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Artificial gravity is the theoretical increase or decrease of apparent gravity (g-force) by artificial means, particularly in space, but also on Earth. It can be practically achieved by the use of different forces, particularly the centripetal force and linear acceleration. The creation of artificial gravity is considered desirable for long-term space travel or habitation, for ease of mobility, for in-space fluid management, and to avoid the adverse long-term health effects of weightlessness. A number of methods for generating artificial gravity have been proposed, as well as an even larger number of science fiction approaches using both real and fictitious forces. Practical outer space applications of artificial gravity for humans have not yet been built and flown, principally due to the large size of the spacecraft required to produce centripetal acceleration.〔 〕 ==Requirement for gravity== Without g-force, space adaptation syndrome occurs in some humans and animals. Many adaptations occur over a few days, but over a long period of time bone density decreases, and some of this decrease may be permanent. The minimal g-force required to avoid bone loss is not known—nearly all current experience is with g-forces of 1 ''g'' (on the surface of the Earth) or 0 ''g'' in orbit. There has not been sufficient time spent on the Moon to determine whether lunar gravity is sufficient. A limited amount of experimentation has been done by Dr. Alfred Smith, of the University of California, with chickens, since they are bipeds, and mice experiencing high g-force over long periods in large centrifuges on the Earth.〔Great Mambo Chicken And The Transhuman Condition: Science Slightly Over The Edge〕 Rats have been exposed to continuous artificial gravity of 1 ''g'' during Russian biosatellite missions lasting two weeks. The muscle and bone loss in these animals was found to be less than rats in 0 ''g''. Astronauts were exposed to artificial gravity levels ranging from 0.2 to 1 ''g'' for a few minutes during several spaceflight missions, using linear sleds or rotating chairs. They did not perceive any changes in their spatial orientation when the g level was lower than 0.5 ''g'' at the inner ear level, where the sensory receptors for gravity perception are located.〔Clément G, Bukley A (2007) Artificial Gravity. Springer: New York〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Artificial gravity」の詳細全文を読む スポンサード リンク
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