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Help Gravity

  1. Oct 25, 2004 #1
    Help!! Gravity

    im not sure if im in the right place but, i was wondering if gravity increases when you get near the core of the planet. i have done research and have not found anything conclusive. i need help with this topic. any information or thoughts would be apriciated.
  2. jcsd
  3. Oct 25, 2004 #2


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    Dearly Missed

    No it does not.
    Traveling inwards, and assuming uniform density, only the mass of the interior ball will contribute; the effect from the outer shell is zero.
  4. Oct 25, 2004 #3
    Gravity is the attraction of masses. You are attracted to the Earth and the Earth is attracted to you.

    A logic argument:

    1. If you were only attracted to the Earth, then only you would fall toward the earth.

    2. If the earth were only attracted to you, then only the earth would fall toward you.

    3. If only one object were attracted (as in 1 or 2), how could it hold it's place in space while it attracted the other object? What would it be holding on to for it to pull the other object to it? Nothing. Therefore, both objects must attract each other. (This is dependent upon their quantity of mass.)

    Since you are attracted to the earth and the earth is attracted to you, as you get to the core, you are more and more surrounded by an even mass of earth pulling you with equal force in all directions, while you pull on it in equal directions.

    Gravity will be the same, because gravity occurs because of masses which attract each other. The masses are still there (you and the Earth).
  5. Oct 25, 2004 #4

    Doc Al

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    Sorry, but I can't make any sense out of your "logic" argument. Somehow you have concluded that "gravity will be the same" at the center of the earth. Not true.

    Assuming, as arildno stated, a uniform density for the earth, the weight of an object (the net gravitational pull of the earth on it) will decrease from its usual value at the surface to a value of zero at the center.
  6. Oct 25, 2004 #5


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    Picture this in your head: You have a point inside a shell. What's the force on the point due to gravity?

    Believe it or not, no matter where you put that point inside the circle, the forces sum to 0.

    That means that you can consider every part of the earth outside of where you are as not affecting you at all, only the stuff further in is.

    So when you're in the very middle, everything is in a shell around you... (assuming uniform desnity, etc) 0 force!
  7. Oct 25, 2004 #6
  8. Oct 26, 2004 #7
    The link doesn't work :(
  9. Oct 27, 2004 #8


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    The effect of the mass "surrounding" you (please be more concise with your language to avoid confusion on the part of students) has no gravitational effect (think spherical symmetry and gauss's law for gravity.)
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