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What is 0 gravity? We normally know it as an environment with no gravity. However, this definition is actually unscientific. Gravity actually exists anywhere two quantities of matter exist side by side. Also, gravitational fields exert themselves several miles beyond the massive celestial objects that produce them. So even though astronauts are in orbit seem to be floating free of gravity they actually are not. This is further proven by the fact that a space shuttle is in orbit at all. Its path is still dictated by the force of the Earth’s gravitational field.
So what is actually going on when astronauts are in 0 gravity? It can more accurately be called weightlessness or free fall. This is acutually the result of Einstein’s Physics. Free fall is the effects of weightlessness created when an object falls solely under the acceleration of gravity. The best way to explain this is Eistein’s elevator illustration. Say that you were in an elevator that was suddenly falling from a great height. Since its is an enclosed space you would not be subject to factors like air resistance. So in your own frame of reference it would seem that you are actually floating free of gravity. Zero gravity would only exist as your personal perception in the elevator.
This is what happen with freefall. Back to the space shuttle. What happens is that space shuttle is travelling with constant acceleration similar to that of gravity. This creates the 0 g effect for astronauts. Another interesting thing about the state of weightlessness is the effects that it has on the human body after a long period of time. It has been observed that astronauts who spend a considerable amount of time in space lose bone mass and atrophy of certain muscles. This is because the human body was adapted to exist under the influence of gravity, providing density to bones, and exerting consistent stress on muscles even when at rest.
This has proven to be a major challenge for scientist trying to plan long term missions such as to the Moon and Mars. However, there are many methods of artificial gravity now being considered to counter the problem. One solution is to rotate a space craft using centripetal acceleration to produce gravity. This is a sure solution but there are concern about disorientation caused by a much smaller radius than the earth called the Coriolis effect. However this can be ameliorated by a larger craft. The other solution is to have a spacecraft constantly accelerate at the same rate as Earth’s gravitational constant. This can work but there are no propulsion systems that can yet do this efficiently.
If you enjoyed this article there are several others on Universe Today that you will be sure to enjoy. There is a great article with links on articles explaining gravity. There is also a great article about artificial gravity.