a wide range of movement.

Delta-wye transformer

A type of transformer used in three-phase power systems.

De Moivre–Laplace theorem

In probability theory, the de Moivre–Laplace theorem, which is a special case of the central limit theorem, states that the normal distribution may be used as an approximation to the binomial distribution under certain conditions. In particular, the theorem shows that the probability mass function of the random number of 'successes' observed in a series of ${\displaystyle n}$independentBernoulli trials, each having probability ${\displaystyle p}$ of success (a binomial distribution with ${\displaystyle n}$ trials), converges to the probability density function of the normal distribution with mean ${\displaystyle np}$ and standard deviation${\displaystyle \sqrt{np(1-p)}}$, as ${\displaystyle n}$ grows large, assuming ${\displaystyle p}$ is not ${\displaystyle 0}$ or ${\displaystyle 1}$.

Density

The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is ρ (the lower case Greek letter rho), although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume:^[144]

${\displaystyle \rho =\frac{m}{V}}$

where ρ is the density, m is the mass, and V is the volume. In some cases (for instance, in the United States oil and gas industry), density is loosely defined as its weight per unit volume,^[145] although this is scientifically inaccurate – this quantity is more specifically called specific weight.

Derivative

The derivative of a function of a real variable measures the sensitivity to change of the function value (output value) with respect to a change in its argument (input value). Derivatives are a fundamental tool of calculus. For example, the derivative of the position of a moving object with respect to time is the object's velocity: this measures how quickly the position of the object changes when time advances.

Design engineering

.

Dew point

The pressure and temperature at which air is holding the maximum possible humidity.

Diamagnetism

Diamagnetic materials are repelled by a magnetic field; an applied magnetic field creates an induced magnetic field in them in the opposite direction, causing a repulsive force. In contrast, paramagnetic and ferromagnetic materials are attracted by a magnetic field. Diamagnetism is a quantum mechanical effect that occurs in all materials; when it is the only contribution to the magnetism, the material is called diamagnetic. In paramagnetic and ferromagnetic substances the weak diamagnetic force is overcome by the attractive force of magnetic dipoles in the material. The magnetic permeability of diamagnetic materials is less than μ₀, the permeability of vacuum. In most materials diamagnetism is a weak effect which can only be detected by sensitive laboratory instruments, but a superconductor acts as a strong diamagnet because it repels a magnetic field entirely from its interior.

Dielectric

An insulator, a material that does not permit free flow of electricity.

Differential pressure

.

Differential pulley

A differential pulley, also called Weston differential pulley, or colloquially chain fall, is used to manually lift very heavy objects like car engines. It is operated by pulling upon the slack section of a continuous chain that wraps around pulleys. The relative size of two connected pulleys determines the maximum weight that can be lifted by hand. The load will remain in place (and not lower under the force of gravity) until the chain is pulled.^[146]

Differential signaling

Is a method for electrically transmitting information using two complementary signals.

Diffusion

Engineering Dictionary Free Online

Is the net movement of molecules or atoms from a region of higher concentration (or high chemical potential) to a region of lower concentration (or low chemical potential).

Dimensional analysis

is the analysis of the relationships between different physical quantities by identifying their base quantities (such as length, mass, time, and electric charge) and units of measure (such as miles vs. kilometers, or pounds vs. kilograms) and tracking these dimensions as calculations or comparisons are performed. The conversion of units from one dimensional unit to another is often somewhat complex. Dimensional analysis, or more specifically the factor-label method, also known as the unit-factor method, is a widely used technique for such conversions using the rules of algebra.^{[147][148][149]}

Direct integration of a beam

Direct integration is a structural analysis method for measuring internal shear, internal moment, rotation, and deflection of a beam.For a beam with an applied weight ${\displaystyle w(x)}$, taking downward to be positive, the internal shear force is given by taking the negative integral of the weight:

${\displaystyle V(x)=-\int w(x)dx}$

The internal moment M(x) is the integral of the internal shear:

${\displaystyle M(x)=\int V(x)dx}$ = ${\displaystyle -\int [\int w(x)dx]dx}$

The angle of rotation from the horizontal, ${\displaystyle \theta }$, is the integral of the internal moment divided by the product of the Young's modulus and the area moment of inertia:

${\displaystyle \theta (x)=\frac{1}{EI}\int M(x)dx}$

Integrating the angle of rotation obtains the vertical displacement ${\displaystyle \nu }$:

${\displaystyle \nu (x)=\int \theta (x)dx}$.

