Elemental barium does not occur naturally although it has an abundance within the earth’s crust of 500 ppm.
BA Threads
Clearance and tapping drill sizes for BA threads.
Babbage, Charles
The British inventor known to some as the Father of Computing.
A soft antifriction metal used to line bearings.

Back Bias
An external voltage applied to a diode or semiconductor junction to reduce the flow of electrons across the junction.
Back Draft
Reverse taper which would prevent removal of a pattern from a mould or a core from a corebox.
Back Electromotive Force
The emf that opposes the normal flow of current in a circuit.
Back EMF
Abbreviation of Back Electromotive Force.
Back Focal Length
The distance between the last surface of a lens to its back focal plane.
Back Gears
Gears fitted to a machine to increase the number of spindle speeds obtainable with a cone or step pulley belt drive.
Back Lobe
The energy radiated from a directional antenna in a direction opposite to the axis of the main lobe.
Back Pressure
Pressure exerted backward; in a field of fluid flow, a pressure exerted contrary to the pressure producing the main flow.
Back Titration
Determining the concentration of an analyte by reacting it with a known number of moles of excess reagent.
Back Weld
A weld deposited at the back of a single groove weld.
Back Work Ratio
The fraction of the gas turbine work used to drive the compressor.
Earth or earthen material used to fill the excavation around a foundation; the act of filling around a foundation.
Background Contamination
The total of the extraneous particles which are introduced in the process of obtaining, storing, moving, transferring and analyzing a fluid sample.
Background Noise
Noise from all sources unrelated to a particular sound that is the object of interest.
Backhand Welding
A welding technique in which the flame is directed towards the completed weld.
A counterclockwise shift in the wind direction in the Northern Hemisphere at a certain location. In the Southern Hemisphere, it is clockwise.
Backing Strip
A piece of material used to retain molten metal at the root of the weld.
Backing Weld
A weld bead applied to the root of a single groove joint to assure complete root penetration.
The lost motion or looseness (play) between the faces of meshing gears or threads.
A mutation that causes a mutant gene to revert back to its wild-type genotype.
Backscattered Electron
Produced by an incident electron colliding with an atom in the specimen which is nearly normal to the incident′s path.
Primary radiation deflected or secondary radiation emitted in the general direction of the incident radiation beam.
A sequence in which weld bead increments are deposited in a direction opposite to the direction of progress.
An item kept available to replace an item which fails to perform satisfactorily.
Backward Recognition Masking
The reduction in the ability to recognize a sound pattern due to the subsequent presentation of another sound pattern with similar information content.
Chemical formula for Barium Carbonate.
Bacon, Francis
English natural philosopher.
Bacon, Francis Thomas
English engineer who developed the first practical hydrogen-oxygen fuel cell.
A group of small living organisms made of just one cell.
A pesticide used to control or destroy bacteria, typically in the home, schools, or hospitals.
A virus capable of replicating in a bacterial cell.
Baekeland, Leo Hendrik
Belgian-born American chemist who invented Velox photographic paper and Bakelite.
Baer, Karl Ernst von
German embryologist who developed the science of comparative embryology.
A movable barrier used to achieve separation of signals from different sources.
Baffle Plate
A metal plate that acts as a baffle.
Bag Moulding
A technique in which the composite material is placed in a rigid mould and covered with a flexible bag, with pressure applied by vacuum, autoclave, press, or by inflating the bag.
An austenitic transformation product found in some steels and cast irons.
Baird, John Logie
Scottish engineer most notable for his invention of the television.
The first industrial thermoset plastic.
Baker, Sir Benjamin
The chief designer of the railway bridge over the Firth of Forth.
Baker′s Dozen
Thirteen pieces of something.
Bakers Salt
Old name for Ammonium Carbonate.
Balance Pipe
A pipe connecting two points of a system to even out pressure fluctuations.
Balanced Circuit
A circuit having symmetrical sections above ground potential.
Balanced Construction
A method of constructing manufactured wood products so that moisture content changes will be uniformly distributed and therefore will not cause warping.
Balanced Diet
The right amount of food and food types to meet a bodies needs.
Balanced Equation
A description of a chemical reaction that gives the chemical formulas of the reactants and the products of the reaction, with coefficients introduced so that the number of each type of atom and the total charge is unchanged by the reaction.
A procedure for adjusting the mass distribution of a rotor so that vibration of journals, or the forces on the bearings at once-per-revolution, are reduced or controlled.
A false balcony constructed with a low railing outside a window.
A projection from an upper story window or door surrounded by railing.
A richly ornamented canopy structure supported by columns, suspended from a roof, or projected from a wall, as over an altar.
Balfour, Francis M
An English embryologist who wrote a comprehensive book. Comparative Embryology, thus ushering in this phase of the science.
A sphere together with its interior.
Ball Bearing
A bearing designed to reduce rotational friction and support radial and axial loads.
Ball Bearing Hinge
Hinge with ball bearings between the hinge knuckles to reduce friction.
Ball Burnishing
The smoothing of surfaces by means of tumbling parts in the presence of hardened steel balls, without abrasives.
Ball Check Valve
A fitting with a small ball that seals against a seat preventing flow in one direction and allowing flow in the other direction.
Ball Joint
A flexible joint consisting of a ball in a socket - locks the two parts in translation, but allows all degrees of rotation.
Ball Lightning
A relatively rare form of lightning, consisting of a reddish, luminous ball, of the order of 0.3m in diameter, which may move rapidly along solid objects or remain floating in midair.
Ball Peen Hammer
A hammer with two ends on the head, one that is round and the other flat.
Ball Pien Hammer
A hammer with two ends on the head, one that is round and the other flat.
Ball Valve
A valve using a spherical closure element which is rotated through 90° to open and close the valve.
Any liquid or solid weight placed in a vehicle to change the weight distribution or trim.
Ballast Tank
Tanks at the bottom or sides of a ship which are filled with seawater for ballasting purpose.
Ballast Tube
A current-controlling resistance device designed to maintain substantially constant current over a specified range of variation in applied voltage or resistance of a series circuit.
Ignoring the curvature of the Earth, frictional losses and that g is constant it is possible to calculate the trajectory of a projectile that is fired with a given initial velocity and elevation.
A lighter than air craft. The Montgolfier brothers made the first flight in a hot air balloon in 1783.
Balloon Type Rocket
A liquid-fuel rocket that requires the pressure of its propellants within it to give it structural integrity.
A threaded shaft and nut assembly supported by angular contact bearings, normally found on machine tools.
Ballscrew Lead
The linear distance a carriage will travel for one revolution of the ball screw.
A cross between a balloon and a parachute, used to brake the free fall of sounding rockets.
Balmer Series
A series of lines in the emission spectrum of hydrogen that involve transitions to the n=2 state from states with n>2.
Balsa Wood
The wood from Ochroma Lagopus.
Light oily aromatic extracts from trees which cure into resins.
The name of a wine bottle equivalent to the volume of 16 standard bottles or 12 litres.
A transformer circuit that couples a balanced transmission line to an unbalanced transmission line.
Small turned, square, or flat column that supports a rail; also used to form chair backs.
A series of balusters supporting the railing of a stairs or balcony.
A natural material with a great strength to weight ratio. It was used in the early construction of aircraft wings and fuselages.

