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As a relativity theorist, I have to inject a couple of other comments
As an oceanographer, I feel some sort of duty to interject something
here.
A. R. Marlow <marlow@beta.loyno.edu> feels strongly that the word
"force" is improper to use when referring to phenomena, such as the
Coriolis effect (clever sidestepping, eh?), that are observed only in
non-inertial reference frames. It seems to me, though, that one
important consequence of general relativity is that there are *no*
preferred reference frames for doing physics: non-inertial frames are
just as valid as inertial frames, as long as we're explicit about
precisely what kind of reference frame we're dealing with.
To put it another way: Galilean relativity tells us that a man in a
windowless carriage moving at constant velocity (relative to an
inertial frame) is perfectly correct when he says that he is
motionless, and when he does his physics accordingly. General
relativity tells us that a man in a falling elevator is correct when
he says that there is no gravitational force (except the tiny forces
due to his mass and the elevator's mass) observable *in his reference
frame* and does his physics accordingly. Likewise, a man in a
windowless, accelerating rocket ship is perfectly correct, in a
general-relativistic sense, if he chooses to say that *in his
reference frame* he observes a "downward" force that acts on all
objects, and that the strength of that force is proportional to a
given object's mass. We (in an inertial frame) could re-write his
equations, substituting the rocket's acceleration for his observed
"force," but our equations are no better than his. We observe his
spaceship to be accelerating; he observes a force on all the objects
in it.
In that case, it should be perfectly acceptable to take the surface of
the spinning Earth as our reference frame, and to formulate our
equations accordingly.
Ari Epstein
P.S. I agree that what we have here is primarily a linguistic
argument; it depends what we mean when we say the word "force."