# Gravity: Newton՚s Law of Gravitation, Kepler՚s Law of Planetary Motion (For CBSE, ICSE, IAS, NET, NRA 2022)

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## What is Gravitation?

- Gravitation or just gravity is the force of attraction between any two bodies
- When we talk about gravitation or gravity it is a naturally occurring phenomenon or a force which exists among all material objects in the universe.
- All the objects in the universe attract each other with a certain amount of force, but in most of the cases, the force is too weak to be observed due to the very large distance of separation.
- Though, gravity՚s range is infinite but the effect becomes weaker as objects move away.
- Each body in this universe attracts other bodies towards itself with a force known as Gravitational Force, thus gravitation is a study of the interaction between two masses.
- The heavier one is called source mass and the lighter one is called test mass, Out of the two masses,

## Newton՚s Law of Gravitation

- The newton՚s law of universal gravitation shows us that the gravitational force of attraction between two substance let their masses be and , separated by the distance (r)
- According to Newton՚s law of gravitation, Every particle in the universe attracts every other particle with a force whose magnitude is,
- Directly proportional to the product of their masses i.e.. ,
- Inversely proportional to the square of the distance between their centre i.e.. ,

## Kepler՚s Law of Planetary Motion

Kepler՚s laws of planetary motion state that:

(a) All planets move in elliptical orbits with the Sun at one of the focal points

### First Law

(b) The radius vector drawn from the Sun to a planet sweeps out equal areas in equal time intervals. This follows from the fact that the force of gravitation on the planet is central and hence angular momentum is conserved.

### Second Law

(C) The square of the orbital period of a planet is proportional to the cube of the semi-major axis of the elliptical orbit of the planet