Fundamental and Derived quantities | Definition , Examples and Differences

For define Physics and its law we use some quantities , these quantities are  called Physical quantities . We can differentiate Physical quantities in mainly two types that are fundamental and derived quantities . Although one other type of physical quantities also exist that’s supplementary quantities .

Fundamental Quantities

Fundamental quantities are quantities which do not depend upon other quantities for their complete identification ( definition ) .
There are 7 fundamental quantities. 

( i ) Lenght

( ii ) Mass

( iii ) Time

( iv ) Electric current

( v ) Thermodynamic temperature

( vi ) Amount of substance

( vii ) Luminous intensity

Unit of fundamental quantities are called fundamental units .

  • ( i ) Length – Length is basically the straight-line distance between two points . There are lots of popular unit of length but , SI unit of length is meter , while in CGS system the unit of is centimeter .
  • ( ii ) Mass – In simple term we can say that ” Mass is a measure of how much matter there is in an object ” .  SI Unit of mass is Kg and CGS unit of mass is gram .
  • ( iii ) Time – Time is one of the most popular fundamental quantity due to their various application in real life , all the things in real life is counted in time . We can define Time as the progression of events from the past ( previous ) to the present then into the upcoming ( future ) . Now physicist consider Time as the fourth dimension of reality , used to describe events in three-dimensional space . SI unit and CGS Unit of time is same , that is second .
  • ( iv ) Electric current – Electric current  is a measure of the quantity of charge passing any point of the wire or conductor  per unit of time . SI unit of Electric current is Ampere and CGS unit is biot .
  • ( v ) Thermodynamic temperature – Temperature is the measure of hotness or coldness of body in terms of any of several scales, including Fahrenheit and Celsius and kelvin.  Temperature indicates the direction in which heat energy will be spontaneously flow — i.e., from a hotter body (one at a higher temperature) to a colder body (one at a lower temperature) . SI unit of temperature is Kelvin .
  • ( vi ) Amount of substance – Amount of substance is the number of constituent particles contained in it, atoms, ions or molecules . Generally we use this term in chemistry  . Unit of Amount of substance is mole .
  • ( vii ) Luminous intensity –  Luminous intensity is a measure of the power emitted by a light source ( in form of photon ) in a particular direction per unit solid angle . The SI unit of luminous intensity is the candela (cd) and Stilb (sb) is the CGS unit of luminous intensity .

Derived Quantities

Derived quantities are those quantities that can  be expressed in terms of  fundamental quantities by means of the mathematical symbols of multiplication and division only (no addition or subtraction or any other sign). Basically they may be divided into two categories. The first group consists of derived quantities , which have proper units. Their units can be expressed in terms of units of base units and  the second class consists of quantities that do not have units expressed in terms of base quantities these quantities  are known as dimensionless quantities .

eg – Velocity = Distance / time .

– Acceleration = Distance/( Time )2 

– Force = Mass × Acceleration =( mass × Distance)/ ( Time )2

 Units of derived quantities are called derived units . 

Note – Generally  we define derived quantities in term of fundamental and derived quantities both for better understanding , but we can define all derived quantities only in term of fundamental quantities .

Difference between Fundamental and Derived quantities .

1 . Fundamental quantities are base quantities,  these quantities doesn’t depend on other quantities while derived quantities depend on Fundamental quantity.  
2 . Fundamental quantities can not be further reduce to elementary level , but derived quantities can be reduced in elementary level ..
3 . There are only 7 fundamental quantities that’s exist but there are lot of derived quantities exist .

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