Dispersion

In optics, dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency.^[150]Media having this common property may be termed dispersive media. Sometimes the term chromatic dispersion is used for specificity.Although the term is used in the field of optics to describe light and other electromagnetic waves, dispersion in the same sense can apply to any sort of wave motion such as acoustic dispersion in the case of sound and seismic waves, in gravity waves (ocean waves), and for telecommunication signals along transmission lines (such as coaxial cable) or optical fiber.

Displacement (fluid)

In fluid mechanics, displacement occurs when an object is immersed in a fluid, pushing it out of the way and taking its place. The volume of the fluid displaced can then be measured, and from this, the volume of the immersed object can be deduced (the volume of the immersed object will be exactly equal to the volume of the displaced fluid).

Displacement (vector)

Is a vector whose length is the shortest distance from the initial to the final position of a point P.^[151] It quantifies both the distance and direction of an imaginary motion along a straight line from the initial position to the final position of the point. A displacement may be identified with the translation that maps the initial position to the final position.

Distance

is a numerical measurement of how far apart objects are.

Doppler effect

The Doppler effect (or the Doppler shift) is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source.^[152] It is named after the Austrian physicist Christian Doppler, who described the phenomenon in 1842.

Dose–response relationship

.

Drag

In fluid dynamics, drag (sometimes called air resistance, a type of friction, or fluid resistance, another type of friction or fluid friction) is a force acting opposite to the relative motion of any object moving with respect to a surrounding fluid.^[153] This can exist between two fluid layers (or surfaces) or a fluid and a solid surface. Unlike other resistive forces, such as dry friction, which are nearly independent of velocity, drag forces depend on velocity.^[154][155]Drag force is proportional to the velocity for a laminar flow and the squared velocity for a turbulent flow. Even though the ultimate cause of a drag is viscous friction, the turbulent drag is independent of viscosity.^[156] Drag forces always decrease fluid velocity relative to the solid object in the fluid's path.

Drift current

In condensed matter physics and electrochemistry, drift current is the electric current, or movement of charge carriers, which is due to the applied electric field, often stated as the electromotive force over a given distance. When an electric field is applied across a semiconductor material, a current is produced due to the flow of charge carriers.

Ductility

Is a measure of a material's ability to undergo significant plastic deformation before rupture, which may be expressed as percent elongation or percent area reduction from a tensile test.

Dynamics

Is the branch of classical mechanics concerned with the study of forces and their effects on motion. Isaac Newton defined the fundamental physical laws which govern dynamics in physics, especially his second law of motion.

Dyne

Is a derived unit of force specified in the centimetre–gram–second (CGS) system of units, a predecessor of the modern SI.

E[edit]

Economics

The scientific study of the production, distribution and consumption of goods.

Effusion

In physics and chemistry, effusion is the process in which a gas escapes from a container through a hole of diameter considerably smaller than the mean free path of the molecules.^[157]

Elastic modulus

The amount a material will deform per unit force.

Elasticity

In physics, elasticity is the ability of a body to resist a distorting influence and to return to its original size and shape when that influence or force is removed. Solid objects will deform when adequate forces are applied to them. If the material is elastic, the object will return to its initial shape and size when these forces are removed.

Electric charge

is the physical property of matter that causes it to experience a force when placed in an electromagnetic field. There are two types of electric charges; positive and negative (commonly carried by protons and electrons respectively). Like charges repel and unlike attract. An object with an absence of net charge is referred to as neutral. Early knowledge of how charged substances interact is now called classical electrodynamics, and is still accurate for problems that do not require consideration of quantum effects.

Electric circuit

Is an electrical network consisting of a closed loop, giving a return path for the current.

Electric current

Is a flow of electric charge.^[158]:2 In electric circuits this charge is often carried by moving electrons in a wire. It can also be carried by ions in an electrolyte, or by both ions and electrons such as in an ionised gas (plasma).^[159]The SI unit for measuring an electric current is the ampere, which is the flow of electric charge across a surface at the rate of one coulomb per second. Electric current is measured using a device called an ammeter.^[160]

Electric displacement field

In physics, the electric displacement field, denoted by D, is a vector field that appears in Maxwell's equations. It accounts for the effects of free and bound charge within materials. 'D' stands for 'displacement', as in the related concept of displacement current in dielectrics. In free space, the electric displacement field is equivalent to flux density, a concept that lends understanding to Gauss's law. In the International System of Units (SI), it is expressed in units of coulomb per meter squared (C⋅m⁻²).

Electric generator

In electricity generation, a generator,also called electric generator, electrical generator, and electromagnetic generator. is a device that converts motive power (mechanical energy) into electrical power for use in an external circuit. Sources of mechanical energy include steam turbines, gas turbines, water turbines, internal combustion engines and even hand cranks.

Electric field

Surrounds an electric charge, and exerts force on other charges in the field, attracting or repelling them.^[161][162] Electric field is sometimes abbreviated as E-field.

