I was recently arguing about the nature of "force" with some guy on
sci.physics. I remembered yet another textbook misconception which is
very widespread. It caused me a slight bit of confusion for decades,
because for me it muddled the definition of "force." As a student I
thought I understood force, and I believed that gravity was a force.
THERE ARE FOUR KNOWN FORCES: EM, WEAK, STRONG, GRAVITY
This is wrong? Yes. Think for a moment. How strong is the force of
gravity at the earth's surface? Please express your answer in Newtons!
This should be easy, since gravity is a force. :)
But obviously we can give no answer. We can measure Gravity at a
particular spot on the earth, but the result will not be in Newtons. We
can measure the e-field too, but the answer will be volts/meter, not
Newtons. Same with b-field, and weak and strong nuclear "forces".
What is force? Exaclty what do students typically think it is? Were they
like me in thinking that "force" was something other than the quantity
measured in Newtons, the quantity expressed by F=MA or F=KX?
The above misconception could be changed thus:
THERE IS ONLY ONE KIND OF FORCE. HOWEVER, FORCES ARISE WHEN
VARIOUS FIELDS INTERACT WITH MATERIAL PARTICLES, AND THERE ARE FOUR
KNOWN FIELDS: ELECTROMAGNETISM, WEAK, STRONG, GRAVITY
I have no illusions that any such change would stick. ;)
Politics/society/tradition interferes when we nitpickers wish to wreak
improvements on technical language. The weak and strong nuclear forces
are not forces? Should we always say "weak and strong fields"? Yes.
After all, we say "magnetic field" and we say "electric field", we should
therefor NOT say "strong nuclear force." Tell that to the particle
physics community.
Anyway, I think we would do some good if we warned students that gravity
is not a force, e-field is not a force, there is no "force of magnetism,"
etc. Try to undo the damage that the "four known forces" concept has
done. Make everyone feel uncomfortable when they accidentally say that
"electric force" fills the dielectric of a charged(!) capacitor, or that
the "force of gravity" fills the region surrounding the earth.
Another tack: does the word "force" have more than one definition?
Perhaps it also means "field", and therefor "field" and "force" can be
used interchangably. I certainly hope not. When we discuss "strong
nuclear force", we're really talking about a Gauge field and its
associated exchange particles, and such things are not measured in terms
of Newtons. We certainly should not say "force" if we mean "field."