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Thisglossary of mechanical engineering terms pertains specifically tomechanical engineering and its sub-disciplines. For a broad overview of engineering, seeglossary of engineering.

• Abrasion – is the process of scuffing, scratching, wearing down, marring, or rubbing away. It can be intentionally imposed in a controlled process using an abrasive. Abrasion can be an undesirable effect of exposure to normal use or exposure to the elements.
• Absolute zero – is the lowest possibletemperature of a system, defined as zerokelvin or −273.15 °C. No experiment has yet measured a temperature of absolute zero.
• Accelerated life testing – is the process of testing a product by subjecting it to conditions (stress,strain, temperatures, voltage, vibration rate, pressure etc.) in excess of its normal service parameters in an effort to uncover faults and potential modes of failure in a short amount of time.^[1][2] By analyzing the product's response to such tests,engineers can make predictions about the service life and maintenance intervals of a product.^[3][4]
• Acceleration – Inphysics,acceleration is therate of change ofvelocity of an object with respect to time. An object's acceleration is the net result of any and allforces acting on the object, as described byNewton's second law.^[5] TheSI unit for acceleration ismetre per second squared(m s⁻²). Accelerations arevector quantities (they havemagnitude anddirection) and add according to theparallelogram law.^[6][7] As avector, the calculated netforce is equal to the product of the object's mass (ascalar quantity) and its acceleration.
• Accelerometer – is a device that measuresproper acceleration.^[8] Proper acceleration, being theacceleration (orrate of change ofvelocity) of a body in its own instantaneousrest frame,^[9] is not the same as coordinate acceleration, being the acceleration in a fixedcoordinate system.
• Accuracy and precision – In measurement of a set,accuracy is closeness of the measurements to a specific value, whileprecision is the closeness of the measurements to each other. More commonly, accuracy ortrueness is a description ofsystematic errors, a measure ofstatistical bias, while precision is a description ofrandom errors, a measure ofstatistical variability; the two concepts are independent of each other. Alternatively,ISO defines^[10] accuracy as describing a combination of both random and systematicobservational error, so high accuracy requires both high precision and high trueness.
• Ackermann steering geometry – a geometric arrangement of linkages in thesteering of a car or other vehicle designed to solve the problem of wheels on the inside and outside of a turn needing to trace out circles of differentradii. It was invented by the German carriage builderGeorg Lankensperger in Munich in 1817, then patented by his agent in England,Rudolph Ackermann (1764–1834) in 1818 for horse-drawn carriages.Erasmus Darwin may have a prior claim as the inventor dating from 1758.^[11]
• Acoustic droplet ejection– (ADE) uses a pulse of ultrasound to move low volumes of fluids (typically nanoliters or picoliters) without any physical contact. This technology focuses acoustic energy into a fluid sample in order to eject droplets as small as apicoliter. ADE technology is a very gentle process. This feature makes the technology suitable for a wide variety of applications includingproteomics and cell-based assays.
• Active cooling – anactive cooling system is one that involves the use of energy to cool something, as opposed topassive cooling that uses no energy. Such systems circulate acoolant totransfer heat from one place to another. The coolant is either a gas, such as inair cooling ofcomputers, or a liquid such as in acar engine. In the latter case, liquid is pumped to transfer heat from the engine to the radiator, which in turn is cooled by passing air over it. Other active cooling systems make use of arefrigeration cycle.
• Actual mechanical advantage – Theactual mechanical advantage (AMA) is the mechanical advantage determined by physical measurement of the input and output forces. AMA takes into account energy loss due to deflection, friction, and wear.
• Adjoint equation – is alinear differential equation, usually derived from its primal equation usingintegration by parts. Gradient values with respect to a particular quantity of interest can be efficiently calculated by solving the adjoint equation. Methods based on solution of adjoint equations are used inwing shape optimization, fluid flow control anduncertainty quantification. For example${\displaystyle d{X}_t=a(X_t)dt+b(X_t)dW}$ this is anItō stochastic differential equation. Now by using Euler scheme, we integrate the parts of this equation and get another equation,${\displaystyle X_{n+1}=X_n+a\mathrm{\Delta }t+\zeta b\sqrt{\mathrm{\Delta }t}}$, here${\displaystyle \zeta }$ is a random variable, later one is an adjoint equation.
• Aerodynamics – the study of the motion ofair, particularly its interaction with a solid object, such as anairplane wing. It is a sub-field offluid dynamics andgas dynamics, and many aspects of aerodynamics theory are common to these fields.
• Agitator (device) – adevice ormechanism to put something intomotion byshaking orstirring. Agitators usually consist of animpeller and a shaft; an impeller is a rotor located within a tube or conduit attached to the shaft, which helps enhance the pressure in order for the flow of a fluid be done.^[12]
• Air handler – anair handler, orair handling unit (often abbreviated toAHU), is a device used to regulate and circulate air as part of a heating, ventilating, and air-conditioning (HVAC) system.^[13]
• Air compressor – a device thatconverts power (using an electric motor, diesel or gasoline engine, etc.) intopotential energy stored in pressurized air (i.e.,compressed air). By one of several methods, an air compressor forces more and more air into a storage tank, increasing the pressure. When tank pressure reaches its engineered upper limit the air compressor shuts off. The compressed air, then, is held in the tank until called into use.^[14]
• Air conditioner –Air conditioning (often referred to asAC,A/C, orair con)^[15] is the process of removing heat and moisture from the interior of an occupied space, to improve the comfort of occupants. Air conditioning can be used in both domestic and commercial environments.
• Air preheater – (APH) any device designed to heatair before another process (for example,combustion in aboiler) with the primary objective of increasing the thermal efficiency of the process. They may be used alone or to replace arecuperative heat system or to replace a steam coil.
• Airflow –Airflow, orair flow, is the movement of air from one area to another. The primary cause of airflow is the existence ofpressure gradients. Air behaves in afluid manner, meaning particles naturally flow from areas of higher pressure to those where the pressure is lower.Atmospheric air pressure is directly related to altitude, temperature, and composition.^[16][17] Inengineering, airflow is a measurement of the amount ofair per unit of time that flows through a particular device.
• Allowance – a planned deviation between an exact dimension and anominal ortheoretical dimension, or between an intermediate-stage dimension and an intended final dimension. The unifying abstract concept is that a certain amount of differenceallows for some known factor of compensation or interference. For example, an area of excess metal may be left because it is needed to complete subsequent machining. Common cases are listed below. Anallowance, which is aplanned deviation from an ideal, is contrasted with atolerance, which accounts for expected but unplanned deviations.
• American Society of Mechanical Engineers – TheAmerican Society of Mechanical Engineers (ASME) is aprofessional association that, in its own words, "promotes the art, science, and practice of multidisciplinary engineering and allied sciences around the globe" via "continuing education, training andprofessional development, codes andstandards,research, conferences and publications, government relations, and other forms of outreach."^[18]
• Ampere – thebase unit ofelectric current in theInternational System of Units (SI).^[19][20] It is named afterAndré-Marie Ampère (1775–1836), French mathematician and physicist, considered the father ofelectrodynamics.
• Applied mechanics – describes the behavior of a body, in either a beginning state of rest or of motion, subjected to the action of forces.^[21] Applied mechanics, bridges the gap between physical theory and its application totechnology. It is used in many fields ofengineering, especiallymechanical engineering andcivil engineering. In this context, it is commonly referred to asengineering mechanics.
• Archimedes' screw – also known by the nameArchimedean screw orscrew pump, is amachine used fortransferring water from a low-lying body of water intoirrigation ditches. Water is pumped by turning a screw-shaped surface inside a pipe. Thescrew pump is commonly attributed toArchimedes,^[22]
• Artificial intelligence – (AI), sometimes calledmachine intelligence, isintelligence demonstrated bymachines, in contrast to thenatural intelligence displayed by humans and other animals. Incomputer science AI research is defined as the study of "intelligent agents": any device that perceives its environment and takes actions that maximize its chance of successfully achieving its goals.^[23] Colloquially, the term "artificial intelligence" is applied when a machine mimics "cognitive" functions that humans associate with otherhuman minds, such as "learning" and "problem solving".^[24]
• Assembly drawing –see Technical drawing.
• Automaton clock – Anautomaton clock orautomata clock is a type ofstriking clock featuringautomatons.^[25] Clocks like these were built from the 1st century BC through toVictorian times in Europe. Acuckoo clock is a simple form of this type of clock.
• Automobile – a wheeledmotor vehicle used fortransportation. Most definitions ofcar say they run primarily on roads, seat one to eight people, have fourtires, and mainly transport people rather than goods.^[26][27]
• Automobile handling –Automobile handling andvehicle handling are descriptions of the way a wheeled vehicle responds and reacts to the inputs of a driver, as well as how it moves along a track or road. It is commonly judged by how a vehicle performs particularly duringcornering, acceleration, and braking as well as on the vehicle'sdirectional stability when moving in steady state condition.
• Automotive engineering –Automotive engineering, along withaerospace engineering andmarine engineering, is a branch of vehicle engineering, incorporating elements ofmechanical,electrical,electronic,software andsafety engineering as applied to the design, manufacture and operation ofmotorcycles,automobiles andtrucks and their respective engineering subsystems. It also includes modification of vehicles. Manufacturing domain deals with the creation and assembling the whole parts of automobiles is also included in it. The automotive engineering field is research -intensive and involves direct application of mathematical models and formulas. The study of automotive engineering is to design, develop, fabricate, and testing vehicles or vehicle components from the concept stage to production stage. Production, development, and manufacturing are the three major functions in this field.
• Axle – a central shaft for arotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to the vehicle, with the wheels rotating around the axle.^[28] In the former case,bearings orbushings are provided at the mounting points where the axle is supported. In the latter case, a bearing or bushing sits inside a central hole in the wheel to allow the wheel or gear to rotate around the axle. Sometimes, especially on bicycles, the latter type axle is referred to as aspindle.

