Documents for "Technology: Terms and Concepts":

• abacus in architecture, flat slab forming the top member of a capital. In classical orders it varies from a square form having unmolded sides in the Greek Doric, to thinner proportions and ovolo molding...

• ABM see guided missile.

• abrasive material used to grind, smooth, cut, or polish another substance. Natural abrasives include sand , pumice , corundum , and ground quartz. Carborundum ( silicon carbide ) and alumina (aluminum...

• adding machine see calculator.

• adze tool similar in purpose and use to an axe but with the cutting edge at right angles to the handle rather than aligned with it. The details of construction of a particular adze will depend on its...

• aerosol dispenser device designed to produce a fine spray of liquid or solid particles that can be suspended in a gas such as the atmosphere. The dispenser commonly consists of a container that holds under pressure...

• air bag see automobile.

• air brake see brake.

• air conditioning mechanical process for controlling the humidity, temperature, cleanliness, and circulation of air in buildings and rooms. Indoor air is conditioned and regulated to maintain the...

• air lock compartment connecting two different environments, usually at different pressures, that enables personnel to transfer from one environment to the other. Space capsules have air locks to enable...

• air-cushion vehicle (ACV), craft designed to travel close to but above ground or water. It is also called a ground-effect machine or Hovercraft. These vehicles are supported in various ways. Some of them have a specially designed wing that will lift them just off the surface over which they travel when they have reached a sufficient...

• aqueduct [Lat.,=conveyor of water], channel or trough built to convey water, chiefly for providing a densely populated region with a supply of freshwater. The flow in aqueducts is ordinarily by means of...

• Archimedes' screw a simple mechanical device believed to have been invented by Archimedes in the 3d cent. BC It consists of a cylinder inside of which a continuous screw, extending the length of the cylinder, forms...

• assembly line manufacturing technique in which a product is carried by some form of mechanized conveyor among stations at which the various operations necessary to its assembly are performed. It is used to...

• atomic clock electric or electronic timekeeping device that is controlled by atomic or molecular oscillations. A timekeeping device must contain or be connected to some apparatus that oscillates at a uniform...

• atomic force microscope (AFM), device that uses a spring-mounted probe to image individual atoms on the surface of a material. Unlike the scanning tunneling microscope , which is also a scanning probe microscope, the AFM can be used on materials that do not conduct electricity. In the original AFM, the probe traverses the surface, moving upward due to bumps and...

• auger see drill.

• automated teller machine (ATM), device used by bank customers to process account transactions. Typically, a user inserts into the ATM a special plastic card that is encoded with information on a magnetic strip. The strip...

• automation automatic operation and control of machinery or processes by devices, such as robots that can make and execute decisions without human intervention. The principal feature of such devices is their...

• automaton see robot ; robotics.

• automobile self-propelled vehicle used for travel on land. The term is commonly applied to a four-wheeled vehicle designed to carry two to six passengers and a limited amount of cargo, as contrasted with a truck , which is designed primarily for the transportation of goods and is constructed with larger and heavier parts, or a bus (or omnibus or coach), which is a large public conveyance designed to carry a large number of passengers and sometimes additionally small amounts of cargo. For operation and technical features of...

• awl see drill.

• balance instrument used in laboratories and pharmacies to measure the mass or weight of a body. A balance functions by measuring the force of gravity that the earth exerts on an object, i.e., its weight...

• ball bearing see bearing.

• ball joint see ball-and-socket joint.

• ball-and-socket joint in engineering, mechanical connection used between parts that must be allowed some relative angular motion in nearly all directions. As the name implies, the joint consists essentially of a...

• barbed wire wire composed of two zinc-coated steel strands twisted together and having barbs spaced regularly along them. The need for barbed wire arose in the 19th cent. as the American frontier moved...

• bearing machine part designed to reduce friction between moving parts or to support moving loads. There are two main kinds of bearings: the antifriction type, such as the roller bearing and the ball bearing, operating on the principle of rolling...

• bellows expansible, gas-tight chamber used to pump or store a gas. One of the simplest and most familiar types of bellows is the manual one used for providing a forced draft to a fire. The expansible...

• Ben Day process see printing.

• bicycle light, two-wheeled vehicle driven by pedals. The name velocipede is often given to early forms of the bicycle and to its predecessor, the dandy horse, a two-wheeled vehicle moved by the thrust of the rider's feet upon the ground. Probably the first practical...