A set of closely spaced energy levels in an atom, molecule, or metal.
Band Clamp
For clamping round, oval and odd-shaped pieces. Consists of nylon band and ratchet mechanism.
Band Gap Energy
For semiconductors and insulators, the energies that lie between the valence and conduction bands.
Band Reject Frequencies
A tuned circuit that does not pass a specified band of frequencies.
Band Spectrum
An emission spectrum that contains groups of sharp peaks that are so close together that they are not distinguishable separately.
Band Stop Filter
An electronic network which passes signals having frequencies above and below the band-elimination frequency span.
The range of energies between existing energy bands where no energy levels exist.
Bandpass Filter
An electronic network which transfers through it a specific band of signal frequencies.
A power saw, the blade of which is a continuous, narrow, steel band having teeth on one edge and passing over two large pulley wheels.
The bandwidth of a filter is the separation between the lower and upper frequencies at which the amplitude of a sinusoidal signal is attenuated by a factor of 2.
Bandwidth Time Product
Used in calculating the confidence limit of a measurement.
Bank Cubic Metre
Represents the contents of a cubic metre of rock in place, before it is drilled and blasted.
A handrail with supporting posts on a stairway.
Chemical formula for Barium Oxide.
Chemical formula for Barium Dioxide.
A derived unit of pressure used in meteorology. 1 bar = 1x105 Pa.
Bar Chart
A strong graphical representation of data.
Bar Clamp
A tool with a stationary head and a sliding foot for clamping purposes.
Bar Code
Coded labels that contain information about the item they are attached to, the information is contained in a numerical code, usually containing 12 digits.
Bar Litre
Unit of energy used to measure the potential energy of gases under pressure.
Bar Stock
Metal bars of various lengths, made in flat, hexagon, octagon, round, and square shapes from which parts are machined.
Barany Box
Clockwork noise generator used when necessary as a masker in tuning fork or clinical speech tests.
An abbreviation for bar gauge.
The finish board covering the projecting portion of a gable roof or part of the car body mounted vertically located between the front wheels.
Most commonly found mineral of Barium Sulphate.
Elemental barium does not occur naturally although it has an abundance within the earth’s crust of 500 ppm.
Barium Carbonate


