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Sir Isaac Newton Fundamentals to physics Gravitation With all the things that Isaac Newton did some of his most renowned works was with that of gravitation. Newton was one of the foremost scientific intellects so fall time. Newton is also considered one of, if not the most influential astronomers of all time (web 1). Besides his contributions to this field he gave physicists an easier way and more comprehendible way of doing physics. This was due to these three laws that he came up with that where named after him. They were as follows: Newton’s First Law A body at rest will remain at a rest or a body in motion will remain in constant motion unless a force is applied to it. Newton’s Second Law F=ma (Force= Mass x Acceleration) (One of the most used equations in physics) Newton’s Third Law For every force there is an equal and opposite reaction. Newton’s first law applies to anything that is in motion or standing still. It goes on to say that everything will stay the way it was unless a force is applied to it (Holliday). Like a ball will stay in one place forever if nothing ever applies a force to it. Newton’s second law applies to just about every single equation that we use today in physics. This equation gives us the acceleration due to gravity, 9.8 meters per second. It is also used in every equation that has a mass in it because it gives the weight of the mass when it is derived. Newton’s third law is basic common sense that says that when something gives a force there is an equal force being applied to it. Like when you push on a wall the wall pushes back with the same force and also the earth pulling down on you, you are pushing on the earth(web 3). Besides these three laws that Newton gave us he also gave us the reason behind why the moon doesn’t fall out of the sky (web 4). To understand some of the principles in this paper you have to understand some of the language that is used in physics. One term that is used is “in a Newtonian world”. This refers to the fact that a lot of Newton’s principles only work if there is no friction at all. This means no air friction acting on objects and no friction form the ground on objects. This makes it so there is nothing resisting the objects as they fall or move. One example of this can be seen in figure 1. In this figure you can see that the feather and an apple are falling at exactly the same rate. But how can this be, everyone know that an apple will hit the ground before a feather but in the picture they fall at the same rate? This is because there is no friction in this picture all of the air has been sucked out of the room-causing there to be no friction. From this only one force is acting on the feather and apple and that is gravity. They both fall at 9.8 meters per second and so they both hit the ground at exactly the same time. This only happens with no friction and is usually accomplished when all the air is sucked out of a room with a compressor or other device that takes air out of a room (Holliday). One of my favorite and interesting demonstrations with gravity is also proven with Newton’s three laws. This is when two balls of equal mass are shot and dropped at exactly the same time. When this is done the ball that is dropped is expected to hit the ground first before the one that is shot does but they both fall at the same rate and hit at the same time as you can see in figure 2. This is because gravity is acting on the two balls with the same force down. Having them both falls at 9.8 meters per second has them hit at exactly the same time. This also applies to a bullet when it is fired and dropped at the same time in a Newtonian world. But as you can guess it only happens in a Newtonian world because there is no air friction then. But since there is air frictional and the bullet is designed not to fall because of its shape and spin that it is given a bullet that is dropped will hit the ground before the bullet that is fired will. This still amazes me every time I see it because the two balls do hit at the same time (Holliday). Newton applied these three laws to Kepler’s laws of orbit to come up with the law of universal gravitation. This gave us the reason why the moon doesn’t fall out of the sky and hit the earth (web 2). This came about through a well-known story; it was on seeing an apple fall in his orchard that Newton conceived that the same force governed the motion of the Moon and the apple (web1). He calculated the force needed to hold the Moon in its orbit, as compared with the force pulling an object to the ground. Newton identified gravitation as the fundamental force controlling the motions of the celestial bodies. He never found its cause. To contemporaries who found the idea of attractions across empty space unintelligible, he conceded that they might prove to be caused by the impacts of unseen particles (web 1). He thought out the fundamental principles of his theory of gravitation, namely, that every particle of matter attracts every other particle, and he suspected that the attraction varied as the product of their masses and inversely as the square of the distance between them (web 5). Leaving out the details and only taking round numbers, his reasoning at this time on the theory of gravitation seems to have been as follows. He suspected that the force, which retained the moon in its orbit about the earth, was the same as terrestrial gravity ( web 4). He knew that, if a stone were allowed to fall near the surface of the earth, the attraction of the earth caused it to fall 9.8 meters per second. The moon's orbit relative to the earth is nearly a circle, taking it to be so, he knew the distance of the moon, and therefore the length of its path; he also knew that the time it took the moon to go around the earth once was a month. From this he could easily find its velocity at any point such as M on figure 3. He could from there find the distance MT through which it would move in the next second if it were not pulled by the earth's attraction. At the end of that second it was however at M', and from that the earth E must have pulled it a distance TM' in one second (assuming the direction of the earth's pull to be constant). Now he and several physicists of the time had conjectured from Kepler's third law that the attraction of the earth on a body would be found to decrease as the body was moved farther away from the earth and inversely from the center of the earth. If this were the actual law, and if gravity were the sole force which retained the moon in its orbit, then TM' should be 9.8 meters per second inversely as the square of the distance of the moon from the center of the earth to the square of the radius of the earth. Later when Newton repeated the investigation, TM' was found to have the value which was required by the hypothesis, and the verification was complete; but in 1666 his estimate of the distance of the moon was inaccurate, and when he made the calculation he found that TM' was about one-eighth less than it ought to have been on his hypothesis (web 4). This didn’t however discourage his faith in the belief that gravity extended as far as the moon and varied inversely as the square of the distance. It seems, moreover, that Newton already believed firmly in the principle of universal gravitation, that is, that every particle of matter attracts every other particle, and suspected that the attraction varied as the product of their masses and inversely as the square of the distance between them (web 4). And that was just some of the major parts that Newton gave future physicist to think about. He was very helpful in this department and if it wasn’t for his conjectures it might have set back physics decades before someone else ever came accost it again and proved it as he did.
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