System of Units

The International System of Units (SI), which began as the decimal metric system
during the French Revolution, deals with the definitions, terminology, proper
usage, and modifications of scientific units.
The metric system was established officially in France on June 22, 1799, and
consisted of two standard measures: the meter for length and the kilogram for
mass.
The German mathematician and astronomer Carl Friedrich Gauss (1777–1855)
promoted the use of the metric system and in 1832 added the second as the unit
of time.
The British Association for the Advancement of Science (BAAS) in 1874 introduced
an alternative system, known as the cgs system, whose units of measure were the
centimeter, gram, and second. Until 1889 the scientific community had two
metric standards for length, mass, and time.
The International System of Units (SI)
~ Standard International ~
NIST SPECIAL PUBLICATION 330
2008 EDITION
THE INTERNATIONAL SYSTEM OF UNITS (SI)

The first General Conference on Weights and Measures (Conférence Générale des
Poids et Mesures, or CGPM) in 1889 sanctioned a new system, the mks system,
that included the international prototypes for the meter and kilogram and the
astronomical second as the unit of time.
Fifty years later, in 1939, the International Committee for Weights and Measures
(Comité International des Poids et Mesures, or CIPM), under authority of the
CGPM, proposed a four-unit mks system with the addition of the ampere for
electric current. Official recognition of the ampere had to wait until 1946, after
World War II had ended.
The tenth CGPM in 1954 added two more standards when it officially approved
both the kelvin for thermodynamic temperature and the candela for luminous
intensity.
In 1960 the eleventh CGPM renamed its mks system of units the International
System of Units, and in 1971 the fourteenth CGPM completed the seven-unit
system in use today, with the addition of the mole as the unit for the amount of a
substance, setting it equal to the gram-molecular weight of a substance.
read more: http://www.chemistryexplained.com/Hy-Kr/International-System-of-
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Base Quantity Base Unit Symbol
Length meter m
Mass kilogram kg
Time second s
Electric current ampere A
Thermodynamic temperature kelvin K
Amount of substance mole mol
Luminous intensity candela cd
SOURCE:Taylor, Barry N., ed., and National Institute of Standards and Technology (1995). Guide for
the Use of the International System of Units (SI). Special Publication 811. Washington, DC: U.S.
Government Printing Office.

Derived Quantity Name Symbol
Area square meter m 2
Volume cubic meter m 3
Velocity meter per second m/s
Acceleration meter per second squared m/s 2
Wave number reciprocal meter m −1
Mass density kilogram per cubic meter kg/m 3
Specific volume cubic meter per kilogram m 3 /kg
Current density ampere per square meter A/m 2
Amount-of-substance concentration mole per cubic meter mol/m 3
Luminance candela per square meter cd/m 2
SOURCE:Taylor, Barry N., ed., and National Institute of Standards and Technology (1995). Guide for
the Use of the International System of Units (SI). Special Publication 811. Washington, DC: U.S.
Government Printing Office.

Derived Quantity
Force Newton (N) = kg m / s2
Work Newton-meter = kg m2 / s2
Energy Joule (J) = N m
Pressure Pascal (Pa) = N / m2
Temp Kelvin (K) = °C + 273.15
Gravity g = 9.80665 m / s2

cgs units
centimeter (cm) gram (g) second (s)
1 g mass (g) : 103 kg mass
1 cm : 102 m
1 dyne (dyn) : 1 g cm / s2 = 105 N
1 erg : 1 dyn cm = 107 J
g = 980.665 cm / s2
British units
foot (ft) pound (lb) second (s)
1 pound mass (lbm) : 0.453 kg
1 pound force (lbf) : 4.4482 N
1 foot (ft) : 30.48 cm
1 lbf ft : 1.35582 N m = 1.35582 J
1 psia : 6.89476  103 N / m2
g = 32.74 ft / s2

Pressure
1 atm : absolute pressure = 0°C, 760 mm Hg
: 29.921 inch Hg column = 14.696 lbf / in2 = psia
1 psia : 4°C, 33.9 ft H2O column
1 psig : gauge pressure
For example, a bicycle tire pumped up to 65 psi above local
atmospheric pressure (say, 14.7 psia locally), will have a
pressure of 65 + 14.7 = 79.7 psia or 65 psig.
1 psia : 6.89476  103 Pa (N/m2 )
1 atm : 1.01325  105 Pa
Blaise Pascal
1623-1662

