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# Get off those edges. - Page 9

Quote:
 Originally Posted by Martin Bell Out of interest, PM, are these velocity-generated forces of interaction with the snow dependent on the skier's kinetic energy or his/her momentum? My vague recollections of high school physics (George Watsons, daslider) tell me there are different formulae for those.

Very, very good question. The dynamical aspects of the analysis of the dynamics of a group of objects interacting with others (eg, a ski with the skier and snow) are essentially axiomatic. In other words, they are usually little more than separate F=m*a equations for each object, with the equations written in some appropriate coordinate system (eg, linear, spherical, cylindrical, etc.), and in some convenient frame of reference (eg, stationary with respect to the earth, in uniform linear motion, in steady circular motion, located on one of the objects, moving with the center of mass of all the objects, etc.). The simplicity of these equations (and underlying concepts) is why I can be so completely dogmatic and unambiguous about these aspects of just about any dynamics analysis.

OTOH, writing F=m*a a bunch of times does not provide a complete, solvable set of equations with which you can turn the mathematical crank and find out how the objects will move. The missing part of the puzzle is a mathematical description of the interactions between the objects under analysis. These formulae are usually termed the “materials equations”, “force fields”, or “constitutive relations”, and are almost always the most complicated part of a statics or dynamics analysis. Sometimes these relations can come from elaborate side analyses (eg, quantum mechanics), but often, they are little more than curve fits to empirical data. The latter is the case for a ski interacting with the snow.

While one typically can’t write down a complete formula for the materials equation for a given type of interaction, there are procedures (one of which is called “dimensional analysis” – Google this phrase plus “fluid mechanics”) which can at least suggest which sets of variables must appear in these equations, which variables can be immediately eliminated, the exponent to which the variable must appear, etc.

The question you asked about whether the ski-snow interactions are best described in terms of momentum or kinetic energy falls exactly into this category.

Consider a ski held in a fixed orientation (edge angle, angle of attack, and tip up-down angle) and dragged over or through the snow at some velocity (ie, both speed and direction) while being pressed into the snow by a specified weight. The sideways force of the ski on the snow (either drag or holding) is then measured.

Clearly, the direction the ski is traveling (everything else held constant) will make a big difference in the drag the ski will experience. Skidded sideways in one direction, a ski will tend to ride up and over the snow, while in the opposite direction, it will dig into the snow.

Since kinetic energy (KE = 1/2 times mass times speed squared) is a scalar, not a vector, this means that it contains no information on the direction of motion of the object (the ski), so we can immediately rule it out as a fundamental quantity in a description of ski-snow interactions. Of course, one could combine other more fundamental variables like mass and velocity to construct kinetic energy as a variable which could be used in such a materials interaction formula, but you would still always need to have mass and vector velocity around in any equation to fully specify the ski-snow interaction.

Momentum (mass times vector velocity) is a more promising variable since it does contain directional information. The real question about it is whether mass and velocity can always appear linked together (as they do in momentum), or need to appear separately in order to reasonably describe the interaction of the ski with the snow. A moment’s reflection should make it apparent that mass itself is not a fundamental parameter in determining the (skier+ski) interactions with the snow, but is the vertical component of the force with which the skis are being pressed into the snow that will determine the sideways drag force. The distinctions here that have to be thought about include sloped surfaces, and is it really mass or downward force (which might easily include centrifugal components) that is important. Clearly it is the latter.

So, after all this analysis, the short answer to your question, “…are these velocity-generated forces of interaction with the snow dependent on the skier's kinetic energy or his/her momentum?” is that these forces can, of course be said to be dependent on either variable, but the simplest, most useful, and most concise description will use neither of these combination-type variables but use (a) downward force, (b) velocity, and (c) ski angular orientation as the fundamental variables. If I remember correctly, these are exactly what Twardokens’ father used in his famous sled experiments.

Quote:
 Originally Posted by Martin Bell …Look forward to seeing the forces table. Any World Cup ski tech can tell you that considerable friction takes place at the section of the ski base that is adjacent to the metal edge, causing the dreaded "edge burn".

