# Gravitation

### Gravitation

Gravitation, also called gravity, Gravity is everywhere, it is the force that keeps us stuck to the ground, drives the planets around the sun and the same force that pulls you down a slide. So, what is gravity?

Gravity is the force of attraction between any two bodies in this universe, yes everything attracts everything else in the universe with some amount of force, but this force is too weak to be observed in most of the cases. Sir Isaac Newton proposed the universal law of gravitation in the year 1680. So, what is the law of gravity?

The law of gravity states that any two bodies in the universe attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

Force of Gravitation: Consider two bodies A and B with mass m₁ and m₂ respectively, then according to newton’s law of gravitation body A and B will attract each other with a same force (F₁ = F₂ = F) which is proportional to the product of their masses and inversely proportional to the square of the distance between them hence,

F = m₁m₂

$$F\,\,=\,\,\frac{1}{{{r}^{2}}}$$

To get an equation we will now introduce a proportionality constant in this expression,

$$F\,\,=\,\,G\frac{{{m}_{1}}{{m}_{2}}}{{{r}^{2}}}$$

Where,

G = Gravitational Constant = 6.674 x 10⁻¹¹ Nm²/kg².

On earth the force of gravity acting on a body would be that body’s weight, this explains to us why astronauts experience less weight on the surface of moon and can easily jump and stay airborne for several seconds, as the mass of moon is approximately 80 times less than that of earth and the radius of moon is ¼ of that of earth’s, therefore, using the law of gravitation the force of gravity on the surface of moon is roughly ⅙ of that on earth.

Applications: Gravity has various applications, most of our deep space missions and other interplanetary missions like the mars orbiter mission – Mangalyaan made use of what is called interplanetary slingshot which basically means using gravity of other celestial bodies like planets and moons to propel a spacecraft, this is the most efficient mode of transport, gravity is used to power hydroelectric power plants where the flowing of water downstream due to gravity rotates a turbine to generate electricity.