PPT on Motion & Law of Motion with Descriptive Study
A body is said to be in motion (or moving) when it position
changes continously with respect to a stationary object taken
as refrence point.
For eg: A moving car as shown below in the Image is in
A Body has a
uniform motion if it
travel equal distance
in equal interval of
The Distance Time
Graph for a body
Motion in a
A Body has a non-
uniform motion if it
distance in equal
interval of time.
Foreg:a carrunningat a constantspeedof 10mp/s.it
meanscarcoveringdistance a distance 10m p/s.so, Its
motionwill be in uniformmotion.
Foreg:themotionof a freefallingbodyis
Travel equal distance in equal
interval of time.
The distance-time graph for a
body having uniform motion is
a straight line.
Travel unequal distance in equal
interval of time.
The distance-time graph for a
body having non-uniform
motion is a curved line.
Speed of a body is the distance
travelled by it in per unit
time.Tht speed of a body can
be calculated by Dividing the
‘Distance Travelled’ by the
‘Time Taken’ to travel this
Distance. So, the formula can
be written as :
The average speed of a body is the total distance travelled
divided by the total time taken to cover the Distance.
For eg : A car which travels a distance of 100km in
4hours, the average speed is 100/4 =25km per hour.
Although the average speed of car is 25 km per hour, it
does not mean that car is moving at this speed all the
time. When the road is Straight,or free the speed may be
much more than 25km per hour. But on Bends (curved
road), hills or in a crowded area, the speed may fall well
bellow this average value.
Formula for Average Speed =
TotalDistanceTravelled/Total Time Taken
The Distance travelled by a body is the actual
length of the path covered by a moving body
irrespective of the direction in which the body
Distance is a scalar quantity(Because it has
magnitude only, it has no specified direction).
Distance can not be ZERO.But if the object or
body travells from initial position to final
position.Then we can say that Distance is
When a body moves from one position to another the
Shortest (straight line)distance between the initial
position & the final position of the body, along with
direction, is Known as Displacement.
Displacement is a vector quantity(because it has
magnitude as well as direction).
The distance travelled by a moving body cannot be
zero but the final displacement of a moving body can
Distance is a scalarquantitybecause it has the
magnitude butnot the specifieddirection.
Displacement is a vector quantitybecause it has
the magnitude as wellas the direction.
The Distance travelled
by a body is the actual
length of the path.
Distance is a Scalar
Distance can not be
Displacement is the Shortest
Distance between the initial
position & the final
Displacement is a vector
Displacement can be
Velocity of a body is the distance travelled
by it per unit time in a given direction.
Velocity=Distance travelled in a given
direction /time Taken.
The si unit of velocity is the same as that of
speed namely, metres per second(m/s or m
The direction of velocity is the same as the
direction of displacement of the body.
Acceleration of a body is defined as the rate
of change of its velocity with time.
Acceleration=change in velocity/time taken
The change in velocity is the difference
between the final velocity & the initial
velocity.that is, change in velocity= final
A=final velocity-initial velocity/time taken.
The si unit of acceleration is ‘’metre per
second’’ or ‘’metre per second square’’.
A bodyhasa uniformvelocityif it travelsin a specifieddirectionina straightline&
TheVelocityof a bodycanbe changedintwoways :-
By changingthespeedof thebody.
By keepingthespeedconstantbutby changingthedirection.
A body has a uniform accerelation if it travels in
a straight line & its velocity increases by equal
amount in equal interval of time.
Some example of uniformly accelerated motion :-
The motion of a freely falling body is an example
of uniformly accelerated motion.
The motion of a bicycle going down the slope of a
road when the rider is not pedalling & wind
resistance is negligable, also an example of
uniform accelerated motion.
A bodyhas a non-uniformaccelerationif its
velocityincreasesby unequalamountsin equal
Example of non-uniformlyacceleratedmotion:-
The speed(or velocity)of a carrunningon a
momentthevelocityof a carincreaseswhereasat
anothermomentit decreases. So, themovementof
a caron a crowdedcityroadis an example of
If the velocity of a body increases, the accerelation is positive, & if the velocity of a body
decreases, the accerelation is negative.
