- SI Base Quantities and Units
- Systems of Units and SI Units
The International System Units
Internationally accepted system of units is Système Internationale d’ Unites (French for International system of Units) or SI. It was developed and recommended by General Conference on Weights and Measures in 1971. In earlier times, scientists of different countries were using different systems of units for measurements.
Systems of Units:-
A system of units is the complete set of units, both fundamental and derived, for all kinds of physical quantities. The common system of units which is used in mechanics are given below:
CGS System: In this system, the unit of length is centimetre, the unit of mass is gram and the unit of time is second.
FPS System: In this system, the unit of length is foot, the unit of mass is pound and the unit of time is second.
MKS System: In this system, the unit of length is metre, the unit of mass is kilogram and the unit of time is second.
SI System: This system contain seven fundamental units and two supplementary fundamental units.
|Amount of Substance||mole||mol|
Supplementary Fundamental Units
Radian and steradian are two supplementary fundamental units. It measures plane angle and solid angle respectively.
Some units retained for general use
|Name||Symbol||Value in SI Unit|
|hour||h||60 min = 3600 s|
|day||d||24 h = 86400 s|
|year||y||365.25 d = 3.156 × 107 s|
|degree||o||1o = (`pi`/180) rad|
|litre||L||1 dm3 = 10-3 m3|
|bar||bar||0.1 MPa = 105 Pa|
|curie||Ci||3.7 × 1010 s-1|
|roentgan||R||2.58 × 10-4 C/kg|
|barn||b||100 fm2 = 10-28 m2|
|are||a||1 dam2 = 102 m2|
|hectare||ha||1 hm2 = 104 m2|
|standard atmospheric temperature||atm||101325 Pa = 1.013 105 Pa|