- Books Name
- Science Made Easy Science Book

- Publication
- Science Made Easy

- Course
- CBSE Class 9

- Subject
- Science

**Introduction**

→ **Gravitational Force of Earth**: If we release a small stone without pushing it from a height, it

accelerates towards earth. Earth attracts everything towards it by an unseen force of attraction. This force of attraction is known as gravitation or gravitational pull

**Universal Law of Gravitation**

**→** Sir Isaac Newton in 1687 proposed a law about the force of attraction between the

objects in the universe which is known as Newton’s law of gravitation.

**According to Universal law of Gravitation**

→ Every mass in this universe attracts every other mass with a force which is directly proportional to

the product of two masses and inversely proportional to the square of the distance between them

**• Let masses (M) and (m) of two objects are distance (d) apart, then force of attraction (F) between**

**them**

F ∝ M×m

F ∝ 1/d^{2}

F ∝ Mm/d^{2}

F = (GMm)/d^{2}

where,

G is a constant and is known as Gravitational constant.

Value of G = 6.67×10^{-11} Nm^{2}/kg^{2}

G is called universal gravitational constant.

→ If unit of F is in Newton, m is in kg, d is in mere, then unit of G can be calculated as :

G = (F×d^{2})/Mm, therefor unit will be Nm^{2}/kg^{2}

^{Importance of universal law of gravitation}

^{(i) The force that binds us to the earth.}

^{(ii) The motion of moon around the earth.}

^{(iii) The motion of earth around the sun.}

^{(iv) The tides due to moon and the sun.}