| The International System of
Units (SI), the modern metric system of measurement, has long been
the language universally used in science. The SI was established in
1960 by the 11th General Conference on Weights and Measures (CGPM).
The CGPM is the international authority that ensures wide
dissemination of the SI and modifies the SI as necessary to reflect
the latest advances in science and technology. To learn more about
SI, CGPM and their backgrounds, visit: National Institute of
Standards and Technology.
|
| The
Seven SI Base Units |
|
| Physical Quantity |
Dimension
Symbol |
Unit Name |
Unit Symbol |
| Mass |
M |
kilogram |
kg |
| Length |
L |
meter |
m |
| Time |
T |
second |
s |
| Temperature |
Q |
kelvin |
K |
| Amount of Substance |
N |
mole |
mol |
| Electric Current |
I |
ampere |
A |
| Luminous Intensity |
J |
candela |
cd |
| The Two
SI Supplementary Units |
|
| Physical Quantity |
Dimension
Symbol |
Unit Name |
Unit Symbol |
| Plane Angle |
a |
radian |
rad |
| Solid Angle |
W |
steradian |
sr |
| * |
These are non-dimensional units that are
sometimes included in the dimensional expression of a unit for
clarity purposes. |
| meter: |
|
The meter is the length of the path traveled by light
in vacuum during a time interval of 1/299,792,458 second. [17th CGPM
(1983), Resolution 1] |
|
| kilogram: |
|
The kilogram is the unit of mass equal to the mass of
the international prototype of kilogram. [1st CGPM (1889), 3rd CGPM
(1901)] |
|
| second: |
|
The second is the duration of 9,192,631,770 periods
of the radiation corresponding to the transition between the two
hyperfine levers (F=4, mF=0 to F=3, mF=0) of
the ground state of the cesium 133 atom. [13th CGPM (1967)] |
|
| ampere: |
|
The ampere is the constant current which, if
maintained in two straight parallel conductors of infinite length,
of negligible circular cross-section, and placed 1 meter apart in
vacuum, would produce between these conductors a force equal to
2x10-7 newton per meter of length. [9th CGPM (1948),
Resolution 2 and 7] |
|
| kelvin: |
|
The kelvin, unit of thermodynamic temperature is the
fraction 1/273.16 of the thermodynamic temperature of the triple
point of water. [13th CGPM (1967), Resolution 4] |
|
| mole: |
|
The mole is the mount of substance of a system which
contains as many elementary entities as there are atoms in .012 kg
of carbon 12 (about 6.022x1023 atoms). When the mole is
used, the elementary entities must be specified and may be atoms,
molecules, ions, electrons, other particles, or specified groups of
such particles. [14th CGPM (1971), Resolution 3] In this definition,
it is understood that the carbon 12 atoms are unbound, at rest and
in their ground state. |
|
| candela: |
|
The candela is the luminous intensity, in a given
direction, of a source that emits monochromatic radiation of
frequency 540x1012 Hz and that has a radiant intensity in
that direction of 1/683 watt per steradian. [16th CGPM (1979),
Resolution 3] |
|
