1 International Systems of Units
Measurement
It is the process of assigning a number to an attribute (or phenomenon) according to a rule or set of rules.
Units
- A unit is the chosen standard of measurement of quantity, which has the same nature as the quantity.
- To express any physical quantity completely, we need the numerical value and the unit (u).
Physical quantity =Â nu
Fundamental Units:Units for fundamental or base quantities (length, mass and time)
Derived Units:Units obtained from fundamental units
Example:
Unit of speed (ms−1)
Speed 
∴Unit of speed
Systems of Units
- CGS System: Base units for length, mass and time in this system are centimetre, gram and second respectively.
- FPS System: Base units for length, mass and time in this system are foot, pound and second respectively.
- MKS System: Base units in this system are metre, kilogram and second.
- International System (SI) of Units: Based on seven base units; at present the internationally accepted system
SIÂ Base Quantities and Units
- Length − metre (m)
- Mass − kilogram (kg)
- Time − second (s)
- Electric current − ampere (A)
- Thermodynamic temperature − kelvin (K)
- Amount of substance − mole (mol)
- Luminous intensity − candela (cd)