By:- Avipsit Rath
Class:- 11th Sec:- “A”
School:- Kendriya Vidyalaya
Sir Isaac Newton
English mathematician and
Birth:- December 25, 1642
Death :-March 20, 1727
Place of Birth:- Woolsthorpe, England
Known for Inventing, in part, the branch
of mathematics now known as calculus
Formulating the three laws of motion,
which describe classical mechanics
Proposing the theory of universal
gravitation, which explains that all
bodies are affected by the force called
Career 1661 Entered Trinity College,
University of Cambridge
1665-1666 Developed what he called the
fluxional method (now known as
calculus) while living in seclusion to
avoid the plague
1669-1701 Served as Lucasian Professor
of Mathematics at the University of
1687 Published his seminal work,
Philosophiae Naturalis Principia
Principles of Natural Philosophy),
which contained his three laws of motion
and the theory of gravitation
1703-1727 Acted as president of the
Royal Society, an organization that
promotes the natural sciences
1704 Published Opticks (Optics),
describing his theory that white light is a
blend of different colors .
Sir Isaac Newton’s work represents one of the greatest
contributions to science ever made by an individual. Most
notably, Newton derived the law of universal gravitation,
invented the branch of mathematics called calculus, and
performed experiments investigating the nature of light and
Newtonian Reflecting Telescope
The first reflecting telescope was designed by Sir Isaac Newton in 1668.
Starting about 1665, at the age of 23, Newton enunciated the principles of mechanics,
formulated the law of universal gravitation, separated white light into colors,
proposed a theory for the propagation of light, and invented differential and integral
ROLE IN HISTORY OF PHYSICS
The subsequent development of physics owes much to Newton's laws of
motion, notably the second, which states that the force needed to accelerate
an object will be proportional to its mass times the acceleration.
If the force and the initial position and velocity of a body are given,
subsequent positions and velocities can be computed, although the force
may vary with time or position; in the latter case, Newton's calculus must be
This simple law contained another important aspect: Each body has an
inherent property, its inertial mass, which influences its motion. The greater
this mass, the slower the change of velocity when a given force is impressed.
Even today, the law retains its practical utility, as long as the body is not very
small, not very massive, and not moving extremely rapidly.
Newton's laws of motion are three physical laws which provide
relationships between the forces acting on a body and the motion of the
The net force on an object is the vector sum
of all the forces acting on the object.
Newton's first law says that if this sum is
zero, the state of motion of the object does
not change. Essentially, it makes the
following two points:
An object that is not moving will not move
until a net force acts upon it.
An object that is in motion will not change its
velocity (accelerate) until a net force acts
IN OTHER WORDS:-
Newton’s first law states “A body in motion
remains in motion (with constant velocity)
unless acted upon by an external force.” Rest,
in Newton’s laws, is merely an example of
motion with zero velocity. So force is defined
as the agency that changes the state of
motion, and thus the velocity, of a body.
This is often paraphrased as "zero net
force implies zero acceleration”.
Law of Inertia
NEWTON’s SECOND LAW
The rate of change of momentum of a body is
proportional to the resultant force acting on
the body and is in the same direction.
Using modern symbolic notation, Newton's second
law can be written as a vector differential equation:
is the force vector
is the velocity vector
If the mass of the object in question is constant, as it always is in classical
physics, this differential equation can be rewritten as:
is the acceleration.
Taking Special Relativity into consideration, the equation becomes
m0 is the rest mass or invariant mass.
c is the speed of light.
Newton’s second law relates net force and acceleration. A net force on an
object will accelerate it—that is, change its velocity. The acceleration will be
proportional to the magnitude of the force and in the same direction as the
force. The proportionality constant is the mass, m, of the object.
F = ma
NEWTON’s SECOND LAW
In the International System of Units (also known as SI, after
the initials of Système International), acceleration, a, is
measured in meters per second per second. Mass is
measured in kilograms; force, F, in newtons. A newton is
defined as the force necessary to impart to a mass of 1 kg an
acceleration of 1 m/sec/sec; this is equivalent to about
A massive object will require a greater force for a given acceleration
than a small, light object. What is remarkable is that mass, which is a
measure of the inertia of an object (inertia is its reluctance to change
velocity), is also a measure of the gravitational attraction that the object
exerts on other objects.
The second law holds in the original form, which says that the
force is the derivative of the momentum of the object with respect to
time, but some of the newer versions of the second law (such as the
constant mass approximation above) do not hold at relativistic
Newton’s third law of motion
states that an object experiences a
force because it is interacting with
some other object. The force that
object 1 exerts on object 2 must be
of the same magnitude but in the
opposite direction as the force that
object 2 exerts on object 1. If, for
example, a large adult gently
shoves away a child on a skating
rink, in addition to the force the
adult imparts on the child, the
child imparts an equal but
oppositely directed force on the
adult. Because the mass of the
adult is larger, however, the
acceleration of the adult will be
Law of Reciprocal Actions
This law of motion is commonly paraphrased as: "To every action force
there is an equal, but opposite, reaction force".
All forces occur in pairs, and these two forces are equal in
magnitude and opposite in direction.
To every Action there is always opposed an equal Reaction: or the
mutual actions of two bodies upon each other are always equal, and
directed to contrary parts.
Whatever draws or presses another is as much drawn or pressed by that
other. If you press a stone with your finger, the finger is also pressed by
the stone. If a horse draws a stone tyed to a rope, the horse (if I may so
say) will be equally drawn back towards the stone: For the distended
rope, by the same endeavour to relax or unbend it self, will draw the
horse as much towards the stone, as it does the stone towards the horse,
and will obstruct the progress of the one as much as it advances that of
As shown in the diagram opposite,
the skaters' forces on each other are
equal in magnitude, and opposite in
direction. Although the forces are
equal, the accelerations are not: the
less massive skater will have a greater
acceleration due to Newton's second
law. It is important to note that the
action/reaction pair act on different
objects and do not cancel each other
out. The two forces in Newton's third
law are of the same type, e.g., if the
road exerts a forward frictional force
on an accelerating car's tyres, then it
is also a frictional force that Newton's
third law predicts for the tyres
pushing backward on the road.
To every Action there is always
opposed an equal Reaction.
Whenever a particle A exerts a force on another particle B, B
simultaneously exerts a force on A with the same magnitude in the
opposite direction. The strong form of the law further postulates that
these two forces act along the same line. This law is often simplified into
the sentence "Every action has an equal and opposite reaction".
Newton’s third law also requires the conservation of momentum, or the
product of mass and velocity.
For an isolated system, with no external forces acting on it, the
momentum must remain constant.
In the example of the adult and child on the skating rink, their initial
velocities are zero, and thus the initial momentum of the system is zero.
During the interaction, internal forces are at work between adult and
child, but net external forces equal zero. Therefore, the momentum of
the system must remain zero. After the adult pushes the child away, the
product of the large mass and small velocity of the adult must equal the
product of the small mass and large velocity of the child. The momenta
are equal in magnitude but opposite in direction, thus adding to zero.
By:- Avipsit Rath