I agree completely with Marlow on the fact that centrifugal and coriolis
forces are non-existent, and he has expressed this very well. I will
just add a few more words. First, when in my physics course we reach
circular motion I find that most students have heard of "centrifugal force"
and almost none of "centripetal force." Then I tell them that centrifugal
force does not exist, that it is a myth. Most students are unbelieving,
but only at first. I go through a number of examples, in particular the
passenger in the car when the driver turns left. As I explain the effect
I also tell them that I think that is the way the myth got started. When
the car turns left and if there is no seat belt or much friction with the
seat then the passenger continues in a straight line horizontally
according the Newton's first law, and the car would leave the passenger
except for the door, which hits the right arm of the passenger and forces
him to procede in a circular path via the centripetal force it is
applying. The passenger is not propelled to the door, he was already in
motion, it is the door that as part of the car gets in the way of the
passenger and forces the circular motion. The myth then arises, I think,
as follows. When the door applies a force on the arm, the arm presses
against the door by Newton's third law, this bodily sensation is one of
pushing against the door, but the passenger is passive and not trying to
push, such as when one pushes againt an object to make it move. The only
other time when one pushes against a wall or door unwillingly is when someone
else or some other object pushes one against the wall or door, such as in
a fight where one crashes against an intervening object. Our psychological
response to the sensation of pressing the door of the car seems to require
that something be pushing us against it and it has been called centrifugal
force even though there is no such thing. I also cover the spindle-top and
the centrifuge. The students are pretty convinced and never again use that
term.
Second, I think bringing in general relativity is totally unnecessary, in
fact irrelevent to a problem of a myth that is resolvable with Newtonian
physics. Bringing in GR simply is an attempt to make a force real by
going more abstract, in college it was called a "snow job." Our TA's
sometimes did that. I certainly am not going to bring in GR to my
freshman level physics course.
Third, some have been insisting on keeping the term centrifugal "force" even
though there is no body that is exerting it, locally or at a distance. Some
simply want to call it by another name, such as inertial "force." I
remember once Feynman accelerated a beaker with water and the water level
slanted and he said it was a kinematical effect and called it a pseudo-
force. Actually, the best name for a force that does not exist is to call
it a poltergeist. Call it the centrifugal poltergeist.