My table will provide a very accurate number for the total normal (ie, perpendicular) forces on the base and side of the ski, but it won’t say anything about whether the upward force on the base is concentrated near the edge or spread out across the width of the base. My analysis is intentionally limited in scope in this way in order to make it extremely general, accurate, and use the absolute minimum number of parameters and assumptions. An analysis which would predict the distribution of forces across the width of the ski would require an accurate model of the mechanical strength of the snow underfoot. Unfortunately, that is empirical data which varies greatly from one patch of snow to the next, so I didn’t even try to include it.

Tom / PM
Quote:
 Originally Posted by daslider … However in downhill skiing is it so absurd to point out gravity's role as prime mover? …

It is not at all absurd to point this out. In fact it is absolutely (and obviously) true. The problem I had was with your earlier statement, “… Of course it is this reaction force his ski can use but that itself arises out of the influence of gravity…”, and other similar comments, which strongly but erroneously imply that the reaction force arises directly out of the influence of gravity with no intermediate step.

In addition to being logically correct (as per my previous comments about jet powered skiers not using gravity but still turning), I think that the inclusion of the intermediate step: Gravity => Velocity over the snow => Force from the snow that pushes on moving skis and makes you turn, makes the understanding of the problem easier for everyone, not just physicists. I think that people know intuitively how gravity causes things going down hills to speed up. I think they also can easily visualize (even if they don’t understand all the details) of how a moving (bent and sidecut) ski could cut a curved path through snow, especially if the famous shaped index card model is run over something like a chairlift cushion. IMHO, trying to describe the process as gravity directly generating the needed reaction force will confuse the living daylights out of just about everyone (in addition to being wrong). This is what I meant when I commented earlier that you are conceptually mixing separate parts of the analysis.

Quote:
 Originally Posted by daslider I suppose what I am trying to construct here is an explanation which keeps the skier in the driving seat rather than the centrifugal diagram which imo makes out the skier is having to react to a force being imposed on him … I know early skiers can find the whole thing daunting and the more they can feel in control of events, the better.

I absolutely agree with you that many early skiers can find speed and direction control daunting, and that the more they feel in control, the better. However, IMHO, now you are talking about finding optimal teaching techniques and progressions for this group (ie, big wedges, little wedges, no wedges, lot of rotary, no rotary, etc.). This is very different from trying to come up with optimally simplified mechanical explanations. The former has been discussed ad nauseam on this forum. I have never once used (or needed) the latter with any low level class that I have taught.

If some ATM level 1-4 student asks me how to turn the skis, or how to “turn them better”, within the parameters of the techniques and progressions mentioned above, I show them, I tell them what they should be doing, I tell them what they should be feeling when things are working right, I ask them what they think they are doing and feeling, etc.. Never once have I ever told some level 1 – 4 student that the snow pushes laterally on a moving tipped ski, let alone continue on to say that that force is the centripetal force that makes you turn.

All last season, I only had two students with whom discussions even came remotely close to this level of detail. One was a level 5 and one was a level 6. Both students were “thinkers” and old-time skiers who were taking a lesson to help them transition to modern deeply sidecut skis. Both seemed eminently and immediately satisfied when I pulled out my trusty little plastic card with one concave and one straight edge, and had them run each edge over the chairlift seat cushion and repeat it at different edging angles.

Thus, I really don’t believe your stated quest for optimal (ie, proactive, in the driver’s seat, etc.) mechanical explanations will have any application whatsoever to low to-intermediate level skiers.

Even for high level skiers (thinking about the instructor’s clinics that I have attended), the need for full-bore or simplified discussions of the physics of skiing are quite rare, and if they occur, are satisfied easily. Even within this group, the shaped plastic model of a ski satisfies 99% of the discussions of ski-snow mechanics, and if such an advanced skier wants to become more proactive, more in the driver’s seat, etc., you don't give them a physics lesson, but you try to remove any remnants of back seat driving, get them on their edges earlier in the turns, etc.

About the only place where discussions of mechanics ever occur in depth and with any regularity is in the odd little microenvironment of this forum, so I again have to wonder for exactly whom you are pursuing your quest.

Tom / PM
Sorry to interrupt but I've been lurking and have a quick question that's been driving me nuts. I need to form an image of people when I read messages from them, and cant find any clue if daslider is a guy or a gal. Which is it?

