Actinium is a radioactive element.
AC Brownout
The condition that exists when the ac line voltage drops below some specified value.
AC coupling
Circuit that passes an AC signal while blocking a DC voltage.
ac ft
Abbreviation of acre foot, a volume one foot deep covering an area of one acre.
ac in
Abbreviation of acre inch, a volume one inch deep covering an area of one acre.
AC Induction Motors
These are generally used for constant speed applications where a fixed frequency power source such as 60 Hz or 400 Hz is available.
AC Line
The set of conductors that route ac voltage from one point to another.
AC Line Filter
A circuit filter placed in the ac line to condition or smooth out variations that are higher in frequency than the line frequency.
AC Voltage
The AC voltage is normally given as the RMS value.
An electric current whose direction changes direction with a frequency independent of circuit components.
Abbreviation of acre.
Abbreviation of Air Conditioning.
A durable wood used for palings and posts.
If a system is acausal it means the output begins before the input.
For a point excitation of a mechanical system this is the complex ratio of acceleration to applied force.
To increase the speed of an object.
Accelerated Life Test
A component test over a shortened timescale that has been designed to represent complete life history.
Accelerating Electrode
An electrode in an electron tube which is maintained at a positive potential with respect to the cathode and any other electrodes situated between the cathode and the accelerating electrode, thus imparting acceleration to electrons in the direction away from the cathode.
Accelerating Grid
An accelerating electrode in the form of a grid.
Accelerating Rate Calorimetry
An important method for studying the thermal behaviour of materials.
The change in velocity divided by the time it takes to make the change.
A machine used to accelerate particles to high speeds.
Accelerator Pedal
A pedal that when pressed is connected to the engine and demands more torque.
Accelerator Valve
A thermionic valve employed as a particle accelerator.
An instrument for measuring acceleration, as of aircraft or guided missiles.
Acceptance Test
An examination of a part or its assembly to determine if it meets a prescribed standard.
An atom which is likely to take on one or more electrons when placed in a crystal.
A way of reaching something that is usually hidden or covered.
Access Hole
An opening through which you can reach something.
Access Time
The average time interval between a storage peripheral receiving a request to read or write a certain location and returning the value read or completing the write.
Accessible Emission Level
Magnitude of accessible laser radiation of a specific wavelength or emission duration at a particular point.
Accidental Error
In experimental observations, an error which does not always recur when an observation is repeated under the same conditions.
The adjustments of a human body or other organism to a new environment.
The process by which the terrestrial planets grew.
Accretion Disc
An accretion disc is a disc-shaped rotating mass formed by gravitational attraction.
Accumulation Theory
The theory by which planetesimals are assumed to collide with one another and coalesce, eventually sweeping up enough material to form the planets.
A device by which energy or power can be stored.
Accuracy is the correctness of a single measurement.
The European Automobile Manufacturers Association or Association des Constructeurs Européens d’Automobiles from which the abbreviation is made.
Found in petroleum residues.


A polycyclic aromatic hydrocarbon derived from naphthalene that is insoluble in water, but soluble in alcohol. It is used as an intermediate for the manufacturing of dyes, pharmaceuticals and pesticides.

A polycyclic aromatic hydrocarbon.


More commonly known as ACP it is a phenothiazine derivative antipsychotic drug.

Formed by the oxidation of ethanol this is a colourless fruity smelling liquid that with further oxidation forms acetic acid.
Colourless crystalline used industrially as a solvent.


More commonly known as Paracetamol, a widely used over-the-counter analgesic.

Also known as Antifebrin this is a white crystalline solid.
An ion formed by removing the acidic hydrogen of acetic acid.
Acetic acid
The acid contained in vinegar.
Acetic Anhydride
The anhydride of acetic acid, used in the manufacture of plastics.


Used as a raw material for guanamine resins. It is used as a modifier and flexibilizer of formaldehyde resins and as a intermediate for pharmaceuticals.

