A number of systems of units based upon the metric system, have been in use. Initially the CGS system based upon the centimeter for length, the gram for mass and the second for time, was widespread. It has, however, largely be replaced by the MKS system. In MKS system, the basic unit for length is meter for length, the kilogram is for mass and the second is for time.
Now SI units are applied for all scientific and technical measurements or purposes. The Si units are in general use for most of the other purposes in the majority of countries.
The base units for SI system are as following:
- meter: the unit of length
- Kilogram: the unit of mass
- Second: the unit of time
- Ampere: the unit of electric current
- Kelvin: the degree of temperature measured on Kelvin scale.
- Candela: the unit of luminous intensity
- Mole: the unit of substance.
Derived Units
Quantity
|
Unit
|
Symbol
|
Area
|
Square meter
|
m2
|
Volume
|
Cubic meter
|
m3
|
Velocity
|
Meter per second
|
m.s-1
|
Angular velocity
|
Radian per second
|
rad s-1
|
Acceleration
|
Meter per second squared
|
m.s-2
|
Angular acceleration
|
Radian per second squared
|
rad s-2
|
Frequency
|
Hertz
|
Hz
|
Density
|
Kilogram per cubic meter
|
Kg. m-3
|
Momentum
|
Kilogram meter per second
|
Kg.m.s-1
|
Angular momentum
|
Kilogram meter squared per second
|
Kg.m2.s-1
|
Moment of inertia
|
Kilogram meter squared
|
Kg.m2
|
Force
|
Newton
|
N
|
Pressure, stress
|
Pascal
|
Pa
|
Energy, work quantity of heat
|
Joule
|
J
|
Power
|
Watt
|
W
|
Surface tension
|
Newton per meter
|
N.m-1
|
Dynamic viscosity
|
Meter second per meter squared
|
N.s.m-2
|
Kinematic viscosity
|
Meter squared per second
|
m2.s-1
|
Temperature
|
Degree Celsius
|
oC
|
Thermal coefficient of linear expansion
|
Per degree Celsius or per kelvin
|
oC, K-1
|
Thermal conductivity
|
Watt per meter degree C
|
W.m-1 oC-1
|
Heat capacity
|
Joule per kelvin
|
J.k-1
|
Specific heat capacity
|
Joule per kilogram kelvin
|
J.kg-1.K-1
|
Specific latent heat
|
Joule per kilogram
|
J.kg-1
|
Electric charge
|
Coulomb
|
C
|
Electromotive force , potential difference
|
Volt
|
V
|
Electric resistance
|
ohm
|
Ω
|
Electric conductance
|
Siemens
|
S
|
Electric capacitance
|
Farad
|
F
|
Inductance
|
Henry
|
H
|
Magnetic flux
|
Weber
|
Wb
|
Magnetic flux density
|
Testa
|
T
|
Magneto motive force
|
Ampere
|
A
|
Luminous flux
|
Lumen
|
Lm
|
Illumination
|
Lux
|
Lx
|
Radiation activity
|
Becquerel
|
Bq
|
Radiation absorbed dose
|
Gray
|
Gy
|
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