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B What kind of force acts in the center of the Earth?

  1. Apr 4, 2016 #1
    What kind of force acts in the centre of the earth ? What is the intensity ?
     
  2. jcsd
  3. Apr 4, 2016 #2

    BvU

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    There is quite some pressure there and it is pretty hot as well.
     
  4. Apr 4, 2016 #3

    Svein

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    And, of course, the force from the sun according to Newton's law (and from several other celestial bodies...).
     
  5. Apr 4, 2016 #4
    What about the gravitational force acts by the earth ?
     
  6. Apr 4, 2016 #5

    Doc Al

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    If you assume the earth has a spherically symmetric mass distribution, the gravitational force of the earth on an object at the center of the earth would be zero.
     
  7. Apr 4, 2016 #6

    ProfuselyQuarky

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    Could you say normal force is acting on the center, or no?
     
  8. Apr 4, 2016 #7

    A.T.

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    Normal to what?
     
  9. Apr 4, 2016 #8

    ProfuselyQuarky

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    Normal force meaning any force acting on something at a ##90^{\circ}## (right) angle. If we’re talking about a single point in the center of the earth, would that mean that normal force is acting on the point in all directions?
     
  10. Apr 4, 2016 #9

    Doc Al

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    A "normal" force is usually a force between an object and some supporting surface (and normal to that surface). What did you have in mind?
     
  11. Apr 4, 2016 #10

    ProfuselyQuarky

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    Normal meaning orthogonal. I didn’t know there had to be a supporting surface.
    I had that in mind. I was wondering if that was correct or incorrect. I guess it's incorrect?
     
  12. Apr 4, 2016 #11

    mfb

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    90 degree angle relative to what? Any direction looks the same, there is no normal force because the concept does not even make sense.
    And a force from what?
     
  13. Apr 4, 2016 #12

    A.T.

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    That is pressure in a fluid, not normal force.
     
  14. Apr 4, 2016 #13

    ProfuselyQuarky

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    That’s what I was asking about. Since the 90 degrees would not be relative to any specific surface, I thought that would mean that the force could be acting on the point in all directions.
    Okay, fine. The idea is jargon.
    I see . . . thanks for the explanation :)
     
  15. Apr 4, 2016 #14

    BvU

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    I figured that's what you were really inquiring about -- and teasingly avoided that in my first answer. The Doc made good on that, but perhaps it's good to elaborate a bit more. For ##1/r^2## laws such as Newton's law of gravity ( and following ) and Coulomb's law one can derive Gauss' theorem that popularly says: you only have to take into account what's underneath you -- the contributions from the part of the sphere with a greater distance to the center cancel.

    And it makes sense: along a hole through the earth something has to happen with the force from gravity, because at the other end it has the same magnitude but points the opposite way.
     
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