Also known as Dimethyl Ketone, often used as a solvent.
Also known as Methyl Cyanide, a colourless poisonous liquid, used as a solvent and in organic synthesis.
Colourless sweet smelling liquid, also known as Acetylbenzene and Phenyl Methyl Ketone.
Acetyl Chloride
Also known as Ethanoyl Chloride it is a colourless pungent liquid.
Alternative name for Acetophenone.
Also known as Ethyne it is made by the action of water on calcium carbide.
Acetyl-Salicyclic Acid


Commonly known as Aspirin, a white solid. Used in medicine as an antipyretic and analgesic.

Acheson Process
The Acheson process is an industrial process for the manufacture of graphite by heating coke mixed with clay.
Achromatic Lens
Lens for which all light colours have the same focal length.


One of the most commonly-used antiviral drugs, it is primarily used for the treatment of herpes simplex virus infections.

Compound that gives off H+ ions in solution.
Acid Air
Alternative name for Hydrogen Chloride.
Acid Anhydride
Nonmetallic oxides or organic compounds that react with water to form acids.
Acid Cleaning
The process of cleaning components with dilute acid followed by a wash or inhibitor to stop further corrosion.
Acid Dissociation Constant
The equilibrium constant for the dissociation of an acid into a hydrogen ion and an anion.
Acid Embrittlement
A form of hydrogen embrittlement that may be induced in some metals by an acid.
Acid Error
A systematic error that occurs when glass pH electrodes are used in strongly acidic solutions.
Acid Gas Scrubbing System
A wet scrubbing system capable of achieving high acid gas removal efficiency by introducing water, caustic, or hydrated lime into the gas stream.
Acid Halide
Compounds containing a carbonyl group bound to a halogen atom.
Acid Number
The quantity of base, expressed in milligrams of potassium hydroxide, that is required to neutralize the acidic constituents in 1 g of sample.
Acid of Vinegar
Another name for Acetic Acid.
Acid Rain
Rain that is weakly acidic due to pollution.
Acid Sludge
The residue left after treating petroleum oil with sulphuric acid for the removal of impurities.
Acid Treating
A refining process in which unfinished petroleum products, such as gasoline, kerosene, and lubricating oil stocks, are contacted with sulphuric acid to improve their colour, odour, and other properties.
Acid-Base Indicator
A weak acid that has acid and base forms with sharply different colours.
Describes a solution with a high concentration of H+ ions.
Acidic Solution
A solution in which the hydrogen ion activity is higher than that of the hydroxide ion, when the solvent is water.
A condition in which blood pH decreases, either for metabolic or respiratory reasons.
A substance added to food or beverages to lower pH and to impart a tart, acid taste.
In telecommunications, this is the acknowledge character in many data codes; used most commonly for an affirmative response of correct receipt.
Ackermann Angle
The toe-out or toe-in of a vehicle with Ackermann steering when the wheels are positioned straight ahead.
Ackermann Curve
The graph created by plotting the difference between the real outer wheel turn angle and the ideal angle against all possible wheel positions from extreme right to extreme left turn.
Ackermann Deviation
The difference between the calculated ideal Ackermann angle and the actual outside wheel angle.
Ackermann Steering
A double-pivoting steering system.
Aclinic Line
The line through those points on the earth′s surface at which magnetic dip is zero.
Acme Thread
A screw thread having a 29 degree included angle. Used largely for feed and adjusting screws on machine tools.
The science of remedies.
Acorn Valve
An acorn valve is a form of thermionic valve used at ultra-high frequencies.
Acoustic Absorption
Reduction of sound pressure level through sound absorption.
Acoustic Admittance
This is the ratio of volume velocity to pressure, the reciprocal of Acoustic Impedance.
Acoustic Agglomeration
High intensity sound waves are used in a fluid to group suspended particles into larger aggregates.
Acoustic Barriers
An acoustic barrier between two rooms.
Acoustic Calibrator
A device which produces a known sound pressure on the microphone of a sound level measurement system.
Acoustic Cavity
The acoustics of enclosed volumes are important when considering sound propagation within the volume.
Acoustic Centre
The point in space of the origin of sound.
Acoustic Coupler
An acoustic coupler is means of connecting external devices to a telephone handset avoiding direct electrical connection.