Chemical used in rat poison, bricks, ceramic glazes and cement.

Barium Dioxide
A white toxic powder obtained by heating barium oxide in air.
Barium Monoxide
An oxide of barium; a whitish toxic powder.
Barium Oxide
An oxide of barium; a whitish toxic powder.
Barium Peroxide
A white toxic powder obtained by heating barium oxide in air.
Barium Protoxide
An oxide of barium; a whitish toxic powder.
Barium Sulphate


A white insoluble solid used as a pigment and filler in plastics. Most commonly found as the mineral Barite.

Barium White
An ancient name for Barium Sulphate.
The Bark is the standard unit corresponding to one critical band width of human hearing.
Barkhausen Effect
Phenomenon of short, sudden changes in the magnetism of a ferromagnetic substance occurring when the intensity of the magnetizing field is continuously altered.
A unit of nuclear cross section, 1 Barn = 10-28m2.
Barnard, Christiaan Neethling
South African heart surgeon who developed surgical procedures for organ transplants, invented new heart valves, and performed the first human heart transplant.
A continuous trace of air pressure variation with time, typically produced by a barograph.
A recording type instrument that provides a continuous trace of air pressure variation with time.
A device for measuring atmospheric pressure.
Barometric Pressure
The total pressure exerted by the atmosphere.
The unit of length used in graduating a mercury barometer in the centimetre-gram-second system.
A style that flourished in the seventeenth and eighteenth centuries.
A unit of capacity in the oil industry.
Barrel Bulk
Commercial unit of volume equal to exactly 5 cubic feet or 0.141 584 cubic metres.
Barrel of Oil Equivalent
A unit of energy equal to approximately 6.1 gigajoules.
Barrell Burnishing
The smoothing of surfaces by means of tumbling a part in rotating barrels in the presence of metallic or ceramic shot, without abrasives.
A type of bolometer characterized by an increase in resistance as the dissipated power rises.
A physical structure which blocks or impedes something.
Barrier Film
A thin, continuous, non-porous, electrically insulating film on metal surfaces that is usually comprised of oxides.
A large French wine barrel holding 225 litres.
Bartels Rotation Number
The serial number assigned to 27-day recurrence periods of solar and geophysical parameters.
This is the centre of gravity of 2 or more masses.
The CGS unit of pressure, equal to 1 dyne per square centimetre.
A particle with spin 1/2 (or 3/2) which consists of three elementary particles known as quarks.
Baryon Number
A quantum number assigned to elementary particles.
Any of several compounds of barium.
Basal Metabolic Rate
The rate of oxygen consumption by an animal′s body at complete rest under fasting conditions.
Dark colored rocks formed by the rapid cooling and hardening of lava flows.
Bascule Bridge
The deck is raised with counterweights like a drawbridge.
Substance which gives off hydroxide ions (OH-) in solution. In the expression xy, x is called the base and y is the exponent.
Base Band
The frequency band occupied by information-bearing signals before combining with a carrier in the modulation process.
Base Hydrolysis Constant
The equilibrium constant for the hydrolysis reaction associated with a base.
Base Metal
The metal to be welded or cut. In alloys, it is the metal present in the largest proportion.
Base Number
Another name for Acid Number.
Base Oil
A liquid having a suitable boiling range and viscosity for use in lubricating oils.
Base Pair
Two nucleotides in nucleic acid chains that are paired by hydrogen bonding of their bases.
Base Station
A focal point for data and communications.
Base Terminal
That electrode of a transistor which compares generally to the grid of a vacuum tube.
Base Unit
Base units are units that are fundamental building blocks in a system of measurement.
The surface to which the feet of a machine are attached.
A high-level programming language designed at Dartmouth College as a learning tool.
Basic Impulse Insulation Level
A reference impulse insulation strength expressed in terms of the crest value of the withstand voltage of a standard full impulse voltage wave.
Basilar Membrane
A membrane inside the cochlea that vibrates in response to sound, exciting the hair cells.
Basis Function
A mathematical function that can be used to build a description of wavefunctions for electrons in atoms or molecules.
Basis Set
A set of mathematical functions that are combined to approximate the wavefunctions for electrons in atoms and molecules.
Chemical formula for Barium Sulphate.
The lower range of audible frequencies.
Bass Boost
The increase in level of the lower range of frequencies, usually achieved by electrical circuits.
Bass Ratio
In concert hall acoustics, the ratio of the average reverberation times at 125 and 250 Hz to the average of the RT′s at 500 and 1000 Hz. It is determined only for a hall when fully occupied.
Threads, parts, tools, and sizes that are not standard.
Bath Metal
A cheap bronze made with 21 parts copper and 5 parts zinc. The same as pinchbeck.

