|the state or condition of weightlessness|
The condition of real or apparent weightlessness occurring when any gravitational forces acting on a body meet with no resistance so the body is allowed to accelerate freely. Bodies in free fall (including trajectories like orbits) experience zero gravity; bodies at rest on the Earth's surface do not, since they are subject to the counterforce of the surface supporting them.
condition experienced while in free-fall (q.v.), in which the effect of gravity is canceled by the inertial (e.g., centrifugal) force resulting from orbital flight. The term zero gravity is often used to describe such a condition. Excluding spaceflight, true weightlessness can be experienced only briefly, as in an airplane following a ballistic (i.e., parabolic) path
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