• Babbitt – also calledBabbitt metal orbearing metal, is any of severalalloys used for thebearing surface in aplain bearing. The original Babbitt alloy was invented in 1839 byIsaac Babbitt^[29] inTaunton,Massachusetts, United States.
• Backdrive – a component used in reverse to obtain its input from its output. This extends to many concepts and systems from thought based to practical mechanical applications.
• Backlash – sometimes calledlash orplay, is a clearance or lost motion in a mechanism caused by gaps between the parts. It can be defined as "the maximum distance or angle through which any part of amechanical system may be moved in one direction without applying appreciable force or motion to the next part in mechanical sequence",^[30]p. 1-8.
• Balancing machine – a measuring tool used for balancing rotating machine parts such as rotors forelectric motors, fans,turbines,disc brakes,disc drives,propellers andpumps.
• Ball detent – a simple mechanical arrangement used to hold a moving part in a temporarily fixed position relative to another part. Usually the moving parts slide with respect to each other, or one part rotates within the other.
• Ball screw – a mechanicallinear actuator that translates rotational motion to linear motion with littlefriction. A threaded shaft provides a helical raceway forball bearings which act as a precision screw. As well as being able to apply or withstand high thrust loads, they can do so with minimum internal friction.
• Ball spline –Ball splines (Ball Splinebearings) are a special type oflinear motion bearing that are used to provide nearly frictionless linear motion while allowing the member to transmit torque simultaneously. There aregrooves ground along the length of the shaft (thus formingsplines) for the recirculating ground balls to run inside. The outer shell that houses the balls is called a nut rather than abushing, but is not a nut in the traditional sense—it is not free to rotate about the shaft, but is free to travel up and down the shaft.
• Beale number – a parameter that characterizes the performance ofStirling engines. It is often used to estimate the power output of a Stirling engine design. For engines operating with a high temperature differential, typical values for the Beale number range from ( 0.11 ) to ( 0.15 ); where a larger number indicates higher performance.
• Bearing – amachine element that constrains relative motion to only the desired motion, and reducesfriction betweenmoving parts.
• Bearing pressure – a particular case ofcontact mechanics often occurring in cases where a convex surface (male cylinder or sphere) contacts a concave surface (female cylinder or sphere:bore orhemispherical cup). Excessive contact pressure can lead to a typical bearing failure such as a plastic deformation similar topeening. This problem is also referred to asbearing resistance.^[31]
• Bearing surface – thearea of contact between two objects. It usually is used in reference tobolted joints andbearings, but can be applied to a wide variety of engineering applications. On ascrew the bearing area loosely refers to the underside of the head.^[32] Strictly speaking, the bearing area refers to the area of the screw head that directly bears on the part being fastened.^[33] For a cylindrical bearing it is theprojected area perpendicular to the applied force.^[34] On aspring the bearing area refers to the amount of area on the top or bottom surface of the spring in contact with the constraining part.^[35] The ways ofmachine tools, such as dovetail slides, box ways, prismatic ways, and other types of machine slides are also bearing surfaces.
• Belt – a loop of flexible material used to link two or more rotatingshafts mechanically, most often parallel. Belts may be used as a source of motion, totransmit power efficiently or to track relative movement. Belts are looped overpulleys and may have a twist between the pulleys, and the shafts need not be parallel.
• Belt friction – describes the friction forces between abelt and a surface, such as a belt wrapped around abollard. 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 thetension in the belt can be different at both ends of the belt. Belt friction can be modeled by theBelt friction equation.^[36]
• Bending – Inapplied mechanics,bending (also known asflexure) characterizes the behavior of a slenderstructural element subjected to an externalload applied perpendicularly to a longitudinal axis of the element.
• Biomechatronics – an appliedinterdisciplinary science that aims to integratebiology,mechanics, andelectronics. It also encompasses the fields ofrobotics andneuroscience. Biomechatronic devices encompass a wide range of applications from the development ofprosthetic limbs to engineering solutions concerning respiration, vision, and the cardiovascular system.^[37]
• Body in white – orBIW refers to the stage inautomobile manufacturing in which a car body's components have been joined together, using one or a combination of different techniques: welding (spot, MIG/MAG), riveting, clinching, bonding, laser brazing etc. BIW is termed before painting and before the engine, chassis sub-assemblies, or trim (glass, door locks/handles, seats, upholstery, electronics, etc.) have been assembled in the frame structure.
• Bogie – achassis or framework that carries awheelset, attached to a vehicle—amodular subassembly ofwheels andaxles. Bogies take various forms in various modes of transport.
• Bonded seal – a type ofwasher used to provide aseal around a screw or bolt. Originally made byDowty Group, they are also known as Dowty seals or Dowty washers.^[38] Now widely manufactured, they are available in a range of standard sizes and materials^[39][40][41]
• Brittleness – A material isbrittle if, when subjected tostress, it breaks without significantplastic deformation. Brittle materials absorb relatively littleenergy prior to fracture, even those of highstrength.
• Buckling – instability that leads to afailure mode. When a structure is subjected tocompressivestress, buckling may occur. Buckling is characterized by a sudden sideways deflection of a structural member. This may occur even though the stresses that develop in the structure are well below those needed to cause failure of the material of which the structure is composed.
• Bus – Abus (archaically alsoomnibus,^[42]multibus,motorbus, andautobus) is aroad vehicle designed to carry manypassengers.
• Bushing – orrubber bushing is a type ofvibration isolator. It provides an interface between two parts, damping the energy transmitted through the bushing. A common application is invehicle suspension systems, where a bushing made ofrubber (or, more often,synthetic rubber orpolyurethane) separates the faces of two metal objects while allowing a certain amount of movement. This movement allows the suspension parts to move freely, for example, when traveling over a large bump, while minimizing transmission of noise and small vibrations through to the chassis of the vehicle. A rubber bushing may also be described as aflexible mounting orantivibration mounting.
• Boiler – a closedvessel in whichfluid (generally water) is heated. The fluid does not necessarilyboil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications,^[43][44] includingwater heating,central heating,boiler-based power generation,cooking, andsanitation.

