System of Units : There are four systems of units to measure a physical quantity.
- C. G. S. System : The units of length, mass and time are respectively cm, gram and second.
- F. P. S. System : Units of length, mass and time are respectively foot, pound and second.
- M. K. S. System : Units of length, mass and time are respectively metre, kilogram and second.
- S. I. Units (International System of Units) : There are seven basic units namely —
1. Metre for length
2. Kilogram for mass
3. Second for time
4. Kelvin (K) for temperature
5. Ampere (A) for current
6. Candela for luminous intensity
7. Mole for amount of substance.
In addition to this there are two supplementary S. I. Units.
- Radian for plane angle
- Steradian for solid angle