leong Posted October 11, 2014 Share Posted October 11, 2014 (edited) Last posting on vectors (aren't you glad?) This one shows a graphical way to figure the ferry angle. Looks good , John, but I think you meant to say something like this:Then I first drew the current paddling velocity vector, put the drift vector current velocity vector at it’s tip (arrowhead) and then drew the resulting course bearing velocity vector, and then measured it.-Leon Edited October 11, 2014 by leong Quote Link to comment Share on other sites More sharing options...
JohnHuth Posted October 11, 2014 Author Share Posted October 11, 2014 Whoops! I'll look it over but I certainly could have slipped up. Thanks for pointing it out! Quote Link to comment Share on other sites More sharing options...
JohnHuth Posted October 12, 2014 Author Share Posted October 12, 2014 Tides, Part 1 Quote Link to comment Share on other sites More sharing options...
JohnHuth Posted October 21, 2014 Author Share Posted October 21, 2014 Static theory of tidesThis one is very math-y, so stay away unless you want the gory details. I'm mainly putting this up there for anyone who has taken a course in physics and wants to see how the static theory can be derived without reference to a centrifugal force. Quote Link to comment Share on other sites More sharing options...
josko Posted October 22, 2014 Share Posted October 22, 2014 (edited) Beautiful, clean and elegant, John. Edited October 22, 2014 by josko Quote Link to comment Share on other sites More sharing options...
leong Posted October 23, 2014 Share Posted October 23, 2014 Static theory of tidesThis one is very math-y, so stay away unless you want the gory details. I'm mainly putting this up there for anyone who has taken a course in physics and wants to see how the static theory can be derived without reference to a centrifugal force. John,Nice derivation and easy to follow. For the fun of it I programmed the expressions in Mathcad and verified your results.Searching around the Internet I found NOAA’s explanation for tides that says:“On the opposite side of the Earth, or the “far side,” the gravitational attraction of the moon is less because it is farther away. Here, inertia exceeds the gravitational force, and the water tries to keep going in a straight line, moving away from the Earth, also forming a bulge (Ross, D.A., 1995).”Is this qualitative statement consistent with your tidal field expressions or is it just another explanation relying on ‘centripetal acceleration’.-Leon Quote Link to comment Share on other sites More sharing options...
JohnHuth Posted October 23, 2014 Author Share Posted October 23, 2014 Hi, Leon - It turns out the motivation for the blog *was* NOAA's website. You can do the calculation in an inertial frame, as I did and the construction is to look at the diverging field lines. You can also do the calculation in an accelerating frame and invoke a 'centrifugal force'. Both will give the same results, but I find the accelerating frame calculation unnecessarily complicated. One carries along "test masses" throughout the calculation and it's not intuitive to me that you would derive an away-side bulge that is symmetric to a near side bulge. I'm in contact with the NOAA web maintainers and they say they're going to revise it this year. The reason I like this derivation is that I can also touch base with an accelerating frame in the following way: the average field in effect "goes away" because the earth's center is in free-fall about its barycenter. The remainder are parts of the earth that are not precisely following their geodesic (natural free-fall path) and hence feel a force - but that's simply the residual force given by the tidal field times the mass of the object. Quote Link to comment Share on other sites More sharing options...
JohnHuth Posted October 24, 2014 Author Share Posted October 24, 2014 Origin of the tides, part 2 Quote Link to comment Share on other sites More sharing options...
JohnHuth Posted November 1, 2014 Author Share Posted November 1, 2014 Here's a write-up on Figuring out TidesI *think* the postings now represent more or less a complete set of what I presented at the two REI workshops. I'm now going to make an introduction with links to each of the postings and make sure they're all cross linked. I also need to update a few based on some helpful comments I've received. If anyone has a topic that I didn't cover in the postings that were in the workshop, or they feel should be addressed, please let me know. Quote Link to comment Share on other sites More sharing options...
leong Posted November 9, 2014 Share Posted November 9, 2014 Static theory of tidesThis one is very math-y, so stay away unless you want the gory details. I'm mainly putting this up there for anyone who has taken a course in physics and wants to see how the static theory can be derived without reference to a centrifugal force. John,Perhaps you’ve seen this video. Without showing the math, it has a nice simulation of the tidal force around the earth. I think it helps one to understand why it’s the net differential force (after subtracting out the average force) that causes the tides.-Leon Quote Link to comment Share on other sites More sharing options...
JohnHuth Posted November 9, 2014 Author Share Posted November 9, 2014 Hi, Leon - Yes, it's a pretty good graphic and description. Good thing it's out there.John Quote Link to comment Share on other sites More sharing options...
JohnHuth Posted November 15, 2014 Author Share Posted November 15, 2014 OK, I cleaned up some of the details and provided an introductory piece that also has a table of contents. Although I'm sure there are some errors left in the entire series, I consider this reasonably complete and am grateful for some of the suggestions and discussions I've had - corrected some major errors on my part. Here's the introduction. Corrections, comments still welcome, of course! Quote Link to comment Share on other sites More sharing options...
gyork Posted November 18, 2014 Share Posted November 18, 2014 John, thanks for all your efforts for developing this valuable resource! The approaching season allows ample opportunities to practice, practice, practice what you have so clearly outlined. Quote Link to comment Share on other sites More sharing options...
JohnHuth Posted November 23, 2014 Author Share Posted November 23, 2014 You're welcome! I'd heard a critique that the variation lines will obscure important features, such as rocks or a buoy. I grabbed one of mine at random and scanned it. You can see them attached. Even when the line drawn goes right over a feature, like a rock or a buoy, it's still plainly visible. The main thing is to use a relatively sharp and narrow pencil, and not a thick sharpie. Quote Link to comment Share on other sites More sharing options...
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