Information AboutWeightlessness |
| CATEGORIES ABOUT WEIGHTLESSNESS | |
| gravity | |
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Weightlessness is experienced by people during Free-fall . Although the term ' Zero Gravity ' is often used as a synonym, weightlessness in orbit is not the result of gravity itself being eliminated or even reduced significantly (in fact, the Acceleration due to Gravity at an altitude of 100 km is only 3% less than at the earth's surface — a person ''at rest'' at that altitude would accelerate to earth at a familiar rate). Weightlessness (roughly speaking) occurs when a body (e.g. a person) is: falling freely; in orbit; in outer 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 one of several other (even more unusual) frames of reference. More generally, weightlessness occurs when a person (or object) is subject (at most) to the ''single'' non-contact force of gravity (or is not acted upon by any accelerating force), vs. the far more typical (in human experience) cases in which a contact force is acting — such as:
(The principal difference is that gravity is a field force acting directly on a person and/or other bodies, just like on the vehicle's mass — whereas forces like atmospheric drag and thrust act through contact on the vehicle body itself (and are transmitted, in turn, through the contact between the vehicle and the person). In the first case the person and the vehicle floor are not 'pushed' towards one another; in the other cases, the force is transmitted ''through'' the vehicle's structure ''to'' the person and/or contents.) OVERVIEW What humans perceive as "weight" is not actually the ". ''(In the remainder of this article, the term 'weight', without 'apparent', is used in this sense.)'' While this is not always intuitive, imagine the floor dropping out from under you: without it, you'd be falling — and experiencing weightlessness. It's the floor supporting you ''against'' gravity's pull — and which keeps you from falling to the center of the Earth — that creates the sensation of "weight".'' For example: a person in a broken lift in Free-fall "experiences" weightlessness. This is because there is no force from the lift's floor on the person's feet, ''against'' the pull of gravity, as both the lift and the person are being pulled down with the same acceleration. When the lift is at rest on the ground, however, the force of gravity pulling downwards on the person is exactly matched (in the opposite direction, and by the same amount) by the support of the lift floor. Because the person's skeleton is solid, each horizontal cross section of the person experiences not only the force due to gravity on it, but also the weight of whatever portion of the person is above it. ''(In the case of an object, or portion thereof, which is not supported from below, but suspended from above, a 'negative pressure', or tension gradient exists. It occurs because each cross section of a hanging object, a rope for instance, must support the weight of every piece below it.)'' Part of feeling "weight", then, is actually experiencing such a pressure/tension gradient within one's own body parts (e.g.: while standing on one foot, the foot on the ground would feel the ''pressure'' of the entire body's weight, whereas the other leg and both arms would feel/be subjected to the ''tension'' gradients of their own weight being pulled down against their sockets). In free-fall, a person or object experiences no measurable (or apparent) weight because all parts of the object are accelerating uniformly (any variations in acceleration due to Tidal Forces being imperceptible). TERMINOLOGY Zero gravity |
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