Electric field gradient

In atomic, molecular, and solid-state physics, the electric field gradient (EFG) measures the rate of change of the electric field at an atomic nucleus generated by the electroniccharge distribution and the other nuclei.

Electric motor

Is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and winding currents to generate force in the form of rotation. Electric motors can be powered by direct current (DC) sources, such as from batteries, motor vehicles or rectifiers, or by alternating current (AC) sources, such as a power grid, inverters or electrical generators. An electric generator is mechanically identical to an electric motor, but operates in the reverse direction, accepting mechanical energy (such as from flowing water) and converting this mechanical energy into electrical energy.

Electric potential

(Also called the electric field potential, potential drop or the electrostatic potential) is the amount of work needed to move a unit of positive charge from a reference point to a specific point inside the field without producing an acceleration. Typically, the reference point is the Earth or a point at infinity, although any point beyond the influence of the electric field charge can be used.

Electrical potential energy

Electric potential energy, or electrostatic potential energy, is a potential energy (measured in joules) that results from conservativeCoulomb forces and is associated with the configuration of a particular set of point charges within a defined system. An object may have electric potential energy by virtue of two key elements: its own electric charge and its relative position to other electrically charged objects. The term 'electric potential energy' is used to describe the potential energy in systems with time-variantelectric fields, while the term 'electrostatic potential energy' is used to describe the potential energy in systems with time-invariant electric fields.

Electric power

Is the rate, per unit time, at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second..

Electrical engineering

Is a technical discipline concerned with the study, design and application of equipment, devices and systems which use electricity, electronics, and electromagnetism. It emerged as an identified activity in the latter half of the 19th century after commercialization of the electric telegraph, the telephone, and electrical power generation, distribution and use. .

Electrical conductance

The electrical resistance of an object is a measure of its opposition to the flow of electric current. The inverse quantity is electrical conductance, and is the ease with which an electric current passes. Electrical resistance shares some conceptual parallels with the notion of mechanical friction. The SI unit of electrical resistance is the ohm (Ω), while electrical conductance is measured in siemens (S).

Electrical conductor

Is an object or type of material that allows the flow of charge (electrical current) in one or more directions. Materials made of metal are common electrical conductors. Electrical current is generated by the flow of negatively charged electrons, positively charged holes, and positive or negative ions in some cases.

Electrical impedance

Is the measure of the opposition that a circuit presents to a current when a voltage is applied. The term complex impedance may be used interchangeably.

Electrical insulator

Is a material whose internal electric charges do not flow freely; very little electric current will flow through it under the influence of an electric field. This contrasts with other materials, semiconductors and conductors, which conduct electric current more easily. The property that distinguishes an insulator is its resistivity; insulators have higher resistivity than semiconductors or conductors.

Electrical network

.

Electrical resistance

.

Electricity

.

Electrodynamics

.

Electromagnet

.

Electromagnetic field

.

Electromagnetic radiation

.

Electromechanics

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Electron

.

Electronvolt

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Electron pair

.

Electronegativity

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Electronics

.

Elemental analysis

.

Endothermic

A reaction which requires the absorption of heat.

Energy

.

Engine

.

Engineering

.

Engineering economics

.

Engineering ethics

.

Environmental engineering

.

Engineering physics

.

Enzyme

.

Escape velocity

The minimum velocity at which an object can escape a gravitation field..

Estimator

.

Euler–Bernoulli beam equation

.

Exothermic

A reaction which produces heat.

F[edit]

Factor of safety

(FoS), also known as (and used interchangeably with) safety factor (SF), expresses how much stronger a system is than it needs to be for an intended load.

Falling bodies

.

Farad

The SI unit of capacitance.

Faraday

.

Faraday constant

Denoted by the symbol F and sometimes stylized as ℱ, is named after Michael Faraday. In physics and chemistry, this constant represents the magnitude of electric charge per mole of electrons.^[163] It has the value

96485.33212... C mol⁻¹.^[164]

This constant has a simple relation to two other physical constants:

${\displaystyle F=e{N}_A}$

where

e = 1.602176634×10⁻¹⁹ C;^[165]

N_A = 6.02214076×10²³ mol⁻¹.^[166]

Both of these values have exact defined values, and hence F has a known exact value. N_A is the Avogadro constant (the ratio of the number of particles, N, which is unitless, to the amount of substance, n, in units of moles), and e is the elementary charge or the magnitude of the charge of an electron. This relation holds because the amount of charge of a mole of electrons is equal to the amount of charge in one electron multiplied by the number of electrons in a mole.