Also, are you trying to get to the bottom of this technical stuff because you are a ski instructor?

YOT
Rick said: "The skier can be in control, but not of both the elements you refer to simultaneously. He must choose one or the other. If one chooses to control the path of travel down the slope then the magnitude and the resultant angular orientation of those forces is out of his control, he must react to them and manage them. If he desires to exercise an element of control over the forces generated while he skis then the line of travel becomes subservient."

RicB: I know I got to this point in distinction between creating and managing in another disscussion last year, and I'm still not resolved to the point you seem to be here. To me the question still remains do our movements to create the turn and direction always create the need for seperate movments to manage the turn forces created? In a perfect world, can our movements serve both masters at the same time. Can our movements we use to create a turn move us into dynamic posture(s) that gives us equilibrium to the forces?

If we view our balance as constant never ending adjustments to gravity or "behavioural gravity", then it seems they would remain always seperate. In the real world of skiing I see us constanly moving, not only to find equilibrium, but to also constantly change or control our direction. How often do we create a radius in our turn and stay in that radius? In our journey to perfect our skiing, to get to where we have no extra movements aren't we really trying to get to where our movements serve both masters?

I didn't get this resolved in my head last year, and it's still not resolved, though I do understand the distinction you lay out, because I've lead myself there before. I guess this is one of those black and white situations where I see the posibility of gray.

Yd said "In skiing the main forces we deal with are gravity, the forces our muscles can generate, and the force the ski generates. Gravity is constant and acts only in one direction, toward the center of the earth. Our muscles can only provide a force that will change our motion in a fleeting manner."

RicB: Yd, it's only your last sentence that I don't fully agree with, and it's not that it's only in a fleeting manner, but that the fleeting maner in which we change our motion seems to be constant in good skiing. Even in the either/or situation described by Rick above, one could certainly break it down to half the time, which would add up to more than fleeting in my book. Maybe it's only a difference in assigning importance, and not one of principle, but looking at and studying the science, hasn't explained it away for me. Maybe this is simply my own hard headedness.

PM said "So, after all this analysis, the short answer to your question, “…are these velocity-generated forces of interaction with the snow dependent on the skier's kinetic energy or his/her momentum?” is that these forces can, of course be said to be dependent on either variable, but the simplest, most useful, and most concise description will use neither of these combination-type variables but use (a) downward force, (b) velocity, and (c) ski angular orientation as the fundamental variables."

RicB: This is what I've had in my head when talking about "Body Power", though I incorrectly called it weight, but I always had in mind that it multiplies or grows as the turn progresses so to speak. I do use the term body power in my teaching. I want to help my students understand and feel how to use that downward force, and where to place it over the ski. For some reason your answer to Martin's question closed a gap for me. This does draw the attention to teaching and how we choose which part of the equation to teach to. We an evening clinic two years ago with downward force, weight, and gravity as the topic, but nothing was resolved and the leading clinicain was searching along with the rest of us.

Later, Ric.
PM

"and other similar commentswhich strongly but erroneously imply that the reaction force arises directly out of the influence of gravity with no intermediate step."

there are numerous posts showing these steps (ad nauseam?) and you choose to highlight the abbreviated form for whatever reason in what appeared blatant ridicule.

I am not suggesting an increased theoretical input into early instruction, but teaching 'how' without some implicit understanding of 'why' on the part of the instructor is unrealistic. I am just not convinced (generally) of that technical background that must inform any instruction, save possibly the 'follow me' approach. The emphasis for my money is too much on the 'reaction on the skier' rather than the 'action by the skier' which stems directly from the accepted theoretical basis.

I am also not saying that basis is wrong, maybe inappropriate and possibly coming from the race-based outlook where movement is disciplined by course settings. There is ample scope for all that, but maybe after the initial stages are grasped with more 'freedom of the mountain' feeling, where turns are not technical problems but joyous expressions. This would be a 'slow' approach and the antithesis to the blue-red-black progress many learners are expected to require. progress would not be how steep can you ski, but how well you can ski the 'easy' stuff.