• CAD –see Computer-aided design.
• CAM –see Computer-aided manufacturing
• CAID –see Computer-aided industrial design.
• Calculator – Anelectronic calculator is typically a portableelectronic device used to performcalculations, ranging from basicarithmetic to complexmathematics.
• Calculus – themathematical study of continuous change.
• Car handling –Automobile handling andvehicle handling are descriptions of the way a wheeled vehicle responds and reacts to the inputs of a driver, as well as how it moves along a track or road. It is commonly judged by how a vehicle performs particularly duringcornering, acceleration, and braking as well as on the vehicle'sdirectional stability when moving in steady state condition.
• Carbon fiber reinforced polymer – orcarbon fiber reinforced plastic, orcarbon fiber reinforced thermoplastic (CFRP,CRP,CFRTP, or often simplycarbon fiber,carbon composite, or evencarbon), is an extremely strong and lightfiber-reinforced plastic which containscarbon fibers.
• Carbon fibers – orcarbon fibres (alternativelyCF,graphite fiber orgraphite fibre) arefibers about 5–10micrometres in diameter and composed mostly ofcarbon atoms. Carbon fibers have several advantages including high stiffness, high tensile strength, low weight, high chemical resistance, high temperature tolerance and low thermal expansion. These properties have made carbon fiber very popular in aerospace, civil engineering, military, and motorsports, along with other competition sports. However, they are relatively expensive when compared with similar fibers, such asglass fibers or plastic fibers.
• Classical mechanics – describes themotion ofmacroscopic objects, fromprojectiles to parts ofmachinery, andastronomical objects, such asspacecraft,planets,stars andgalaxies.
• Clean room design – the method of copying a design byreverse engineering and then recreating it without infringing any of thecopyrights associated with the original design. Clean-room design is useful as a defense against copyright infringement because it relies on independent invention. However, because independent invention is not a defense againstpatents, clean-room designs typically cannot be used to circumvent patent restrictions.
• Clevis fastener – a fastener consisting of a U-shaped bracket through which a pin is placed
• Clock – an instrument used to measure, keep, and indicatetime. The clock is one of the oldest humaninventions, meeting the need to measure intervals of time shorter than the natural units: the day, thelunar month, and the year. Devices operating on several physical processes have been used over the millennia.
• Clutch – a mechanical device which engages and disengages power transmission especially fromdriving shaft to driven shaft.
• CNC – (CNC)), theautomated control ofmachining tools (drills, boring tools, lathes) by means of acomputer. An NC machine alters a blank piece of material (metal, plastic, wood, ceramic, or composite) to meet precise specifications by following programmed instructions and without a manual operator.
• Coefficient of thermal expansion – describes how the size of an object changes with a change in temperature. Specifically, it measures the fractional change in size per degree change in temperature at a constant pressure. Several types of coefficients have been developed: volumetric, area, and linear. The choice of coefficient depends on the particular application and which dimensions are considered important.
• Coil spring – also known as ahelical spring, is a mechanical device which is typically used to store energy and subsequently release it, to absorb shock, or to maintain a force between contacting surfaces. They are made of anelastic material formed into the shape of ahelix which returns to its natural length when unloaded.
• Combustion – also known asburning when accompanied by fire, is a high-temperatureexothermicredoxchemical reaction between afuel (the reductant) and anoxidant, usually atmosphericoxygen, that produces oxidized, often gaseous products, in a mixture assmoke. Generally, thechemical equation forstoichiometric combustion of ahydrocarbon in oxygen is${\displaystyle {\text{C}}_{\mathit{\text{x}}}^{}{\text{H}}_{\mathit{\text{y}}}^{}+\mathit{\text{z}}{\text{O}}_2^{}⟶\mathit{\text{x}}{\text{CO}}_2^{}+\frac{\mathit{\text{y}}}{2}{\text{H}}_2^{}\text{O}}$, where${\displaystyle z=x+\frac{y}{4}}$.
• Composite material – (also called acomposition material, or shortened tocomposite), is a material made from two or more constituent materials with significantly differentphysical orchemical properties that, when combined, produce a material with characteristics different from the individual components. The individual components remain separate and distinct within the finished structure, differentiating composites frommixtures andsolid solutions.
• Compression ratio – The staticcompression ratio, (symbol${\displaystyle \epsilon }$),^[45] of aninternal combustion engine orexternal combustion engine is a value that represents theratio of the volume of itscombustion chamber from its largest capacity to its smallest capacity. It is a fundamental specification for many common combustion engines.
• Compressive strength – orcompression strength, is the capacity of a material or structure to withstand loads tending to reduce size, as opposed totensile strength, which withstands loads tending to elongate. In other words, compressive strength resistscompression (being pushed together), whereas tensile strength resiststension (being pulled apart). In the study ofstrength of materials, tensile strength, compressive strength, andshear strength can be analyzed independently.
• Computational fluid dynamics – (CFD) a branch offluid mechanics that usesnumerical analysis anddata structures to analyze and solve problems that involvefluid flows. Computers are used to perform the calculations required to simulate the free-stream flow of the fluid, and the interaction of the fluid (liquids andgases) with surfaces defined byboundary conditions. With high-speedsupercomputers, better solutions can be achieved, and are often required to solve the largest and most complex problems.
• Computer – a device that can be instructed to carry outsequences ofarithmetic orlogical operations automatically viacomputer programming. Modern computers have the ability to follow generalized sets of operations, calledprograms. These programs enable computers to perform an extremely wide range of tasks. A "complete" computer including thehardware, theoperating system (mainsoftware), andperipheral equipment required and used for "full" operation can be referred to as acomputer system. This term may as well be used for a group of computers that are connected and work together, in particular acomputer network orcomputer cluster.
• Computer-aided design – (CAD) the use ofcomputer systems (orworkstations) to aid in the creation, modification, analysis, or optimization of adesign.^[46] 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.^[47] CAD output is often in the form of electronic files for print, machining, or other manufacturing operations. The termCADD (forComputer Aided Design and Drafting) is also used.^[48]
• Computer-aided industrial design – (CAID) a subset ofcomputer-aided design (CAD) software that can assist in creating the look-and-feel, or industrial design aspects of a product in development.
• Computer-aided manufacturing – (CAM) the use of software to controlmachine tools and related ones in themanufacturing of workpieces.^{[49][50][51][52][53]} This is not the only definition for CAM, but it is the most common;^[49] 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.^[54][55]
• Computer numerical control –Numerical control (NC), (alsocomputer numerical control (CNC)), is theautomated control ofmachining tools (drills, boring tools, lathes) and3D printers by means of acomputer. An NC machine alters a blank piece of material (metal, plastic, wood, ceramic, or composite) to meet precise specifications by following programmed instructions and without a manual operator.
• Conservation of mass – Thelaw of conservation of mass orprinciple of mass conservation states that for anysystem closed to all transfers ofmatter andenergy, themass of the system must remain constant over time, as system's mass cannot change, so quantity can neither be added nor be removed. Hence, the quantity of mass is conserved over time.
• Constant-velocity joint – (also known ashomokinetic orCV joints), allow adrive shaft to transmit power through a variable angle, at constant rotational speed, without an appreciable increase in friction orplay. They are mainly used infront wheel drive vehicles. Modernrear wheel drivecars withindependent rear suspension typically use CV joints at the ends of the rear axle halfshafts and increasingly use them on thedrive shafts.
• Constraint –
• Continuum mechanics – a branch ofmechanics that deals with the mechanical behavior of materials modeled as a continuous mass rather than as discrete particles.
• Control theory – incontrol systems engineering is a subfield ofmathematics that deals with the control of continuously operatingdynamical systems in engineered processes and machines. The objective is to develop a control model for controlling such systems using a control action in an optimum manner withoutdelay or overshoot and ensuring controlstability.
• Corrosion – anatural process that converts a refined metal to a more chemically-stable form, such as itsoxide,hydroxide, orsulfide. It is the gradual destruction of materials (usuallymetals) by chemical and/or electrochemical reaction with their environment.Corrosion engineering is the field dedicated to controlling and stopping corrosion.
• Cotter pin – a pin or wedge passing through a hole to fix parts tightly together.
• Crankshaft – a mechanical part able to perform a conversion betweenreciprocating motion androtational motion. In areciprocating engine, it translatesreciprocating motion of thepiston into rotational motion; whereas in areciprocating compressor, it converts the rotational motion into reciprocating motion. In order to do the conversion between two motions, the crankshaft has "crank throws" or "crankpins", additional bearing surfaces whose axis is offset from that of the crank, to which the "big ends" of theconnecting rods from each cylinder attach.
• Cybernetics –

