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    Re: Coriolis and gyros (second attempt)(typos corrected)
    From: Frank Reed
    Date: 2009 Sep 3, 22:57 -0700

    Sorry to be late in replying on this topic. I was travelling for much of August.
    Gary L, you wrote:
    "Note, I am not saying that the use of a "fiction" might not be useful in 
    making an explanation for what an observer is seeing just like you telling 
    your young child that the stork brought the new baby."
    If you really believe that that's a legitimate comparison, then you have been 
    seriously misled. The replies you got from Peter H. were excellent and right 
    on the money, so I will only add a little more for now...
    I do understand (I think) why you have some misgivings about the use of 
    Coriolis force in describing various phenomena since it has been grossly 
    abused in some explanations of simple things --the notorious tall tales about 
    the swirling of common sink drains in the northern and southern hemispheres 
    being the worst abuse. But I can assure you that there are many phenomena in 
    physics which benefit greatly from the use of a rotating frame of reference 
    --which necessarily includes centrifugal acceleration and Coriolis 
    acceleration. Some among these that come to mind off the top of my head are 
    the ocean tides, ocean circulation generally, most of meteorology, 
    gravitational phenomena like the stability of the Lagrangian points, common 
    laboratory centrifuges, spacecraft centrifuges (remember the one imagined in 
    the movie 2001 over forty years ago?), and a great many other circumstances. 
    Any time you have a large number of objects participating in a common 
    rotation, especially when fluids are involved, you will generally find that 
    physics is much easier to work in a rotating frame of reference. And these 
    frames of reference are not used merely to teach 'young children' as you've 
    suggested above. They're used by professional physicists without the 
    slightest misgivings. The Coriolis and centrifugal accelerations are rigorous 
    The NavList posts which previously claimed that it was incorrect to understand 
    the behavior of a gyrocompass by reference to Coriolis force were WRONG. You 
    don't necessarily have to work in a rotating frame of reference, if such 
    things confuse you, but it is legitimate to do so. Whether it is enlightening 
    or not depends significantly on the background of the student.
    Somewhere else, you asked about the behavior of a gyrocompass near the equator 
    since the equation you know for Coriolis has a factor of sin(Latitude) in it. 
    That equation does not properly describe the Coriolis acceleration. It is a 
    shortened version given to pilots and others who need only a basic 
    understanding of the phenomenon. The Coriolis acceleration is not zero at the 
    equator (as the equation you learned implies). Rather, something unusual 
    happens to it in low latitudes. If a plane is flying east above the equator, 
    in what direction does the Coriolis acceleration point?? I will leave that as 
    something for you to explore on your own...
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