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    Coriolis and gyros
    From: Frank Reed
    Date: 2009 Aug 20, 06:02 -0700

    As Douglas Denny stated originally (later withdrawn), the Coriolis 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 
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