Name: Ken A.
In the traditional sense of escaping earth's gravitional
pull, how high up from sea level must one go to achieve weightlessless?
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
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
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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Update: June 2012