In our everyday life we observe that some
effort is required to put a stationary object
into motion or to stop a moving object. We
ordinarily experience this as a muscular effort
and say that we must push or hit or pull on
an object to change its state of motion. The
concept of force is based on this push, hit or
A force can be seen.A force can be judged only by the effect which
it can produce in various bodies (objects) around us.A force can
produce the following effects:
1. A force can move a stationary body.
2. A force can stop a moving body
3. A force can change the speed of the moving body
4. A force can change the direction of the moving body
5. A force can change the shape (and size) of a body
Effect of force
*If the resultant of all the force acting on a body is zero , the force
are called the balanced force.
*Please note that the force of our push on the book is balanced by
force of friction, and the force of gravity is balanced by the force
of reaction of the ground.
If the resultant of all force acting on a body is not zero, the force
are called unbalanced force
Please note that when an unbalanced force acts on a body, it
produce motion in the body. Another point is to be noted that an
unbalanced force can also stops a moving body.
Newton has given three laws to describe the motion of
bodies.These laws are known as Newton’s laws of motion. The
newton’s laws of motion give a precise definition of force and
establish a relationship between the force applied on the body and
the state of motion acquired by it. We will now discuss these law’s
of motion and consider some of their important application. Let
us start with first law of motion………
NEWTON’S LAWS OF MOTION
Some of the bodies (or object) around us are
at rest that is they are stationary ,whereas
other are in motion. Newton's first law
describe the behavior of such bodies which
are in a state of rest or of uniform motion in a
straight line. According to the 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 with uniform speed, unless it is
compelled by an external force to change its
state of rest or of uniform motion.
*It should be noted that Newton’s first law of
motion is also some times called Galileo’s
laws of motion
NEWTON’S FIRST LAW OF MOTION
Let us take some examples to make the first law of motion more
clear. Suppose a book 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
external force that is our hands,that is, when we lift the book from
the table. Thus, the position of rest of the book has been changed
by external force of our hand. And this observation support the
first part of the first law of motion.
Before external force After external force
*The tendency of a body to remain at rest (stationary) or, if
moving, to continue moving in a straight line, is called inertia.
*Inertia is that property of a body due to which it resists a change
in its state of rest or of uniform motion.
*Greater the inertia of a body, greater will be the force required to
bring a change in its state of rest or of uniform motion.
*In fact mass is measure of the inertia of a body
*If the body has more mass, it has more inertia
*That is, heavier object has more inertia than lighter objects
*For example: 1.the stone has more inertia than a rubber ball
2.A cricket ball has more inertia than a rubber ball
of the same size.
Inertia and mass
From the above discussion we conclude that to overcome the inertia
and make a body move from rest , we must apply an external force.we
can illustrate the Newton’s first law of motion or property of inertia of a
body with simple experiment describe below:
Take an empty glass tumbler and put it on a table. Cover the tumbler by
a stiff playing card over its mouth. Now place a coin on the card as
shown in fig. Give a sudden, sharp horizontal flick to the card with a
finger. The card moves along the direction of flick but coin is found to
fall vertically into the glass tumbler due to its inertia of rest.
*We will now consider the second part of the first laws of motion
which say that a body in uniform motion will continue to move
unless a force compels it to change its state of uniform motion in a
*At first site it would be appear wrong that a body moving at
uniform speed in a straight line will continue to move for ever
without coming to rest. Because if we stop pedaling a bicycle
, which is moving at a uniform speed, the bicycle does not go on
moving for ever, it comes to rest after some time.
*The moving bicycle has been compelled to change its state of
uniform motion by external force of air resistance and friction. If
there were no air resistance and no friction to oppose the motion
of a bicycle, then according to the first law of motion a moving
bicycle will go on motion for ever. It will not stop by itself.
In order to understand the Newton’s second law of motion, we
should first know the meaning of term momentum:
We know that a cricket ball is much heavier than a tennis ball.
suppose we throw a cricket ball and a tennis ball, both with the
same velocity. It is found that more force is required to stop the
cricket ball (which has more mass) and less force is required to
stop the tennis ball (which has less mass).
*so we conclude that force required to stop the moving ball is
directly proportional to its mass
Now if we throw two cricket balls of the same size at different
speed or velocity. It will be found that more force is required to
stop the cricket ball which is moving with higher velocity and less
force is required to stop the cricket ball moving with lower
*So we conclude that the force required to stop a moving body is
directly proportional to its mass.
more force required to stop the ball moving with higher velocity
Less force required to stop the ball moving with lower velocity
Thus, the quantity of motion in a body depends on the mass and
velocity of the body. This gives the other term known as
‘’Momentum’’. The momentum on a body is defined as product of
mass and velocity.
Thus, Momentum = mass x velocity
Or, p = m x v
where p = momentum
m = mass of the body
v = velocity (or speed) of the body
*It is clear that if a body at rest its velocity is zero and hence its
momentum is also zero.
*Now mass is measured in kg and velocity is measured in m/s
So the SI unit of momentum is kg.m/s or kg.ms-1
When two bodies a heavy one and a light
one, are acted upon the same force for the same
time, the light body attains a high velocity than
the heavy one. But the momentum gained by
both the body is the same the link between
force and momentum is expressed in Newton’s
second law of motion.
