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Why is the strong nuclear force the strongest of the four fundamental forces?

  1. Oct 9, 2014 #1
    Is more force required at smaller distances like the nucleous of an atom? Since strong force applies itself at the level of the atom does that prove that more force is required at smaller distances to attract according to the inverse square law? Does strong nuclear force obey the inverse square law?

    Or

    The force of strong nuclear force is more because it has to work against the repulsion of the protons? (Due to electromagnetic force).
     
  2. jcsd
  3. Oct 9, 2014 #2

    Drakkith

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    We don't know why the strong force (also known as the color force) is the strongest. It's just the way it is.
    The strong force does not follow the inverse square law. In fact, its strength doesn't drop off at all with distance, leading to something called "color confinement": http://en.wikipedia.org/wiki/Color_confinement
     
  4. Oct 9, 2014 #3

    Bandersnatch

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    I'm hardly an expert, but I don't think avito009 was asking about colour force. The force between nucleons is, if I understand it correctly, a residual effect of the colour force, and as such it follows quite different rules than the colour force does.
    For one, it's strength varies with distance quite substantially:
    350px-Nuclear_force.png
    (from http://en.wikipedia.org/wiki/Nuclear_force)

    You're thinking about it backwards. No force "has to be" anything. They are what they are, and in combination with all the other forces they produces emergent structures like nucleons, atoms, molecules, planets etc.

    Having said that, on the scale of an atom, the gravitational force is completely negligible, the weak force is only rarely in play, and the two forces that determine the structure of an atom are electromagnetic and strong, as well as the Pauli exclusion principle.
    The EM force is long-range(falling at inverse square of distance), while the strong force is very stongly attractive at close range, quickly falling in strength as shown on the graph above.
    The repulsive effect starting at about 0.8 fm is due to Pauli's. EM dominates the interaction when a nucleus gets too large, leading to unstability(radioactive decay).
    If a nucleus is small, the strong force holds the constituent protons and neutrons against the EM repulsion of protons, while Pauli exclusion principle doesn't allow the nucleus to collapse to an even more tightly bound state.
     
  5. Oct 9, 2014 #4

    Drakkith

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    The nuclear force is not one of the 4 fundamental forces, but perhaps you are right and he wasn't asking about the color force.
     
  6. Oct 9, 2014 #5

    sophiecentaur

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    It's a shame that picture doesn't appear to show the 'signs of both forces' and thus how the electric and nuclear forces act together so that lower (potential well) curve is greater in magnitude than the repulsive (++ charges of protons) curve value - producing net attraction. Why just show the magnitude of FI?
     
  7. Oct 9, 2014 #6

    Bandersnatch

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    Yeah, this one seems much better:
    http://www.boredofstudies.org/wiki/images/b/bb/Sci_phys_quanta_strong_force.png
     
  8. Oct 9, 2014 #7

    sophiecentaur

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    I love it. Couldn't find one as good as that in the brief search I tried.
     
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