Gravitation (Introduction to Gravitation) Class - 11 Video Lecture - Class 11

hello friends this video on gravitation
part 1 is brought to you by exam Fiat
form no more fear from exams topics
which we'll cover in this lesson an
introduction universal law of
gravitation the gravitational constant
acceleration due to gravity of the earth
acceleration due to gravity below and
above the surface of the earth
gravitational potential energy Kepler's
laws escape speed earth satellites
energy of an orbiting satellite
geostationary and polar satellites and
weightlessness so let the start with
what is gravitation all of us would have
observed such phenomenon like an apple
falling down the tree to the surface of
the ground but there is a mystery behind
what makes the Apple fall to the ground
similarly you would have seen that when
you throw a ball up it comes back and
falls in your hand
similarly in a rainy season the rain
drops that is the water droplets fall
towards the ground if you see in all
these phenomenon there is some force
which is responsible for the objects
falling towards the surface of the earth
so these are the examples which we see
around us in the terrestrial world even
if you see in the universe if you see
the planetary motion there is some force
which holds the planets in a particular
orbit we all know that all the planets
move in a particular orbit so the
specific orbit of the planets are also
held by certain kind of forces so
gravitation is responsible for all such
phenomena gravitation is nothing but a
force which is exerted by the surface of
the earth so in this chapter we will
study in detail all the principles of
gravitation we will see how was the law
of
gravitation brought into the picture of
science and we'll study all the
planetary motion as well so let us go
ahead and see what made the origin of
gravitation introducing Newton's view
towards gravitation so Newton was the
scientist who actually studied about
gravitation in fact he was the one who
thought about what is gravitation and he
defined the force of gravitation so how
did this idea click Newton it once
happened that Newton was having a cup of
tea in his garden when he saw an apple
falling down the tree to the ground so
Newton thought what made this Apple fall
to the ground he did lots of studies and
investigations he performed several
experiments and finally concluded that
there was a force which is exerted by
the surface of the earth because of
which the Apple gets attracted towards
the surface of the earth and falls
towards it but then when he performs so
many experiments he concluded that it
was not only the surface of the earth
which exerts force on an object in the
entire universe all the objects exert a
force on another object that means all
the objects in this universe attract
every other object with a force so this
force was nothing but the force of
gravitation so this is how Newton deduce
to the idea of gravitation and he
defined the force of gravitation which
later came to be known as the famous
universal law of gravitation so we will
now we'll start this chapter with
universal law of gravitation
so universal law of gravitation what
does this law states see if you see the
name of the Lord is universal that means
it is true for everything something
which is universal is something which is
applicable to all the objects in this
universe so this law states that every
body in the universe
attracts every other body
with our force which is directly
proportional to the product of their
masses and inversely proportional to the
square of the distance between them that
means that any object which you see
around us or which you can think of in
this entire universe attracts every
other body so there is a force of
attraction between any two bodies in
this universe and this force of
attraction is directly proportional to
the product of their masses that means
the product of the masses of the two
bodies and it is inversely proportional
to the square of the distance between
them what do you mean by directly
proportional and inversely proportional
when I say directly proportional I mean
that if the product of the masses
increases the force will also increase
when I say inversely proportional I mean
if the square of the distance increases
the force will decrease that means if
two objects are directly proportional
that means the two objects increase or
decrease together
similarly if two quantities are
inversely proportional that means if one
quantity increases the other quantity
decreases so let us see let us suppose
we have two objects say this is a ball
of mass m1 and this is a box of mass m2
now according to universal law of
gravitation even these two objects tends
to attract each other with a force say F
like that force B F which is directly
proportional to the product of the
masses that is m1 m2 and it is inversely
proportional to the square of the
distance between them so we considered
m1 and m2 are two masses let us suppose
the distance between them is R then the
force of attraction between them is
directly proportional to the product of
the masses that means if m1 or m2
increases this force will also increase
similarly it is inversely proportional
to the
square of the distance that means closer
these two objects come the force will be
more because as as close as they come
the value of art will decrease now value
of art decreases means the value of F
will increase so this was basically the
universal law of gravitation which was
given by Newton and it holds true
universally for all the objects in this
universe now let us see the mathematical
expression for the universal law of
gravitation just now I told you in the
previous slide that the force of
gravitation is directly proportional to
the product of the masses that is M 1 M
2 and it is inversely proportional to
the square of the distance between them
now we know that that means from these
two we can say that force is directly
proportional to M 1 M 2 divided by R
square correct now to convert this
proportional to an equality we need to
introduce a constant that is we can
write this as F is equal to some
constant into M 1 M 2 by R squared right
now what is this constant this constant
is nothing but capital G that is the
universal gravitational constant so we
say that force is equal to G M 1 M 2 by
R square where G is known as the
universal gravitational constant and it
is universally constant that means its
value the value of G remains constant
everywhere in this universe this
valuable neighbor change so this is
basically the mathematical expression of
the universal law of gravitation where G
is the universal gravitational constant
M 1 M 2 are the masses of the two bodies
and R is the distance between them right
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