subject: Weightlessness [print this page] We shall now let our imagination run on a "thought experiment". Suppose we were to stand on a spring weighing machine at the equator and that, by some means, the earth's rotation could be speeded up, carrying its atmosphere with it.
With increasing speed, more and more of the earth's gravitational force would be used in providing the extra centripetal force required in the circumstances. Our weight, which is equivalent to the difference between the total gravitational power and the centripetal force, would therefore be less. Consequently the weighing machine would indicate a smaller weight.
If the earth's rotational speed continued to increase, then at a certain critical speed, the necessary centripetal force would be just equal to the total gravitational force. No resultant force would be left over to provide weight and so the weighing machine would read zero. In other words we have become weightless although the full gravitational force still continues to act.
Weightlessness in space vehicles:
It is a well-known fact that astronauts experience weightlessness when their spacecraft are in orbit about the earth. In such circumstances, the earth's gravitational pull is just sufficient to provide the centripetal force required for their particular speed and orbital radius. Mechanically speaking they are in a similar position to the person we have just described on a fast rotating earth.
When an astronaut goes outside his cabin, the situation as far as the earth's pull goes is still the same. There is, of course, gravitational attraction between the astronaut and his cabin in accordance with Newton's law but, owing to the comparatively very small masses of both, the attraction between them is exceedingly small. It is far too small, in fact, to bring him back if he jumped off and so he has to use a life line.
Artificial weight in a space station:
Weightlessness in a space vehicle is highly inconvenient to an astronaut in many ways. For example, he cannot pour liquid into a cup, neither can he drink from it: controlled movement is possible only by the use of handrails and so on.
It has been suggested that the space stations of the future for use as manned observatories or as staging posts for space exploration might be built in the form of large wheels with hollow rims. These would be set in rotation so that the outer rim, which acts as the floor, would have to apply a radial centripetal force to the occupants or any objects inside to keep them moving in a circle.
The equal and opposite reaction to this centripetal force which any person or object exerts on the floor would act as an artificial weight, thus allowing eating drinking and working in comparative comfort. The value of this weight would be made equal or less than the normal earth weight simply by adjustment to the speed of rotation.
As an interesting sidelight, the reader will realize that if a person walked round the station in the direction of its rotation his weight would increase, while walking in the opposite direction would cause it to decrease.
Weightlessness
By: Bilal M Mirza
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