(Pa) (bar) (atm) (Torr) (psi)
1 Pa ≡ 1 N/m2 10−5 9.8692×10−6 7.5006×10−3 1.450377×10−4
1 bar 105 ≡ 100 kPa≡
106 dyn/cm2 0.98692 750.06 14.50377
1 atm 1.01325×105 1.01325 1 ≡ 760 14.69595
1 Torr 133.3224 1.333224×10−3 1.315789×10−3 ≡ 1/760 atm≈
1 mmHg
1.933678×10−2
1 psi 6.8948×103 6.8948×10−2 6.8046×10−2 51.71493 ≡ 1 lbF /in2

Temperature
conversion formulae:
°F = 32 + 1.8 °C °R = °F + 460 K = °C + 273.15
°C °F K °R
Boiling water 100 212 373.15 671.7
Melting ice 0 32 273.15 491.7
Absolute zero -273.15 -459.7 0 0
Anders Celsius
1701-1744
Gabriel Fahrenheit
1686-1736
William T. Kelvin
1824-1907
William J. M. Rankine
1820-1872

from Celsius to Celsius
Fahrenheit [°F] = [°C] × 9⁄5 + 32 [°C] = ([°F] − 32) × 5⁄9
Kelvin [K] = [°C] + 273.15 [°C] = [K] − 273.15
Rankine [°R] = ([°C] + 273.15) × 9⁄5 [°C] = ([°R] − 491.67) × 5⁄9
Delisle [°De] = (100 − [°C]) × 3⁄2 [°C] = 100 − [°De] × 2⁄3
Newton [°N] = [°C] × 33⁄100 [°C] = [°N] × 100⁄33
Réaumur [°Ré] = [°C] × 4⁄5 [°C] = [°Ré] × 5⁄4
Rømer [°Rø] = [°C] × 21⁄40 + 7.5 [°C] = ([°Rø] − 7.5) × 40⁄21
conversion formulae:

Ideal Gas Law (BOYLE’s law)
T P V n R
K N/m2 m3 kg mol 8314.3 kg m2 / kg mol s2 K
°R atm ft3 lb mol 0.7302 ft3 atm / lb mol °R
K atm cm3 g mol 82.057 cm3 atm / g mol K
Robert Boyle
1627-1691
Boyle's Law, published in 1662, states that, at constant temperature, the product of the
pressure and volume of a given mass of an ideal gas in a closed system is always constant.
It can be verified experimentally using a pressure gauge and a variable volume container.
It can also be derived from the kinetic theory of gases: if a container, with a fixed number of
molecules inside, is reduced in volume, more molecules will strike a given area of the sides
of the container per unit time, causing a greater pressure.

Values of R Units
8.3144598(48) J K−1 mol−1
8.3144598(48)×107 erg K−1 mol−1
8.3144598(48) L kPa K−1 mol−1
8.3144598(48)×103 cm3 kPa K−1 mol−1
8.3144598(48) m3 Pa K−1 mol−1
8.3144598(48) cm3 MPa K−1 mol−1
8.3144598(48)×10−5 m3 bar K−1 mol−1
8.3144598(48)×10−2 L bar K−1 mol−1
1.987 cal/mole-K
8.314 J/mole
0.0821 L-atm/mole-K
82.1 cm3-atm/mole-K

1 calorie will raise the temperature of 1 g of water by 1 C°.
The “dietary” calorie is actually 1 kcal.
1 cal = 4.184 J
1 BTU (British Thermal Unit) will raise the temperature of
1 lb of water by 1F°.
1 BTU = 1055 J
The erg is the c.g.s. unit of energy and a very small one; the work
done when a 1-dyne force acts over a distance of 1 cm.
1 J = 107 ergs
1 erg = 1 d-cm = 1 g cm2 s–2
The electron-volt is even tinier: 1 e-v is the work required to
move a unit electric charge (1 C) through a potential difference of
1 volt.
1 J = 6.24 × 1018 e-v
The Watt is a unit of power, which measures the rate of energy
flow in J sec–1. Thus the Watt-hour is a unit of energy.
An average human consumes energy at a rate of about 100 Watts;
the brain alone runs at about 5 Watts.
1 J = 2.78 × 10–4 W-h
1 W-h = 3.6 kJ
The liter-atmosphere is a variant of force-displacement work
associated with volume changes in gases.
1 L-atm = 101.325 J
The huge quantities of energy consumed by cities and countries
are expressed in quads; the therm is a similar but smaller unit.
1 quad = 1015 Btu = 1.05 × 1018 J
If the object is to obliterate cities or countries with nuclear
weapons, the energy unit of choice is the ton of TNT equivalent.
1 ton of TNT = 4.184 GJ
(by definition)
In terms of fossil fuels, we have barrel-of-oil equivalent, cubic-
meter-of-natural gas equivalent, and ton-of-coal equivalent.
1 bboe = 6.1 GJ
1 cmge = 37-39 mJ
1 toce = 29 GJ

System of Units

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System of Units