Fermat's principle

In optics, Fermat's principle or the principle of least time, named after French mathematician Pierre de Fermat, is the principle that the path taken between two points by a ray of light is the path that can be traversed in the least time. This principle is sometimes taken as the definition of a ray of light.^[167] However, this version of the principle is not general; a more modern statement of the principle is that rays of light traverse the path of stationary optical length with respect to variations of the path.^[168] In other words, a ray of light prefers the path such that there are other paths, arbitrarily nearby on either side, along which the ray would take almost exactly the same time to traverse.

Fick's laws of diffusion

Describe diffusion and were derived by Adolf Fick in 1855. They can be used to solve for the diffusion coefficient, D. Fick's first law can be used to derive his second law which in turn is identical to the diffusion equation.

Finite element method

.

FIRST

For Inspiration and Recognition of Science and Technology – is an organization founded by inventor Dean Kamen in 1989 to develop ways to inspire students in engineering and technology fields.

Fission

.

Fixed capacitor

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Fixed inductor

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Fixed resistor

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Flow velocity

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Fluid

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Fluid dynamics

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Fluid mechanics

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Fluid physics

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Fluid statics

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Flywheel

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Focus

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Foot-pound

In the systems that use feet, the unit of work.

Fracture toughness

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Fraunhofer lines

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Free fall

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Frequency modulation

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Freezing point

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Friction

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Function

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Fundamental frequency

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Fundamental interaction

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Fundamental theorem of calculus

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Fundamentals of Engineering Examination (US)

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Fusion

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G[edit]

Galvanic cell

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Gamma rays

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Gas

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Gauge pressure

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Geiger counter

A device that measures radioactivity.

General relativity

.

Geometric mean

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Geometry

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Geophysics

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Geotechnical engineering

.

Gluon

.

Graham's law of diffusion

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Gravitation

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Gravitational constant

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Gravitational energy

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Gravitational field

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Gravitational potential

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Gravitational wave

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Gravity

.

Ground state

.

H[edit]

Half-life

The period at which one-half of a quantity of an unstable isotope has decayed into other elements; the time at which half of a substance has diffused out of or otherwise reacted in a system.

Haptic

Tactile feedback technology using the operator's sense of touch. Also sometimes applied to robot manipulators with their own touch sensitivity.

Hardness

.

Harmonic mean

.

Heat

The energy of molecular vibration.

Heat transfer

.

Helmholtz free energy

.

Henderson–Hasselbalch equation

.

Henry's law

.

Hertz

The SI unit of frequency, one cycle per second.

Hexapod

(platform) – a movable platform using six linear actuators. Often used in flight simulators they also have applications as a robotic manipulator.

Hexapod

(walker) – a six-legged walking robot, using a simple insect-like locomotion.

Hoist

.

Horsepower

In measurement systems that use feet, the unit of power.

Hot working

Or hot forming, any metal-working procedure (such as forging, rolling, extruding, etc.) carried out above the metal's recrystallization temperature.

Huygens–Fresnel principle

.

Hydraulics

The study of fluid flow, or the generation of mechanical force and movement by liquid under pressure.

Hydrocarbon

A compound containing hydrogen and carbon atoms only; petroleum is made of hydrocarbons.

I[edit]

Ice point

.

Ideal gas

A model for gases that ignores inter-molecular forces. Most gases are approximately ideal at some high temperature and low pressure.

Ideal gas constant

The constant in the gas law that relates pressure, volume and temperature.

Ideal gas law

An equation defining behavior of an ideal gas.

Indefinite integral

.

Identity

.

Impedance (electrical)

.

Inertia

.

Infrasound

.

Integral

.

Integral transform

.

International System of Units

.

Interval estimation

.

Ion

.

Ionic bond

.

Ionization

.

Impedance

The measure of the opposition that a circuit presents to the passage of a current when a voltage is applied.

Inclined plane

.

Inductance

.

Inductor

.

Industrial engineering

.

Inorganic chemistry

.

Isotope

.

J[edit]

Joule

The SI unit of energy.

Joule heating

.

K[edit]

Kalman filter

In statistics and control theory, Kalman filtering, also known as linear quadratic estimation (LQE), is an algorithm that uses a series of measurements observed over time, containing statistical noise and other inaccuracies, and produces estimates of unknown variables that tend to be more accurate than those based on a single measurement alone, by estimating a joint probability distribution over the variables for each timeframe. The Kalman filter has numerous applications in technology.

Kelvin

The Kelvin scale is an absolutethermodynamic temperaturescale using as its null point absolute zero, the temperature at which all thermal motion ceases in the classical description of thermodynamics. The kelvin (symbol: K) is the base unit of temperature in the International System of Units (SI).

