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B Weightlessness in space

  1. Apr 5, 2017 #1
    Another Doubt
    Guys, I was watching this video on youtube. it is about weightlessness in space. it states that the astronauts inside a space ship fly in space not due to zero gravity but due to centripetal force with which the satellite is revolving the earth. My question is "then why the astronauts outside the space ship are not pulled by earth's graviy???

    this is the link
     
  2. jcsd
  3. Apr 5, 2017 #2

    Doc Al

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    Astronauts, whether inside or outside the ship, are pulled by gravity just like the ship itself is.
     
  4. Apr 5, 2017 #3

    Grinkle

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    The astronaut is also in the same orbit - the person is not needing to be 'pushed' by the space station. They were put into orbit by the space shuttle, and once in a stable orbit, they will stay there. If they are in an identical orbit to the space station, they can move around in it etc and look weightless inside the space station as they do so. But once placed into orbit by the space shuttle, they would stay there, with or without a space station nearby that they might crawl inside of.
     
  5. Apr 5, 2017 #4

    A.T.

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    They are. Why should it matter whether they are outside or inside the ship?
     
  6. Apr 5, 2017 #5

    Nugatory

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    It's never a good idea to try to learn physics from youtube videos, but this one is not bad. The problem is that you've misunderstood it - it does not say that "the astronauts inside a space ship fly ...... due to centripetal force with which the satellite is revolving the earth." They float inside the station because they and the station are both in free fall, moving freely under the influence of gravity.
     
  7. Apr 5, 2017 #6

    ZapperZ

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    Now think about this a bit. Let's say you have a man in an elevator on earth in a free fall. There's another man next to him, outside of the elevator, who also jumped at about the same time as when the elevator+man starts to free-fall.
    elevator.jpg
    Ignoring air resistance, do you think they will fall at different rate? Doesn't the man in the elevator experiences weightlessness the same way as the man outside the elevator?

    If the astronaut is orbiting the earth, he/she and all the contents of his body are also orbiting the earth, whether he/she is inside, outside, on top, on the side... of any vessel. This means that the centripetal force in the form of gravitational force is acting on all of them, and they are all having the same centripetal acceleration. Thus, the weightlessness.

    Zz.
     
  8. Apr 5, 2017 #7
    then why they didnt fall
     
  9. Apr 5, 2017 #8
    Ok then, How astronauts float in outer space? is it due to zero gravity?
     
  10. Apr 5, 2017 #9

    russ_watters

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    The do fall - at the same rate whether inside outside. That's what an orbit is! (falling forever and never hitting earth).
    Inside the ship or out, the zero *apparent* gravity is due to being in orbit.
     
  11. Apr 5, 2017 #10
    For a Space ship, it revolve around the orbit due to the orbital velocity. But a man outside space. Is he moving at the same orbital velocity as the space ship ??
     
  12. Apr 5, 2017 #11

    ZapperZ

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    Is here next to the ship all the time? Astronauts that do space walk in the ISS are in a relatively stationary frame as the ISS. If the ISS is orbiting the earth, doesn't this automatically imply that so does the astronaut?

    Zz.
     
  13. Apr 5, 2017 #12

    russ_watters

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    Well sure; he got outside by climbing out through the airlock. He got into orbit with the ship, in the same way it did; by sitting atop a giant rocket. He's not wearing a giant rocket on his back when climbing out the airlock, so he has no way to greatly change his orbital velocity.
     
  14. Apr 5, 2017 #13
    I can understand you but how does the centripetal acceleration acts for person outside the space ship. In space ship it is due to velocity with which it rotates.
    So will the person outside the spaceship will also have the same velocity?
     
  15. Apr 5, 2017 #14
    Then the motion is relative,
     
  16. Apr 5, 2017 #15

    Doc Al

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    They'd better, don't you think? If they want to go home!
     
  17. Apr 5, 2017 #16
    I am really sorry I cant get you
     
  18. Apr 5, 2017 #17

    russ_watters

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    Sure, motion is always relative. The motion that matters here is the orbital speed, which doesn't change when the astronaut exits the airlock.
     
  19. Apr 5, 2017 #18

    russ_watters

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    If the astronaut has a different velocity than the spaceship they will move apart, and the astronaut won't be able to go home.
     
  20. Apr 5, 2017 #19
    Thank you all for clearing my doubt
    I find this forum very helpful and I am going to use it to clear all my doubts:wink::wink::wink::wink::wink:
     
  21. Apr 5, 2017 #20

    A.T.

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    Just like inside, the centripetal force is provided by gravity.

    No, the centripetal acceleration is due to gravity.
     
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