Units & Measurements

Measurement has an essential role in our everyday life. If you enter a shop and ask for kilogram of sugar, you are not satisfied if shopkeeper just pours some quantity of sugar in bag and hands it over to you. You insist upon the measurement of its weight, because only then can you be sure that you have got the correct quantity. 

The measurement of a physical quantity involves the comparison of that quantity with some accepted standard for example, when we say that the mass of an object is 10 kilogram, we are stating that 1 kilogram is the standard used for the measurement of mass and that the given mass is to times as large as the mass of 1 kilogram. The standard used too the measurement of physical quantity is called the unit of that quantity. Thus in above example kilogram is the unit of mass and the 10 gives the relation between the given mass and its unit.

System of units:

The number of physical quantities is quite large and we need a unit for the measurement of each physical quantity. However, it is not necessary to define a separate unit for each physical quantity. There are only seven quantities which do not depend upon any other quantity for their measurement. These quantities are called as fundamental quantities, and untis of these quantities are called as fundamental or bas unit.

All the other physical quantities are depend upon fundamental quantities and therefore called   derived quantities and units of these quantities are called as derived units.

The fundamental units together with all derived unit form a system of units. The most commonly used systems are.

• The CGS system: Centimeter gram second
• The FPS system: Foot – pound – second system it is also called British system
• The MKS system: meter kilogram second
• The SI system: System International units’. This system replaces all the system mention above.