Acoustic Delay Line
A device used in a communications link or a computer memory in which the signal is delayed by the propagation of a sound wave.
Acoustic Duct End Correction
The correction to the physical length of a duct to take into account the impedance of the termination and the effect on the acoustic length.
Acoustic Ducts
Ducts with an acoustic treatment or shaped to reduce or control acoustic wave propagation.
Acoustic Emission
A measure of integrity of a material determined by sound emission when a material is stressed.
Acoustic Excitation
The process of inducing vibration in a structure by exposure to sound waves.
Acoustic Feedback
Acoustic feedback is the return of acoustic energy from the output of a sound reproducing equipment.
Acoustic Filter Elements
There are a number of different types of acoustic filter elements that are used in many different applications.
Acoustic Generator
A transducer which converts electric, mechanical, or other forms of energy into sound.
Acoustic Impedance
The total reaction of a medium to the transmission of sound through it.
Acoustic Inertance
The impeding effect of inertia upon the transmission of sound in a duct, equal to the mass of the vibrating medium divided by the square of the cross section.
Acoustic Intensity
The quotient obtained when the average rate of energy flow in a specified direction and sense is divided by the area, perpendicular to that direction, through or toward which it flows.
Acoustic Mass
Another name for Acoustic Inertance.
Acoustic Material
Any material considered in terms of its acoustical properties.
Acoustic Microscopy
A general term referring to the use of high resolution, high frequency ultrasonic techniques to produce images of surface or near surface features.
Acoustic Mirrors
They are used today for sound source location in wind tunnels and for listening to conversations.
Acoustic Mobility
This is the ratio of volume velocity to pressure, the reciprocal of Acoustic Impedance.
Acoustic Noise Source
Any unwanted acoustic noise.
Acoustic Ohm
The unit of acoustic impedance.
Acoustic Origin
The point in time at which the signal originates.
Acoustic Pack
Name given to all of the soft absorptive parts used to reduce noise in a vehicle.
Acoustic Radiation Pressure
A unidirectional, steady-state pressure exerted upon a surface exposed to a sound wave.
Acoustic Reactance
Acoustic impedance caused by the inertia and elasticity of the transmitting medium.
Acoustic Refraction
The process by which the direction of sound propagation is changed due to spatial variation in the speed of sound in the medium.
Acoustic Resistance
Acoustic impedance caused by the internal friction of the transmitting medium.
Acoustic Screen
A moveable screen, usually covered in sound absorbent material on one side and having a reflective surface on the other.
Acoustic Source Location
There are a number of different ways by which the location of a noise source may be found.
Acoustic Sources
The simplest acoustic source is the monopole.
Acoustic Streaming
Unidirectional flow currents in a fluid that are due to the presence of sound waves.
Acoustic Tile
A descriptive term often used to describe commercially available room acoustic treatment.
Acoustic Trauma
Damage to the hearing mechanism caused by a sudden burst of intense noise, or by a blast.
Acoustic Wave
Another name for Sound Wave.
Acoustic Wedges
The acoustic treatment used on all surfaces of an anechoic chamber.
From the Greek akouein ( "to hear") a term sometimes used for the science of sound in general.
The process of locating the orbit of a satellite or trajectory of a space probe so that tracking or telemetry data can be gathered.
Alternative name for Acrolein.
A British unit of area, traditionally used in agriculture.
Acre Foot
A volume one foot deep covering an area of one acre.
Acre Inch
A volume one inch deep covering an area of one acre.


A colourless solid, was first isolated from coal tar. It is a raw material used for the production of dyes and some valuable drugs.

Acroleic Acid
Alternative name for Acrylic Acid.


the simplest unsaturated aldehyde. It has a piercing, disagreeable, acrid smell similar to that of burning fat.

Across Corners
The distance on a nut from one corner to the opposite corner.
Across Flats
The distance on a nut from one flat surface to the opposite flat surface.


A white odourless crystalline solid, soluble in water, ethanol, ether and chloroform.

