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JEE Main Gravitation Revision Notes

## JEE Main Gravitation Revision Notes - PDF Download

From the Latin word gravitas, the term Gravity has been derived, which means gravitation or 'weight', and it is defined as a natural phenomenon by which all things with energy or mass—including planets, galaxies, stars, and even light—are brought toward or gravitate toward one another. On planet Earth, gravity provides weight to physical objects, and the gravity of the moon causes the ocean tides. The attraction of gravitation of the original gaseous matter present in the Universe caused it to begin coalescing and forms stars and causes the stars to group together into galaxies.

So gravity is responsible for many things such as large-scale structures in the Universe. Gravity has a huge effect, although its effects become increasingly weaker as objects get far away. In 1915, gravity was most accurately described by the general theory of relativity which was proposed by Albert Einstein, which describes gravity not as a force, but as a consequence of spacetime curvature due to the uneven distribution of mass. One of the most extreme examples of this curvature of spacetime is a black hole, from which not even a single ray of light can escape once past the black hole's even horizon. For most applications, however, gravity is very well approximated by Newton's law of gravity, which clearly describes that gravity is a force, which causes any two bodies to be attracted to one another. The force is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

Gravity is the weakest of the four fundamental interactions of Physics which we know already, approximately 1038 times weaker than the strong interaction force, which is 1036 times weaker than the electromagnetic force, and 1029 times weaker than the weak interaction forces as well. As a consequence, it has no significant influence on the subatomic particle level. In contrast to this, it is the dominant interaction at the macroscopic level and is only the cause of the formation, trajectory, and shape or orbit of astronomical bodies.

The earliest possible instances of gravity in the universe, in the form of quantum gravity, gravitational singularity or supergravity, along with ordinary time and space, developed during the Planck epoch up to 10−43 seconds after the birth of the Universe, from a primeval state, example as a false vacuum, quantum vacuum or particles which are virtual, in an unknown manner. Attempts for developing a theory of gravity consistent with quantum mechanics, a quantum theory of gravity that allows gravity to be united in a common mathematical framework, a theory of everything with the other three fundamental interactions of physics, are important areas of research in that field.

### Ancient World

The ancient Greek philosopher, Archimedes discovered the center of gravity of a triangle. He also postulated that if two equal weights do not have the same center of gravity, the center of gravity of the two weights together would be in the middle of the line that joins their centers of gravity.

The Roman architect-engineer Vitruvius and in De Architectura postulated that the gravity of an object did not depend on weight but its "nature".

In ancient India, Aryabhata first identified the force to explain why objects are not thrown outward when the earth is in rotation motion. Brahmagupta described gravity as an attractive force and used the term "gurutvakarshan" to define the process of gravity.

### Newton’s Theory of Gravitation

An English mathematician Sir Isaac Newton published a theory in 1687, that hypothesizes the inverse-square law of universal gravitation. Sir Isaac Newton deduced that there must be a force reciprocally which keep the planets in their orbits, as the square of their distance from the centers about which they revolve and to keep the Moon in her orbit. It thereby compared a requisite force with the force of gravity at the surface of the Earth.

Its greatest success is enjoyed by Newton's theory when it was used to predict the Neptune existence based on motions of Uranus that could not be accounted for by the actions of the other planets. The calculations of John Couch Adams and Urbain Le Verrier predicted the general position of the planet and the discovery of Neptune by Johann Gottfried Galle was led by Le Verrier's calculations.

A flaw in Newton's theory was pointed out by the discrepancy in Mercury's orbit. It was known that its orbit showed slight perturbations that could not be accounted for entirely under Newton's theory by the end of the 19th century. However, all searches had been fruitless for another perturbing body (such as a planet orbiting the Sun even closer than Mercury). By the new theory of Albert Einstein of general relativity, the issue was resolved in 1915, which accounted for the small discrepancy in the orbit of Mercury. In the perihelion of 42.98 arc seconds per century of Mercury, this discrepancy was advanced.

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1. Define Gravitation?

Bodies exert the force of attraction on one another as a result of their masses. An example of a process that is caused by this interaction is falling off a body on the surface of the earth is due to the gravitational force.

2. Explain the Difference Between Gravity and Gravitation.

Though both the terms sound the same but they are different terms, gravitation is defined as the force between two bodies on the other hand gravity is defined as force occurring between earth and body.

3. At What Height Gravity Ends?

At sea level that is near to the surface of the earth the gravity decreases by the height such that linear extrapolation gives zero gravity at the height of half of the earth's radius and altitude in meters.

4. Why is Only Gravitational Called as a Universal Law?

This law is called so because it is applicable to all the bodies having mass. All the bodies are governed by the same law that is the law of gravitation by Newton, so it is called the universal law of gravitation.