Physical quantities which can completely be specified by a number (magnitude) having an appropriate unit are known as "SCALAR QUANTITIES".

Scalar quantities do not need direction for their description.

Example: Work, energy, electric flux, volume, refractive index, time, speed, electric potential, potential difference, viscosity, density, power, mass, distance, temperature, electric charge, electric flux etc

Physical quantities having both magnitude and direction with appropriate unit are known as "VECTOR QUANTITIES".

We can't specify a vector quantity without mention of direction.

Velocity, electric field intensity, acceleration, force, momentum, torque, displacement, electric current, weight, angular momentum etc.

"Kinematics is the branch of Physics in which we discuss bodies at rest or motion without the reference of external agent that causes motion or rest."

OR ,

"The branch of physics which deals with the description of motion of objects without reference to the force or agent causing motion in it, is called Kinematics."

"If a body does not change its position with respect to its surroundings then

the body is said to be in a state of rest."

"If a body continuously changes its position with respect to its surrounding

than it is said to be in a state of motion."

Motion of objects can be divided into three categories.

(i) TRANSLATIONAL MOTION (ii) ROTATIONAL MOTION (iii) VIBRATIONAL MOTION

"Motion of a body in which every particle of the body is being displaced by the same amount is called Translational Motion".

EXAMPLE: (i) Motion of a person on a road. (ii) Motion of a car or truck on a road.

"Type of motion in which a body rotates around a fixed point or axis is called Rotational Motion."

EXAMPLE: (i) Motion of wheel (ii) Motion of the blades of a fan

"Type of motion in which a body or particle moves to and fro about a fixed point or mean position is called Vibratory Motion."

EXAMPLE: (i) Motion of simple pendulum (ii) Motion of the wires of guitar (iii) Motion of swing

"Distance between two points in a particular direction is called Displacement."

OR

Displacement may also be defined as "the minimum distance between two points in a particular direction."

It is a vector quantity and is always directed from the initial point to the terminal point

It is denoted by "d".

SPEED

"Distance covered by a moving body in one second is called its Speed".

OR

"Distance covered by a body in unit time is called Speed". Speed is a scalar quantity.

Speed = Distance traveled/Time taken OR v = S/t Unit of speed in S.I system is "m/sec".

VELOCITY

"Distance covered by a body in a particular direction in one second is called Velocity".

OR "Displacement of a body in unit time is called Velocity".

OR "Change of position of a body per second in a particular direction is called Velocity."

velocity = displacement/time In S.I system unit of velocity is meter/second.

It is a vector quantity.

ACCELERATION

"The rate of change of velocity of a body is called Acceleration."

OR "Change in velocity of a body in unit time is called its acceleration." It is denoted by "a".

It is a vector quantity.

If a body moves with uniform velocity or constant velocity then its acceleration will be zero. UNIT: m/sec2.

Acceleration = change in velocity/time OR; a = DV/t

FIRST EQUATION OF MOTION

Vf = Vi + at

Consider a body initial moving with velocity "Vi". After certain interval of time "t", its velocity becomes "Vf". Now

Change in velocity = Vf - Vi

OR

DV =Vf – Vi

Due to change in velocity, an acceleration "a" is produced in the body. Acceleration is given by

a = DV/t

Putting the value of "DV"

a = (Vf – Vi)/t

at = Vf – Vi

at + Vi =Vf

SECOND EQUATION OF MOTION

OR S = Vit + 1/2at2

Consider a car moving on a straight road with an initial velocity equal to ‘Vi’. After an interval of time ‘t’ its velocity becomes ‘Vf’. Now first we will determine the average velocity of body.

Average velocity = (Initial velocity + final velocity)/2

OR

Vav = (Vi + Vf)/2

but Vf = Vi + at

Putting the value of Vf

Vav = (Vi + Vi + at)/2

Vav = (2Vi + at)/2

Vav = 2Vi/2 + at/2

Vav = Vi + at/2

Vav = Vi + 1/2at.......................................(i)

we know that

S = Vav x t

Putting the value of ‘Vav’

S = [Vi + 1/2at] t

THIRD EQUATION OF MOTION

OR

2aS = Vf2 – Vi2

Initial velocity, final velocity, acceleration, and distance are related in third equation of motion.

Consider a body moving initially with velocity ‘Vi’. After certain interval of time its velocity becomes ‘Vf’. Due to change in velocity, acceleration ‘a’ is produced in the body. Let the body travels a distance of ‘s’ meters.

According to first equation of motion:

Vf = Vi + at

OR

Vf – Vi = at

OR

(Vf – Vi)/a = t....................(i)

Average velocity of body is given by:

Vav = (Initial velocity + Final velocity)/2

Vav = (Vi + Vf)/2.................. (ii)

we know that :

S = Vav x t.................. (ii)

Putting the value of Vav and t from equation (i) and (ii) in equation (iii)

S = { (Vf + Vi)/2} { (Vf – Vi)/a}

2aS = (Vf + Vi)(Vf – Vi)

According to [ (a+b)(a-b)=a2-b2]

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