Just my thoughts.
Yikes, daslider! I don't care why my car works, I only care that it works! I know there are people who care very much about why. They are called mechanics, and I consult them when my car's not working.

Ditto the public and ski instructors.

I agree that a skier mechanic needs to know why and how the whole hangs together, but I strongly disagree that the usual student would relish detailed explanations such as those offered in this thread. I also think we've gone so far to the side of complexity that we need to push through it to the simplicity that we all feel as skiers.

As Ric said, gravity is the constant. Whether you wish to regard it as a friend you play with or a foe you defend against is sport psychology, not physics. I teach the idea of using the available natural forces so as not to have to spend your own energy through muscular effort, which gives you more energy to spend on getting a full day of skiing and the fullest range of runs and conditions. Skiing smarter not harder doesn't require a passing grade in high school physics.
Quote:
 Originally Posted by daslider ...there are numerous posts showing these steps (ad nauseam?) and you choose to highlight the abbreviated form...
I certainly did not intend to selectively quote you out of context, but:

a) There is a big difference between an abbreviated form of an explanation and an incorrect explanation. In the former case, you can fill in the blanks and it will not change the meaning. In the latter, when you fill in the blanks, the meaning changes completely and the process of filling in the blanks sounds more like specifying the meaning of earlier weasel words, not further and deeper exposition of the subject. IMO, the quote that I focused on was blatantly incorrect (for the reasons I gave in an earlier post), very similar in structure and content to previous posts by you, and in no way could be construed as abbreviated.

b) The wording of technical discussions where the participants are not face-to-face needs to be as precise as humanly possible to avoid the sort of misunderstanding that you suggest happened, and IMHO, yours were consistently far from accurate. In fact, while you may feel differently, I am hard pressed to find any of your writings on the subject of "what makes a turn" that makes the two step link in a way that would be so clear as to not be subject to "misinterpretation". Instead, what I see is a clear change in your position with respect to two-step vs one-step (ie, gravity gets re-directed) in just the last couple of days.

c) The wording of technical discussions also needs to be extremely accurate because people with only a casual interest in the subject will usually remember only the "short version", and if this is in error, the error will become their understanding and the understanding of the lay community. We saw a prime example of this with the use of terms like "mythical" to describe centrifugal forces.

Quote:
 Originally Posted by daslider ...I am not suggesting an increased theoretical input into early instruction, but teaching 'how' without some implicit understanding of 'why' on the part of the instructor is unrealistic. ... The emphasis for my money is too much on the 'reaction on the skier' rather than the 'action by the skier' which stems directly from the accepted theoretical basis. ...
For many people, including myself, your first sentence (teaching without some implicit understanding of the mechanics) is absolutely true. However, what I suggested in my previous post was that a more than adequate implicit understanding of the "why" (for almost all levels of skiers) can come from very simple experiences such as "the credit card carve", the exercise of attempting to pull them downhill by their poles, etc. These are things which are currently done.

With respect to emphasizing actions initiated by the skier (ie, versus re-actions), I see no vast imbalance in favor of the latter approach in my ski school colleagues or the instructor clinics which I have taken. There is a huge amount of time spent coaching people to "get forward", "make more edge angle", "give me more edge early in the turn", etc., all proactive actions initiated by the skier. OTOH, there will almost always be a number of people in every group lesson that need to "feel the turn", and if you don't devote a bit of your energies towards satisfying their learning approach, you will have not done your duty as an instructor. Thus, balance in approach is needed.

Quote:
 Originally Posted by daslider ...I am also not saying that basis is wrong, maybe inappropriate and possibly coming from the race-based outlook where movement is disciplined by course settings. There is ample scope for all that, but maybe after the initial stages are grasped with more 'freedom of the mountain' feeling, where turns are not technical problems but joyous expressions. This would be a 'slow' approach and the antithesis to the blue-red-black progress many learners are expected to require. progress would not be how steep can you ski, but how well you can ski the 'easy' stuff.
Like Fastman questioned earlier, I really have to wonder how much data you have to come to the conclusion that instructors favor steepness as a metric vs. technically good skiing on the 'easy' stuff. The latter is what I pound into my students, is what my SSD and TD want me to pound in to them, is what my colleague instructors do, and is essentially the only position ever advocated by the instructors on Epic. Judging a skier by the steepness of the runs they can survive is a sophmoric concept that I see rampant among recreational skiers, particularly under-35 males and non-skiers. When someone is in one of my lessons and has this attitude, I spend quite a bit of energy getting them to see things differently. Unfortunately, it is such a pervasive attitude among non-skiers and recreational skiers that it is very difficult to change their attitude in just a few lessons.

