## Reference Notes | SLC

Newton’s Universal Law of Gravitation

For: Science Class 10

**Force**

It is defined as a push or pull that change or tends to change the state of rest or of uniform motion of a body along a straight line.

**Newton’s Universal law of gravitation**

“Everybody in this universe attracts every another body with a force which is:

- directly proportional to the product of their masses and,
- inversely proportional to the square of the distance between their centers”.

Consider a body of mass m_{1} attracts another body of mass m_{2} with a force F towards its centre O_{1}. The body of mass m_{2} in turn attracts the body of mass m_{1} with the same force F towards its centre O_{2}. Suppose the distance between their centers is‘d’ then, according to Newton’s universal law of gravitation, we have:

Where G is called a proportionally constant or universal gravitational constant. The value of The G is determined form experiment. Hence, the equation (iii) gives the measure of the gravitational force between two masses.

**Universal gravitational constant ‘G’**

Universal gravitational constant ‘G’ can be defined as the force of gravitation that is exerted between two unit masses, separated from one another by a unit distance.

* The SI unit of G is Nm ^{2}kg^{-2}.*

*The approximate value of G is 6.67 X 10*

^{-11}Nm^{2}kg^{-2}.**Properties of G**

i. The value of G is independent of the nature and chemical composition of the masses of the bodies, and the medium in which the bodies are occurred.

ii. The value of G is unaffected by temperature and pressure.

**Consequences of gravitational force**

i. The presence of solar system and planets revolve round the sun due to the presence of gravitational force.

ii. The presence of atmosphere on the earth is due to the gravitational force.

iii. The gravitational force of the earth keeps us firmly on the surface of the earth.

iv. Tides in seas and oceans are due to the gravitational force of the sun and moon.

**Special features of gravitational force**

i. The gravitational forces between two bodies constitute on action and reaction pair.

ii. The gravitational force between two bodies does not depend upon the nature of the intervening medium.

iii. The gravitational force between light bodies is extremely small and hence such smaller force is not felt in practice. However, it becomes appreciable in case of massive bodies.