• binocular small optical instrument consisting of two similar telescopes mounted on a single frame so that separate images enter each of the viewer's eyes. As with a single telescope, distant objects appear magnified, but the binocular has the additional advantage that...

• bit see drill.

• blast cleaning see sandblast.

• blasting shattering, breaking, or splitting of rock or other material by the discharge of an explosive placed within or in contact with it. It is a necessary part of many engineering operations. An ancient method of breaking rock consisted of heating the rock by fire and then pouring water on it,...

• block and tackle see pulley.

• blueprint white-on-blue photographic print, commonly of a working drawing used during building or manufacturing. The plan is first drawn to scale on a special paper or tracing cloth through which light can...

• boiler device for generating steam. It consists of two principal parts: the furnace, which provides heat, usually by burning a fuel, and the boiler proper, a device in which the heat changes water into...

• boring mill machine tool used to increase the size of a hole previously made in a workpiece, usually with the purpose of obtaining a required degree of finish and accuracy in the final hole. In a horizontal...

• brace see drill.

• brake in technology, device to slow or stop the motion of a mechanism or vehicle.

• brick ceramic structural material that, in modern times, is made by pressing clay into blocks and firing them to the requisite hardness in a kiln. Bricks in their most primitive form were not fired but...

• bridge structure built over water or any obstacle or depression to allow the passage of pedestrians or vehicles. See also viaduct.

• bullet train see railroad.

• Bunsen burner gas burner, commonly used in scientific laboratories, consisting essentially of a hollow tube which is fitted vertically around the flame and which has an opening at the base to admit air. A...

• bus [Lat. omnibus =for all], large public conveyance. A horse-drawn urban omnibus was introduced in Paris in 1662 by Blaise Pascal and his associates, but it remained in operation for only a few years. The omnibus...

• cable originally wire cordage of great strength or heavy metal chain used for hauling, towing, supporting the roadway of a suspension bridge, or securing a large ship to its anchor or mooring. Today a...

• caisson [Fr.,=big box], in engineering, a chamber, usually of steel but sometimes of wood or reinforced concrete, used in the construction of foundations or piers in or near a body of water. There are...

• calculator or calculating machine, device for performing numerical computations; it may be mechanical, electromechanical, or electronic. The electronic computer is also a calculator but performs other functions...

• calendering a finishing process by which paper, plastics, rubber, or textiles are pressed into sheets and smoothed, glazed, polished, or given a moiré or embossed surface. The material is passed through a...

• cam mechanical device for converting a rotating motion into a reciprocating, or back-and-forth, motion, or for changing a simple motion into a complex one. A simple form of cam is a circular disk set...

• camera lightproof box or container, usually fitted with a lens, which gathers incoming light and concentrates it so that it can be directed toward the film (in an optical camera) or the imaging device (in...

• canal an artificial waterway constructed for navigation or for the movement of water. The digging of canals for irrigation probably dates back to the beginnings of agriculture, and traces of canals have...

• cantilever beam supported rigidly at one end to carry a load along the free arm or at the free end. A slanting beam fixed at the base is often used to support the free end, as in a common bracket. The...

• carburetor part of a gasoline engine in which liquid fuel is converted into a vapor and mixed with a regulated amount of air for combustion in the cylinders. Land vehicles, boats, and light aircraft have a...

• carpentry trade concerned with constructing wood buildings, the wooden portions of buildings, or the temporary timberwork used during the construction of buildings. It comprises the larger and more...

• carriage wheeled vehicle, in modern usage restricted to passenger vehicles that are drawn or pushed, especially by animals. Carriages date from the Bronze Age; early forms included the two-wheeled cart and...

• catalytic converter see internal-combustion engine.

• catgut or gut, cord made from the intestines of various animals (especially sheep and horses, but not cats). The membrane is chemically treated, and slender strands are woven together into cords of great...

• CB radio see radio.

• CD-ROM see compact disc.

• cement binding material used in construction and engineering, often called hydraulic cement, typically made by heating a mixture of limestone and clay until it almost fuses and then grinding it to a fine...

• centrifuge device using centrifugal force to separate two or more substances of different density, e.g., two liquids or a liquid and a solid. The centrifuge consists of a fixed base or frame and a rotating...

