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?

The Gravitation and Gravity
  • 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

The Image Og 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

The 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

Third Law

The 3rd Law

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