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force
frequency (of a periodic phenomenon)
illuminance
inductance
luminous flux
magnetic flux
magnetic flux density
power, radiant flux
pressure, stress
quantity of electricity, electric charge
gray
becquerel
farad
siemens
volt
ohm
joule
newton
hertz
lux
henry
lumen
weber
tesla
watt
pascal
coulomb
ANNEX 5 19 2611 1/81
Annex 5 - Units of Measurement to be used in Air
and Ground Operations Attachment B
1.5 The S1 is a rationalized selection of units from
the metric system which individually are not new. The great
advantage of S1 is that there is only one unit for each physical
quantity - the metre for length, kilogram (instead of gram)
for mass, second for time, etc. From these elemental or base
units, units for all other mechanical quantities are derived.
These derived units are defined by simple relationships such
as velocity equals rate of change of distance, acceleration
equals rate of change of velocity, force is the product of mass
and acceleration, work or energy is the product of force and
distance, power is work done per unit time, etc. Some of
these units have only generic names such as metre per
second for velocity; others have special names such as
newton (N) for force, joule (J) for work or energy, watt (W)
for power. The S1 units for force, energy and power are the
same regardless of whether the process is mechanical,
electrical, chemical or nuclear. A force of 1 newton applied
for a distance of 1 metre can produce 1 joule of heat, which is
identical with what 1 watt of electric power can produce in
1 second.
1.6 Corresponding to the advantages of S1, which
result from the use of a unique unit for each physical
quantity, are the advantages which result from the use of a
unique and well-defined set of symbols and abbreviations.
Such symbols and abbreviations eliminate the confusion that
can arise from current practices in different disciplines such
as the use of "b" for both the bar (a unit of pressure) and
barn (a unit of area).
1.7 Another advantage of SI is its retention of the
decimal relation between multiples and sub-multiples of the
base units for each physical quantity. Prefixes are established
for designating multiple and sub-multiple units from "exa"
(lola) down to "atto" (10-18) for convenience in writing
and speaking.
1.8 Another major advantage of S1 is its
coherence. Units might be chosen arbitrarily, but making an
independent choice of a unit for each category of mutually
comparable quantities would lead in general to the
appearance of several additional numerical factors in the
equations between the numerical values. It is possible,
however, and in practice more convenient, to choose a
system of units in such a way that the equations between
numerical values, including the numerical factors, have
exactly the same form as the corresponding equations
between the quantities. A unit system defined in this way is
called coherent with respect to the system of quantities and
equations in question. Equations between units of a coherent
unit system contain as numerical factors only the number 1.
In a coherent system the product or quotient of any two unit
quantities is the unit of the resulting quantity. For example,
in any coherent system, unit area results when unit length is
multiplied by unit length, unit velocity when unit length
is divided by unit time, and unit force when unit mass is
multiplied by unit acceleration.
Note.-Figure B-1 illustrates the relationship of the units of
the Sf.
2.-Mass, force and weight
2.1 The principal departure of S1 from the
gravimetric system of metric engineering units is the use of
explicitly distinct units from mass and force. In SI, the name
kilogram is restricted to the unit of mass, and the kilogramforce
(from which the suffix force was in practice often
erroneously dropped) is not to be used. In its place the SI
unit of force, the newton is used. Likewise, the newton
rather than the kilogram-force is used to form derived
units which include force, for example, pressure or stress
(N/m2 =Pa), energy (N . m = J), and power (N . m/s = W).
2.2 Considerable confusion exists in the use of the
term weight as a quantity to mean either force or mass. In
common use, the term weight nearly always means mass;
thus, when one speaks of a person's weight, the quantity
referred to is mass. In science and technology, the term
weight of a body has usually meant the force that, if applied
　
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