Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

B Strong Force versus EM force

  1. Nov 29, 2018 #1
    So I am aware that the strong force is the strongest force with the electromagnetic force being the second strongest force. I am wondering how we go about the process of deciding which force is stronger.
    I am visualizing a helium nucleus; two protons, two neutrons. The two protons are pushing away from each other with the electric repulsive force, while there is a strong force connection between each of the hadrons. It seems to me that because the protons are neither moving away nor moving towards each other, the electromagnetic force and strong force are in equilibrium. If this is true how can it be claimed the strong force is stronger than the electromagnetic force. I believe I read somewhere that it is 137 times stronger. Would love an explanation about this!
     
  2. jcsd
  3. Nov 30, 2018 #2

    davenn

    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    does this help ....

    Four-Fundamental-Forces.gif


    Fundamental-Forces.jpg


    note the distances over which they act
     
  4. Nov 30, 2018 #3

    Drakkith

    User Avatar
    Staff Emeritus
    Science Advisor

    There's a misunderstanding here. The protons don't move towards or away from each other because they are in stable or metastable states. Much like how electrons exist in atomic orbitals and neither move away from or towards the atom. They would certainly move closer in towards the nucleus if they could, but such a lower energy state either doesn't exist or is already filled by other electrons. The laws of nature apparently forbid fermions from occupying identical states, and it is this that keeps both protons from moving closer together as well.

    One thing to notice is that the repulsive force from protons on each other increases as you add more and more protons, and this happens without limit because the range of the EM force is infinite. However, the strong nuclear force (the residual part of the color force to be more specific) is very short range, and only a handful of nucleons will attract each other via it. So it must be the case that the strong nuclear force is overwhelming the EM force until you gather together dozens and dozens of protons. Otherwise we would see stable light nuclei falling apart as soon as you add a couple of protons together.
     
  5. Dec 4, 2018 #4
    The average positions must be stationary, otherwise the system would fall apart, but equally the nucleons must be in motion with respect to each other, otherwise one would have a fixed position is a frame of reference defined by the others and hence zero momentum in that frame, which violates the Uncertainty Principle. If we assume an underlying Lagrangian (which the standard model has) and some form of function for the potential energy, then the viral theorem defines a relationship between kinetic and potential energies for bound states. For those interested in oddities, the first theoretical attempt at predicting the nuclear energy relied on electromagnetism, and it got the energies fairly well up to oxygen (Volochine, F. E. 1925. C. R. des Séances de la Société Polonaise de Physique, Fasc V.: 61 – 73.) Additionally, he correctly predicted the spin magnetism of the yet to be discovered neutron. While this was wrong because he needed the proton and neutron to be about 6-7 times smaller than they actually are, this work showed that electromagnetism can have more effect than most think. Since this is not the place for speculative theories, one cannot go further here, but it may not be totally impossible to go further.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted