Suppose i ask you "what is 5? what will be your answer? your answer would be " Are you kidding. Is not that obvious."

5 --- is a constant (or) number (or) numeric

10 , 15 20......???? all are numeric

The i add a post-fix to the constant like..

5 Kg .. what does it sense? It defines a mass or weight..

10 cm - Length

15 newton - force

20 hour / hr - time

__PHYSICAL QUANTITY__:

The quantities which can be measured are called Physical Quantity. Ex : Length , Mass , Time, Volume, Area , etc

__UNIT__:

The Standard of measurement of the physical quantity is called unit . Ex : meter, centi-meter, klio-meter are the unit of length.

__SYSTEM :__

A system of units defines a minimum number of physical quantities taken as fundamental to give a consistent and unambiguous description all physical quantity.

Is it requires for a common international forum of all scientist and engineers concern with measurement.

There are 4 system in use :-

1) C.G.S. system 2) F.P.S. system 3) M.K.S. system 4) S.I. system

1) F.P.S. System : The fundamental unit of length , mass, and time are respectively foot (ft), pound (p) and second (s).

2)M.K.S. System : The fundamental unit of length , mass, and time are respectively meter (m),kilo gram (kg) and second (s).

3)C.G.S. System : The fundamental unit of length , mass, and time are respectively centimeter (cm), gram (gm) and second (s).

4) S.I. System : ( International System of unit)

The S.I. units were approved by the C.G.P.M in 1960 and endorsed by both the ISO( International Organisational for Standardization ) and the IEC ( International Electrotechincal Comission ) in 1967.

The S.I unit consists of 7 base unit and 2 supplementary unit.

The S.I. unit are

*Coherent system of unit. i.e. all other physical quantity are derived from the S.I. units by simple multiplication and division without any numerical.*__Base Unit (7)__

1. Length - meter (m)

2. Mass - kilogram (kg)

3. Time - Second (s)

4. Temperature - kelvin (k)

5. Luminous Intensity - candela (cd)

6. Electric Current - ampere (A)

7. Amount of substance - mole (mol)

__Supplementary Unit (2)__

1. Plane angle - radian (rad)

2. Solid angle - steradian (sr)

Example : find the unit of velocity?

we know velocity = displacement / time

= m / s = ms

^{-1}^{}

^{Some of the derived physical quantities are }

^{}

^{}

**DIMESIONS :**

The dimension of a physical quantity are the powers to which fundamental unit must be raised to obtain the unit of that quantity.

**DIMESIONAL FORMULA :**

It is a formula which tells how and which of the fundamental units have been used for the measurement of that unit.

**DIMESIONAL EQUATION :**

An equation written in the following manner is called dimensional equation .

Example :

a) Area = length x breadth = [ L x L ] = [ L

^{2}] = [ M^{0}L^{2}T^{0}]
1. Dimension of area is 0,2,0 of mass , length and time respectively

2. Dimensional Formula is [ M

^{0}L^{2}T^{0}]
3. Dimensional equation is Area = [ M

^{0}L^{2}T^{0}]
b) Acceleration = Velocity / Time = Displacement / time x (time) = Displacement / time

^{2}^{ = L / }T

^{2 = }[ M

^{0}L

^{1}T

^{-2}]

1. Dimension of area is 0,1,-2 of mass , length and time respectively

2. Dimensional Formula is [ M

^{0}L^{1}T^{-2}]
3. Dimensional equation is Velocity = [ M

^{0}L^{1}T^{-2}]

**Steps for determination of dimension :**- Write the formula of the physical quantity of L.H.S. of the equation.
- Convert all the quantity of R.H.S. into the fundamental quantity Mass, Length and Time .
- Substitute M, L, and T for Mass, Length and Time respectively.
- Collect terms of M,L,T and find their resultant power which give the dimension of a quantity in Mass, Length and Time respectively.

*Application of dimensional analysis :*- To check the correctness of a given relation .
- To convert the value of physical quantity from one system to another.
- To derive a relation between various physical quantity.

*you can ask your queries by commenting*

*below. I will try to solve your problem.*