The measurement of a physical quantity is one of the most important functions in engineering. For measurement of a physical quantity a standard of reference is necessary. This reference is called unit. Or units are accepted standard for measuring a quantity. Example: The length of the table is 6 meters, it means standard adopted is meter and numerical value is 6.
Classifications of Units:
Units are mainly classified into the following types.
1) Fundamental Units
2) Derived Units
Every physical quantity can be expressed in terms of fundamental quantities length, mass and time. The units of these fundamental quantities are called fundamental units.
Units which are derived from fundamental units are called derived units. Or the units which are also expressed in other units called as derived units.
Example: unit of velocity, acceleration, pressure, area etc.
System of Units:
There are three systems of units, which are commonly used and internationally recognized.
1) C.G.S. System
2) F.P.S. System
3) M.K.S. System
1) C.G.S. System: In this system, the fundamentals units of length, mass and time are centimeter, gram and second.
2) F.P.S. System: In this system, the fundamentals units of length, mass and time are foot, found and second.
3) M.K.S. System: In this system, the fundamentals units of length, mass and time are meter, kilogram and second.