![]() In this scenario, the gravitational force is mostly, but not entirely, diminished anyone in the elevator would experience an absence of the usual gravitational pull, however the force is not exactly zero. A classic example is an elevator car where the cable has been cut and it plummets toward Earth, accelerating at a rate equal to the 9.81 meters per second per second. in an inertial reference frame) the force of gravity on an object in free fall is exactly the same as usual. Speed, not position or lack of gravity, keeps satellites in orbit around the earth.įrom the perspective of an observer not moving with the object (i.e. Satellites stay in space because of their tremendous horizontal speed, which allows them-while being unavoidably pulled toward Earth by gravity-to fall "over the horizon." The ground's curved withdrawal along the Earth's round surface offsets the satellites' fall toward the ground. What's missing is "weight", the resistance of gravitational attraction by an anchored structure or a counterforce. It keeps satellites from flying straight off into interstellar emptiness. Of course, this isn't true gravity still exists in space. The myth that satellites remain in orbit because they have "escaped Earth's gravity" is perpetuated further (and falsely) by almost universal misuse of the word "zero gravity" to describe the free-falling conditions aboard orbiting space vehicles. Space journalist James Oberg explains the phenomenon this way: In Newtonian physics, the sensation of weightlessness experienced by astronauts is not the result of there being zero gravitational acceleration (as seen from the Earth), but of there being no g-force that an astronaut can feel because of the free-fall condition, and also there being zero difference between the acceleration of the spacecraft and the acceleration of the astronaut. ![]() a) Zero gravity and weightless b) Zero gravity but not weightless (Spring is rocket propelled) c) Spring is in free fall and weightless d) Spring rests on a plinth and has both weight 1 and weight 2. In the right half, it is in a uniform gravitation field. In the left half, the spring is far away from any gravity source. This condition is known as microgravity, and it prevails in orbiting spacecraft. In the case of the Earth, the effects are minor, especially on objects of relatively small dimensions (such as the human body or a spacecraft) and the overall sensation of weightlessness in these cases is preserved. Near a black hole, such tidal effects can be very strong. When the gravitational field is non-uniform, a body in free fall experiences tidal effects and is not stress-free. A sensation of weight is also produced, even when the gravitational field is zero, when contact forces act upon and overcome a body's inertia by mechanical, non- gravitational forces- such as in a centrifuge, a rotating space station, or within an accelerating vehicle. These weight-sensations originate from contact with supporting floors, seats, beds, scales, and the like. Weight is a measurement of the force on an object at rest in a relatively strong gravitational field (such as on the surface of the Earth). Micro-g environment (also μg, often referred to by the term microgravity) is more or less synonymous, with the recognition that g-forces are never exactly zero. It is also termed zero gravity, zero G-force, or zero-G. Weightlessness is the complete or near-complete absence of the sensation of weight. ![]() Michael Foale can be seen exercising in the foreground. Astronauts on the International Space Station experience only microgravity and thus display an example of weightlessness.
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