RE: When and How Strong?

[willis@niuhep.physics.niu.edu]

Tom writes:

When did scientists, like Rutherford, Chadwick, and
Bohr come to the realization that there must be a strong force acting within
the newly discovered nucleus.  Who named it the strong force and, on a
magnitude scale, how many times greater is it compared to the E-M force?
Also, why is the weak force called weak and what is its relative strength?  

The existence of the strong force was realized when it became
clear that the nucleus contained only positive charges; at first
it was thought that there were negative charges as well (presumably
electrons), but it soon became clear that this was not the case.
(I believe it was spin considerations that made this clear, but
am at home without reference materials at the moment, so am
writing this off the top of my head...). Since the Coulomb
repulsion would be expected to blow the nucleus apart, it was
obvious that there must be some other, much stronger force,
that was holding it together. It is stronger than the E-M force
by a factor of alpha (the fine structure constant), or 1/137;
I don't know who first called it the strong force. The weak force
is called weak because it *is* weak; on the same scale it has a 
relative strength of about 10^(-13). (The strengths of the
interactions vary with energy, in general; these comparisons are
for interactions at zero energy. The weak force, in particular,
is much stronger at masses larger than the W and Z masses).

There are some good on-line introductions to particle physics
(which is what this is); one is at http://pdg.lbl.gov/cpep/adventure.html.
Hope this helps -

		Sue Willis

              Suzanne Willis, Professor, Physics Department
            Northern Illinois University, DeKalb, IL 60115 USA
    http://niuhep.physics.niu.edu/~willis/              swillis@niu.edu
phone: 815-753-0667                                 fax:   815-753-8565