Synthetic resin made from acrylic acid or a derivative thereof; acrylics possess the property of transparency and offer flame resistance.
Acrylic Acid


The simplest unsaturated carboxylic acid with a vinyl group at the a-carbon position and a carboxylic acid terminus.

Acrylic Aldehyde
Alternative name for Acrolein.


Pungent-smelling colourless liquid that often appears yellow due to impurities. It is an important monomer for the manufacture of useful plastics.

Acrylonitrile Butadiene Styrene
A common thermoplastic used to make light, rigid, moulded products such as piping.

Acryloyl Chloride


A clear, light yellow, flammable liquid with an acrid smell.

A protein making up the thin filaments of muscle and cytoskeleton of eukaryotic cells.
Pertaining to electromagnetic radiation capable of initiating photochemical reactions.
Actinic Ray
A ray of light of short wavelengths, as ultraviolet or violet, that produces photochemical effects.
Elements 89-102 are called actinides.
A radioactive element.
An actinometer is an instrument for measuring heat radiation.
The science of measurement of radiant energy.
Refers to an effective motion or mechanism as for example the breech action of a gun.
Action Based Planning
The goal is to determine how to decompose a high level action into a network of sub-actions that perform the required task.
Action Level
An action level is basically a noise exposure level at which employers are required to take certain steps to reduce the harmful effects of noise on hearing.
Activated Carbon
Also known as Activated Charcoal.
Activated Carbon Canister
An automotive filter in which activated carbon is used to trap fuel tank vapours, which have accumulated when the vehicle is not running.
Activated Charcoal
A porous form of carbon that acts as a powerful adsorbent.
Activated Complex
State of highest energy during a reaction.
Activation Energy
For the forward reaction is the energy required to go from reactants to the transition state.
Activation Overpotential
The overpotential which results from the restrictions imposed by the kinetics of charge transfer at an electrode.
Substance that enhances the ability of a flux to remove oxides and other contaminants from surfaces being joined.
Active Cell Balancing
This operates by moving energy from cells with a high SoC to cells with a lower SoC.
Active Constraint
An inequality constraint that holds with equality (at a point).
Active Crossover
A loudspeaker crossover requiring power to operate.
Active Device
A component that has gain or operates in a non-linear fashion to change the basic character of an electric signal by, for example, amplification or rectification.
Active High
The active, true, one, or asserted case of a binary signal is the high or most positive voltage level.
Active Iron
The amount of iron in the stator and rotor of a motor.
Active Leg
An electrical element within a transducer which changes its electrical characteristics as a function of the application of a stimulus.
Active Low
The active, true, one, or asserted case of a binary signal is the low or less positive voltage level.
Active Material
The material in the electrodes that takes part in the electrochemical reactions which store-deliver the electrical energy.
Active Metal
A metal that is easily oxidized in air.
Active Network
A circuit that produces gain.
Active Noise Control
This is an electronic method of reducing or removing unwanted sound by the production of a pressure wave of equal amplitude but opposite sign to the nwanted sound.
Active Power
The real power supplied by a system to the electrical load.
Active Satellite
A satellite which transmits a signal, in contrast to passive satellite.
Active Site
A pocket or crevice on an enzyme molecule that fits reactant molecules like a hand in a glove.
Active Sun
The Sun during its 11-year cycle of activity when spots, flares, prominences, and variations in radio frequency radiation are at a maximum.
Active Suspension
A suspension that uses sensors to determine conditions and responds to these different conditions by making compensatory adjustments to the suspension.
Active Transport
Energy-requiring transport of a solute across a membrane in the direction of increasing concentration.
Active Volcano
A volcano that is erupting.
Active Window
The top or front window in a multiple window environment.
The rate at which a collection of radioactive nuclei decay.
Activity Coefficient
The ratio of activity to concentration.
Actuating System
A mechanical system that supplies and transmits energy for the operation of other mechanisms or systems.
A device which controls or operates another device.
Acute Angle
A positive angle that is less than 90 degrees.
Acute Triangle
A triangle in which all of the angles are less than 90 degrees.