Perhaps things are different where you ski, but I would ask exactly how many different instructors have you taken lessons from over the past few years, and what fraction of them advocated judgement by steepness. I suspect you are extrapolating the all-too-common recreational skier macho view to professional instructors.

Tom / PM

PS - Until the lurker's comment, I must say that I never even gave it a thought whether you might be a woman or an instructor. Obviously, it's your call whether to disclose such personal information or not, but it might help us understand where you are coming from if we had a bit more information about you and your skiing background.
as a matter of interest, just how much difference would it make if I were a woman?

I am not that interested in this point scoring; if I do find such examples I will let you know but I do not propose to go looking specifically, I am quite happy about my general train of thought which has not changed significantly because of your recent (and overly personal) contributions. You were right to point out specific loose comment, but not to draw the conclusions you did. Of course in many ways this thread has been very educational.

I am glad we agree about steep and good re progress and no I do not have survey data but I suspect too many people regard skiing progress in the blue-red-black paradigm. I have been told on several occasions that clients should 'by now be off the nursery slopes' when imo they were not ready, perhaps only having skiid a day or two. I have also seen others on that same conveyor belt because by the end of a week they wanted to have skiid the mountain (perceived or actual ambition?), rather than actually learn to ski. Many resorts do not make it that easy to attempt both, unsuitable balance of terrain etc. Perhaps others have comparable experiences?
Hopefully, none - It's just that for me, much like YoungOldTimer said, I find it vaguely disconcerting to be engaged in extensive communications with someone, but all exchanges are made exclusively by typing, without having even a clue as to the voice, interests, personality, age, or even gender of the individual at the other end of the wire. Just call me old fashioned.

With respect to pressure within the industry to get students to progress to steeper slopes, because of the pervasiveness of this desire/attitude among recreational skiers, ski area management and ski school management certainly knows about it, but they also know the pitfalls of moving someone up the mountain too fast and thus have to balance skier returns/retention/interest, safety considerations, the desirability of “under-terraining”during instruction, etc. Management decisions with respect to these trade-offs obviously must vary from area to area, but I can say unambiguously that at the area I teach at, the oft-repeated guidance to instructors was to be very cautious in taking students onto steeper trails too early in their skiing careers.

I would say that if anything, we probably lost some repeat business at the ski school when I had to unambiguously tell several students during the course of the season that they simply weren’t ready for more advanced slopes even though they thought they were. On the other hand, we gained at least one return student, when I told her at the end of her lesson not to go up on our main green slope. Later in the day, she did, and I happened to find her crying and immobilized with fear at the edge of the trail as the soft snow of the afternoon turned into rock hard ice at night. She acknowledged the appropriateness of my advice and showed up the next week for another lesson.

Tom / PM
Ric,

Again we run into the limits of communicating with the written word filtered through the personal biases of the reader. When I say the muscles can only provide a motive force that is fleeting I am thinking in terms of the muscles being able to 'push us over there'. Only by contracting in such a way as to extend our various joints can the muscles directly move our body about and this type of movement is either provides a lot of force in a short time period or a little force spread out over a longer time period. Compared to the the time duration of the force that I can generate by using my muscles in such a manner as to create and control the force generated by the skis and then transmit that force to my CoM the direct motive force of my muscles is fleeting. Further if I were using my muscles to directly accelerate my body in the ways I observe happening in a ski turn I would be unable to make more than one or two turns.

On another point. One of the reasons I like my way of thinking of skiing is that the movements that I make to create the force generated by the ski, get the ski tipped up on its edge, are tied directly to the movements I make to line up my skeletal structure to efficently transmit this force to my CoM. In plan terms, to tip my skis on edge my CoM must move to the inside of my feet. To line everything up to transmit the force generated by my tipped skis I must move my CoM to the inside of my feet. My movements to create the force and my movements to transmit the force are the same.