*According to the Newton’s second law of
motion: The rate of change of momentum of a
body is directly proportional to the applied
force and takes place in the direction in which
the force act
NEWTON’S SECOND LAW OF MOTION
The rate of change of momentum of a body can be obtain by
dividing ‘’change in momentum” by time ‘’taken for this change’’
*So Newton’s second law of motion can be expressed as:
change in momentum
Time taken for change
Consider a body of mass m having initial velocity u. the initial
momentum of the body will be mu. Suppose a force f acts on this
body for time t and causes the final velocity to become v. The final
momentum of the body will be mv. Now, the change in
momentum of this body is mv-mu and time taken for change is t.
so according to the newton's law of motion:
mv-mu or f ∝ m(v-u)
But v-u represent change in velocity which is known as acceleration.
so by wring a in the above relation we get :
f ∝ m x a Thus, f = k x m x a (k constant)
force = mass x acceleration
Thus Newton’s second law of motion gives relationship between
force and acceleration. when a force acts on a body it produces
acceleration in the body, the acceleration produce may be positive
*Acceleration produce in the body is directly proportional to the
force acting on it and inversely proportional to the mass of the
*if the mass of the body is doubled its acceleration will be halved.
And if mass is halved then the acceleration will get doubled
(provided the force remain the same)
*The SI unit of force is Newton which is denoted by N. a newton is
that force which when acting on a body of mass 1 kg produces an
acceleration 1m/s in it. We have just seen that:
f = m x a 1 newton = 1kg x 1 m/s2
Sample problem : calculate the force required to impart to a car
velocity of 30 m/s in 10 seconds starting from rest. The mass of
the car is 1500 kg .
Solution : here mass, m= 1500 kg
Let us calculate the value of acceleration using the first equation
Now, initial velocity u = 0
final velocity v = 30 m/s
time taken t = 10s
Now putting these value in the equation :
v = u + at
30 = 0 + a x 10
10a = 30c
a = 30 m/s2 acceleration, a = 3 m/s2
Now, putting m = 1500kg a = 3m/s2 in equation:
we get f = m x a
f = 1500 x 3N
Thus the force required in this case is of 4500 newtons.
When a body exerts a force on the wall, the
exerts an equal and opposite force on the
body. This is just illustration of Newton’s
third law of motion.
*According to the newton’s third law of
motion : whenever one body exerts a force
on another body, the second body exerts
equal and opposite force on the first body.
*The force exerted by the first body on the
second body is known as ‘’action’’ and the
force exerted by the second body on the
first body is known as ‘’reaction’’. It should
be noted that ‘’action‘’ and ‘’reaction’’ are
NEWTON’S THIRD LAW OF MOTION
To every action there is an equal and opposite reaction. Action
and reaction acts on two different bodies but they act
simultaneously. we will now describe a simple experiment to
prove the Newton’s third law of motion, that is, to prove that
action and reaction are always equal and opposite.
*We take two similar spring balance A and B and join them hook
to hook as shown in figure. The another end of spring balance B is
attached to hook H fixed in a wall. Let pull the free end of the
spring balance A to right side of our hand. We find that both the
spring balances shows the same reading. For example, in
figure, both the spring balances show the same reading of 4N.
This can be explained as follows:
When we pull the balance B, It exerts a force of 4N on the balance
A. The balance A pulls the balance B with equal force of 4N,but in
*We conclude that the action and reaction forces are equal in
magnitude. In the figure we find that the action force is acting
toward the east and the reaction force is acting toward west. Thus
action and reaction forces act in opposite directions.
Action and reaction acts on two
Suppose a box is resting on the ground. The
box is exerting a downward force of its weight
on the ground. The downward weight of the
box is balanced by an equal, upward force
supplied by the ground. Now, the force exerted
by the weight of the box is ‘’action’’ and its act
on the ground whereas the force exerted by the
ground on the box is known as ‘’reaction’’ and
it acts on the box. Since the box is in
equilibrium under two forces, it neither goes
up nor goes down, the action of the box must
be equal and opposite to the reaction of the
ground. It is obvious that action of the box acts
on the ground and reaction of ground acts on
box. Thus action and reaction acts on two
According to the laws of conservation of momentum: When one
or more bodies act upon one another, their total momentum
remains constant (or conserved ) provided no external force are
acting. The law of conservation of momentum means that
whenever one body gains momentum, then some other body
must loose an equal amount of momentum. This law can also be
stated as: Momentum is never created or destroyed.
CONSERVATION OF MOMENTUM
Schoolboy 'genius' solves puzzles posed by Sir Isaac Newton that have baffled
mathematicians for 350 years
Shouryya Ray put the historical breakthrough down to 'schoolboy
Modest Shouryya began solving complicated equations as a six year old
but says he's no genius
A 16-year-old has managed to crack puzzles which have baffled the world of
maths for more than 350 years.
Shouryya Ray has been hailed a genius after working out the problems set by
Sir Isaac Newton.
The schoolboy, from Dresden, Germany, solved two fundamental particle
dynamics theories which physicists have previously been able to calculate only
by using powerful computers.
His solutions mean that scientists can now calculate the flight
path of a thrown ball and then predict how it will hit and bounce
off a wall.
Shouryya only came across the problems during a school trip to
Dresden University where professors claimed they were uncrack
'I just asked myself, 'Why not?',' explained Shouryya.
'I think it was just schoolboy naivety. I didn't believe there
couldn't be a solution,' he added.
MADE BY MD ZAKARIA AND MEMBERS OF OUR GROUP :
1. MD ZAKARIA
2. VIKASH KUMAR SHARMA
3. AMIT CHAUHAN
4. PUSHKAR SINGH JANTWNAL
5. ANKIT TIWARI