Gravity is most accurately described by the general theory of relativity (proposed by Albert Einstein in 1915) which describes gravity not as a force, but as a consequence of the curvature of spacetime caused by the uneven distribution of mass. The most extreme example of this curvature of spacetime is a black hole, from which nothing—not even light—can escape once past the black hole's event horizon. However, for most applications, gravity is well approximated by Newton's law of universal gravitation, which describes gravity as a force which causes any two bodies to be attracted to each other, with the force 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 forces of physics, approximately 1038 times weaker than the strong force, 1036 times weaker than the electromagnetic force and 1029 times weaker than the weak force. As a consequence, it has no significant influence at the level of subatomic particles. In contrast, it is the dominant force at the macroscopic scale, and is the cause of the formation, shape and trajectory (orbit) of astronomical bodies. For example, gravity causes the Earth and the other planets to orbit the Sun, it also causes the Moon to orbit the Earth, and causes the formation of tides, the formation and evolution of the Solar System, stars and galaxies.
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| Aryabhata (476 CE - 550 CE) |
History of Gravitational Theory
Aryabhata (the first of the major mathematician-astronomers from the classical age of Indian mathematics and Indian astronomy) first identified the force to explain why objects do not fall when the earth rotates. Brahmagupta described gravity as an attractive force and used the term "gruhtvaakarshan" for gravity.Modern work on gravitational theory began with the work of Galileo Galilei in the late 16th and early 17th centuries. In his famous (though possibly apocryphal) experiment dropping balls from the Tower of Pisa, and later with careful measurements of balls rolling down inclines, Galileo showed that gravitational acceleration is the same for all objects. This was a major departure from Aristotle's belief that heavier objects have a higher gravitational acceleration. Galileo postulated air resistance as the reason that objects with less mass fall more slowly in an atmosphere. Galileo's work set the stage for the formulation of Newton's theory of gravity.
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| English phycist and mathematician, Sir Isaac Newton (1642 - 1727) |
Where F is the force, m1 and m2 are the masses of the objects interacting, r is the distance between the centers of the masses and G is the gravitational constant.
Newton's theory enjoyed its greatest success when it was used to predict the existence of Neptune based on motions of Uranus that could not be accounted for by the actions of the other planets. Calculations by both John Couch Adams and Urbain Le Verrier predicted the general position of the planet, and Le Verrier's calculations are what led Johann Gottfried Galle to the discovery of Neptune.
A discrepancy in Mercury's orbit pointed out flaws in Newton's theory. By the end of the 19th century, it was known that its orbit showed slight perturbations that could not be accounted for entirely under Newton's theory, but all searches for another perturbing body (such as a planet orbiting the Sun even closer than Mercury) had been fruitless. The issue was resolved in 1915 by Albert Einstein's new theory of general relativity, which accounted for the small discrepancy in Mercury's orbit. This discrepancy was the advance in the perihelion of Mercury of 42.98 arcseconds per century.
Although Newton's theory has been superseded by Einstein's general relativity, most modern non-relativistic gravitational calculations are still made using Newton's theory because it is simpler to work with and it gives sufficiently accurate results for most applications involving sufficiently small masses, speeds and energies.
Equivalence Principle
The equivalence principle, explored by a succession of researchers including Galileo, Loránd Eötvös, and Einstein, expresses the idea that all objects fall in the same way, and that the effects of gravity are indistinguishable from certain aspects of acceleration and deceleration. The simplest way to test the weak equivalence principle is to drop two objects of different masses or compositions in a vacuum and see whether they hit the ground at the same time. Such experiments demonstrate that all objects fall at the same rate when other forces (such as air resistance and electromagnetic effects) are negligible. More sophisticated tests use a torsion balance of a type invented by Eötvös. Satellite experiments, for example STEP, are planned for more accurate experiments in space.
Earth's Gravity
Every planetary body (including the Earth) is surrounded by its own gravitational field, which can be conceptualized with Newtonian physics as exerting an attractive force on all objects. Assuming a spherically symmetrical planet, the strength of this field at any given point above the surface is proportional to the planetary body's mass and inversely proportional to the square of the distance from the center of the body.
That value, denoted g, is g = 9.80665 m/s2 (32.1740 ft/s2).The strength of the gravitational field is numerically equal to the acceleration of objects under its influence. The rate of acceleration of falling objects near the Earth's surface varies very slightly depending on latitude, surface features such as mountains and ridges, and perhaps unusually high or low sub-surface densities. For purposes of weights and measures, a standard gravity value is defined by the International Bureau of Weights and Measures, under the International System of Units(SI).
The standard value of 9.80665 m/s2 is the one originally adopted by the International Committee on Weights and Measures in 1901 for 45° latitude, even though it has been shown to be too high by about five parts in ten thousand. This value has persisted in meteorology and in some standard atmospheres as the value for 45° latitude even though it applies more precisely to latitude of 45°32'33".
