NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Coriolis and gyros (second attempt)(typos corrected)
From: Frank Reed
Date: 2009 Sep 3, 22:57 -0700
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 physics. 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... -FER --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---