Kelvin–Planck statement

(Or the Heat Engine Statement), of the second law of thermodynamics states that it is impossible to devise a cyclically operating heat engine, the effect of which is to absorb energy in the form of heat from a single thermal reservoir and to deliver an equivalent amount of work.^[169]This implies that it is impossible to build a heat engine that has 100% thermal efficiency.^[170]

Kinematics

Is a branch of classical mechanics that describes the motion of points, bodies (objects), and systems of bodies (groups of objects) without considering the forces that caused the motion.^{[171][172][173]}

L[edit]

Laminar flow

.

Laplace transform

.

LC circuit

A circuit consisting entirely of inductors (L) and capacitors (C).

Le Chatelier's principle

.

Lenz's law

.

Lepton

.

Lever

.

L'Hôpital's rule

.

Light

.

Linear actuator

A form of motor that generates a linear movement directly.

Linear algebra

The mathematics of equations where the unknowns are only in the first power.

Linear elasticity

.

Liquid

.

Logarithm

.

Logarithmic identities

.

Logarithmic mean temperature difference

.

Lumped capacitance model

.

Lumped element model

.

M[edit]

Macaulay's method

(The double integration method) is a technique used in structural analysis to determine the deflection of Euler-Bernoulli beams. Use of Macaulay’s technique is very convenient for cases of discontinuous and/or discrete loading. Typically partial uniformly distributed loads (u.d.l.) and uniformly varying loads (u.v.l.) over the span and a number of concentrated loads are conveniently handled using this technique.

Mach number

The ratio of the speed of an object to the speed of sound..

Machine

.

Machine code

.

Machine element

.

Machine learning

.

Maclaurin series

.

Magnetic field

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Magnetism

.

Manufacturing engineering

.

Mass balance

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Mass density

.

Mass moment of inertia

.

Mass number

.

Mass spectrometry

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Material failure theory

.

Material properties

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Materials science

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Mathematical optimization

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Mathematical physics

.

Mathematics

.

Matrix

.

Matter

.

Maximum-distortion energy theory

.

Maximum-normal-stress theory

.

Maximum shear stress

.

Maxwell's equations

A number of basic laws describing the behavior of electric current and potential.

Mean

.

Measures of central tendency

.

Mechanical advantage

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Mechanical engineering

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Mechanical filter

.

Mechanical wave

.

Mechanics

.

Mechanism

.

Median

.

Melting

.

Melting point

.

Meson

.

Metal alloy

.

Metallic bond

.

Mid-range

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Midhinge

.

Mining engineering

.

Miller indices

.

Mobile robot

.

Mode

.

Modulus of elasticity

.

Mohr's circle

A graphical method of analyzing the three-dimensional stresses in a system that has a loading force applied to it.

Molality

.

Molar concentration

.

Molar absorptivity

.

Molar mass

.

Molarity

.

Molding

.

Molecule

.

Molecular physics

.

Moment of inertia

.

Multibody system

.

Multidisciplinary design optimization

.

Mutual inductance

.

Muon

.

N[edit]

Nanoengineering

.

Nanotechnology

The technology of systems built with moving parts on the order of a nanometre in size.

Navier–Stokes equations

.

Neutrino

A neutral particle.

Newtonian fluid

.

Norton's theorem

.

Nozzle

.

nth root

To put a number of function to the exponential power of 1/n.

Nuclear binding energy

Teh difference between the total mass energy of a nucleus and the mass energy of the isolated nucleons.

Nuclear engineering

The profession that deals with nuclear power.

Nuclear physics

The science that describes the components of atoms.

Nuclear potential energy

The energy that is given up in decay of an unstable nucleus.

Nuclear power

The use of energy derived from nuclear chain reactions for electricity production or ship propulsion.

O[edit]

Ohm

The SI unit of electrical resistance.

Ohm's law

A law describing the relationship between resistance, current, and voltage.

Optics

The study of light.

Organic chemistry

The study of carbon compounds.

Osmosis

The spontaneous movement of molecules or ions through a semi-permable membrane, tending to equalize concentration on both sides.

P[edit]

Parallel circuit

A circuit that begins and ends at the same node as another circuit.

Parity (mathematics)

.

Parity (physics)

.

Paraffin

A hydrocarbon compound, solid at room temperature.

Paramagnetism

.

Particle accelerator

.

Particle displacement

.

Particle physics

.

Pascal's law

Pascal's law (also Pascal's principle^{[174][175][176]} or the principle of transmission of fluid-pressure) is a principle in fluid mechanics that states that a pressure change occurring anywhere in a confined incompressible fluid is transmitted throughout the fluid such that the same change occurs everywhere.^[177] The law was established by FrenchmathematicianBlaise Pascal^[30] in 1647–48.^[178]

Pendulum

.

