## Wednesday, 22 July 2015

### UNIT & DIMENSION

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)
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 ] = [ L2] = [ M0L2T0 ]

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

2. Dimensional Formula is [ M0L2T0 ]
3. Dimensional equation is Area = [ M0L2T0 ]

b) Acceleration = Velocity / Time = Displacement / time x (time) = Displacement / time 2
= L / T2  = [ M0L1-2 ]
1. Dimension of area is 0,1,-2 of mass , length and time respectively
2. Dimensional Formula is [ M0L1-2 ]
3. Dimensional equation is Velocity = [ M0L1-2 ]

Steps for determination of dimension :

1. Write the formula of the physical quantity of L.H.S. of the equation.
2. Convert all the quantity of R.H.S. into the fundamental quantity Mass, Length and Time .
3. Substitute M, L, and T for Mass, Length and Time respectively.
4. 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 :
1. To check the correctness of a given relation .
2. To convert the value of physical quantity from one system to another.
3. To derive a relation between various physical quantity.

## Friday, 10 July 2015

### PHYSICS INTRODUCTION

WHAT IS PHYSICS ?

Physics has been derived from the Ancient Greek word " phusikḗ " which means " knowledge of nature "  . Physics is the study of nature. The way things connects one another.  These connection are underlined by concepts. and those concepts are beautifully expressed in mathematically.

Each and everything happen in our real world has a secret behind it. Like we wake up and see sun light is all over and when day passes it vanishes and the same thing happen next day , how?  We see some flowers are looking red some are white, how? When we push a thing it moves away, when we pull thing it comes towards, why? If we go nearer to sun we feel mot hot, but at the top of the mountain we feel cold, as the mountain is more close to sun than ground. why? A rocket falls down but satellite does not why? There is a secret behind everything happen in our universe.

The universe is full of magical things patiently waiting for our wits to grow sharper. Physics is the gateway to those magical things. "

Consider a smart phone.Physics describes how electricity interacts with the various circuits inside the device. This knowledge helps engineers select the appropriate materials and circuit layout when building the smart phone. Next, consider a GPS system. Physics describes the relationship between the speed of an object,the distance over which it travels, and the time it takes to travel that distance. When you use a GPS device in a vehicle, it utilizes these physics equations to determine the travel time from one location to another.

## IS IT REALLY IMPORTANT TO LEARN PHYSICS?

Assume you and your mom watching a base ball match, you are really enjoying the match , and your mom feeling bore as she has no idea about the rules of the match. So your mom did not appreciate the match. To enjoying something or to appreciate something you must know the rule behind it. And physics is the rule of nature. If you know the rule of nature you will alive what is going around you. Physics will help you to appreciate the world more.

Life is physics.Every truth, known or unknown, is physics. The best illusion, the most awe-inspiring phenomenon, is physics. It is the foundation on which every one of our achievement, our understanding is built on. After all, the universe is physics!

In the beginning i ask " what is Physics? " I was wrong.  The real question is "what is not physics?" . Every thing is all about physics .