All physics topics ,PHYSICS for competition exams, physics for RRB,SSC,UPSC,state leve and Technical exams

PHYSICS

PHYSICS – Physics is that branch of physical science in which the matter and energy 

mutually interact to each other. 

MATTER – That substance which occupies space and possesses mass, that which we 

can experience from our senses. 

MASS – Quantity of matter in a substance is called mass. Mass of a thing is always 

remains fixed. 

WEIGHT – Weight is that force through which earth attracts a thing. Its unit is Newton. 

Value of weight is dependent of gravitational acceleration, Hence mass of a thing 

always remain unchanged but its weight is less at the poles an when we move towards 

equator weight of a thing increases. 

ENERGY – Capacity of a physical system to perform work is called Energy. 

 Energy can be experienced through senses. 

 Energy can be transformed into mass. According to Einstein 

E = Energy 

M= Mass 

C = Velocity of light 

UNITS – Units are standards for measurement of physical quantities. Units are of two types. 

1. Fundamental Units:- Those units which do not need any other units for their 

expression are called Fundamental Units. Example – Meter for distance, kg for mass, 

seconds for time, etc. 

2. Derived Units:- Which need two or more than two fundamental units for their

expression are called Derived Units. Example – m2

– Area, m3 

– Volume, etc. 

 Systems of Units:- 

i. MKS System – That system in which meter, kilogram and second are used to 

express distance, mass and time respectively. 

ii. CGS System – In it for distance centimeter, for mass gram and for time second is used. CGS is also called Metric or French system of units. 

iii. FPS System – Mass-pound, distance-foot, time-second. Also called British 

System of units. 

iv. SI System (International System of Units) – SI System was adopted in the 

international conference of weights and measures at Geneva in 1960. 

There are Seven Fundamental and two Supplementary units in SI System. 

Seven Fundamental Units are:- 

i. Length – Meter 

ii. Mass – Kilogram 

iii. Time – Second 

iv. Temperature – Kelvin 

v. Electric Current – Ampere 

vi. Luminous Intensity – Candela 

vii. Amount of Substance – Mole 

Supplementary Units of SI System:- 

i. Plane Angle – Radian 

ii. Solid Angle – Steradian 

 Various Exponents of 10:- 

i. 101

– Deca (da) 10-1

– Deci (d) 

ii. 102 

– Hecto (h) 10-2

– Centi (c) 

iii. 103 

– Kilo (K) 10-3

– Mili (m) 

iv. 106 

– Mega (M) 10-6

– Micro (u) 

v. 109 

– Giga (G) 10-9

– Nano (n) 

vi. 1012 

– Tera (T) 10-12

– Pico (p) 

vii. 1015 

– Peta (P) 10-15

–Femto (f) 

viii. 1018 

– Exa (E) 10-18

– Atto (a) 

i. Astronomical Unit (AU) – It is a unit of distance. It is mean distance between Sun 

and Earth. 

ii. Light Year – Distance travelled by light in vacuum in one year. 

iii. Par sec (Parallax Second) = Largest unit of distance among all the astronomical 

units. 

These Units are used to calculate distance between astronomical bodies. 

 Physical Quantities:- 

Quantities expressed in the terms of law of physics are called physical 

quantities. They are of two types. 

1. Scalars:- Those physical quantities which have magnitude only and no other 

characteristics. Consideration are called Scalars, example- Mass, Temperature, 

Density, Volume. 

2. Vectors:- Those physical quantities which have both magnitude and direction. 

Example- Velocity, acceleration, displacement, linear momentum, etc. 

MOTION:- If position of any-body changes with time then that body is said to be

in motion. Motion is always relative. For example if A is in motion with respect to 

B then it can be at rest with respect to C. 

- Real Time Example:-

 A person sitting in a train is in motion with respect to 

another person standing at platform but he is at rest with respect to person 

sitting next to him.  

- Motion are of three type:- 

1 Linear Motion: When a thing moves in linear direction. Example -Man moving 

on road. 

2. Rotational Motion:- When a thing moves around its axis, then such motion is 

called Rotational motion. 

