Man experiences weightlessness in a spacecraft. Anything that is not fixed or tied down just floats. Astronauts have to use special devices to eat and drink. The crew members have to learn to adjust the vigour of their actions to keep from crashing into the walls and equipments. During sleep also astronauts feel unstable and that is why they use belts during sleep. Let us understand more about this phenomenon.
The mass of a body is the amount of matter contained in it. In fact, it is the measure of inertia of the body. The weight of a body is the force with which the body is attracted towards the centre of the earth. Weightlessness occurs when there is no gravitational pull on the body such as in a spacecraft or when a satellite orbits the earth. If the force of gravity is balanced by the centrifugal force, the man in the spacecraft experiences a state of weightlessness. A body falling freely under gravity also experiences weightlessness.
Sometimes, weightlessness causes nausea and giddiness because the working of the balancing organs in the inner ear gets upset. Particles floating in the spacecraft do not settle down easily and may be harmful for health. Astronauts are able to adapt to weightlessness through training.
To make up for lack of gravity, regular exercise is essential in a spacecraft to keep the muscles in a good condition. It has been observed that in space, astronauts tend to ‘grow’ taller. This is because the pads of cartilage between the bones of the spine are no longer under pressure from gravity, and they expand. This increase in height can be as much as 5 cm. However, the astronaut returns to his original height when he returns to earth.
Under the conditions of weightlessness it is possible to conduct certain scientific experiments that are impossible on earth. Absolutely perfect crystals can be grown and alloys of very high homogeneity can be made under the conditions of weightlessness which are very difficult to make under the pull of gravity.
Scientists have been conducting experiments to find out whether a woman may become pregnant in weightlessness condition — and if so, what could be the effect of zero gravity on such children. In recent years, it has been discovered that prolonged periods of weightlessness can cause depletion of calcium in astronauts.