• Damping ratio – an influence within or upon anoscillatory system that has the effect of reducing, restricting or preventing its oscillations. In physical systems, damping is produced by processes that dissipate the energy stored in the oscillation.^[56] Examples includeviscousdrag in mechanical systems,resistance inelectronic oscillators, and absorption and scattering of light inoptical oscillators.
• Deformation (engineering) – refers to the change in size or shape of an object. Deformation that is reversible is termed aselastic deformation, while irreversible deformation is termedplastic deformation.Strain is the relative deformation of an infinitesimally small cube of material, and is generally linearly proportional to the forces orstresses acting on the cube while the deformation is elastic. The determination of the stress and strain throughout a solid object is given by the field ofstrength of materials and for a structure bystructural analysis.
• Delamination – is a mode of failure where a materialfractures into layers. A variety of materials includinglaminatecomposites^[57] andconcrete can fail by delamination.
• Design –
• Design for manufacturability – (also sometimes known as design for manufacturing or DFM), is the general engineering practice ofdesigning products in such a way that they are easy to manufacture. The concept exists in almost all engineering disciplines, but the implementation differs widely depending on the manufacturing technology.
• Diesel engine – (also known as a compression-ignition or CI engine), named afterRudolf Diesel, is aninternal combustion engine in whichignition of thefuel is caused by the elevated temperature of the air in the cylinder due to the mechanical compression (adiabatic compression).
• Differential –A differential is a gear train with three shafts that has the property that the rotational speed of one shaft is the average of the speeds of the others, or a fixed multiple of that average.
• Dimensionless number – aquantity to which nophysical dimension is assigned. Dimensionless quantities arewidely used in many fields, such asmathematics,physics,chemistry,engineering, andeconomics.
• Diode – a two-terminalelectronic component that conductscurrent primarily in one direction (asymmetricconductance); it has low (ideally zero)resistance in one direction, and high (ideally infinite)resistance in the other. A diodevacuum tube orthermionic diode is a vacuum tube with twoelectrodes, a heatedcathode and aplate, in which electrons can flow in only one direction, from cathode to plate. Asemiconductor diode, the most commonly used type today, is acrystalline piece ofsemiconductor material with ap–n junction connected to two electrical terminals.^[58]
• Diode laser –
• Docking sleeve –
• Drafting –
• Drifting –
• Driveshaft – a component for transmitting mechanicalpower andtorque and rotation, usually used to connect other components of adrivetrain that cannot be connected directly because of distance or the need to allow for relative movement between them.
• Dynamics – thebranch ofclassical mechanics that is concerned with the study offorces and their effects onmotion.
• Dynamometer – a device for simultaneously measuring thetorque androtational speed (RPM) of anengine,motor or other rotatingprime mover so that its instantaneouspower may be calculated.

