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How do satellites stay in orbit?

  1. Mar 20, 2006 #1
    Hi, this is my first post. I have been trying to find an answer out of my own interest but is unable to do so. while searching I found this wonderful website. I hope you guys can help.

    I came across a series of questions today and one of the question asks "What keeps satellites in orbit?" The answer choices were inertia, free fall, and centripetal acceleration (I knew it wasnt inertia so im down to free fall and centripetal) I picked free fall. HOWEVER, the answer was actually centripetal acceleration. I think that, with the amount of speed and height, a satellite can travel faster than it can fall and thus continue try to fall but unable to do so because it is traveling too fast about the earth's curvature. Can someone explain this? Thanks

    By the way, one of the results i came across is found on:
    http://www.boeing.com/companyoffices/aboutus/wonder_of_flight/iss.html [Broken]

    Thanks for any explanation , im quite curious.
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Mar 20, 2006 #2


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    How did you know that? Perhaps you have a wrong idea of what inertia means?
  4. Mar 20, 2006 #3


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    Uh, where is this "series of questions?" I can't even think of a more poorly-presented physics problem. All of the answers are, in fact, correct -- or as "correct" as answers to open-ended question can be.

    - Warren
  5. Mar 21, 2006 #4

    Come on Warren, no need to be rude.

    ORBITS: My understanding of orbits is that the further away from Earth you are, the less Earth's gravity acts upon you (it gets weaker with distance). If you were 'plopped' 100 miles above Earth, you would be accelerated back down to Earth by gravity and you would crash into the ground.

    However, If I 'plopped' you in the same spot and oriented you so that when you looked down, you saw your feet, and saw Earth directly below them, I could put a rocket on your back that would propel you forward fast enough so that for every foot gravity pulled you towards the Earth, your rocket propelled you foward a foot.

    This means that you are constantly falling towards the Earth, but you are also constantly moving past the Earth. In this manner you circle the Earth. You never pass the Earth and you never fall into it. That is orbit!
  6. Mar 21, 2006 #5
    To selfadjoint: my perspective of inertia is the tendency to remain in motion and can include a straight line.

    To chroot: Sorry if this upsets you, this is actually TAKS review. Some state standardized kinda thing and I totally agree with you how this question was poorly stated.
  7. Mar 21, 2006 #6
    To chaos': So is it centripetal or free fall? :p
  8. Mar 21, 2006 #7


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    If someone asked me this question, then I would say gravity. Since gravity is the centripetal force for a satellite's orbit, I suppose that last answer makes some sense. I don't usually think of "acceleration" as acting on an object, though, I think of it as a property of an object. As for "free fall", the satellite is experiencing it, but it's a matter of semantics to say whether or not it's what keeps the satellite in orbit. If it weren't following a geodesic, then it might not stay in orbit, but then it still might.

    All in all, I agree with chroot. This question is poorly phrased.
  9. Jan 4, 2009 #8
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