Weightlessness

Weightlessness is a consequence of the equality of centripetal and centrifugal forces. During the levitation bodies lose its weight, but not the mass and inertia. This type of levitation is a functional and absolutely economical and at the very large distances of celestial bodies in relation to that which occur. It is necessary for the maintenance of artificial satellites in their orbits.
To maintain the real levitation requires no energy. Some satellite or celestial body can mediate between in relation to another heavenly body, many billions of years, and did not consume any energy. An illustrative example for this are geostationary satellites that hover motionless above a point on the equator, absolutely not wasting any energy. Energy must be spent only to achieve the speed of levitation and uplift above the atmosphere, ie the gas layer of those heavenly bodies that have it. Because of its peculiarities, this aspect of the real levitation is an extremely cost-effective means of satisfying some of the vital needs of humankind, but it is harmful to human health.
Crew  must prepare to live and work in a weightless state, so trainings are required. American astronauts trainees weightlessness first experience in a large transport aircraft KC135. This aircraft first climbs to a great height, and then sharply daffodils carefully calculating the curved path. Thus, the plane actually comes into a state of free fall, so passengers do not lose weight. Then the passengers by float in plane not feeling any more weight and trying to perform certain actions to see whether it would work well in space.
Some aspects of weightlessness trainees can experience working under water. They install equipment and perform repairs hovering underwater in space suits. Buoyancy as it creates water reverses the action of gravity. But stay under water is not equal in all to floating in space, because that can act on astronauts body in a very strange way.
The first few days in orbit most astronauts suffer various negative consequences, together called space disease. It lasts until the body adapts to new conditions, but even when the astronauts cease to feel bad, weightlessness can still harm the body because it causes loss of calcium from the bones and they become so fragile.