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| If an object with comparable mass to that of the Earth were to fall towards it, then the corresponding acceleration of the Earth would be observable. |
Assuming the standardized value for g and ignoring air resistance, this means that an object falling freely near the Earth's surface increases its velocity by 9.80665 m/s (32.1740 ft/s or 22 mph) for each second of its descent. Thus, an object starting from rest will attain a velocity of 9.80665 m/s (32.1740 ft/s) after one second, approximately 19.62 m/s (64.4 ft/s) after two seconds, and so on, adding 9.80665 m/s (32.1740 ft/s) to each resulting velocity. Also, again ignoring air resistance, any and all objects, when dropped from the same height, will hit the ground at the same time.
According to Newton's 3rd Law, the Earth itself experiences a force equal in magnitude and opposite in direction to that which it exerts on a falling object. This means that the Earth also accelerates towards the object until they collide. Because the mass of the Earth is huge, however, the acceleration imparted to the Earth by this opposite force is negligible in comparison to the object's. If the object does not bounce after it has collided with the Earth, each of them then exerts a repulsive contact force on the other which effectively balances the attractive force of gravity and prevents further acceleration.
The force of gravity on Earth is the resultant (vector sum) of two forces: (a) The gravitational attraction in accordance with Newton's universal law of gravitation, and (b) the centrifugal force, which results from the choice of an earthbound, rotating frame of reference. The force of gravity is the weakest at the equator because of the centrifugal force caused by the Earth's rotation and because points on the equator are furthest from the center of the Earth. The force of gravity varies with latitude and increases from about 9.780 m/s2 at the Equator to about 9.832 m/s2 at the poles.
5 Places on Earth where Gravity Becomes Zero
Let's get to the best part, have you ever find a place where your foot don't even step on the ground anymore ? Well if you haven't, let's see these 5 places !
Because of the gravitational force we walk on the earth, meaning that it binds everything at the surface of the earth. But there are some places on earth where the gravitational force becomes zero and strange phenomena occur. Through this article, you will learn about the places where gravitational force does not work or becomes zero.
Gravity is the force that holds the sun and other planets in the solar system. This is the force that holds us and everything on the surface of the earth or draws towards the center of the Earth. In simple words, if you bend more, then you can fall, but where the gravitational force does not work, instead of after bending you will not be able to fall. We all know about Newton's popular story that when he was sitting under an apple tree, an apple fall on his head and suddenly he started thinking why anything falls from the top. After this he propounded the law of gravity or law of universal gravitation, according to which the force of attraction acting between any two particles is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. But there are some places where gravity becomes zero on earth or where gravitational force does not work.
1. Mystery Spot, Santa Cruz California
Source: www.firesideinnsantacruz.com
This place was discovered in 1939 by a group of surveyors and was opened to the public by George Prather in 1940. They stated that during the time of searching the place they felt that some different forces work here. They claim that there is some different type of irregularity in the magnetic field here and this magnetic irregularity is seen only in 150 square feet of the circular area, which is also called Mystery Spot. This is a place where you will see strange irregularities in gravity, such as flowing of water in the upward direction, deflection of magnetic compasses at different angles, changes in the size of people and things. At this place you can also stand at an angle without falling down.
2. St. Ignace mystery spot, Michigan
Source: www.sideshowworld.com
When some people were doing surveys in the 1950s, suddenly their devices stopped working secretly, when they conducted extensive surveys of this place, they found that it was only happening in the area of 300 square feet. Not only this, animals in this area also refrain from coming. Even here also some strange phenomena are seen due to the lack of gravitational force, such as standing on the wall, people can do a variety of tricks such as keeping the chair on the wall and enjoy sitting in which two feet of the chair remains on the wall and two bizarre in the air, after staying here for a long time, you will feel that your head is getting lighter.
3. Cosmos Mystery Area, Rapid City
Source: www.cloudfront.net.com
Moving to this place, you will see some trees which are mysteriously bowed. Like mystery spots, you can stand here without falling at an angle. Along with this some more phenomena’s were seen like the ball going upward and not much that when you went upwards places felt to be changed.
4. Spook Hill, Florida
Source: www.florida-backroads-travel.com
This is a gravity hill place where the car appears to roll up the spooky hill which is an optical illusion. If you stop your vehicle or make it neutral, then you will see that it is being pulled up towards the mountain. When the Native-Americans eventually lost their land to settlers, the pioneer mail riders noticed their horses labouring downhill, which led to them nicknaming the spot “Spook Hill”.
5. Magnetic Hill, Leh
Source: www.cloudfront.net.com
It is a small route which stretches about 30 km from Leh towards Kargil and is known as the Magnetic Hill of Ladakh. On this special route of the Srinagar-Leh highway, you would see that the road ahead going uphill. However, if you turn off the engine and keep your vehicle in neutral, then on its own, it will start moving slowly and can go up to 20 kilometers per hour. It is said that behind this mysterious phenomena there is a magnetic force that pulls the car uphill. Even the aircraft passing over this region increases their altitude to avoid magnetic interference.
From this article we come to know that there are some places on the earth where strange or mysterious phenomena occurred and is said that it is because of the gravitational force which becomes zero.
Well, that's all from me about natural phenomena, hope you like it !!
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