# Strong nuclear force vs. electromagnetism

## Main Question or Discussion Point

Hello,

I'm wondering, which force is stronger, SNF or EM, how was it proven that specific force is stronger than the other, and are there actually any cases where the weaker force is actually the stronger one.

Thanks for all the help

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Meir Achuz
Homework Helper
Gold Member
The Coulomb EM potential energy of two protons can be written as
V_EM=e^2/r, while the Yukawa potential energy (the Strong Force equivalent of the EM Coulomb potenetial energy) of two protons is
V_S=g^2 exp(-r/r_0)/r. In appropriate units (called "natural units"),
e^2 and g^2 are dimensionless coupling constants, with
e^2=1/137 and g^2~1, and r_0~1 fm. Thus at short distances
(r<1 fm or so), where the exponential factor is large, the Strong Force is stronger than EM. However, as r increases above 1 fm, the EM force becomes stronger than the Strong Force.

A simpler way to see that the strong force beats EM is to note that atomic nuclei don't fly apart. Any nucleus with two or more protons experiences EM repulsion between the protons. Some stronger force must be holding them together.

Meir Achuz
Homework Helper
Gold Member
The EM force causes U235 to fly apart in spontaneous fission.

The EM force is reduced by proximity as the field of one proton reaching beyond the field of the other proton attracts rather than repels ... After you account for the EM-deduction you can account for the SNF ... and then ask your question as to which is stronger ....

Basically, we know that the SNF is stronger because the energy in fusioning D+D is potentially much greater than the electrostatic repulsion (sub-MeV) for opposing D-charges reaching nucleon-radius distance.

Ray.

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