Petroleum engineering

.

pH

A logarithmic measure of the concentration of hydrogen ions in an acid or base solution.

Phase (matter)

.

Phase (waves)

.

Phase diagram

.

Phase equilibrium

.

Photon

A particle with no rest mass that carries electromagnetic energy.

Physical chemistry

.

Physical quantity

.

Physics

.

Planck constant

.

Plasma physics

.

Plasticity

.

Pneumatics

The control of mechanical force and movement, generated by the application of compressed gas.

Point estimation

.

Polyphase system

An electrical system that uses a set of alternating currents at different phases.

Power (electric)

.

Power (physics)

.

Power factor

.

Pressure

The force per unit area .

Probability

.

Probability distribution

.

Probability theory

.

Psi particle

.

Pulley

.

Pump

.

Q[edit]

Quantum electrodynamics

In particle physics, quantum electrodynamics (QED) is the relativisticquantum field theory of electrodynamics. In essence, it describes how light and matter interact and is the first theory where full agreement between quantum mechanics and special relativity is achieved. QED mathematically describes all phenomena involving electrically charged particles interacting by means of exchange of photons and represents the quantum counterpart of classical electromagnetism giving a complete account of matter and light interaction.

Quantum field theory

.

Quantum mechanics

.

Quantum physics

.

R[edit]

Regelation

The phenomena of melting under pressure, then freezing when the pressure is reduced.

Relative density

.

Relative velocity

.

Reliability engineering

.

Resistivity

.

Resistor

.

Reynolds number

.

Rheology

.

Rigid body

.

Robonaut

A development project conducted by NASA to create humanoid robots capable of using space tools and working in similar environments to suited astronauts..

Robotics

.

Root-mean-square

.

Root-mean-square speed

.

Rotational energy

.

Rotational speed

.

S[edit]

Safety data sheet

.

Sanitary engineering

.

Saturation (chemistry)

.

Saturated compound

.

Scalar (mathematics)

.

Scalar (physics)

.

Scalar multiplication

.

Screw

.

Series circuit

An electrical circuit in which the same current passes through each component, with only one path.

Servo

A motor that moves to and maintains a set position under command, rather than continuously moving.

Servomechanism

An automatic device that uses error-sensing negative feedback to correct the performance of a mechanism.

Shadow matter

.

Shear flow

.

Shear strength

.

Shear stress

.

Shortwave radiation

.

SI units

.

Signal processing

.

Simple machine

A mechanical device that changes the direction or magnitude of a force.

Siphon

A closed tube that conveys liquids between two levels without pumping.

Solid mechanics

.

Solid-state physics

.

Solid solution strengthening

.

Solubility

.

Solubility equilibrium

.

Sound

.

Special relativity

.

Specific heat

The amount of energy required to change the temperature of a unit mass of substance by one degree.

Specific gravity

The ratio between the mass density of a substance to that of water.

Specific volume

The volume of a unit mass of a substance.

Specific weight

The weight of a substance per unit volume.

Spontaneous combustion

.

Stagnation pressure

.

Standard electrode potential

.

State of matter

.

Statics

The study of forces in a non-moving, rigid body.

Statistics

.

Steam table

.

Stefan–Boltzmann law

.

Stewart platform

a movable platform using six linear actuators, hence also known as a Hexapod.

Stiffness

.

Stoichiometry

.

Strain

.

Strain hardening

.

Strength of materials

.

Stress

.

Stress–strain analysis

.

Stress–strain curve

.

Structural analysis

.

Structural load

.

Sublimation

.

Subsumption architecture

a robot architecture that uses a modular, bottom-up design beginning with the least complex behavioral tasks.

Surface tension

.

Superconductor

.

Superhard material

.

Supersaturation

.

Surgical robot

a remote manipulator used for keyhole surgery.

T[edit]

Tangential acceleration

.

Technical standard

.

Temperature

The measure of heat energy in an object or fluid.

Tempering (metallurgy)

Heat treatment to alter the crystal structure of a metal such as steel.

Tensile force

Pulling force, tending to lengthen an object.

Tensile modulus

.

Tensile strength

.

Tensile testing

.

Tension member

.

Thermal conduction

.

Thermal equilibrium

.

Thermal radiation

.

Thermodynamics

The science of the flow of heat.

Theory of relativity

.

Thévenin's theorem

.

Three-phase

Electric power using three alternating currents, displaced in time.

Torque

Twisting force.

Torsional vibration

.

Toughness

.

Trajectory

.

Transducer

.

Transformer

.

Trigonometric functions

.

Trigonometry

.

Trimean

.

Triple point

.

Trouton's rule

.

Truncated mean

.

Truss

.

Turbine

.

Turbomachinery

.

Turbulence

.

U[edit]

Ultimate tensile strength

Ultimate tensile strength (UTS), often shortened to tensile strength (TS), ultimate strength, or Ftu within equations,^{[179][180][181]} is the capacity of a material or structure to withstand loads tending to elongate, as opposed to compressive strength, which withstands loads tending to reduce size. In other words, tensile strength resists tension (being pulled apart), whereas compressive strength resists compression (being pushed together). Ultimate tensile strength is measured by the maximum stress that a material can withstand while being stretched or pulled before breaking. In the study of strength of materials, tensile strength, compressive strength, and shear strength can be analyzed independently.

Uncertainty principle

In quantum mechanics, the uncertainty principle (also known as Heisenberg's uncertainty principle) is any of a variety of mathematical inequalities^[182] asserting a fundamental limit to the precision with which certain pairs of physical properties of a particle, known as complementary variables, such as positionx and momentump, can be known.

Unicode

.

Unit vector

In mathematics, a unit vector in a normed vector space is a vector (often a spatial vector) of length 1. A unit vector is often denoted by a lowercase letter with a circumflex, or 'hat': ${\displaystyle \hat{ı}}$ (pronounced 'i-hat'). The term direction vector is used to describe a unit vector being used to represent spatial direction, and such quantities are commonly denoted as d. .

Unsaturated compound

.

Upthrust

.

Utility frequency

.

V[edit]

Vacuole

.

Vacuum

An absence of mass in a volume.

Valence

In chemistry, the valence or valency of an element is a measure of its combining power with other atoms when it forms chemical compounds or molecules. The concept of valence developed in the second half of the 19th century and helped successfully explain the molecular structure of inorganic and organic compounds.^[183] The quest for the underlying causes of valence led to the modern theories of chemical bonding, including the cubical atom (1902), Lewis structures (1916), valence bond theory (1927), molecular orbitals (1928), valence shell electron pair repulsion theory (1958), and all of the advanced methods of quantum chemistry.

Valence band

.

Valence bond theory

.

Valence electron

.

Valence shell

.

Valve

A device for controlling fluid flow.

van der Waals equation

.

van der Waals force

.

van 't Hoff equation

.

van 't Hoff factor

.

Variable capacitor

.

Variable resistor

.

Vector space

.

Venturi effect

.

Vibration

.

Viscoelasticity

.

Viscosity

The viscosity of a fluid is the measure of its resistance to gradual deformation by shear stress or tensile stress.^[184] For liquids, it corresponds to the informal concept of 'thickness': for example, honey has a higher viscosity than water.^[185]

Volt-ampere

.

Volt-ampere reactive

.

Volta potential

The Volta potential (also called Volta potential difference, contact potential difference, outer potential difference, Δψ, or 'delta psi') in electrochemistry, is the electrostatic potential difference between two metals (or one metal and one electrolyte) that are in contact and are in thermodynamic equilibrium. Specifically, it is the potential difference between a point close to the surface of the first metal, and a point close to the surface of the second metal (or electrolyte).^[186]

Voltage

Voltage, electric potential difference, electric pressure or electric tension is the difference in electric potential between two points. The difference in electric potential between two points (i.e., voltage) is defined as the work needed per unit of charge against a static electric field to move a test charge between the two points. In the International System of Units, the derived unit for voltage is named volt.^[187] In SI units, work per unit charge is expressed as joules per coulomb, where 1 volt = 1 joule (of work) per 1 coulomb (of charge). The official SI definition for volt uses power and current, where 1 volt = 1 watt (of power) per 1 ampere (of current).^[187]

Volumetric flow rate

Also known as volume flow rate, rate of fluid flow or volume velocity, is the volume of fluid which passes per unit time; usually represented by the symbol Q (sometimes V̇). The SI unit is m³/s (cubic metres per second).

von Mises yield criterion

The von Mises yield criterion (also known as the maximum distortion energy criterion^[188]) suggests that yielding of a ductile material begins when the second deviatoric stress invariant${\displaystyle J_2}$ reaches a critical value.^[189] It is part of plasticity theory that applies best to ductile materials, such as some metals. Prior to yield, material response can be assumed to be of a nonlinear elastic, viscoelastic, or linear elastic behavior.In materials science and engineering the von Mises yield criterion can also be formulated in terms of the von Mises stress or equivalent tensile stress, ${\displaystyle {\sigma }_v}$. This is a scalar value of stress that can be computed from the Cauchy stress tensor. In this case, a material is said to start yielding when the von Mises stress reaches a value known as yield strength, ${\displaystyle {\sigma }_y}$. The von Mises stress is used to predict yielding of materials under complex loading from the results of uniaxial tensile tests. The von Mises stress satisfies the property where two stress states with equal distortion energy have an equal von Mises stress.

W[edit]

Watt

The SI unit of power, rate of doing work.

Wave

Is a disturbance that transfers energy through matter or space, with little or no associated mass transport. Waves consist of oscillations or vibrations of a physical medium or a field, around relatively fixed locations. From the perspective of mathematics, waves, as functions of time and space, are a class of signals.^[190]

Wavelength

Is the spatial period of a periodic wave—the distance over which the wave's shape repeats.^[191][192] It is thus the inverse of the spatial frequency. Wavelength is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings and is a characteristic of both traveling waves and standing waves, as well as other spatial wave patterns.^[193][194] Wavelength is commonly designated by the Greek letterlambda (λ). The term wavelength is also sometimes applied to modulated waves, and to the sinusoidal envelopes of modulated waves or waves formed by interference of several sinusoids.^[195]' .

Wedge

Is a triangular shaped tool, and is a portable inclined plane, and one of the six classical simple machines. It can be used to separate two objects or portions of an object, lift up an object, or hold an object in place. It functions by converting a force applied to its blunt end into forces perpendicular (normal) to its inclined surfaces. The mechanical advantage of a wedge is given by the ratio of the length of its slope to its width.^[196][197] Although a short wedge with a wide angle may do a job faster, it requires more force than a long wedge with a narrow angle.

Weighted arithmetic mean

The weighted arithmetic mean is similar to an ordinary arithmetic mean (the most common type of average), except that instead of each of the data points contributing equally to the final average, some data points contribute more than others. The notion of weighted mean plays a role in descriptive statistics and also occurs in a more general form in several other areas of mathematics. If all the weights are equal, then the weighted mean is the same as the arithmetic mean. While weighted means generally behave in a similar fashion to arithmetic means, they do have a few counterintuitive properties, as captured for instance in Simpson's paradox.

Wet-bulb temperature

The temperature of a wetted thermometer with an air current across it. Used in psychrometry. .

Wheel and axle

Are one of six simple machines identified by Renaissance scientists drawing from Greek texts on technology.^[198] The wheel and axle consists of a wheel attached to a smaller axle so that these two parts rotate together in which a force is transferred from one to the other. A hinge or bearing supports the axle, allowing rotation. It can amplify force; a small force applied to the periphery of the large wheel can move a larger load attached to the axle.

Winsorized mean

Is a winsorizedstatisticalmeasure of central tendency, much like the mean and median, and even more similar to the truncated mean. It involves the calculation of the mean after replacing given parts of a probability distribution or sample at the high and low end with the most extreme remaining values,^[199] typically doing so for an equal amount of both extremes; often 10 to 25 percent of the ends are replaced. The winsorized mean can equivalently be expressed as a weighted average of the truncated mean and the quantiles at which it is limited, which corresponds to replacing parts with the corresponding quantiles.

Work hardening

Also known as strain hardening, is the strengthening of a metal or polymer by plastic deformation. This strengthening occurs because of dislocation movements and dislocation generation within the crystal structure of the material.^[200]

X[edit]

X-coordinate

.

Y[edit]

Y-coordinate

.

Yield

The point of maximum elastic deformation of a material; above yield the material is permanently deformed.

Young's modulus

A measure of the stiffness of a material; the amount of force per unit area require to produce a unit strain.

Z[edit]

Zero defects

A quality assurance philosophy that aims to reduce the need for inspection of components by improving their quality.

Zero force member

In the field of engineering mechanics, a zero force member is a member (a single truss segment) in a truss which, given a specific load, is at rest: neither in tension, nor in compression. In a truss a zero force member is often found at pins (any connections within the truss) where no external load is applied and three or fewer truss members meet. Recognizing basic zero force members can be accomplished by analyzing the forces acting on an individual pin in a physical system.NOTE: If the pin has an external force or moment applied to it, then all of the members attached to that pin are not zero force members UNLESS the external force acts in a manner that fulfills one of the rules below:

• If two non-collinear members meet in an unloaded joint, both are zero-force members.
• If three members meet in an unloaded joint of which two are collinear, then the third member is a zero-force member.

Reasons for Zero-force members in a truss system

Mechanical Engineering Dictionary Pdf

• These members contribute to the stability of the structure, by providing buckling prevention for long slender members under compressive forces
• These members can carry loads in the event that variations are introduced in the normal external loading configuration.

Zeroth law of thermodynamics

Free Dictionary Pdf

The equivalence principle applied to temperature; two systems in thermal equiplbirum with a third are also in thermal equilibrium with each other.

Civil Engineering Dictionary Pdf

See also[edit]

References[edit]

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