3. Vibrational Motion: When a thing moves back and forth to a point. Example –

Pendulum of watch 

DISTANCE – The total length of the path followed by anybody in any time 

interval is called distance. It’s a scalar quantity and is never negative, its SI unit 

is meter. 

DISPLACEMENT – The least distance between the initial and final point of the 

body executing a straight line motion in a definite direction is called 

displacement. It is a vector quantity. It may be positive, negative or Zero. 

SPEED – Distance travelled by the body in unit time. It’s a scalar quantity, its 

unit is m/sec. 

VELOCITY- It is a vector quantity, that an object or particle undergoes with 

respect to time. 

RELATIVE VELOCITY- Relative Velocity of one body with respect to another is 

the rate of change of displacement of one body with respect to another and vice￾versa. 

 VA = Velocity of body A 

 VB = Velocity of body B 

 VAB = Relative velocity of A with respect to B 

ACCELERATION – Rate of change of velocity is called acceleration. It is a 

vector quantity with unit m/s2

. 

NEWTON’S LAW OF MOTION:- 

1. Law of Inertia:- A body continues to be at rest or in uniform motion in the

same direction unless some external force is applied to it. Bodies have tendency 

to remain in rest until a net external force acts upon it, this provides definition of 

force. That is force is that factor which brings changes in the state of a body. 

Example: If a train start moving suddenly from rest then a sitting passenger 

leans in it opposite direction to the direction in which train start to move, falling of 

fruits when one shakes the tree, to remove the dirt from a coat when it is hit by 

the stick. 

2. Second Law - Law of Measurement of Force:- Rate of change of linear
momentum (P = mv) is proportional to the force applied and it takes places in the
direction of the force that is
 F  mv
 t K = Proportional constant
 F = K[mv] if K = 1
 t a = V
 t
and velocity unit Kg. m/s
IMPULSE – If any external force be operative on an object or a body for a short
time span then the product of such force and time is called Impulse.
 Kg.m/s

Example: Cricket player move their hands in the direction of motion of the ball to
avoid the injuries.
3. Third law:- Law of Action & Reaction:- In a system of two or more bodies. To
every action or force applied by one body on another, there is an equal and
opposite reaction by second body on first. This law is called law of action and
reaction.

Example: Imagine hitting a baseball, the bat exerts a force on the ball. This is the
action force. The ball exerts an equal and opposite force on the bat, this is the
reaction force.

 Law of conservation of momentum:- 

- It’s an outcome of 2nd and 3rd law.
- In a system of two or more bodies linear momentum remains conserved.
Momentum generated in one body in a particular direction is balanced by
momentum generated in another body in opposite direction.

Example: when a bullet is fired from a gun. Momentum generated in bullet in
forward direction is balanced by momentum generated in the gun in opposite
direction.
FORCE – Force is that factor which brings changes in the state of a thing. Its SI
unit = Newton and GS Unit = Dyne
Types of Forces:-
There are four types of forces in our nature
 i. Gravitational Force
 ii. Weak Force
 iii. Electromagnetic Force
 iv. Nuclear Force

I. Gravitational Force:- Attraction force between two bodies having mass is called
Gravitational Force. This force is negligible in bodies of very less mass, it

increases as mass increases. It is weakest among all existing forces. Example:
Earth attracts things towards it (apple always falls down)
II. Weak Force:- In it a nucleus neutron is converted into proton by the exchange of
 meson and consequently  meson further decays into electron and anti
neutrino. This process occurs in nucleus due to weak force.
 n (Neutron) P (Proton) + 
-1 (meson) p (proton) + e- + u (Anti neutrino)
III. Electromagnetic Force:- Force applicable between two charged particles is
called Electromagnetic Force. It is both attractive and repulsive. A positive
charge attracts negative charge and repels other positive charge.
IV. Nuclear Force (Strong Force):- This force is responsible for keeping protons
together in the nucleus. It is many times powerful then electromagnetic force.
This force is strongest among all the types of forces.

. FRICTIONAL FORCE:- Force applicable between two contacting bodies which 

opposes the motion is called Frictional Force.
- Frictional Force depends on the nature of the thing, on smooth surface frictional force
is less while on hard surface it is more.