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Re: non-inertial frames



As an addendum to the post on centrifugal force and bruises, someone
brought up the objection (paraphrased) "Don't tell me Coriolis forces
aren't real -- I had my house flattened by hurricane Andrew!"

Just as in the case of the centrifuge, the force that flattens houses
is a very real destructive wind force, and no mystery about it, but it
is not "Coriolis force," it is plain old Newtonian wind force. The
way the term "Coriolis" gets injected into hurrican discussions is simply
that G. G. Coriolis (in 1835) published the mathematical expressions for
correcting for the fact that you were making measurements relative to
accelerating axes. Hence the term "Coriolis accelerations" for
accelerations that are present solely because of the screwy reference
frame you are using.

Now the fact is that if you try to predict how much force a hurricane's
winds will pack, and you do not take account of the fact that any
reference frame fixed to the Earth's surface is accelerating, you are
going to be making wrong predictions, and you will be very surprised when
the hurricane hits. You must start, as in every mechanics problem, by
setting up Newton's laws or their equivalent relative to an inertial
reference frame, and the Earth's surface simply isn't one. You end up
correcting for the "Coriolis acceleration" of the Earth's surface relative
to an inertial reference frame. Sloppy phraseology then creates the fiction
of a corresponding "Coreolis force," and in the mind of the public at large
this is what sticks as the cause of hurricanes. Coriolis acceleration is
very real; Coriolis "force" is a complete fiction, and has never damaged
anyone's house. The force of wind, however, is another matter...

A. R. Marlow E-MAIL: marlow@beta.loyno.edu
Department of Physics PHONE: (504) 865 3647 (Office)
Loyola University 865 2245 (Home)
New Orleans, LA 70118 FAX: (504) 865 2453