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Why does anything with mass have it's own gravitational field?

  1. Feb 23, 2008 #1
    I have just learned that all objects with mass attract eachother. So if I took the example of an apple falling out a tree. The apple is under the earths gravitational force, but the earth is also under some gravitational force from the apple though this force is far less. My question is why? Why does anything with mass have it's own gravitational field? I know that the earth and other planets orbit the sun and that it is to do with again a gravitational pull, or atleast that is what I think, but why is this?

    I have an image below that I have seen alot when talking about gravitational fields, but I am struggling to interperate it, questions like why do the planets not just get drawn straight towards to sun? If you have an links to information or anything that may help I would most appreciate it. My question might have a very simple answer, but it is one that I haven't found.

  2. jcsd
  3. Feb 23, 2008 #2
    thine answer IS orbit
    is when we are circling in the gravitational field of a large mass, but are travaling at a fast enough speed to not be pulled into the center, this also applies for celestial bodies, the only reason we are shooting straight through the floor is because of the ground, otherwise we would become a singularity with the core of earth, thats is why earth isn't pulled towards the sun.

    as for WHY all masses had a gravitational field...thats beyond me.

    if I am not answering your question, sorry in advance.
  4. Feb 23, 2008 #3
    No, it's the same. What is different is the gravitational field.

    Why you don't disintegrate but you stay intact? Because of electrostatic interaction. Why two charges attracts or repel? Because they do it. :smile: You can explain something if you have something else, that is a theory that can describe it, but, before or less, you will find some "basic concept" that it's not yet explained. This is not true only for physics, but for everything.

    About gravity, you're lucky, because there are many of such theories, the widely accepted is "Einstein's General Relativity". To say it in very simple terms: mass, but also energy density, generates a warping of the space-time, imposing the other objects to follow this warping trajectory, instead of a rectilinear one, as a ball running on the pavement must follow a warped trajectory when it meet a hollow in it. Remember however that the last is just a metaphor, not what really happens with gravity, because with gravity the space is 3D, not 2D and there it's space-time, not only space, to be warped.

    That's very simple: because they have an orbital speed. For example, the little roulette's ball doesn't fall down until it has slowed down, if you go fast with the car in a parabolic bend you can stay up, ecc.
    Last edited: Feb 23, 2008
  5. Feb 23, 2008 #4
    Thank you for your help Havoc and lightarrow. Thank you for explaining that diagram. Why is the earth moving at the speed it does and why does it not vary or lose speed, wpuld there not have to be a continuos force acting on the earth to keep it moving at the speed it is.
  6. Feb 23, 2008 #5


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    If something is already moving, it will continue to move until a force stops it. So the earth does not need a continuous force to carry on orbiting. However, there is something holding it in orbit - the gravitational field.
  7. Feb 23, 2008 #6
    Thanks for clearing that up.
  8. Feb 23, 2008 #7


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  9. Feb 23, 2008 #8
    If I am totally honest I didn't even consider newton's laws of motion :blushing:
  10. Feb 23, 2008 #9
    Mass is a form of energy and a marginally unstable form. It wants to return to a more fundamental energy state. There is an extremely small energy ingress which is compounded -the larger the mass the larger the overall ingress. It is this energy flow which causes gravity. Well, that's the way I see it.

  11. Feb 23, 2008 #10


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    Not so. Mass can be converted to energy, but they are not the same thing, as common experience tells us. The rest of your post, insofar as it makes sense, sounds like a private theory.
  12. Feb 25, 2008 #11
    I agree that they are not the same thing but, similarly, neither is water and ice but they come from the same stuff.
  13. Feb 25, 2008 #12


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    Yes, according to the standard model all the matter we see is the result of a tiny imbalance in the matter/antimatter ratio when the energy cooled enough. So it is tempting to think of matter as 'frozen' energy. It is also true that the binding energy of matter contributes E/C^2 to the inertial mass. I don't want to push the analogy though because I got slightly beaten up in another thread when I hinted at it.
  14. Feb 25, 2008 #13
    Explaining gravity by falling back on Relativity explains nothing. Why should mass/energy warp the space-time around it?
  15. Feb 25, 2008 #14


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    Why not ? I don't think science can give the kind of explanation you're after.
    It's doubtful if space-time is actually 'warped' but the model is a very good description and predictor of gravitational interactions.
  16. Feb 25, 2008 #15
    I'm more comfortable with it being a model, rather than explaining what is actually going on in reality.
  17. Feb 25, 2008 #16


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    Me too, especially because there are other theories of gravity that have different, or no space-time curvature.
  18. Feb 25, 2008 #17
    I think the reality is obscured from us by the fact that we can easily visualise things that are matter based, ie. things we can touch and move about. The difficulty comes when trying to get an understanding of the energy side of the equation.

    For me, I feel comfortable with the idea of energy coming in three basic or primitive states, wave energy (oscillatory), energy associated with mass (rotary) and lastly, gravity, which is the linear version. All other types of energy can fit into one of these categories.

  19. Feb 25, 2008 #18


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    Interesting. In which category does the energy of an electric field fall ?

    Tread carefully, your post might be interpreted by a mentor as a private theory.
  20. Feb 25, 2008 #19
    It's rotary
  21. Feb 27, 2008 #20
    I still dont see how it is possible for orbit to be the one thing that creates gravity. I have read many presuppotions on the new theories of gravity, including the Final Theory, and in the book it is stated that there is no possible way to find the true source of gravity's power. Sure the orbit of the planets would have some effect but it really explains nothing. On another note what about the law of conservation of energy? The power or energy that powers tyhat particular force never changes or ever disperse to another form. What is your theory on this.
    Last edited: Feb 27, 2008
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