• ceramics materials made of nonmetallic minerals that have been permanently hardened by firing at a high temperature, or objects made of such materials. Most ceramics resist heat and chemicals and are poor...

• chain flexible series of connected links used in various ways, especially for the transmission of motive power, for hoisting (see pulley ), and for securing or fastening. Commonly, mechanical energy from a motor or other source applied to a sprocket wheel is conveyed by means of an endless chain to another sprocket wheel for driving...

• chariot earliest and simplest type of carriage and the chief vehicle of many ancient peoples. The chariot was known among the Babylonians before the introduction of horses c.2000 BC and was first drawn by...

• chemical engineering see engineering.

• chronometer instrument for keeping highly accurate time, used especially in navigation. Before the advent of radio time signals it was the only device that provided the time accurately enough for a ship at...

• citizens band radio see radio.

• civil engineering see engineering.

• clepsydra or water clock, ancient device for measuring time by means of the flow of water from a container. A simple form of clepsydra was an earthenware vessel with a small opening through which the water dripped; as the...

• clock instrument for measuring and indicating time. Predecessors of the clock were the sundial , the hourglass , and the clepsydra. See also watch.

• clutch in automobiles: see transmission.

• coaxial cable see cable.

• cofferdam temporary barrier for excluding water from an area that is normally submerged. Made commonly of wood, steel, or concrete sheet piling (see pile ), cofferdams are used in constructing the foundations of dams, bridges, and similar subaqueous structures and for temporary drydocks. If double sheeting is utilized, the space between the sheets is...

• cold storage see refrigeration.

• collotype see printing.

• compass 1 In mathematics, an instrument for making circles and measuring distances. Frequently called a pair of compasses, it consists of two metal legs with one end of each attached to a pivot to form a...

• composite material or composite, any material made from at least two discrete substances, such as concrete. Many materials are produced as composites, such as the fiberglass -reinforced plastics used for automobile bodies and boat hulls, but the term usually is used to describe any of various modern industrially manufactured composites, such as carbon fiber-reinforced...

• composition board wood product produced in the form of a board or sheet, formed of cellulose fibers or particles derived from wood or other sources, and used principally as a building material. The oldest type of...

• compressed air air whose volume has been decreased by the application of pressure. Air is compressed by various devices, including the simple hand pump and the reciprocating, rotary, centrifugal, and axial-flow compressors. Compressed air exerts an expansive force that can be controlled and used in various devices including tires, air brakes, caissons, and diving suits. As a source of power it is used to operate pneumatic tools , e.g., pneumatic hammers and drills and spraying equipment. It is widely employed for cleaning dust and dirt out of mechanical equipment. It is used also in mining, tunneling, and the manufacture...

• compression external stress applied to an object or substance, tending to cause a decrease in volume (see pressure ). Gases can be compressed easily, solids and liquids to a very small degree if at all. Water, for example, is practically incompressible, thus making it especially useful for hydraulic machines. According to the kinetic-molecular theory of gases , when the molecules of a gas are brought close enough together by compression, the gas (under certain conditions of temperature) undergoes liquefaction. This principle is applied commercially to several gases, including liquid oxygen and the so-called bottled gas (a mixture of hydrocarbons) used as a fuel. Boyle's law deals with the decrease in...

• compressor machine that decreases the volume of air or other gas by the application of pressure. Compressor types range from the simple hand pump and the piston-equipped compressor used to inflate tires to machines that use a rotating, bladed element to achieve compression. The four basic types of compressors are reciprocating, rotary screw,...

• concrete structural masonry material made by mixing broken stone or gravel with sand, cement , and water and allowing the mixture to harden into a solid mass. The cement is the chemically active element, or matrix; the sand and stone are the inert elements, or aggregate. Concrete is...

• control systems combinations of components (electrical, mechanical, thermal, or hydraulic) that act together to maintain actual system performance close to a desired set of performance specifications. Open-loop...

• convector see heating.

• cooling system see air conditioning ; internal-combustion engine ; refrigeration.

• copying processes see printing ; photocopying.

• cordage kôr´dĬj , collective name for rope and other flexible lines. It is used for such purposes as wrapping, hauling, lifting, and power transmission. Early man used strips of hide, animal hair, and plant...

