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Presence of gravity?

  1. Jul 19, 2013 #1
    I would like to know if the following statements are true:

    Gravity is a force that exists regardless of pull or push. It is actually a force that depends on two masses and the distance between those two masses.

    Imagine the following scenario:
    You are being shot into a travelling capsule in a tunnel that has no air resistance.

    It does not matter whether you are being shot forward in the capsule tunnel or sucked backwards since gravity is not a force reliant on direction
    but a force between one body of mass and another body of mass.
    The only factors that matter in gravity are acceleration, mass and distance.

    The existence of gravity is not dependent on a push/pull action because those are directional vectors and gravity only concerns with acceleration, mass and distance as stated previously. This can be verified by looking at Sir Isaac Newton's equation of Gravitational force:


    Gravity exists everywhere in the universe.

    Thank you.
  2. jcsd
  3. Jul 19, 2013 #2


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    Staff Emeritus
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    This is VERY puzzling, and I have no idea where you got some of these things.

    There is a constant repetition that gravity is "not direction" and not dependent on "push/pull". I have no idea what that is, but the first is definitely wrong. BY DEFINITION, a "force" MUST have direction, it is a vector! Gravity is a force. Try finding the gravity acting on a mass due to the presence of two other masses in different locations!

    Secondly, why is gravity dependent on "acceleration" in your equation? Where does acceleration comes in? All I see is that it is dependent on G, the two masses, and the distance between them. So where is this "acceleration" that you talk about? Do you even know this equation and somehow not realize that what you said contradicts the equation that you are citing?

  4. Jul 19, 2013 #3
    What do you mean regardless of a "push or pull"? Forces do "push and pull" on objects. I think you mean that gravity does not require physical contact.

    I have no idea what you're trying to say with the rest of your post.
  5. Jul 19, 2013 #4


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    I have no idea what you mean by "regardless of pull or push"!

    Yes, that is true.

    The question of "shot forward" or "sucked backwards" is not relevant to the question of "gravity".

    Yes, but that has nothing to do with "those are directional vectors". Gravitational force is also a "directional vector". (You don't need the word "directional" here, all vectors are "directional".)

    What in the world was your purpose in posting this? What you say is correct but can be found in any "general science" text book, much less a physics text. Do you have a question about gravity?
  6. Jul 19, 2013 #5
    Everything that you have said is essentially correct, but certain statements could be rewritten in a clearer way. For example, I am not sure what is meant by a "push" or "pull" force. In a sense Newtonian gravity is a "pull" force, because the force between two masses is always attractive. If you are instead remarking on the tendency of an observer orbiting in space to be unable to "feel" the gravitational force (except perhaps for a very small tidal force) then you are on your way to stumbling into Einstein's "principle of equivalence". This principle led Einstein to hypothesize that gravity is an "inertial force" that emerges from the Riemann intrinsic curvature of space-time, thus leading to general relativity, which remains the most accurate theory of gravity to this day.
  7. Jul 19, 2013 #6
    I mean that the existence of gravity is not dependent on it being a force that pushes or pulls. It does both.
  8. Jul 19, 2013 #7
    The equation you give can be stated in words as
    "every body in the universe attracts every other body with a force proportional to the product of their masses and inversely proportional to the square of the distance between them."
    I.e. the force is ALWAYS attractive (the square of the distance must be positive as must the two masses. Hence push/pull is irrelevant - the force is along the straight line between them and in the direction from one to the other.) I.e. with two bodies A and B, A experiences a force towards B and B experiences a force towards A.
  9. Jul 19, 2013 #8


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    Staff: Mentor

    Please give an example of gravity that "pushes".
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