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Thread: Gravity of two objects

  1. #1 Gravity of two objects 
    The Doctor Quantime's Avatar
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    What is the gravity exerted on an object that sits between two objects of equal gravitational force? Say for instance we sit at the same distance from two identical Jupiters so much that both the Jupiters gravitational fields create a vesica pisces, if we sit at the centre of the two, would we be indifferent to the gravitational pull of both objects and hypothetically be at rest relative to the two jupiters?


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    Forum Senior TheObserver's Avatar
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    Yep.


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    The Doctor Quantime's Avatar
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    Now lets extend that to black holes, if we are one metre from the singularity of both black holes would we still feel a net zero gravitational pull and effectively not feel any tidal forces?
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    Forum Senior TheObserver's Avatar
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    If the black holes were small and you were not within the schwarzschild radius then it would be an identical situation. I don't really know what would happen when two black holes had their event horizons intersect to be honest.
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    Forum Senior TheObserver's Avatar
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    But realistically since you aren't a point particle, you would probably be ripped in half being that close to even a small black hole.
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    The Doctor Quantime's Avatar
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    Thanks. I was just wondering in a hypothetical situation, there is probably a distance between two singularities at which a person can occupy without being spaghettified, yet wouldn't be able to if there was only one black hole.
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    Geo
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    If the forces acting on a body are balanced, it travels with a constant velocity, which could be zero.
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    Brassica oleracea Strange's Avatar
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    Quote Originally Posted by TheObserver View Post
    I don't really know what would happen when two black holes had their event horizons intersect to be honest.
    They merge to form a bigger black hole. There are some rather good animations of this on the web. The event horizons become non spherical as they "reach out" to meet each other as they get close (at this point, apparently, it is too late for the merger not to happen) then they touch and merge to form a new event horizon with twice the radius. There is a short period of oscillation (I think it is called "ring down") while it stabilises.

    (I only read a little about this because of someone on another forum claiming it was impossible because "time stands still" at the even horizon.)
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    edd
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    Quote Originally Posted by Quantime View Post
    Thanks. I was just wondering in a hypothetical situation, there is probably a distance between two singularities at which a person can occupy without being spaghettified, yet wouldn't be able to if there was only one black hole.
    Just because gravitational forces balance at a point doesn't mean that the tidal forces do. You're actually talking about an L1 Lagrange point and if you read up on them you'll see that they're unstable along the line connecting the two masses precisely because of this.
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  11. #10  
    The Doctor Quantime's Avatar
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    If the gravitational forces balance, but tidal forces do not. Does that not mean there are two seemingly apparent forces acting on said object?
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  12. #11  
    edd
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    Quote Originally Posted by Quantime View Post
    If the gravitational forces balance, but tidal forces do not. Does that not mean there are two seemingly apparent forces acting on said object?
    The gravitational forces only balance at a point. Objects are generally speaking not points - that's how tidal forces arise. They're the difference in gravitational forces across an object.
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  13. #12  
    Forum Bachelors Degree Kerling's Avatar
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    Well actually it is not that simple. You see, sure at the exact equidistand postition the force is zero. But anywhere besided that it of course isn't! There will be gravitational pull. And in the case of black holes you'd be torn apart. Even with a jupiter the forces on matter will be very noticable. In fact the difference in gravitational force is alreayd noticable in a black hole. If you'd put a long metal bard of 3 meter near a black hole, then it will be torn apart before it reached the event horizon. Due to the differences in gravitational pull near there. Gravity isn't a linear thing remember!

    Also if you are in that position of two massive objects, you might not feel the gravitational pull effectively, you'd still be stuck in a low curvature piece of space. Your inner clocks would go slower then people far away from the two massive objects.
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