• cotton gin machine for separating cotton fibers from the seeds. The charkha, used in India from antiquity, consists of two revolving wooden rollers through which the fibers are drawn, leaving the seeds. A...

• crane hoisting machine for lifting heavy loads and transferring them from one place to another, ordinarily over distances of not more than 200 ft (60 m). Cranes have a long reach and can lift loads to...

• crank mechanical linkage consisting of a bar attached to a pivot at one of its ends in such a way that it is capable of rotating through a complete circle about the pivot. One of the principal uses of a...

• crucible vessel in which a substance is heated to a high temperature, as for fusing or calcining. The necessary properties of a crucible are that it maintain its mechanical strength and rigidity at high...

• crusher machine used to reduce materials such as ore, coal, stone, and slag to particle sizes that are convenient for their intended uses. Crushers operate by slowly applying a large force to the material...

• cyanotype see blueprint.

• dam barrier, commonly across a watercourse, to hold back water, often forming a reservoir or lake; dams are also sometimes used to control or contain rockslides, mudflows, and the like in regions where...

• degree-day a unit of measure used to estimate the fuel and power requirements in heating and cooling a building; it is equal to a difference of 1 degree between the outdoor daily average temperature (the mean...

• derrick see crane.

• desalination of water see water, desalination of.

• developer see photographic processing.

• diesel engine type of internal-combustion engine invented by the German engineer Rudolf Diesel and patented by him in 1892. Although his engine was designed to use coal dust as fuel, the diesel engine now burns...

• differential in the automobile, a set of gears used on the driving (usually rear) axle. The two wheels on the driving axle must be interconnected in order to receive their energy from the same source, the...

• dike in technology: see levee.

• drawbridge see bridge.

• dredging process of excavating materials underwater. It is used to deepen waterways, harbors, and docks and for mining alluvial mineral deposits, including tin, gold, and diamonds.

• drill tool used to create a hole, usually in some hard substance, by its rotary or hammering action. Many different tools make up the drill family. The awl is a pointed instrument used for piercing small...

• dry cleaning process of cleaning fabrics without water. Special solvents and soaps are used so as not to harm fabrics and dyes that will not withstand the effects of ordinary soap and water. Dry cleaning began...

• eccentric in mechanics, device for changing rotary to back-and-forth motion. A disk is mounted off center on a shaft. One flat, open, circular end of a rod fits around the edge of the disk; the other end is...

• electric furnace see furnace.

• electrical engineering see engineering.

• electron microscope see microscope.

• electronic engineering see engineering.

• elevator in machinery, device for transporting people or goods from one level to another. The term is applied to the enclosed structures as well as the open platforms used to provide vertical transportation...

• enamelware utensils having a metal foundation and a coating of special glass, called porcelain enamel, applied by fusion. The porcelain enamel, or vitreous enamel, is applied to make the utensils corrosion...

• endless screw screw fixed so that it cannot move longitudinally as it rotates. Thus, instead of the usual action in which a screw advances itself through a medium as it turns, the screw remains stationary and...

• energy, sources of origins of the power used for transportation, for heat and light in dwelling and working areas, and for the manufacture of goods of all kinds, among other applications. The development of science...

• engine see diesel engine ; internal-combustion engine ; steam engine ; rotary engine ; automobile.

• engineering profession devoted to designing, constructing, and operating the structures, machines, and other devices of industry and everyday life.

• engineering psychology see ergonomics.

• exhibition see exposition.

• exposition or exhibition, term frequently applied to an organized public fair or display of industrial and artistic productions, designed usually to promote trade and to reflect cultural progress. Expositions have also been...

• fan device for agitating air or gases or moving them from one location to another. Mechanical fans with revolving blades are used for ventilation, in manufacturing, in winnowing grain, to remove dust,...

• Ferris wheel amusement park ride. It consists of a power-operated wheel that is about 50 ft (15 m) in diameter. It has two rims that are parallel to and equidistant from the shaft about which the wheel rotates...

• fiberglass thread made from glass. It is made by forcing molten glass through a kind of sieve, thereby spinning it into threads. Fiberglass is strong, durable, and impervious to many caustics and to extreme...

• field glass see binocular.

• field-emission microscope see microscope.

• field-ion microscope see microscope.

• fire engine see fire fighting.

• fire extinguisher see fire fighting.

• fire fighting the use of strategy, personnel, and apparatus to extinguish, to confine, or to escape from fire.

