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Nasa speaks of the either the space shuttle or the ISS

  1. Jun 2, 2008 #1
    how come when nasa speaks of the either the space shuttle or the ISS, they speak as if they have left the effects of earths gravity? This is not true. The people in the ISS are falling toward earth at the same speed as the craft around them. When they start their decent back to earth they feel weightless until they touch atmosphere. At that point the atmosphere slows the craft and the people inside feel the G's from that. Are some of the smartest people that nieve to think that we can acually leave the effects of earths gravity, becouse i dont think that is possable.
  2. jcsd
  3. Jun 2, 2008 #2
    What effects are you talking about? Remember that locally it is impossible to establish if you are in a gravitational field. Note that a spacecraft is relatively small.
  4. Jun 2, 2008 #3
    the planets pull on our sun. the earth pulls on the moon and keeps it in an orbit. the collective of our galaxy pulls on other galaxy's. I dont think it is possable to leave the effects of the earths gravity. So how come nasa fumbles these words.
  5. Jun 2, 2008 #4
    I think all NASA are saying is that the effect of gravity on small scale experiments conducted inside the space shuttle is almost zero. This allows them to carry our certain "zero gravity" experiments in the shuttle that would be difficult or impossible within the Earth's atmosphere. Of course it does not mean that gravity does not have an effect on the shuttle.
  6. Jun 2, 2008 #5
    I think there is something you misunderstand about the effects of gravity. One of the effects of gravity we can measure are the so-called tidal effects For a small localized area you can effectively ignore those effects and a spaceship is very small in this respect.

    Of course the curvature of spacetime does influence how objects move with respect to each other and sometimes they bump into each other but that does not influence any laws of physics as the bodies all move inertially. Inside the spaceship there are, except for the extremely small tidal effects, and things like precessions, no effects whatsoever due to gravity.
  7. Jun 2, 2008 #6

    D H

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    neh4pres, you are thinking too little. Of course NASA knows that Earth's gravity doesn't end at the Earth's surface.

    MeJennifer, you are thinking too much. NASA doesn't expect the average citizen of the US to have the foggiest idea about tidal gravity effects.

    NASA use of words like weightlessness and microgravity is (a) often aimed at the average US citizen, and (b) correct. "Weight" comes in two flavors. "Actual weight" is tautologically defined as mass times the acceleration due to gravity. The "actual weight" of an astronaut floating around in the near-weightlessness of the ISS is close to the astronaut's actual weight on the surface of the Earth. Nothing, including a bathroom scale, can measure "actual weight" directly because nothing can sense gravity directly.

    A bathroom scale measures "apparent weight". The "apparent weight" of some object is the net sum of all real forces except for gravity acting on the object. (Note that from a relativistic perspective, apparent weight is the net sum of all real forces acting on an object, period, as gravitation isn't a real force in relativity; it's a pseudoforce instead.) An astronaut in the ISS is not quite in free fall because the astronaut is not at the ISS center of gravity and the ISS is subject to atmospheric drag. The astronaut will fall very slowly toward some surface of the ISS. The acceleration is very, very tiny. Earthbound viewers see the astronauts floating around as if they were weightless. As nothing, including the astronauts themselves, can sense actual weight, the astronauts feels themselves floating around apparently weightless.
  8. May 12, 2009 #7
    Re: Nasa

    thanks... this is very insightful... you think deeply,as do I.
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