resistance when 1 volt is impressed across the resis-
AXLE--A cross support on a vehicle on which a
tance.
supporting wheel, or wheels, turn. There are two
general types: live axles that also transmit power to
ANTI-FRICTION BEARING--A bearing of the
the wheels, and dead axles that transmit no power.
type that supports the imposed load on rolling sur-
faces (balls, rollers, needles), minimizing friction.
BACK PRESSURE--The resistance of liquids and
gases to flow through a system.
ANTI-KNOCK--Refers to substances that are added
to automotive fuel to decrease the tendency to
BACKFIRE--Pre-explosion of the fuel-air mixture so
knock when the fuel-air mixture is compressed and
that the explosion passes back around the opened
ignited in the engine cylinder.
intake valve and flashes back through the intake
manifold.
ANTIFREEZE--A chemical, usually ethylene glycol,
added to the water in cooling system (usually a
BACKLASH--The backward rotation of a driven gear
50/50 mixture) in a liquid-cooled engine to prevent
that is permitted by clearance between meshing
freezing and to raise the boiling point of the
teeth of two gears.
coolant.
BAFFLE--A plate or shield to deflect, check, or
ARMATURE--(1) In a relay, the movable portion of
regulate the flow of a liquid or gas.
the relay. (2) The windings in which the output
BALL BEARING--A type of bearing that contains
voltage is produced in a generator or in which input
steel balls that roll between inner and outer races.
current creates a magnetic field that interacts with
the main field in a motor.
BALLAST RESISTOR--A resistor that changes
voltage in direct proportion to the heat of the
ASBESTOS--A fibrous material that resists heat and
resistance element. Such a resistor is used in the
burning.
ignition system of gasoline engines.
ATDC--After top dead center.
BAROMETER--An instrument that measures
ATMOSPHERE--The mass of air that surrounds the
atmospheric pressure.
earth.
BATTERY--A device consisting of two or more cells
ATMOSPHERIC PRESSURE--The weight of the
for converting chemical energy into electrical
atmosphere per unit area. Atmospheric pressure at
energy.
sea level is 14.7 pounds per square inch (psi).
BATTERY CAPACITY--Rating of a battery's cur-
ATOM--The smallest particle, or part, of an element,
rent output, usually expressed in ampere-hours or
composed of electrons and protons and also of
cold-cranking-amperes.
BATTERY CHARGING--The process of supplying
ATOMIZATION--The spraying of a liquid through a
a battery with a flow of electric current to produce
nozzle so that the liquid is broken into tiny globules
chemical actions in the battery; these actions
or particles.
reactivate the chemicals in the battery so they can
produce electrical energy again.
AUTOMATIC CHOKE--A choke that operates
automatically in accordance with certain engine
BATTERY, MAINTENANCE-FREE--A battery
conditions, usually temperature and intake
that does not require addition of water during its
manifold vacuum (also electrically controlled).
normal life.
AUTOMATIC TRANSMISSION--A transmission
BATTERY RATING--A standardized measurement
that reduces or eliminates the necessity of hand
of a battery's ability to deliver electrical power
shifting of gears to secure different gear ratios in
under certain conditions. See also BATTERY
the transmission.
CAPACITY.
AXIAL--In a direction parallel to the axis. Axial
BBDC--Before bottom dead center.
movement is movement parallel to the axis.
BDC--Bottom dead center; the position of the piston
AXIS--A centerline. The line about which something
when it reaches the lower limit of travel in the
rotates or about which something is evenly divided.
cylinder.
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