Gravitation theory


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Gravitation theory

  2. 2. GRAVITATION THEORY • Gravitation or gravity is a natural phenomenon by which all physical bodies attract each other. It is experienced at the agent that gives weight to objects with a mass which cause them to fall when they are dropped. • Gravitation is one of the four fundamental interactions of nature, in modern Physics, the phenomenon of gravitation is most accurately described by the general theory of relativity by Einstein. Einstein showed that gravitation was not an attractive force, but a manifestation of the distortion of the geometry of space-time under the influence of objects that occupy it.
  3. 3. The Newton's law of universal gravitation postulates the gravity force proportional to masses of interacting bodies and inversely proportional to the square of the distance between them. It provides an accurate approximation for most of the physical situations.
  4. 4. From a cosmological perspective, gravitation causes dispersed of matter to coalesce, and coalesced matter to remain it intact, this explained the existence of planets, stars, galaxies and most of the macroscopic objects in the universe..
  5. 5. Gravity is also important for some factors of the Earth, it is responsible for keeping the Earth and the other planets in their orbits around the Sun, for keeping the Moon in its orbit around the Earth, for the formation of tides, for natural convection, by which fluid flow occurs under the influence of a density gradient and gravity, for heating the interiors of forming stars and planets to very high temperatures, and for various other phenomena observed on Earth and throughout the universe.
  6. 6. EARTH’S GRAVITY • Every body (including the Earth) is surrounded by its own gravitational field, which applies an attractive force on all objects. The strength of this field is proportional to the planetary body's mass and inversely proportional to the square of the distance from the centre of the body. • The strength of the gravitational field is numerically equal to the acceleration of objects under its influence, and its value at the Earth's surface, denoted g = 9.80665 m/s2 = 32.1740 ft/s2). • This means that, without air resistance, an object falling freely near the Earth's surface increases its velocity 9.80665 m/s. so an object starting from rest will gain a velocity of 9.80665 m/s after one second and also all objects, when dropped from the same height, will hit the ground at the same time.
  7. 7. • According to Newton’s 3rd Law, the Earth also accelerates towards the object until they collide. Because the mass of the Earth is huge the acceleration imparted to the Earth by this opposite force is very low in comparison to the object ones. • The force of gravity on Earth is the resultant of the sum of two forces: (a) The gravitational attraction, and (b) the centrifugal force. At the equator, the force of gravity is the lowest due to the centrifugal force caused by the Earth's rotation. The force of gravity varies with latitude and becomes stronger as you increase in latitude toward the poles. The standard value of 9.80665 m/s2 is the one originally
  8. 8. GRAVITY AND ASTRONOMY The discovery and application of Newton's law of gravity accounts for the detailed information we have about the planets in our solar system, the mass of the Sun, the distance to stars, quasars and even the theory of dark matter. Although we have not travelled to all the planets nor to the Sun, we know their masses. These masses are obtained by applying the laws of gravity to the measured characteristics of the orbit. In space an object maintains its orbit because of the force of gravity acting upon it. Planets orbit stars, stars orbit Galactic Centres, galaxies orbit a centre of mass in clusters, and clusters orbit in super clusters. The force of gravity exerted on one object by another is directly proportional to the product of those objects' masses and inversely proportional to the square of the distance between them.
  9. 9. ISAAC NEWTON (25 December 1642 – 20 March 1727) Isaac Newton was an English physicist and mathematician who is Widely Regarded as one of the Most Influential scientists of all time and as a key figure in the scientific revolution. His book, Philosophiæ Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), first published in 1687, laid the foundations for classical mechanics of Most. Also Newton made ​seminal Contributions to optics and shares credit with Gottfried Leibniz for the invention of the infinitesimal calculus.
  10. 10. NEWTON’S PRINCIPIA Newton's Principia formulated the laws of motion and universal gravitation That Dominated scientists' view of the physical universe for the next three centuries. It Also Demonstrated That the motion of objects on the Earth and of celestial bodies That Could be Described by the same principles. By Deriving Kepler's laws of planetary motion from his mathematical description of gravity, Newton removed the last Doubts about the validity of the heliocentric model of the cosmos.
  11. 11. REFLECTING TELESCOPE Newton built the first practical reflecting telescope and developed a theory of color based on the observation that a prism decomposes white light into the many colors of the visible spectrum. He also formulated an empirical law of cooling and studied the speed of sound. In addition to his work on the calculus, as a mathematician Newton contributed to the study of power series, generalized the binomial theorem to noninteger exponents, and developed Newton's method for approximating the roots of a function.
  12. 12. NEWTON’S THEORY OF GRAVITATION His book (Principia) hypothesizes the inverse-square law of universal gravitation. In his own words, “I deduced that the forces which keep the planets in their orbs must be reciprocally as the squares of their distances requisite to keep the Moon in her Orb with the force of gravity at the surface of the Earth; and found them answer pretty nearly. from the centers about which they revolve: and thereby compared the force.
  13. 13. 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.
  14. 14. 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 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.
  15. 15. Although Newton's theory has been superseded, most modern non-relativistic gravitational calculations are still made using Newton's theory because it is a much simpler theory to work with than general relativity, and gives sufficiently accurate results for most applications involving sufficiently small masses, speeds and energies.
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