Hope these ideas might make things a little clearer,

yd
Nolo

yes, that is what I am saying too. The student seldom needs such input, but an appropriate technical basis needs to inform the teaching, in terminology and analogy and in the way teaching is structured, etc. Yes as well to the psychology point, as I said earlier.

Yd, excellent summary, things very clear. An harmonious coincidence.

PM, economics often prevails and some people will dream of running before walking. But we have slow food now, maybe one day slow skiing as well. Nolo is right, this conversation might been much easier, where are you Psychology Man?
Yd, thanks for hanging in there with me. As I seperate the wheat from the chaf, it really is clear that there is way less difference between most of the posters than one reads into the words. I have taken this as a challenge to myself to take more time with my posts (thanks Rick) and also with reading others posts. I know some might feel belabored by the draging out of some of this (sorry Rick, PM), but if we keep it civil and continue conversation, eventually an understanding of each others position will happen hopefully.

Tis true we all bring our biases to our posts, each and every one of us. But as we like to say about comunication and learning, it's a two way street. It's evident to me that I see nuances and distinctions that others don't find important or choose to view from a different perspective. This doesn't mean that there is disagreement with the priciples and fundamentals of skiing because of this. It will be a good exercise for me to try to move outside of my box in future discussions. It can only help my teaching.

Unfortunately, or maybe fortunately for you all, I'm outta town for a week.

Later, Ric.
Quote:
 Originally Posted by PhysicsMan With respect to pressure within the industry to get students to progress to steeper slopes, because of the pervasiveness of this desire/attitude among recreational skiers, ski area management and ski school management certainly knows about it, but they also know the pitfalls of moving someone up the mountain too fast and thus have to balance skier returns/retention/interest, safety considerations, the desirability of “under-terraining”during instruction, etc. Management decisions with respect to these trade-offs obviously must vary from area to area, but I can say unambiguously that at the area I teach at, the oft-repeated guidance to instructors was to be very cautious in taking students onto steeper trails too early in their skiing careers. Tom / PM
I agree, it's a balancing act: ideally, students should learn the techniques on easier terrain that will then stand them in good stead on steeper terrain. But each individual requires a different approach: if you know that your student has the psychological profile that will drive him/her to seek out the challenge of steeper terrain, after your lesson has ended, is it not safer in the long run to try to prepare him/her for it, and ensure that his/her first encounter with the black run is under your supervision? (Obviously, a return lesson would be ideal, but in today's society too many people expect immediate results.)
BTW, thanks for the kinetic energy / momentum reply! It's interesting to hear that there are limitations in predicting an interface with a natural, inconsistent surface like snow. That must be why they can make Formula 1 cars that are reliably fast, but not DH skis!
Quote:
 Originally Posted by RicB To me the question still remains do our movements to create the turn and direction always create the need for seperate movments to manage the turn forces created? In a perfect world, can our movements serve both masters at the same time. Can our movements we use to create a turn move us into dynamic posture(s) that gives us equilibrium to the forces?

Ric, absolutely!! From the way I read you here I'm in enthusiastic agreement.

I now think our confusion over our separate views on this particular issue was nothing more than word usage and interpretation. Originally, daslider presented the idea that we can simultaneously control turn shape and turn forces. I rejected this idea because of my interpretation of the word "control". The dictionary defines it with such terms as: to hold back, regulate, direct, curb, restrain. In any particular turn there are forces created of a magnitude dictated by mathematics and physics, they can't be curbed, restrained, held back, or regulated. The only way we can alter (control) the magnitude of the turning forces is to alter the shape of the turn. This is why I said we have to choose one or the other to control. We can't control both at the same time.

In this post you use the word "manage". Now you’re talking! This is why I enthusiastically agree. We make the turn shape we desire and we manage the forces that emerge from that turn shape to provide the most efficient balance platform. The two masters you refer to (movements to create a turn, and movements to manage the resultant forces of that turn) can most definitely be simultaneously served, and it should be the goal of the aspiring upper level skier to do so.