A body is said to be retarded if its velocity is decreasing.
Retardation is measured in the same way as acceleration, that is,retardation is equal to
change in velocity
_____________________ & has the same units of
‘’metres per second’’(m s -2)
Retardation is actually acceleration with the negative sign.
Newton has given three laws to describe the motion of bodies.
These laws are known as Newton’s law of motion. The newton’s
law of motion give a precise definition of force & established a
relationship between the force applied on a body and the state of
motion acquired by it.
Some of the bodies(or object)around us are at rest,that is,they are stationary,whereas
others are in motion.Newton’s first law describes the behaviour of such bodies which
are in state of rest or of uniform motion in a straight line. According to Newton’s first
law of motion : A body at rest will remain at rest,and a body in motion will continue in
motion in a straight line with a uniform speed, unless it is compelled by an external
force to change its states. Let us take an example to understand first law of motion
more clear . Suppose we have a book which is lying on the table.It is at rest. The book
will not move by itself that is,it cannot change its position of rest by itself.It can
change its state of rest only when compelled by the force of our hands, that is, when we
lift the book from the table. Thus, the position of rest of the book hass been changed by
the external force of our hands. And this observation supports the first part of the first
law of motion.
The tendency of a body to remain at rest(stationary) or,if moving to continue moving
in a straight line is called Interia. Newton’s first Law recognizes that every body has
some Interia. INTERIA is that property of a body due to which it resists a change in
its state of rest or of uniform motion..Greater the INTERIA of a body,greater will be
the force required to bring a change in its state of rest or uniform motion.In fact mass
is a measure of the interia of a body.If a body has more mass,it has more interia.That is,
heavier object have more interia than lighter object.
oWhen two bodies,a heavy one and a light one,are acted upon by the same force for the same
time,the light body attains a higher velocity(or higher speed) than the heavy one.But the momentum
gained both the bodies is the same.The link between force & momentum is expressed in Newton’s
second law of motion.
oAccording to the Newton’s Second law of motion : The rate of change of momentum of a body is
directly proportional to the applied force & takes place in the direction in which the force acts. The
rate ofchange of momentum of a body can be obtained by dividing the ‘Change in momentum’ by ‘
Time taken’ for change. So, Newton’s second law of Motion can be expressed as :-
oConsider a body of mass m having an Initial velocity v. The initial momentum of this body will
be mv. Suppose a force Facts on this body for time t & causes the final velocity to become v. The
final momentum of this body will be mv. Now,the change in momentum of this body is mv-mu &
the time taken for this change is t. So,according to Newton’s second law of motion :
force=mv-mu/t or f=m(v-u)/t
oThus,the force acting on a body is directly proportional to the product of ‘mass’ of the body &
‘acceleration’ produced in the body by the action of the force,& it acts in the direction of
acceleration. This is another definition of Newton’s Second Law of Motion. The relation F=m X a
can be turned into an equation by putting in a constant K.
oThus, Newton’s Second law of motion give us a relationship between ‘force’ & ‘acceleration’.
oThe acceleration produced in a body is directly proportional to the force acting on it & inversely
proportional to the mass of the body.
When one body influence another body by applying force,we say that
the first body is interacting with the second body. In any interaction
between two bodies,there are always two forces that come into
play.And Newton’s third law of motion describes the relationship
between the forces that come into play when two bodies interact with
According to Newton’s third Law of Motion : Whenever one body
exerts a force on another body , the second body exerts an equal &
opposite force on the first body.The force exerted by the first body on
the second body is known as ‘Action’ & the force exerted by the second
body on the first body is known as ‘Reaction’. Its Should be noted
that’Action’& ‘Reaction’ are just forces.We can now write the another
definition of of Newton’s third law of Motion : To every action there
is an equal & opposite reaction.Action(Forcce) & Reaction(Force) act
on Two different bodies , but they act Simultaneously.