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A trivial question but who can answer it ? (Friend from Algeria)

  1. Jul 21, 2012 #1
    Hello,
    this is my first topic in this forum,
    a few weeks back A friend told me when we were having a discussion about physics that the force coming from earth spin is the force that keeps thing on the planet surface and the gravity has no hand in this,
    well I assumed he is just crazy because I'm pretty much sure that every astronomer says that gravity is the force keeping everything together from small moons to the supermassive black holes.
    When I explained him, He told me that I'm not qualified for telling him this,
    So, I wish if there was among you a professor at university or someone who can give me the answer along with his personnel "self-biography" so I can silence this guy because I fell that what he is saying is an insult to the physics.
    An thanks very much for reading.
    I wish you tell me : is my English good ?
     
  2. jcsd
  3. Jul 21, 2012 #2

    Doc Al

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    You don't need a 'professor' to tell your friend what any freshman physics student should know. Instead, ask him to provide a non-crackpot reference for his claim. He's the one making the silly claim, so make him back it up.
     
  4. Jul 21, 2012 #3
    He'll probably spin a bucket of water around his head to show you it does not flow out. The problem is we live on the exterior of the bucket.
     
  5. Jul 21, 2012 #4
    That exactly what I asked him !
    He study mechanics in our "university" if you can call it that way in our country, their professor gave them an example about "Centrifugal force", and then this guy just came up with this idea, when I asked him to give me a reference he said " we studied it"!
    THAT is exactly what he did !
    An I explained him the same thing! but this guy is opinionated.
    An more on that, He asked ME for a reference !
    That's why I thought maybe one of the staff could help me with his opinion and his resume so this guy stop telling me " we studied it"! Because this is getting me CRAAAZY !!!!!
     
  6. Jul 21, 2012 #5

    Doc Al

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    Ask him if he knows the meaning of the word 'centrifugal'. It means acting away from the center, not towards it.

    Ask him what he thinks would happen if the earth were to spin faster and faster.
     
  7. Jul 21, 2012 #6
    You think like me you know !

    I tried but every time I get him cornered He repeat the same thing "We studied it"
    I just need the post of a professor to prove my opinion.
    If you know any one who can help I will be very grateful. and thanks.
     
  8. Jul 21, 2012 #7

    Doc Al

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    Have your friend go to his professor and ask the the question. (The same one who told him about 'centrifugal force'.) I think he's just pulling your leg (playing a joke on you) and would be too embarrassed to ask his professor such a silly question.

    He should have also studied gravity. Or did he conveniently forget that part of the course?
     
  9. Jul 21, 2012 #8
    this is a long shot
    as they will not continue their studies for about 2 or 3 months.
    yes, they studied gravity in the same course as far as I know.
    To make thing clear I asked him what would happen If earth wasn't spinning,
    can you imagine !
    HE told me that everything on it's surface like the sea would flow to space !
    Now you must understand, I told you this guy is opinionated.
    >I understand that you have PhD, if you can just give me the place of your work and your resume it could help me very much. I doubt he can oppose someone with you grade.
    Or maybe you can give me a book or a Manuel supporting me if you don't feel like sharing your personnel info. and thank you.
     
  10. Jul 21, 2012 #9
    How would he explain the orbit of the moon around the earth? Or the orbit of any body around another?
     
  11. Jul 21, 2012 #10
    what do you mean exactly ?
    are you speaking about relativity ?
     
  12. Jul 21, 2012 #11

    Doc Al

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    I'm certainly not going to post personal information, but there's no need for any of that.

    Do you use a standard textbook? Just about any standard freshman physics textbook will cover this. (Tell me what text you use.)

    In fact a standard problem is to calculate the difference in your apparent weight when standing at the equator compared to standing at the north pole. Your apparent weight is less at the equator due to the spinning of the earth. (See: Q & A: Earth’s rotation and centripetal acceleration)

    Also see: Gravity and Spin
     
  13. Jul 21, 2012 #12

    Doc Al

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    Great question!
     
  14. Jul 21, 2012 #13
    How does one explain the orbit of the moon without gravity?

    Perhaps I misunderstood your original post and your friend actually believes gravity exists, but isn't responsible for keeping things on the surface. That seems just as silly or even more so. It's silly any way you slice it. :tongue:
     
  15. Jul 21, 2012 #14

    I don't study at university I'm still at high school that's why no one listened to me, and our textbooks doesn't contain any of these.
    I think I can solve the problems with the links you gave me. but
    If you can give me the title of the textbook you recommend I would be very grateful.
    I'd like to know more.
     
  16. Jul 21, 2012 #15

    Doc Al

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    Why don't you speak to your high school physics teacher? Hard to believe that your textbook doesn't cover gravity!
     
  17. Jul 21, 2012 #16
    it doesn't !
    our physics is poor you know
    we only study gases and movement and especially chemistry like oxidation.
    this is something very advanced when related to our catastrophic education program.
     
  18. Jul 21, 2012 #17

    Astronuc

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  19. Jul 21, 2012 #18
    So, would your friend say that the weight of objects is due to the rotation of the planet? If so, how would he explain that things weigh only slightly less on Venus as compared to Earth (90%). Yet Venus has a very slow rotation period of 243 days (.4% of Earth's rotational period). I don't think Venus could hold on to its atmosphere if it had to depend on its spin.

    Seems more likely weight is due to surface gravity which depends on the mass and the radius of the planet in question and not spin. Venus is very close to the same size and mass of the earth. Its surface gravity is close to that of Earth as well.

    There are endless arguments one could make to refute your friend's belief.
     
  20. Jul 21, 2012 #19
    Thank you very much
    I think I can take it from here.
    Problem solved. I have what is takes to prove my opinion right.
     
  21. Jul 21, 2012 #20

    Astronuc

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    Objects weigh more at the poles than at lower latitudes. The lighest weight of an object would be at the equator. An object weighs less flying in the direction of rotation than flying opposite.

    The earth's diameter is less at the poles than at the equator.

    Equatorial radius 6,378.1 km[7][8]
    Polar radius 6,356.8 km[9]

    [7] "Selected Astronomical Constants, 2011". The Astronomical Almanac. http://asa.usno.navy.mil/SecK/2011/Astronomical_Constants_2011.txt [Broken]. Retrieved 2011-02-25.
    [8] a b World Geodetic System (WGS-84). Available online from National Geospatial-Intelligence Agency.
    [9] Cazenave, Anny (1995). "Geoid, Topography and Distribution of Landforms". In Ahrens, Thomas J (PDF). Global earth physics a handbook of physical constants. Washington, DC: American Geophysical Union. ISBN 0-87590-851-9. Archived from the original on 2006-10-16. http://web.archive.org/web/20061016024803/http://www.agu.org/reference/gephys/5_cazenave.pdf. Retrieved 2008-08-03.

    Ref: http://en.wikipedia.org/wiki/Earth
     
    Last edited by a moderator: May 6, 2017
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