Weightlessness

From SPACEwiki

Weightlessness is a phenomenon experienced by people during free-fall. The term zero gravity is often used as a synonym. Weightlessness in orbit is not the result of the force of gravity being eliminated, or even significantly reduced, by distance (in fact, the influence of the Earth's gravity at an altitude of 200 km is only 6% less than at the Earth’s surface). Rather, the loss of the influence of gravity is due to the inertial motion of the flight path.

It is helpful to realize that (to an approximation limited by tidal forces) gravity cannot be felt as a force, by either objects or persons. Only the forces that resist gravity, or act apart from it, can be felt by people, or measured by accelerometers. These other forces (such as the force of the ground pushing upward on the feet) are those that produce the sensation and force of weight. Objects following inertial paths do not feel these other forces, and thus feel no g-force, and thus experience weightlessness.

Weightlessness, the sensation of feeling no forces, typically occurs when an object or person is falling freely, in orbit, in deep space (far from a planet, star, or other massive body), in an airplane following a particular parabolic flight path (e.g., the “Vomit Comet”), or in one of several other more unusual situations.