• firebrick brick that can withstand high temperatures, used to line flues, stacks, furnaces, and fireplaces. In general, such bricks have high melting points that range from about 2,800°F (1.540°C) for...

• fireproofing method of making normally combustible materials as nearly noncombustible as possible. Fireproofing generally applies to textiles and construction materials that are treated with a solution or...

• fireworks see pyrotechnics.

• firing process of treating clay or other plastic ceramic materials with heat to produce a hard, durable but brittle material such as pottery. Primitive potters baked their clay in an open fire, but for...

• flywheel heavy metal wheel attached to a drive shaft, having most of its weight concentrated at the circumference. Such a wheel resists changes in speed and helps steady the rotation of the shaft where a...

• fossil fuel see energy, sources of ; fuel.

• four-color process see printing.

• fuel cell electric cell in which the chemical energy from the oxidation of a gas fuel is converted directly to electrical energy in a continuous process (see oxidation and reduction ). The efficiency of conversion from chemical to electrical energy in a fuel cell is between 65% and 80%, nearly twice that of the usual indirect method of conversion in which fuels are used to heat...

• fuel injection system in an internal-combustion engine that delivers fuel or a fuel-air mixture to the cylinders by means of pressure from a pump. It was originally used in diesel engines because of diesel fuel's greater viscosity and the need to overcome the high pressure of the compressed air in the cylinders. A diesel fuel injector sprays an intermittent, timed, metered quantity...

• furnace enclosed space for the burning of fuel. There are many kinds of furnaces, the type depending upon the fuel and the use to which the heat produced within it is put. Most familiar are the furnaces...

• gasoline engine see internal-combustion engine.

• gear toothed wheel, cylinder, or cone that transmits motion from one part of a machine to another; it is one of the oldest means of transmitting motion. When the teeth of two gears are meshed, turning...

• geodimeter see surveying.

• geothermal energy see energy, sources of.

• gimlet see drill.

• glass fiber see fiberglass.

• Global Positioning System see navigation satellite.

• governor automatic device used to regulate and control such variables as speed or pressure in the functioning of an engine or other machine. A governor may be an electric, hydraulic, or mechanical device,...

• grain drill see drill.

• grinding process by which surface material is removed from an object, usually metal, by the abrasive action of a rotating wheel or a moving belt that contains abrasive grains. A grinding wheel can be made...

• ground-effect machine see air-cushion vehicle.

• gunpowder explosive mixture; its most common formula, called "black powder," is a combination of saltpeter, sulfur, and carbon in the form of charcoal. Historically, the relative amounts of the components have varied. An increase in the percentage of saltpeter (potassium...

• gyrocompass see gyroscope.

• gyroscope symmetrical mass, usually a wheel, mounted so that it can spin about an axis in any direction. When spinning, the gyroscope has special properties. Many spinning objects exhibit some of these...

• half tone see photoengraving ; printing.

• harbor see port.

• hardboard see composition board.

• harness comprehensive term for the gear of a draft animal, excluding the yoke, by which it is attached to the load that it pulls. Although harnesses are used on dogs (for drawing travois and dogsleds), on...

• heat pump see air conditioning.

• heating means of making a building comfortably warm relative to a colder outside temperature. Old, primitive methods of heating a building or a room within it include the open fire, the fireplace, and the stove. In ancient Rome a heating system, called a hypocaust, warmed a building by passing hot gases from a furnace through enclosed passages under the floors and behind the walls before releasing them...

• heliograph [Gr.,=sun-writer], signaling device using flashes of sunlight. It has two mirrors that are used to reflect sunlight on a distant point and a shutter through which the sunlight passes so that...

• highway see road.

• hoist see winch.

• horology science of measuring time and technology of constructing instruments for its measurement or recording. Early measurements of the passage of time were based on observations of seasonal cycles and of the apparent motion of...

• horseshoe narrow plate, commonly of iron or steel, shaped to fit a horse's hoof and attached to the hoof by nailing it to the inner edge of the horny wall of the hoof. Horseshoes vary from the light plate...

• hourglass glass instrument for measuring time, usually consisting of two bulbs united by a narrow neck. One bulb is filled with fine sand that runs through the neck into the other bulb in an hour's time. The...

• Hovercraft see air-cushion vehicle.

• human engineering see ergonomics.

