1318 words - 6 pages

Newton's Law of Universal GravitationGravity if one of the four fundamental forces in the universe. Thoughthe fundamental principles of it eluded scientists until Sir Isaac Newton was able to mathematically describe it in 1687 (Eddington 93). Gravity plays a serious part in everyday actions as it keeps everything on the ground; without gravity everything would be immobile unless a force was applied (then it would move infinitely because there would be no force to stop it).Perhaps, the best place to start then would be with such a simple item as an apple (after all it is what "sparked" Newton's creativity). The apple is one of the two curiosities (the other being the moon) that led Newton to ...view middle of the document...

Newton realized then that the moon and the apple were both being pulled towards Earth at the same rate but yet the moon was the only one who resisted the force and stayed in its elliptical orbit (Eddington 94). Newton's Third Law of Motion says that every force exerted by one object on another is equal to a force, but opposite in direction, exerted be the second object on the first (every reaction has an equal but opposite reaction). So the force of the earth pulling the apple to the ground is proportionally the same as the force the apple exerts back on the earth.Now Johannes Kepler lived some forty-five years before Isaac Newton. And he showed that the orbits of the planets in our solar system were elliptical. When the time of Newton came around he mathematically proved that, if Kepler's First Law was true, then the force on a planet varied inversely with the square of the distance between the planet and the sun. He did this using Kepler's Third Law (Zitzewitz 160). The distance in this formula is from the center of the masses and is the average distance over their entire period. It is also important to note that the force acted in the direction of this line (an important factor when dealing with vectors) (Zitzewitz 160).Newton, confident that his idea of all objects exerting a force back on Earth, devised a formula for Universal Gravitation. It is important to note that Newton was not the first to think of Universal Gravitation, he was just the first one to make considerable and remarkable proofs for it based on mathematical explanations. He said that if force is relative to the mass of an object and it's acceleration then the force between two objects must also be the same. Thus he came up with the first part of the equation. Also, as he had proved earlier using Kepler's Third Law of Motion, that the force between two objects is inversely proportional to their distances squared (an inverse square law), then that must also be part of the Universal Gravitation equation. Thus we know that the two masses and the distance are related to the force; and because the distance is inversely proportional then the product of the masses divided by the distance between their centers squared must equal the force between the two objects (Zitzewitz 161).Now earlier, Newton had proved that the force on an object was proportional to an object's mass and its acceleration. And the equation that he had formulated so far did not include anything that would...

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