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Thread: Does our planet orbit the sun the same way the ISS and other satellites orbit our planet?

  1. #1 Does our planet orbit the sun the same way the ISS and other satellites orbit our planet? 
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    Man-made objects in orbit aren't simply floating in space. They're constantly being pulled back to Earth by its gravity, but the reason they're not falling into its atmosphere is that their tangent velocity matches their fall velocity, so they're rotating around the Earth as fast as they're falling into it. Is this what's going between the Earth and the Sun? Is the Earth actually always being pulled into the Sun by its gravity?


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    Yes.


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    Of course the sun is also falling towards the Earth - it's just a touch bigger than us, so it wins.
    Last edited by John Galt; June 4th, 2013 at 11:28 AM. Reason: Correct typo identified by astromark
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    Forum Professor astromark's Avatar
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    Quote Originally Posted by John Galt View Post
    Of course the sun is alos faliing towards the Earth - it's just a touch bigger than us, so it wins.
    Do not answer a question that was not asked. Over complicate and drive away... and " also falling '' .

    The answer to 'rladngus's' question was Yes. As Harold said. Talk of the mass velocity to orbit calculation.. only if asked.
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    Quote Originally Posted by astromark View Post
    Quote Originally Posted by John Galt View Post
    Of course the sun is alos faliing towards the Earth - it's just a touch bigger than us, so it wins.
    Do not answer a question that was not asked. Over complicate and drive away... and " also falling '' .

    The answer to 'rladngus's' question was Yes. As Harold said. Talk of the mass velocity to orbit calculation.. only if asked.
    Thank you for giving me such an erudite, comprehensive and succinct education on how to educate. I expect your admonition will quite change my life. I shall abandon all efforts to encourage people to build upon their knowledge. I shall assume that no forum member is ever ready to take the next step. I shall wait patiently while they stumble on the right questions to ask and remain silent if they never find them. It's so obvious once it is pointed out that I can't imagine how I came to be so screwed up before. By the way, there are no questions in this post, so there is likely no need to reply.
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    Universal Mind John Galt's Avatar
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    astromark, two points:

    1. I've corrected the typo in the original, where I was also failing to type also falling.

    2. I am concerned that, since my ironic dig at your post garnered three Likes, you might feel implicitly attacked. That might discourage you from continued participation in the forum. That would be a loss. Please continue to contribute. (The best plan is to take my wife's approach and ignore me. )
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  8. #7  
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    You probably wouldn't have responded so harshly if he didn't use imperatives.

    Instead of saying

    Quote Originally Posted by astromark View Post
    Do not answer a question that was not asked. Over complicate and drive away... and " also falling '' .

    The answer to 'rladngus's' question was Yes. As Harold said. Talk of the mass velocity to orbit calculation.. only if asked.
    He could have said:

    Quote Originally Posted by what astromark could have said
    It's best not to answer a question that was not asked. It over complicates and can drive away. .... and "also falling".

    The best answer to 'rladngus's' question was Yes. As Harold said. It's a good idea not to go and start talking about mass velocity to orbit calculation if that's not what they were asking about.


    If it was something like that I'm sure you'd have been less harsh. Giving people orders on the internet as though one has fatherly authority or something....when one clearly does not.... That's just kind of disrespectful. If someone tried that with me I'd mock them for it too.
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    Quote Originally Posted by rladngus View Post
    Man-made objects in orbit aren't simply floating in space. They're constantly being pulled back to Earth by its gravity, but the reason they're not falling into its atmosphere is that their tangent velocity matches their fall velocity, so they're rotating around the Earth as fast as they're falling into it. Is this what's going between the Earth and the Sun? Is the Earth actually always being pulled into the Sun by its gravity?
    You have the right idea but it isn't stated quite correctly. The statement their tangent velocity matches their fall velocity is incorrect. The first thing to understand is that we're talking about velocity which is a vector quantity having both magnitude and direction. ThThe velocity of a body in orbit, which is in free-fall, is directed tangent to it's trajectory. The direction of the body's acceration vector is towards the center of the gravitating body (since we're discussing spherically symetric bodies). The centripetal force is balanced exactly by the gravitational force. That's why/how a satellite orbits a gravitating body. But it is correct to say that the body can be thought of as falling around the earth. For a circular orbit the body stays the exact same distance from the planet/star.

    The centripetal force a is equal to the gravitatioal force which is equal and opposite to the centrifugal force, the inertial force which must be balanced to keep a body in orbit. The magnitude of the gravitational force is F = GMm/r2. The magnitude of the centrifugal force is mv2/r. Since these must balance we have



    Cancel the mass on each since to get



    or



    This is the orbital speed of a satellite in a circular orbit. I don't know why but when I finish typing out all that Laytex I just feel like saying Ta da! .. .I don't know why.
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  10. #9  
    Forum Professor astromark's Avatar
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    " Ta Daaa..." OH no not that..... I will stay behind the couch.. Hay! there's food here....
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