SPACE AGE BIOMECHANICS: WEIGHTLESSNESS
Keywords: gymnastics, diving
AbstractWeightlessness There is a common misunderstanding about weightlessness. We have developed the notion that weightlessness and space go together and that people become weightless whenever they go beyond the earth's atmosphere. We have acquired this notion naturally. For years now, we have become accustomed to seeing astronauts and cosmonauts floating around inside their spacecrafts once they achieve earth orbit. Since the orbit altitude usually 150-300 miles, is beyond our atmosphere, it is natural to associate weightlessness with a lack of atmosphere, ie, with space. This association is natural, but in fact, it is only coincidental. According to Newton, every object in the universe attracts every other object. He expressed it this way: G =g.mJ x M .jr 2. What this says is that the amount of attraction that exists between two objects is directly related to their masses and inversely related to the distance they are from each other. Because gravity is universal, a state of absolute weightlessness could exist only ifyou were present in an empty universe. Since that is hardly feasible, our understanding of weightlessness needs to be adjusted. To understand it properly, we need a frame of reference. To illustrate, on earth, we e perience our mass as weight because the earth pushes up on us opposing gravity's pull. Ifthe earth suddenly gave way, we would no longer experience our mass as weight because there would be nothing to oppose the pull of gravity.
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