# Measurement

A unit is defined as a convention to define an amount of physical property in a specific system of units.

Fundamental unit: The units of the fundamental quantities are called fundamental unit. Those units which are independent cannot be derived from other unit is called fundamental unit.

 Physical Quantity Unit Symbol mass kilogram kg length meter m time second s temperature Kelvin K electric current ampere A amount of matter mole mol luminous intensity candela Cd

Derived units are composed of the fundamental units and are originated from the products and ratios of the fundamental units. Derived units belong to physical quantities that are derived from basic physical properties. Examples are:

Velocity – a physical quantity derived from fundamental quantities of length and time

velocity  = distance / time  = m/s

So the units of velocity is ms-1

Difference between fundamental and derived unit

 Fundamental unit Derived unit The units of the fundamental quantities are called fundamental unit. e.g kilogram , meter,  second  are the fundamental units The units which are derived from the fundamental units are called derived units. Newton, joules   are the derived units.

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