|Hello Tom - I've enjoyed reading several of your posts over the few weeks that I've been browsing the Forums and wondered how long someone who calls himself PhysicsMan could stay out of a discussion like this.
Hi Amiles - Unfortunately, for various non-skiing reasons, I haven't been very active on Epic lately, but when I got the email about this thread, I had to see what was going on.
|Of course only a physics person would lump engineers and skiers together into one category - but aren't you afraid that kind of association might offend some skiers?
- sputter ... sputter ... why, some of my very best friends ...
|I agree that it’s not critical for a skier to understand in detail the relationship between pseudo-forces “felt” by an accelerating observer on the one hand, and on the other hand true forces that don't violate energy conservation. I tried (perhaps ineffectively) to make that same point in my first post when I said that the skier will feel an apparent force and that from a practical point of view what’s important is that he or she know how to respond to it.
I did notice that comment, but I felt that it lost much of its impact after the much longer subsequent discussion about "pseudo or not".
|I’m also not dismissing the common utility of performing an analysis from a non inertial reference frame that both you and mdf noted. Of course you do the problem in whatever frame is most natural (ie easiest)...
Same here. I'm not religious about one or the other. In fact, if you look back at previous posts by me, you will see that for some analyses/explanations, I prefer an earth-centric frame, while for other analyses/explanations I will use a skier-centric frame.
|I would be interested to hear more detail about your experience using various approaches (or frames) to try to impart the minimal necessary amount of physics to learning skiers, but I know this has been going on for a while and am perfectly willing to let it die here.
30 years ago, as a young pup, I taught a few of my colleagues (all Ph.D. physicists, chemists & engineers, and no, W. Heisenberg was not one of them
) how to ski, and I can clearly remember two of them making absolutely dreadful progress when I was using the typical visual or kinesthetic teaching approaches, but making a huge (and almost instant) improvement in their skiing after I got them off their skis, into the bar, and drew some free body diagrams for them. Following this success, for the next couple of years I believed that absolutely everyone would ski better if they only understood the underlying mechanics. I "pushed" simple physics/mechanics on anyone that seemed a likely "victim" ;-) Unfortunately, since then, I have *never* found anyone who profited from this type of understanding as much as my original set of friends/colleagues.
Fast forward to the last few years when I was teaching the public at Whitetail. Occasionally, I would get a (skiing) student who would bring up centrifugal/centripetal forces. These folks came in two varieties. The first type would be quite content to learn that what they were feeling was essentially the same as what they experienced while riding a bicycle around a curve. We could then immediately move on (if appropriate for their skiing level) to discuss related ski techniques (eg, "banking a turn" vs angulation, etc. ). Such folks would usually progress quite nicely.
Unfortunately, the second type of individual who brought up centrifugal/centripetal forces was probably 10x more common than the first type. This type of person clearly brought up these issues not to help his own understanding or that of his classmates (in a group lesson), but to show off and "prove" that he (and it was always a "he") knew more about skiing than anyone else in the class. This type of person would love to try to engage me in a long on-the-snow discussion of these issues, and would not care in the least that he was completely derailing the lesson for the rest of the class. While tempted to whip out an omega cross (omega cross r) or two
, my usual response is to say that I would love to discuss this with him, but we should do so during my break, in the lodge. Almost none of them ever show up.
When I really have to bite my tongue is when the person leading a PSIA clinic or exam that I am attending falls into the second category and doesn't know what he (again, it's always a "he") is talking about on this subject.
Basically, in spite of being a physicist and being known for my long-winded detailed explanations on every subject under the sun, when it comes to ski instruction, my take is that the amount of physics that most ski students need to hear on the hill is minimal and is exactly what Rick said in post #43 of in this thread: The faster you go and sharper you turn, the more you will need to move your center of mass to the inside of the turn to remain balanced.
Epicski.com is quite different in that it is off-the-snow discussion, there are many folks here who are quite interested in such issues, and who have a technical background. OTOH, even here, I still feel that the use of modifiers such as "pseudo" hinders general understanding because some of the readers of such a thread will (very reasonably) go directly to a dictionary, equate "pseudo" with "false" or "sham" (because of the common, non-technical usage of the term) and conclude that Coriolis and centrifugal forces are not real, even in the non-inertial coordinate system.
Again, just my personal $0.02 on the subject.
Tom / PM
| As a fellow owner of the big black book, peace.
I'm staying out of this one, but does having Hans Bethe as one's minor advisor in theory count for anything?
BTW, I forgot to say this before - a hearty welcome to Epic. Please stay around and contribute. There are a bunch of extremely nice folks on this forum. What part of the country are you in?