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Gravitational field strength at latitude

  1. Mar 3, 2010 #1
    This figure is captured from my physics textbook and it is about the gravity at latitude

    http://pix.gogobox.com.tw/out.php?i=567045_.JPG [Broken]

    I want to know the difference between mg0 and mg(theta). Which one is the weight of the object? Thank you!
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Mar 3, 2010 #2

    Doc Al

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    Looks to me like mg0 is the gravitational force on the object and mgθ is the apparent weight of the object at latitude θ. The apparent weight is the gravitational force minus the centripetal force. (If you hung an object from a string, the string would end up parallel to the apparent weight.)
     
  4. Mar 3, 2010 #3
    Is gθ called 'apparent gravity'?
     
  5. Mar 3, 2010 #4

    Doc Al

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    That's what I would call it, but it is also called the local value of g as a function of θ. It's somewhat a matter of semantics. What does your textbook call it? (What text are you using?)
     
  6. Mar 3, 2010 #5
    It is a Hong Kong textbook called New Way PHYSICS for Advanced Level
    In the book, gθ is called gravitational field strength at latitude θ
    I think the author uses the wrong name
    The gravitational field strength at latitude θ should be g0, right?

    Here is the related page from my textbook
    http://uploadpie.com/bHHsD [Broken]
     
    Last edited by a moderator: May 4, 2017
  7. Mar 3, 2010 #6

    Doc Al

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    No, the author's terminology is reasonable. When they talk about 'gravitational field strength at latitude θ' they are lumping together the strictly gravitational component (g0) with the effect due to rotation. Think of it as the 'net' or 'apparent' gravitational field strength. (It is a bit confusing, but commonly done.)
     
  8. Mar 3, 2010 #7
    gravity = g0
    apparent gravity / gravity at latitude = gθ
    weight = mg0
    apparent weight = mgθ

    I hope I don't understand wrongly

    So when we measure our body weight, the reading of the balance = mgθ rather than mg0
     
  9. Mar 3, 2010 #8

    Doc Al

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    Looks good to me. (Of course, this is just a simple model of the earth as a sphere, ignoring various complications.)
     
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