The narrow strips of wood nailed vertically over the joints of boards to form board-and-batten siding.
An inclined face of wall; hence battered.
Batter Boards
Horizontal boards at exact elevations nailed to posts just outside the corners of a proposed building.
Batteries in Parallel
The connection of like terminals of cells or batteries to form a system of greater capacity, but with the same voltage.
A device for converting chemical energy into electrical energy.
Battery Abuse Testing
A series of tests to establish that the battery is not a danger to the user or to itself under any conceivable conditions of use or abuse.
Battery Acid
A solution of approximately 6M sulfuric acid used in the lead storage battery.
Battery Bank
A group of batteries used to store energy and so even out supply and demand issues with sources such as wind energy.
Battery Capacity
The amount of energy available from a battery. Battery capacity is expressed in ampere-hours.
Battery Cell Balancing
Where a battery pack consists of more than one cell it is important that the cells are balanced.
Battery Charger
A device capable of supplying electrical energy to a battery.
Battery Conditioning
The initial application of charge-discharge cycling to establish full battery capacity.
Battery Cycle Life
How many charge/discharge cycles the battery can endure before it loses its ability to hold a useful charge.
Battery Discharge Rate
The maximum rate at which a battery may discharged and charged is normally expressed as a fraction or multiplier of the battery capacity.
Battery Efficiency
This the energy out of a battery during discharge divided by the energy in during charging.
Battery Electric Vehicle
An electric vehicle that is driven by an electric motor with energy stored in a battery.
Battery Energy Capacity
The total energy available, expressed in watt-hours, which can be withdrawn from a fully charged cell or battery.
Battery Holder
A component designed to mechanically hold batteries and provide electrical connections.
Battery Internal Short-Circuit
A direct connection between the positive and negative terminals of a cell or battery that provides a virtual zero resistance path for current flow.
Battery Memory Effect
A phenomenon in which a cell, operated in successive cycles to the same, but less than a full, depth of discharge experiences a depression of its discharge voltage and temporarily loses the rest of its capacity at normal voltage levels.
Battery Module
A battery unit manufactured as the basic component of a battery pack.
Battery Pack
A number of batteries connected together to provide the required power and energy for a given application.
Battery Rupture
Mechanical failure of a cells container or battery case induced by an internal or external cause, resulting in exposure or spillage but not ejection of solid materials.
Battery Separator
A porous membrane placed between electrodes of opposite polarity, permeable to ionic flow but preventing electric contact of the electrodes.
Battery String
A number of batteries connected in series.
Battery Testing
The measurement of single or multiple battery cells under given test criteria to determine their operational parameters.
Battery Vent
A safety device built into almost all cells designed to release internal pressure in the case of overcharge, over temperature and other abuses.
Battery Venting
The release of excessive internal pressure from a cell or battery in a manner intended by design to preclude rupture or disassembly.
Baud Rate
The speed of information being transmitted across a serial interface, expressed in units of bits per second (bps).
Baudelot Cooler
Heat exchanger in which water flows by gravity over the outside of the tubes or plates.
The style of the Bauhaus School, founded in Germany by Walter Gropius in 1919, emphasizing simplicity, functionalism, and craftsmanship.
An ore of aluminum consisting of moderately pure hydrated alumina.
A subdivision of the interior space of a building.
Bay Salt
Alternative name for Sodium Chloride.
Bay Window
A window placed in a projection of an exterior wall of a building is called a bay window when the wall projection extends all the way down to a corresponding projection of the foundation.
Bayes Rule
A rule for finding conditional probability.