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Is gravity a weak force

  1. Sep 19, 2011 #1
    Why is gravity thought to be a week force? I would agree that at the surface of our Earth it would appear to be week, after all we can stand on the surface of the Earth without risk of being pulled into it core.

    But a black hole is another kettle of fish altogether, it's almost an atomic waste disposal unit, ripping atomic structures to shreds!

    This then brings me to another question does gravity have a maximum value or strength?? Or is it always proportionate to mass... the greater the mass the greater the gravity "exerted"... to infinity??
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  3. Sep 19, 2011 #2


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    Gravity is both last and foremost of the forces.

    It is the weakest of the four forces, but has the greatest effect on large scale structures.

    The two nuclear forces are strong but of extremely short range.

    The electromagnetic force is both stronger than gravity and a long range force, but is both an attractive and repulsive force, with opposite polarities attracting each other. This tends to cause large bodies to generally be electrically neutral, which in turn tends to cancel out the electromagnetic force over long ranges.

    Gravity is both long range and totally attractive. This makes it the overriding force over long ranges, and allows it to form large structures. You can add more and more mass making it stronger and stronger and more likely to pull in even more mass. (Unlike electromagnetism, where if you keep trying to add more and more like charges to an object, these like charges tend to repel each other and work to tear the object apart.)
  4. Sep 20, 2011 #3
    Compare the pull of gravity between a proton and an electron. Then compare the nuclear forces holding them together.
  5. Sep 20, 2011 #4


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    As noted, on small scales - like the size of atoms - gravity is so feeble physicists ignore it. The nuclear and EM forces dominate interactions at this scale and are many orders of magnitude more powerful than gravity. The weak nuclear force, the next weakest of the four forces is about 10e+25 times more powerful than gravity. EM is about a hundred billion times more powerful than the weak force, but, only about 1% as powerful as the strong nuclear force.
  6. Sep 21, 2011 #5
    To the OP: Some theories of gravity postulate that gravity is weaker because the hypothetical graviton is the only force carrier out of the four basic forces that can travel between all dimensions of space rather than just the three spatial dimensions we experience. This makes gravity highly diluted in our 3D space. In string theory, it has at least six more spatial dimensions to travel through! There are some proposed experiments at CERN that would test for gravity's strength at distances and energies close enough to negate extra-dimensional effects (eg at energies where dimensions are thought to merge). If these tests find an increase in the strength of gravity at these distances, it could prove that extra dimensions do, in fact, exist. I believe Lisa Randall covers some of these ideas in her book "Warped Passages". It could be that when you factor in the dimensional dilution of the graviton that gravity is as strong as all the other forces. Maybe ALL the forces are exactly the same strength but for distinguishing characteristics that cause them to behave differently. I hope these answers come in my lifetime!
  7. Sep 22, 2011 #6
    These days , hearing it a lot many times !! Could you please tell me the reason why it is weak at the surface??
  8. Sep 22, 2011 #7
    Why is it that only Graviton can travel between all dimensions?? what about other particles? don't they travel all the dimensions?? or did I understand it the other way??
  9. Sep 23, 2011 #8


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    I think he means that it is only weak in comparison to the other 3 fundamental forces of nature, not that it is intrinsically weaker compared to somewhere else.

    There is no evidence of this, it is simply a theorized explanation. If it did turn out to be true we would have to do more research to understand why.
  10. Oct 4, 2011 #9
  11. Oct 4, 2011 #10
    Of the planet? It's an intricate question.

    The basic answer is that the planet is most dense toward it's center, therefore the further we go out from the center, the less of a force gravity exhibits on a mass. The surface is as far away as we can get from the core while standing...

    If he was implying that it makes any difference as to whether gravity is stronger or weaker than the atmoic forces, then he was mistaken. I think he just meant that you can tell by lifting rocks and such that it isn't a very strong force in all applications (i.e. in comparrison to say, the pull of Jupiter on one of its moons). Still, though, gravity is considered weak because, at the atomic level, it is pretty insignificant.

    As people said, its power is in its range.
  12. Oct 4, 2011 #11
    Is there a universal particle that unifies all the forces?
  13. Oct 4, 2011 #12
    On Earth its a weak force... at the event horizon of a black hole it's gravity that rips matter to shreds??

    While i total agree that gravity can influence things over a vast distance... when you get close up and personal with a large mass gravity will rip matter apart....

    What I was trying to accertain was: "is there a limit to how strong a gravitational force can be"

    Neutrinos excluded, (for the moment)... it is/was believed that nothing can travel faster than the speed of light.... what I'm trying to find out is there such a limit as to how strong a gravitational force can be, in say a situation where it was possible to have an infinite mass, ( I know it's not possible to have an infinite mass, just for the sake of argument)
  14. Oct 4, 2011 #13


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    Gravity is oblivious to human concepts. Gravity can, and does, overpower all other forces of nature under the right circumstances. Fortunately, that is a fairly rare occurence in the current universe.
  15. Oct 4, 2011 #14
    ??? There are billions of stars in the universe.... matter (asteroids, dust... ) are falling inot these stars all the time... an asteriod that falls into a star is surly annihalated into the most basic of atomic particles?? It can't be that rare??
  16. Oct 5, 2011 #15
    Stars do not "overpower all other forces of nature" as Chronos stated. I think Chronos is referring specifically to Black Holes where curvature is so extreme that all other forces become irrelevant.

    In cases of a star they clearly do not overpower all forces of nature otherwise the star would be a Black Hole!
  17. Oct 5, 2011 #16
    A black hole is a collapsed star.... would there be much difference in mass from the star just prior to it's collapse and the black hole that is created after its collapse??
  18. Oct 5, 2011 #17
    A black hole is a very special case. Most stars do not collapse to black holes. In terms of gravitational "force" or curvature if we are using GR then from a significant distance their is no change. For example if the sun was to instantly turn into a black hole with equivalent solar mass we would not be "sucked" in and would continue to orbit the new black hole in much the same manner as we do the sun - we are outside the Event Horizon.

    The difference with BH's are that once past the event horizon the curvature becomes so extreme all other forces are negligeble - this is not the regular fate of a dying star and is resticted to significantly dense stars.

    For gravity to override all other forces requires a Black Hole and this is far from common.
  19. Oct 5, 2011 #18


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    This is not to say black holes are exceedingly rare in the universe, they appear to be quite numerous. It appears there is a whopper of a black hole in the center of nearly every galaxy. But, compared to the number of stars in your typical galaxy, they are relatively uncommon. It is not even clear how often black holes form directly from core collapse events. Stars less than 20 solar masses are believed to be fated to end as neutron stars of 1-2 solar masses. Even truly gigantic stars [M=40+ solar mass] may have a similar fate [re: http://arxiv.org/abs/0804.4143] [Broken].
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