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Name:  Ken A.
Status:  other
Age:  30s
Location: N/A
Country: N/A
Date: 2000-2001


Question:
In the traditional sense of escaping earth's gravitional pull, how high up from sea level must one go to achieve weightlessless?


Replies:
Right here on earth. Just jump. While you are in the air, you are weightless. Weight is the support force; take away the support force, you are weightless. The astronauts are well within the pull of the earth (230 miles up), since they are in orbit. They are going at such a speed that they fall from a straight line at the same rate as the earth beneath them curves, hence, they fall "around" the earth. That is why they have no support force, and are weightless. Even out at the moon (265,000 miles) the force of the earth's gravity is enough to hold it in orbit. It is not the escape from gravity that causes weightlessness, it is the lack of support force.

See Paul Hewitt's Conceptual Physics textbook for a more in depth discussion.

---Nathan A. Unterman


Since for every action force, there is an equal and opposite reaction force (Newton's Third Law), what you are witnessing is a rebound of the seat (couch) against the astronaut. The six point restraints are tight, particularly against the pelvis bones. Upon release, the "spring force" of the seat propels the astronaut a tiny bit up.

On many roller coasters (The Giant Drop at Six Flags Great America, for one) have points of weightlessness where you have "air time" out of your seat. For safety reasons (so you do not tumble out) you have restraints. But for those brief moments, you are as weightless as the astronauts.

For a more prolonged effect, a diving airplane in hyperbolic flight can simulate the same thing, and NASA uses that as a training vehicle. It has been dubbed the "vomit comet" for those who tend to become ill on it.

The effect can be had right here on earth.

Nathan A. Unterman



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