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You may wonder why astronauts in space experience weightlessness. This is due to the interesting effects of free-fall. This special effect is called zero gravity. However it is not really zero gravity. Even at 600 km above the surface of the Earth astronauts are still under the influence of gravity. As a matter of fact at 200 km above the Earth, the influence gravity is only reduced by 6%.The real reason for the experience of weightlessness can be explained by free fall. This is has to do with the frame of reference and the inertial movement of the space ship’s flight path.
The physics is actually very interesting. A person experiences weightlessness when all forces act uniformly upon them. This is what creates of weightlessness. The main question is why does it happen when both a person and the space craft they in are under the influence of gravity? The reason is that both the orbiting space craft and the person inside are accelerating at the same rate. This creates a unique scenario called free-fall. It is also known as microgravity.
Even though this can be fun for a while it has real consequences for astronauts if they are in this environment for a long period of time. The simple fact is that the human body is made to work under non uniform forces with gravity being the dominant one. This is the reason our skeletal and musculatory systems are designed the way they are. In space the bones in the body become brittle and muscles can atrophy unless they are constantly exercised.
This is a major problem for human space exploration beyond the moon. Scientist are looking at ways to create artificial gravity or shorten the time it takes for interplanetary travel in order to reduce the health risks to astronauts. Different solutions are still being looked at but it seems the best one would be to reproduce gravity on the ship. This could be done by designing a rotating ship or using the thrust of a ship to create gravity over long distances.
We’ve also recorded an entire episode of Astronomy Cast all about Gravity. Listen here, Episode 102: Gravity.