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How cAN YOU fake no-gravity?

  1. Jan 24, 2005 #1
    how cAN YOU "fake" no-gravity?

    i was wondering how can u create "no gravity". or to be precise why does it happen?

    i know there are special flights that can do that but why does it happen?

    is there any machines or anything at NASA that does it?

    basically, if you'll create a negative "g" force on anything it should not move, but how do you do that?

    and why exactly the mass of anything in space would influence it's accelaration? where there is no weight there should be no resistance?

    thanks in advance ( i know it's basic issues but i want to recall...)

  2. jcsd
  3. Jan 24, 2005 #2
    under free fall, you will temperary exprience no gravity.....What the nasa plane did was fly very high and turn off the engine... let the plane and the people and everything inside falling at the same speed...
  4. Jan 24, 2005 #3


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    Hi ymksgreg, welcome to PF. You can also fake zero gravity with neutral bouyancy. This one of the training methods used by NASA for shuttle missions.
  5. Jan 24, 2005 #4


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    NASA has or had at one time a plane called the "vomit comet" that would fly parabolic trajectories to give astronauts the experience of zero-G. This plane was also used to film some of the zero-G scenes in the film "Apollo 13".

    Google finds it's got its own website now,

    http://jsc-aircraft-ops.jsc.nasa.gov/kc135/ [Broken]

    which includes some of the technical details.
    Last edited by a moderator: May 1, 2017
  6. Jan 25, 2005 #5
    thanks everybody, but...

    thanks for the quick reply... but still why does you expirience this "Zero G"?
    shouldn't they stick to their chairs or something?

    and for what i saw they to go to a certain height - is there a reason for that? or can you get it anywhere?

    and why the parobolic trajectury?


  7. Jan 25, 2005 #6
    The vomit comet is just a commercial airliner without the seats, flying up and down.

    Imagine you are in an elevator and it is falling, you will not stick to the floor, you will float relative to the walls. That is what a falling airplane does to simulate zero-g. They can get about 60 seconds of weightlessness or so.

    There are also drop towers. Allowing zero-g for a few seconds. Not for humans though. Just experiments in a box. Although amusement parks do use to the same principle for humans.
  8. Jan 25, 2005 #7


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    Its a parabolic trajectory because acceleration due to gravity is parabolic (linear acceleration, parabolic displacement). All the "vomit comet" does is follow you in freefall. Neglecting wind resistance, it would work the same if you were inside or outside of the vomit comet.
  9. Jan 25, 2005 #8


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    "why does you expirience this "Zero G"? shouldn't they stick to their chairs or something?"

    The plane (and all the seats in it) falls from the sky at the same rate the passengers do. Internally, it is experienced as weightlessness.

    "for what i saw they to go to a certain height - is there a reason for that? or can you get it anywhere?"

    The only reason they go to a certain height is because they'll need the room to pull out of the dive. The higher they start, the longer the fall they can make. It has nothing to do with the weightlessness.

    "and why the parobolic trajectury?"

    That's what a baseball does when you throw it in the air (like everythnig else). It follows a parabola. If you throw a baseball and a marble into the air, they will both follow the same trajectory - staying near each other, until they hit the ground. Pretend the baseball is the plane, and you are the marble.

    (P.S. Now to throw a wrinkle in: technically, the plane, the baseball and the marble are not following a parabolic cuve at all, they are following an elliptical curve whose semimajor axis is about 4000 miles long - i.e. to the Centre of the Earth. :) The objects are actually in orbit around the centre of the Earth - it just happens to be an orbit that intersects the surface of the Earth. But an ellipse with a very looong semimajor axis (i.e. 4000 miles), is effectively a parabola.)
  10. Jan 26, 2005 #9


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    The chairs do gravitate by the way, but the effect is negligable as its mass is tiny compared to the gravitational field of the Earth.
  11. Jan 26, 2005 #10
    thanks everybody. i think i'm starting to get the hang of it.

    i learned physics in the past - and the question are becuase me and a bunch of freinds didn't understand the whole thing.

    one more thing - can anybody eaplain me mathematically why the zero g is happening?

  12. Jan 26, 2005 #11


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    The downward acceleration of the aircraft equals the acceleration due to gravity. They absolutely do not "turn off" the engines. The airplane is falling just as fast as they are if they were free falling.
  13. Jan 26, 2005 #12
    This is starting to make me question it the more I think about it. You ARE accelerating correct? So you should FEEL that change in velocity right? Ignore everything I just said, it seems to be wrong.... Acceleration is not relative like velocity... ANyone?
  14. Jan 26, 2005 #13
    Accelerating with respect to the earth. But the body you are in that is accelerating with respect to the earth is at rest with respect to yourself.
  15. Jan 26, 2005 #14


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    You only feel force if there is something external pushing on your body or an imbalance in net force (like tidal force). If every particle in your body is accelerating at the same rate, there is no force to feel.
  16. Jan 26, 2005 #15
    This is actually not zero gravity at all, but sure sounds like fun. It would not feel exactly like zero gravity because you are under the full effect of gravity. It does trick the eyes and inner ear into the sensation of being weightless, but there are other sensations from zero gravity which we cannot yet simulate, for instance, the change in bloodflow and the fact that internal organs actually are wightless in a true zero gravity environment (Jelly Belly?). Humans have never been in absolute zero gravity, if there is a such thing. It is likely the closest we could get to a real zero gravity environment would be somewhere between the Milky Way and the Andromeda galaxy. Even there, one will be tugging on you.
  17. Jan 26, 2005 #16

    Whether you are free-falling in a drop tower, in a vomit comet, a space shuttle/station or between the M. Way and Andromeda, your body will not know the difference. The physiological differences you state happen in each situation. The only notable difference is how long the effects are present (seconds vs minutes vs days). The gravity between each organ or between organs and shuttle walls is entirely negligeable experimentally. For all practical purpose, this is zero-g, although it is most often called microgravity ("micro" refering to the negligeable g-force between small masses).
  18. Jan 26, 2005 #17


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    Its not zero gravity, but it really is zero weight and is indistinguishable from true zero gravity (as Gonzolo said). There are not other sensations that tell you you are in the presence of a gravitational field - bloodflow is different than when you're standing on earth (your heart doesn't work as hard), organs move around ("up") because they don't feel the gravity pulling them down, etc. There really isn't any way to tell if you're in freefall or truly weightless.
  19. Jan 28, 2005 #18
    Actually it is the same feeling as being in orbit, since g has barely diminished in the Earth's Orbit, and in an orbit the space craft is free falling with respect to Earth, so it is the same principle as free falling in the "Vomit Comet". Only the space craft will not hit the ground, it will continue to 'fall' to earth as it orbits.

    It is hard to escape the effects of gravity even in space.
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