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Introduction

Good morning, my name is Ricardo Sanchez Garcia and I will talk about Gravity. Ok lets go 

Gravitation, or gravity, is one of the four fundamental interactions of nature, and is the means by which objects with mass attract one another. In everyday life, gravitation is most familiar as the agent that lends weight to objects with mass and causes them to fall to the ground whendropped. Gravitation causes dispersed matter to coalesce, thus accounting for the existence of the Earth, the Sun, and most of the macroscopic objects in the universe. 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 convection, by which fluid flow occurs under theinfluence 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.

Modern physics describes gravitation using the general theory of relativity, in which gravitation is a consequence of the curvature of space-time which governs the motion of inertial objects. The simpler Newton's law ofuniversal gravitation provides an accurate approximation for most calculations.

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Newton's law of universal gravitation states that every massive particle in the universe attracts every other massive particle with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. (Separately it was shownthat large spherically-symmetrical masses attract and are attracted as if all their mass were concentrated at their centers.) This is a general physical law derived from empirical observations by what Newton called induction. It is a part of classical mechanics and was formulated in Newton's work Philosophiae Naturalis Principia Mathematica   ("the Principia"), first published on 5 July 1687.(When Newton's book was presented in 1686 to the Royal Society, Robert Hooke made a claim that Newton had obtained the inverse square law from him – see History section below.) In modern language, the law states the following:

Every point mass attracts every single other point mass by a force pointing along the line intersecting both points. The force is directly proportional to the product of thetwo masses and inversely proportional to the square of the distance between the point masses:

[pic],where:

· F is the magnitude of the gravitational force between the two point masses,
· G is the gravitational constant. 
· m1 is the mass of the first point mass,
· m2 is the mass of the second point mass, and
· r is the distance between the two point masses.

AssumingSI unit, F is measured in newtons(N), m1 and m2 in kilograms(kg), r in meters(m), and the constant G is approximately equal to 6.673×10-11 N m2 kg-2. The value of the constant G was first accurately determined from the results of the Cavendish experiment conducted by the British scientist Henry Cavendish in 1798, although Cavendish did not himself calculate a numerical value for G. This experiment wasalso the first test of Newton's theory of gravitation between masses in the laboratory. It took place 111 years after the publication of Newton's Principia and 71 years after Newton's death, so none of Newton's calculations could use the value of G; instead he could only calculate a force relative to another force.

Newton's law of gravitation resembles Columbus law of electrical forces, whichis used to calculate the magnitude of electrical force between two charged bodies. Both are inverse square laws, in which force is inversely proportional to the square of the distance between the bodies. Coulomb's Law has the product of two charges in place of the product of the masses, and the electrostatic constant in place of the gravitational constant.

Newton's law has since been...