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Definition: Physical unit
, n. [Abbrev. from unity.]
1. A single thing or person.
2. (Arith.) The least whole number; one.
Units are the integral parts of any large number.
3. A gold coin of the reign of James I., of the value of
twenty shillings. --Camden.
4. Any determinate amount or quantity (as of length, time,
heat, value) adopted as a standard of measurement for
other amounts or quantities of the same kind.
5. (Math.) A single thing, as a magnitude or number, regarded
as an undivided whole.
, the unit of numeration; one taken in the
abstract; the number represented by 1. The term is used in
distinction from concrete, or determinate, unit, that is,
a unit in which the kind of thing is expressed; a unit of
measure or value; as 1 foot, 1 dollar, 1 pound, and the
(Theory of Numbers), an imaginary number of
the form a + broot-1
, when a^2
, a unit in the scale of numbers increasing
or decreasing by twelves.
, the unit of a fraction; the reciprocal of
the denominator; thus, 1/4 is the unit of the fraction
, the unit of integral numbers, or 1.
, a value or magnitude conventionally adopted
as a unit or standard in physical measurements. The
various physical units are usually based on given units of
length, mass, and time, and on the density or other
properties of some substance, for example, water. See
(Biol.), a unit of the inferior order or orders
(Elec.), a small, insulated Leyden jar, placed
between the electrical machine and a larger jar or
battery, so as to announce, by its repeated discharges,
the amount of electricity passed into the larger jar.
Unit of heat
(Physics), a determinate quantity of heat
adopted as a unit of measure; a thermal unit (see under
). Water is the substance generally employed, the
unit being one gram or one pound, and the temperature
interval one degree of the Centigrade or Fahrenheit scale.
When referred to the gram, it is called the gram degree.
The British unit of heat, or thermal unit, used by
engineers in England and in the United States, is the
quantity of heat necessary to raise one pound of pure
water at and near its temperature of greatest density
(39.1[deg] Fahr.) through one degree of the Fahrenheit
Unit of illumination
, the light of a sperm candle burning
120 grains per hour. Standard gas, burning at the rate of
five cubic feet per hour, must have an illuminating power
equal to that of fourteen such candles.
Unit of measure
(as of length, surface, volume, dry
measure, liquid measure, money, weight, time, and the
like), in general, a determinate quantity or magnitude of
the kind designated, taken as a standard of comparison for
others of the same kind, in assigning to them numerical
values, as 1 foot, 1 yard, 1 mile, 1 square foot, 1 square
yard, 1 cubic foot, 1 peck, 1 bushel, 1 gallon, 1 cent, 1
ounce, 1 pound, 1 hour, and the like; more specifically,
the fundamental unit adopted in any system of weights,
measures, or money, by which its several denominations are
regulated, and which is itself defined by comparison with
some known magnitude, either natural or empirical, as, in
the United States, the dollar for money, the pound
avoirdupois for weight, the yard for length, the gallon of
8.3389 pounds avoirdupois of water at 39.8[deg] Fahr.
(about 231 cubic inches) for liquid measure, etc.; in
Great Britain, the pound sterling, the pound troy, the
yard, or 1/108719 part of the length of a second's
pendulum at London, the gallon of 277.274 cubic inches,
etc.; in the metric system, the meter, the liter, the
Unit of power
. (Mach.) See Horse power
Unit of resistance
. (Elec.) See Resistance
, n., 4, and
Unit of work
(Physics), the amount of work done by a unit
force acting through a unit distance, or the amount
required to lift a unit weight through a unit distance
against gravitation. See Erg
, Foot Pound
(Mech. Physics), stress per unit of area;
intensity of stress. It is expressed in ounces, pounds,
tons, etc., per square inch, square foot, or square yard,
etc., or in atmospheres, or inches of mercury or water, or