• Elasticity – Inphysics, 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 willdeform when adequateforces are applied to them. If the material is elastic, the object will return to its initial shape and size when these forces are removed. Hooke's law states that the force should be proportional to the extension. The physical reasons for elastic behavior can be quite different for different materials. In metals, the atomic lattice changes size and shape when forces are applied (energy is added to the system). When forces are removed, the lattice goes back to the original lower energy state. Forrubbers and other polymers, elasticity is caused by the stretching of polymer chains when forces are applied.
• Electric current – a stream ofcharged particles, such aselectrons orions, moving through anelectrical conductor or space. It is measured as the net rate of flow ofelectric charge through a surface or into acontrol volume.
• Electric motor – anelectrical machine that convertselectrical energy intomechanical energy. Most electric motors operate through the interaction between the motor'smagnetic field andelectric current in awire winding to generate force in the form ofrotation of a shaft. Electric motors can be powered bydirect current (DC) sources, such as from batteries, motor vehicles or rectifiers, or byalternating current (AC) sources, such as a power grid,inverters or electrical generators. Anelectric generator is mechanically identical to an electric motor, but operates in the reverse direction, converting mechanical energy into electrical energy.
• Electrical engineering – Electrical engineering is an engineering discipline concerned with the study, design and application of equipment, devices and systems which use electricity, electronics, and electromagnetism.
• Electrical circuit – an electrical network consisting of a closed loop, giving a return path for the current.
• Electrical network – an interconnection ofelectrical components (e.g.,batteries,resistors,inductors,capacitors,switches,transistors) or a model of such an interconnection, consisting ofelectrical elements (e.g.,voltage sources,current sources,resistances,inductances,capacitances).
• Electromagnetism –
• Electronic circuit – a type of electrical circuit which is composed of individualelectronic components, such asresistors,transistors,capacitors,inductors anddiodes, connected by conductivewires ortraces through whichelectric current can flow.
• Electronics –
• Energy –
• Engine –
• Engineering – the use ofscientific principles to design and build machines, structures, and other items.
• Engineering cybernetics –
• Engineering drawing – a type oftechnical drawing that is used to convey information about an object.Detail drawings commonly specify thedimensions andtolerances for the construction of a single component, while a master drawing orassembly drawing links the detail drawings for each component in a system. Only required information is typically specified, usually only in one place to avoid inconsistency.
• Engineering economics – a subset of economics that studies the behavior of individuals and firms in making engineering decisions regarding the allocation of limited resources. It is a simplified application ofmicroeconomics in that it assumes elements such as price determination, competition and demand/supply to be fixed inputs.
• Engineering ethics – a field that examines and sets the obligations byengineers tosociety, to their clients, and to the profession. Manyengineering professional societies have prepared codes of ethics which are largely similar to each other.
• Engineering management – the combination of technological problem-solving and the organizational, administrative, legal and planning abilities ofmanagement in order to oversee the operational performance of complex engineering driven enterprises.
• Engineering society – aprofessional organization forengineers of variousdisciplines. Some are umbrella type organizations which accept many different disciplines, while others are discipline-specific. There are also many student-run engineering societies, commonly at universities or technical colleges.
• Exploratory engineering – the process of designing and analyzing detailed hypothetical models of systems that are not feasible with current technologies or methods, but do seem to be clearly within the bounds of what science considers to be possible. It usually results inprototypes orcomputer simulations that are as convincing as possible to those that know the relevant science, given the lack of experimental confirmation.

