## Force

The force is the external factor which changes or tends to change state of object.

- The definitin a force is given by first law of motion given by newton
- Its measurement is given by second law of motion
- F=m.a = Mass x acceleration
- Its SI unit is Newton.

## Gravitation

The force of attraction between two bodies is called – Gravitation

Diagram:

- Gravitation is the force and its unit is Newton (N)
- It is denoted by F
- F=G M1 M2

dz

Where ,

M1 & M2 = Mass

d= distance

G= universal gravitational constant

=6.61×10¯¹¹Nm²kg-²

## Gravity

The gravity is the force of attraction one should be bodies in which at least one should be heavenly body.

Diagram:

- F = GMm⁄d²

Where ,

M = Mass of heavenly body

m =Mass of object

d= distance

Example

a) moon and ocean

b) Earth and aeroplane

c) Earth and sun

d) Earth and moon

- Example of gravitation

a) table & book

b) Pen & copy

c) Tree & building

d) vehicale & road

e) Nucleus & electron, etc

## Universal law of Gravitation

It is given by sir I . Newton .

a) The Force of attraction is the directly proportional to the product of masses of two bodies

b) The Force of attraction is the inversely proportional to the square of distance between

From a & b

Where ,

d = distance

G = Universal gravitational constant

= 6. 67x 10–¹¹ Nm² kg –²

## Universal Gravitational contact ( G )

we known that ,

The universal gravitational constant (G) is the force of attraction when two bodies of mass 1kg is a aparted by 1m

G= F x d²⁄ M1 M2

= Nm²⁄kg² = Nm²/ kg²

= Nm² kg–²

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