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As Douglas Denny stated originally (later withdrawn), the Coriolis 
acceleration is most definitely responsible for the north-seeking capability 
of a gyro-compass (IF you work in coordinates rotating with the Earth --the 
natural coordinates for these problems). Just make sure you use the full 
three-dimensional vector cross-product when thinking about the strength of 
the Coriolis acceleration. 

The Coriolis acceleration is frame-dependent --it depends on the choice of a 
rotating frame of reference. It's intriguing to note that there is also an 
extremely tiny physical, non-frame-dependent, version of the Coriolis 
acceleration which is created by spinning masses. This is known as 
"frame-dragging" or "gravito-magnetism" and was measured (barely due to 
various problems with the ultra-sensitive gyroscopes) by a spacecraft known 
as "Gravity Probe B": http://einstein.stanford.edu/highlights/status1.html.

There is a deep, non-accidental analogy between the Coriolis force and the 
common magnetic force. And just as a spinning current loop experiences a 
torque which causes it to precess in a constant magnetic field, a spinning 
"mass loop" (a.k.a. a gyroscope) experiences a torque which causes it to 
precess in a rotating frame of reference.

Finally, for Gary, there is nothing "fictional" about the so-called 
"fictitious forces" in rotating frames of reference. They are every bit as 
real as the common acceleration of gravity, or, if you like, they are every 
bit as un-real. The complicated explanations for various phenomena which you 
have learned that avoid using the expression Coriolis are un-necessary, 
though they can serve as useful reminders that physics can be done in 
different frames of reference and the results have to be the same no matter 
what.

-FER





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