• Fits and tolerances -
• Factor of safety –
• False precision –
• Fast fracture –
• Fatigue –
• Fillet –
• First law of thermodynamics – states thatenergy can neither be created nor destroyed; it can change only from one form to another.
• Finite element analysis –
• Flange -
• Fluid mechanics –
• Flywheel –
• Force – an influence that can push or pull anobject to change itsmotion. A force can cause an object withmass to change itsvelocity (e.g. moving from astate of rest), i.e., toaccelerate. A force has bothmagnitude anddirection, making it avector quantity.
• Force density –
• Forging –
• Four-bar linkage –
• Four-stroke cycle –
• Four wheel drive –
• Friction – theforce resisting the relative motion of solid surfaces, fluid layers, and material elementssliding against each other. There are several types of friction includingstatic friction between non-moving surfaces andkinetic friction between moving surfaces; for two given solid surfaces, static friction is greater than kinetic friction.Fluid friction describes the friction between layers of aviscous fluid that are moving relative to each other.
• Front wheel drive –
• Fundamentals of Engineering exam –
• Fusible plug –
• Fusion deposition modelling –

• Gas compressor –
• Gauge –
• Gear – arotating circularmachine part having cut or inserted teeth which mesh with another compatible toothed part to transmittorque and speed. Each gear tooth essentially functions as alever with its fulcrum at the gear's center.
• Gear coupling – a mechanical device for transmittingtorque between two shafts that are notcollinear. It consists of a flexible joint fixed to each shaft. The two joints are connected by a third shaft, called the spindle.
• Gear ratio – the ratio of thepitch circles of mating gears which defines the speed ratio and themechanical advantage of the gear set.
• Granular material –

• Heat engine – a system that converts heat orthermal energy—andchemical energy—tomechanical energy, which can then be used to domechanical work.^[59][60]
• Heat transfer –
• Heating and cooling systems –
• Hinge –
• Hoberman mechanism –
• Hobson's joint –
• Hooke's law –
• Hotchkiss drive –
• HVAC –
• Hydraulics –
• Hydrostatics –

• Ideal machine –
• Ideal mechanical advantage –
• Imperial College London –
• Inclined plane –
• Independent suspension –
• Inductor –
• Industrial engineering –
• Inertia –
• Institution of Mechanical Engineers –
• Instrumentation –
• Integrated circuit –
• Intelligent pump –
• Invention – a unique or novel device, method, composition, idea or process. Aninventor who creates or discovers a new invention can sometimes receive apatent, or legal right to exclude others from making, using, or selling that invention for a limited time.