• human-factors engineering see ergonomics.

• hydraulic machine machine that derives its power from the motion or pressure of water or some other liquid.

• hydraulics branch of engineering concerned mainly with moving liquids. The term is applied commonly to the study of the mechanical properties of water, other liquids, and even gases when the effects of...

• hydrofoil flat or curved finlike device, attached by struts to the hull of a watercraft, that lifts the moving watercraft above the water's surface. The term is often extended to include the vessel itself...

• hydrology study of water and its properties, including its distribution and movement in and through the land areas of the earth. The hydrologic cycle consists of the passage of water from the oceans into the...

• hydrometer device used to determine directly the specific gravity of a liquid. It usually consists of a thin glass tube closed at both ends, with one end enlarged into a bulb that contains fine lead shot or mercury to cause the instrument to float upright in a...

• hypocaust see heating.

• ignition apparatus for igniting a combustible mixture. The German engineer Nikolaus A. Otto, in his first gas engine, used flame ignition; another method was heating a metal tube to incandescence. Ignition...

• Imhoff tank see septic tank.

• incinerator furnace for burning refuse. The older and simpler kind of incinerator was a brick-lined cell with a metal grate over a lower ash pit, with one opening in the top or side for loading and another...

• inclined plane simple machine , consisting of a sloping surface, whose purpose is to reduce the force that must be applied to raise a load. To raise a body vertically a force must be applied that is equal to the weight of the...

• industrial engineering see engineering.

• insulation use of materials or devices to inhibit or prevent the conduction of heat or of electricity. Common heat insulators are, fur, feathers, fiberglass, cellulose fibers, stone, wood, and wool; all are poor conductors of heat. The use of asbestos , formerly a common insulating material, has been curtailed due to its implication in lung disease. Industrial furnaces are built of brick, which conducts heat so slowly that a high temperature...

• internal-combustion engine one in which combustion of the fuel takes place in a confined space, producing expanding gases that are used directly to provide mechanical power. Such engines are classified as reciprocating or...

• jack mechanical device used to multiply a relatively small applied force so that it can lift and support heavy loads, or sometimes, move massive objects into a desired position. The lever jack, often...

• jackscrew see screw.

• jeep small, durable automotive vehicle intended for heavy-duty applications and sometimes provided with the capability of delivering driving power to all four wheels. The last feature allows superior...

• kaleidoscope optical instrument that uses mirrors to produce changing symmetrical patterns. Invented by the Scottish physicist Sir David Brewster in 1816, the device is usually a hand-held tube, a few inches to as much as twelve feet in length, and looks like a small telescope. At one end of the tube is an eyepiece; at the other end colored...

• key in mechanics: see lock and key.

• keyless entry see lock and key.

• kiln furnace for firing pottery and enamels, for making brick, charcoal, lime, and cement, for roasting ores, and for drying various substances (e.g., lumber, chemicals). Kilns may be updraft or...

• laminated wood see plywood.

• lathe machine tool for holding and turning metal, wood, plastic, or other material against a cutting tool to form a cylindrical product or part. It also drills, bores, polishes, grinds, makes threads,...

• levee [Fr.,=raised], embankment built along a river to prevent flooding by high water. Levees are the oldest and the most extensively used method of flood control. They are constructed by piling earth on a surface that has been cleared of vegetation and leveled. From a broad base the levee narrows to a flat crown, on which sandbags or some other...

• level see spirit level.

• leveling see surveying.

• lever simple machine consisting of a bar supported at some stationary point along its length and used to overcome resistance at a second point by application of force at a third point. The stationary point of a lever...

• lighting light produced by artificial means to allow visibility in enclosures and at night. For stage lighting, see scene design and stage lighting.

• lightning rod a rod made of materials, especially metals, that are good conductors of electricity, which is mounted on top of a building or other structure and attached to the ground by a cable. By virtue of its...

• lock and key fastening fitted to an entryway, such as a gate or door, or a container, such as a cabinet, drawer or safe, to keep it closed and/or prevent unauthorized access or use. Locks typically consist of a...

• lock, air see air lock.

• lock, canal stretch of water enclosed by gates, one at each end, built into a canal or river for the purpose of raising or lowering a vessel from one water level to another. A lock may also be built into the...

• locomotive vehicle used to pull a train of unpowered railroad cars.

• lub