Concept of Gravitation
Introduction :- The force of attraction between two bodies
by which all bodies attracts towards earth.
Universal Law of Gravitation :- The magnitude of this
gravitation force is directly proportional to the product of masses and inversely
proportional to square of distance between them.
Let m1 and m2 masses are located at r distance from each
other.
F ∝ m1 m2 ….(1)
F ∝
r^2 …..(2)
By equation 1 and 2 we say that
F ∝ m1 * m2 / r^2
F = G m1 m2 / r^2
Where G = Gravitational Constant
G = 6.67 * 10^(-11) (N
m^2) / Kg ^2
If m1 = m2 = 1 Kg and
r = 1 m
F = G
The gravitational constant is equal to the force of
attraction when unit masses put at unit distance.
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Force of Gravitation on earth
1. It binds the objects on earth.
2. It attract all the object towards earth.
Acceleration Due to Gravity
When a object fall freely due to the attraction of earth at
that time increase in velocity per second of object, known as acceleration. It
is represented by ‘g’.
Where g = 9.8
Calculate the value of ‘g’
We know that G = 6.67
* 10^(-11) N m^2 / Kg^2
Mass of earth = 6 * 10^24 Kg
R = 6.4 * 10^6 m
We also know that
g = G M / R
= { 6.67*10^(-11) *
6 * 10^24 } / 6.4 * 10^6
= 9.8 m / sec^2
Note 1:- It does not depend on shape and size of object.
Note 2:- If we go upward from earth surface or downward from
earth surface in both cases the value of gravity ‘g’ decreases.
Mass :- The physical property of any object that it shows the
magnitude of any object. It shows the strength of gravitation force. It is
represented by ‘m’.
Unit of mass = Kg
Weight :- It is the product of mass ‘m’ with gravity ‘g’. It
is represented by ‘W’.
Unit of weight = Kg
W = m g
Note 3 :- The direction of weight is always vertical
downward.
Free Fall :- When a object is falling from a certain height
towards the earth due to the gravitation force, is called free fall of object.
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Mass of object on moon :- Mass of object feels 1/6 on the
moon because the size of moon is 1/10 time of earth. Due to lesser in size the
gravitational force is less on the moon. So we feel weightless on the moon.
Thrust and Pressure
Thrust :- The force
exerted on any area perpendicularly is known as Thrust.
Example :- Force exert on board pin by our thumb.
Pressure :- The force per unit area is known as Pressure.
P = F / A
Unit = N / m^2
Buoyancy :- The force exerted by the fluid on the object
immersed in it, is known as Buoyancy.
Archimedes’ Principle :- According to the Archimedes’
Principle, if the weight of water displaced by the water is less than the
weight of object it means object will sink. In other hand if the weight of
water displaced is equal to the weight of object it means the object floats on
it.
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