There are various methods of angulating and inclinating that will provide the same edge angle, and therefore the same turn shape. But only one of those various body positions will provide the most efficient balance platform. The upper level skier develops an innate sense of what that body position is for various turn shapes at various speeds and assumes it in harmony with the application of the edge angle needed to produce that desired turn shape.

Good post Ric. It takes us beyond the simple foundational physics we for some reason have had a difficult time getting a grip on in this thread, and moves us into a higher level of conversation.

Quote:
 Originally Posted by RicB In the real world of skiing I see us constanly moving, not only to find equilibrium, but to also constantly change or control our direction. How often do we create a radius in our turn and stay in that radius? In our journey to perfect our skiing, to get to where we have no extra movements aren't we really trying to get to where our movements serve both masters?
Most definitely, you've just described the concept of dynamic balance.

FASTMAN
Quote:
 Originally Posted by ydnar Ric, In plan terms, to tip my skis on edge my CoM must move to the inside of my feet. To line everything up to transmit the force generated by my tipped skis I must move my CoM to the inside of my feet. My movements to create the force and my movements to transmit the force are the same. yd
Careful here ydnar. I agree with the distinction you make between efficient muscle usage vs. the muscle usage you refer to with the term "fleeting". The problem I see is in the idea that the movements used to create the force (put the skis on edge) and the movements used to transmit the force efficiently (balance/align) are the same.

They can be the same, they should be the same, but they don't have to be the same. This is the challenge of developing upper level skiing skills, learning how to consistently make them the same.

This relates directly to my discussion with Ric (above post). There are various ways to put a ski on edge, but only one provides balance efficiency. Additionally, what position is efficient for a particular edge angle is dependant on the sidecut of the ski.

You state, "To tip my skis on edge my CoM must move to the inside of my feet".
This is not necessarily true. One can stand on a floor in ski boots and tip them up on edge while remaining in balance. How? By keeping CM over the feet. The same thing can be done on skis. The problem is while moving down a ski slope such a position will not provide lateral balance. That's a gross example, but the important point is that the joints can be articulated to provide a wide assortment of lateral CM locations for a particular edge angle, but only one of those locations provides ultimate balance efficiency. Mastery of the sport involves developing the ability to consistently find that ideal location.

FASTMAN

PS: I'm sure you know this stuff,,,,, just one of those mind to paper translation things again,,,,, hoped to contribute clarity.
Martin Bell

"if you know that your student has the psychological profile that will drive him/her to seek out the challenge of steeper terrain, after your lesson has ended, is it not safer in the long run to try to prepare him/her for it, and ensure that his/her first encounter with the black run is under your supervision?"

The question is surely are they ready in your opinion, and if not, by pandering to their 'psychological profile' rather than their skillbase aren't you just contributing to the problem. Of course many 'clients' don't see 'the problem', if like the tattie sack they can get down the slope, that's good enough for them and whether you think it is good skiing isn't their concern. And maybe until they crash into someone bigtime, it is only their concern, but there is some vicarious liability in all this.

How can you make 'skiing well' the ambition when as you say "in today's society too many people expect immediate results." One day I will found Slow Skiing!
daslider,

The ambition is not to ski well one easy terrain, but to ski well on all terrain. Hence progress is definitely measured by the terrain you can ski (assuming you ski it well and in control).
Quote:
 Originally Posted by daslider ...How can you make 'skiing well' the ambition when as you say "in today's society too many people expect immediate results."...
Here's one way.

On the day before a PSIA certification exam, the novice hill was filled with instructors (not in uniform) trying to perfect various slow skiing skills and drills on which they would likely be tested. Amidst this crowd, one person stood out. He was a lanky guy, about 18 years old, by himself, dressed in sopping wet jeans and a football jacket. He was falling every few feet.

He was nothing, if not persistent, and in an hour or so of non-stop lapping of that hill, he got to the point where he would only fall if he turned. This didn’t bother him in the least – he simply straight-lined the hill (skis parallel, butt and poles way up in the air in the classic 10 y.o. beginner’s impression of a racer’s tuck).

At odds with his advanced technique (he was probably going at least 15 mph, after all), he did have to turn at the bottom of every run to get back on the lift. Initially, he would fall over every time he would attempt this turn, but eventually, he got to the point where he could make the turn successfully.