• Jack chain –
• Jacking gear –
• JIC fitting –
• Joule – theSI unit ofenergy, which uses the symbolJ. It is equal to the amount ofwork done when a force of 1newton displaces a mass through a distance of 1metre in the direction of the force applied. It is also the energy dissipated as heat when anelectric current of oneampere passes through aresistance of oneohm for one second.

• Kelvin – the primarySI unit oftemperature, which uses the symbolK and hasabsolute zero as its zero point. The temperature indegree Celsius is defined as the temperature in kelvins minus 273.15 (i.e. 0 °C is equal to 273.15 K).
• Kinematic determinacy –
• Kinematics –

• Laser –
• Leaf spring –
• Lever – asimple machine consisting of abeam or rigid rod pivoted at a fixedhinge, orfulcrum. A lever amplifies an input force to provide a greater output force, which is said to provideleverage. The ratio of the output force to the input force is themechanical advantage of the lever.
• Liability –
• Life cycle cost analysis –
• Limit state design –
• Linkage –
• Live axle –
• Load transfer –
• Locomotive –
• Lubrication –

• Machine –
• Machine learning –
• Machinery's Handbook – a classic, one-volume reference work in mechanical engineering and practicalworkshopmechanics published byIndustrial Press, New York, since 1914; its 31st edition was published in 2020. Recent editions of the handbook contain chapters on mathematics, mechanics, materials, measuring, toolmaking, manufacturing, threading, gears, and machine elements, combined with excerpts fromANSI standards.
• Magnetic circuit –
• Margin of safety –
• Mass transfer –
• Materials –
• Materials engineering –
• Material selection –
• Mechanical advantage –
• Mechanical biological treatment –
• Mechanical efficiency –
• Mechanical engineering –
• Mechanical equilibrium –
• Mechanical work –
• Mechanics –
• Mechanochemistry –
• Mechanosynthesis –
• Mechatronics –
• Microelectromechanical systems –
• Micromachinery –
• Microprocessor –
• Microtechnology –
• Modulus of rigidity--
• Molecular assembler –
• Molecular nanotechnology –
• Moment –
• Moment of inertia –
• Motorcycle –
• Multi-link suspension –

• Nanotechnology –
• Newton (unit) – theSI unit offorce, which uses the symbolN. It is defined as 1 kg⋅m/s², the force which gives a mass of 1 kilogram an acceleration of 1 metre per second per second. It is named afterIsaac Newton in recognition of his work onclassical mechanics, specificallyNewton's second law of motion.
• Normal stress –
• Nozzle –

• Ohm's law – states that thecurrent through aconductor between two points is directlyproportional to thevoltage across the two points. It is typically expressed as the equationI =V ÷R, whereI is the current through the conductor,V is the voltage measuredacross the conductor andR is theresistance of the conductor.
• Orientation
• Overdrive –
• Oversteer –

• Pascal (unit) – theSI unit ofpressure, which uses the symbolPa and is defined as onenewton per square metre. It is also used to quantifyinternal pressure,stress,Young's modulus, andultimate tensile strength.
• Physics –
• Pinion –
• Piston –
• Pitch drop experiment –
• Plain bearing –
• Plasma processing –
• Plasticity –
• Pneumatics –
• Poisson's ratio –
• Position vector –
• Potential difference –
• Power – the amount ofenergy transferred or converted per unit time. Power is ascalar quantity.
• Power stroke –
• Pressure –
• Process control –
• Product lifecycle management –
• Professional engineer (PE) – In the United States, this designation is given to engineers who have passed thePrinciples and Practice of Engineering exam, or PE exam. Upon passing the PE exam and meeting other eligibility requirements, that vary by state, such as education and experience, an engineer can then become registered in their State to stamp and sign engineering drawings and calculations as a PE.
• Project management –
• Pulley –
• Pump –

• Quality –
• Quality control –
• Quality assurance –

• Rack and pinion –
• Rack railway –
• Railcar –
• Rail gauge –
• Railroad car –
• Railroad switch –
• Rail tracks –
• Random vibration –
• Reaction kinetics –
• Rear wheel drive –
• Refrigeration –
• Reliability engineering –
• Relief valve –
• RepRap Project –
• Resistive force –
• Resistor –
• Reverse engineering –
• Rheology –
• Rigid body –
• Robotics –
• Roller chain –
• Rolling –
• Rotordynamics –
• Rube Goldberg machine –

• Safety engineering –
• Screw theory –
• Seal –
• Second law of thermodynamics – states that whenenergy changes from one form to another form, or matter moves freely,entropy (disorder) in a closed system increases. In other words, heat always moves from hotter objects to colder objects unless energy is supplied to reverse the direction ofheat flow, and not all heat energy can be converted intowork in acyclic process.
• Semiconductor –
• Series and parallel circuits –
• Shear forcediagrams –
• Shear pin –
• Shear strength –
• Shear stress –
• Simple machine –
• Simulation –
• Slide rule –
• Society of Automotive Engineers –
• Solid mechanics –
• Solid modeling –
• Split nut –
• Sprung mass –
• Statics –
• Steering –
• Stress–strain curve – a chart which gives the relationship betweenstress andstrain for a given material. It is obtained by gradually applyingload to a test coupon and measuring thedeformation.
• Structural failure –
• Student Design Competition –
• Surveying –
• Suspension –
• Switch – anelectrical component that can disconnect or connect the conducting path in anelectrical circuit, interrupting theelectric current or diverting it from one conductor to another.

