## Gravitation Define, Gravitation Notes Class 9

**Gravitation Define, Gravitation Notes Class 9:** In 1986, Newton said that: – “Every particle of matter in the universe attracts another particle towards itself. This only is the ‘force of gravity.”

*the formula for gravitational force: *

**F = Gm1m2 / r2**

**Universal Law of Gravitation**

**Newton’s law of Gravitation**

According to Newton’s law of gravity, “The force of attraction between two particles of matter is proportional to the product of the masses of the particles and inversely proportional to the square of the distance between them”.

The direction of this force is along the line joining the two particles.

Let two particles whose masses are m1 and m2 respectively are located at a distance ‘r’ from each other.

If the gravitational force between them is F then

according to the law of gravity

F~m1m2

F~1/r2

F ~ m1m2/ r2

F = Gm1m2/r2

Here, G is the proportionality constant, which is called the *universal gravitational constant.*

## Value of G

**In SI system **

G= 6.67 × 10 -11 Newton×m2/kg.2

**In CGS method**

G= 6.67×10^{-8} d in – cm^{2} \ g ^{2 }

## Acceleration due to Gravity (g)

The rate of change of an object falling towards the earth due to the gravitational force of the earth calls the acceleration due to gravity.

It is represented by** ‘g’.** It does not depend on the size, shape, mass, etc. of the object. Its average value on the earth plane is 9.8 m / s2.

Let the mass of the earth be M and radius R and the total mass of the earth is concentrates at its center. Now if the object of mass m is at a distance r from the center of the earth, then the gravitational force acting on the object.

F = GMm/r^{2}

g = GM/R^{2}

## Gravitational potential Energy

The gravitational potential energy of a particle placed at a point in a gravitational field is defined by the amount of work required to bring it from infinity to that point without changing its kinetic energy.

**Gravitational Potential**

The gravitational field around a massless body cannot be express only by the intensity of the gravitational field but

Can also be expressed by a scalar function Which calls the **gravitational potential V.**

**OR**

Work done in bringing a unit mass from infinity to a point without changing its kinetic energy. That point calls the **gravitational potential.**

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