• Technical drawing – the act anddiscipline of composingdrawings thatvisually communicate how something functions or is constructed. Inindustry andengineering, commonconventions constitute avisual language and help to ensure that the drawing is precise,unambiguous and relatively easy to understand. Many of the symbols and principles of technical drawing are codified in aninternational standard calledISO 128.
• Technology – refers to both the application ofknowledge for achieving practicalgoals in areproducible way, and the products andtools resulting from such efforts.
• Tensile strength – also calledultimate tensile strength orultimate strength, is the maximumstress that a material can withstand while being stretched or pulled before breaking. Inbrittle materials the ultimate tensile strength is close to theyield point, whereas inductile materials the ultimate tensile strength can be higher.
• Tensile stress –
• Testing adjusting balancing –
• Theory of elasticity –
• Thermodynamics – a branch ofphysics that deals withheat,work, andtemperature, and their relation toenergy,entropy, and the physical properties ofmatter andradiation. The behavior of these quantities is governed by the fourlaws of thermodynamics.
• Third law of thermodynamics – states that theentropy of a system approaches a constant value when its temperature approachesabsolute zero, because itsatoms would stop moving. However,heat transfer between the system and its surroundings would prevent the system from ever reaching absolute zero.
• Toe –
• Torque –
• Torsion beam suspension –
• Torsion spring –
• Toughness –
• Track gauge – Spacing of the rails on a railway track
• Transmission –
• Truck –
• Truck (railway) – Chassis for wheels and suspension under railway vehicles,bogie outside U.S.
• Turbine –
• Tribology –
• Touch screen –
• tear –
• Tire manufacturing –

• Understeer –
• Unibody –
• Unsprung weight –

• Verification and Validation –
• Valve – a device or natural object (such as aheart valve) that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, orslurries) by opening, closing, or partially obstructing various passageways
• Vector – a geometric object that hasmagnitude (orlength) anddirection. Avector quantity is differentiated from ascalar quantity which only has magnitude, not direction. Vectors can be added to other vectors according tovector algebra.
• Vertical strength –
• Viscosity –
• Volt – theSI unit ofelectric potential,electric potential difference (voltage), andelectromotive force, which uses the symbolV.
• Vibration –
• Velocity diagrams –

• Wear – is the damaging, gradual removal or deformation of material atsolid surfaces. Causes of wear can be mechanical (e.g.,erosion) orchemical (e.g.,corrosion). The study of wear and related processes is referred to astribology.
• Wedge – atriangular shaped tool, and is a portableinclined plane, and one of the six classicalsimple 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 aforce applied to its blunt end into forces perpendicular (normal) to its inclined surfaces. Themechanical advantage of a wedge is given by the ratio of the length of its slope to its width.^[61][62] 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.
• Weight transfer –
• Wheel – In its primitive form, a wheel is a circular block of a hard and durable material at whose center has been bored a hole through which is placed anaxlebearing about which the wheel rotates whentorque is applied to the wheel about its axis. Thewheel and axle assembly can be considered one of thesix simple machines.
• Wheel and axle – a machine consisting of awheel attached to a smalleraxle so that these two parts rotate together in which a force is transferred from one to the other. The wheel and axle can be viewed as a version of the lever, with a drive force applied tangentially to the perimeter of the wheel and a load force applied to the axle, respectively, that are balanced around the hinge which is the fulcrum.
• Wheelset – thewheel–axle assembly of arailroad car. The frame assembly beneath each end of a car,railcar orlocomotive that holds the wheelsets is called thebogie (or truck inNorth America). Most North Americanfreight cars have two bogies with two or three wheelsets, depending on the type of car; shortfreight cars generally have no bogies but instead have two wheelsets.
• Work – theenergy transferred to or from an object via the application offorce along adisplacement. Work is ascalar quantity.

• X bar charts

• Yield point – Inmaterials science andengineering, the yield point is the point on astress–strain curve that indicates the limit ofelastic behavior and the beginning ofplastic behavior. Below the yield point, a material willdeform elastically and will return to its original shape when the appliedstress is removed. Once the yield point is passed, some fraction of the deformation will be permanent and non-reversible and is known asplastic deformation.
• Yield strength – oryield stress, is amaterial property and is the stress corresponding to the yield point at which the material begins to deform plastically. The yield strength is often used to determine the maximum allowableload in a mechanical component, since it represents the upper limit to forces that can be applied without producing permanent deformation. In some materials, such asaluminium, there is a gradual onset of non-linear behavior, making the precise yield point difficult to determine. In such a case, the offset yield point (orproof stress) is taken as the stress at which 0.2% plastic deformation occurs. Yielding is a gradualfailure mode which is normally notcatastrophic, unlikeultimate failure.
• Young's modulus – Young's modulus${\displaystyle E}$, theYoung modulus or themodulus of elasticity in tension, is a mechanical property that measures the tensilestiffness of asolid material. It quantifies the relationship between tensilestress${\displaystyle \sigma }$ (force per unit area) and axialstrain${\displaystyle \epsilon }$ (proportional deformation) in thelinear elastic region of a material and is determined using the formula:^[63]

${\displaystyle E=\frac{\sigma }{\epsilon }}$

Young's moduli are typically so large that they are expressed not inpascals but in gigapascals (GPa).

• Zero defects – (orZD), was a management-led program to eliminate defects in industrial production that enjoyed brief popularity in American industry from 1964^[64] to the early 1970s. Quality expertPhilip Crosby later incorporated it into his "Absolutes of Quality Management" and it enjoyed a renaissance in the American automobile industry—as a performance goal more than as a program—in the 1990s. Although applicable to any type of enterprise, it has been primarily adopted withinsupply chains wherever large volumes of components are being purchased (common items such as nuts and bolts are good examples).
• Zeroth Law of Thermodynamics – If body A is in thermal equilibrium (no heat transfers between them when in contact) with body C, and body B is in thermal equilibrium with body C, then A is in thermal equilibrium with B.

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