Now that he had at least one turn in his bag of tricks, one would have hoped that he would have worked on putting more turns into each run. WRONG. Instead, he worked on going faster during the straight portion of each run. Using mostly one pole, he polled all the way down like some sort of berserk Venetian boatman.

Seeing that there was absolutely no way he could avoid anyone that happened to be in front of him, and realizing that he looked like he had absolutely no interest in lessons, and that his philosophy of skiing was guaranteed to continue once he got on steeper slopes and he would become a real menace to other skiers, I decided that, in the interest of public safety, I had do something.

I got on the chair with him, introduced myself as an instructor, and while biting my tongue, praised his progress over the past hour. Then came the sneaky part. Building his ego, I told him that I thought he had real “racer” potential, but did he realize that racers had to make lots of turns (where “the flags” are) to win, and if they don’t go around each “flag”, they lose. I then told him that the best way to practice for races is visualize imaginary flags all over the hill and that you have to turn around each one of them, but, of course, you have to keep your speed up as you make each turn. I also pointed out other instructors and told him it was common for instructors to polish their technique on easy terrain.

He said that he was blown away by what I had told him. He told me that he was a 1st day beginner (big surprise), really admired ski racers, and had absolutely no idea about how races actually worked.

I demo’ed the concept of gates a few times with my poles getting more and more offset and left him to his own devices. As the day went on, I would periodically peek at the novice hill and see how he was doing. Not once did I ever see him straightline it again and a couple of my buddies asked, “What the h#ll did you tell him to slow him down?”

Sometimes a carrot is better than a stick.

Tom / PM
Nice story PM. I have troublesome young dog at the moment and have found beating her with a large carrot as effective as anything.

TomB, of course it is the whole mountain, eventually, but where do you best start?

Fastman,

This thread has shown more differences in attitude than in substance (where there is general agreement imo). And at least part of that attitude difference is due to different perspectives on ski learning, what may be appropriate for early recreational skiers may differ from what aspiring racers need. Your interest may be with the latter, mine with the former.

Attitude boils down to whether one is preoccupied with the making of the turn as a single entity, an expressive feeling of movement at one with the mountain, or in managing the consequences of making that turn which is the requirement where turns are premapped and one is at the limits of capability. The former tends to describe skiing as an action, the latter as a reaction. Both are valid attitudes in their differing intents, but they do have different implications to teaching and where and how to begin.

This latter race-orientated attitude has prevailed until now, but I feel there is scope for a shift towards the other position for early skiers (with the option of moving into race-based teaching once the essentials are well mastered) which may explain why in contrast to the attitudes of your Mr Fast, mine have looked like the attitudes of Mr Slow (in the Carlo Petrini sense).
Quote:
 Originally Posted by daslider Fastman, This thread has shown more differences in attitude than in substance (where there is general agreement imo). And at least part of that attitude difference is due to different perspectives on ski learning, what may be appropriate for early recreational skiers may differ from what aspiring racers need. Your interest may be with the latter, mine with the former.

daslider,

This is your thread, and you started it with a focus on the role of edges and sidecut in carved turns. I have directed my comments to that subject here. As a race coach I have adopted/developed/implemented teaching models into my race programs that guide very young kids with limited skiing skills all the way up the skill ladder to FIS level. I place great importance on the quality and method of instruction in the early skill development period, as it sets the foundation for all future success.

Quote:
 Originally Posted by daslider Attitude boils down to whether one is preoccupied with the making of the turn as a single entity, an expressive feeling of movement at one with the mountain, or in managing the consequences of making that turn which is the requirement where turns are premapped and one is at the limits of capability. The former tends to describe skiing as an action, the latter as a reaction. Both are valid attitudes in their differing intents, but they do have different implications to teaching and where and how to begin.

Excuse my bluntness, but what a load of poetic manure. Anyone who exercises control over their course of travel down the mountainside (whether racing of free skiing) is subject to the forces that line of travel produces, and in turn subject to the need to manage those forces.

Quote:
 Originally Posted by daslider This latter race-orientated attitude has prevailed until now, but I feel there is scope for a shift towards the other position for early skiers (with the option of moving into race-based teaching once the essentials are well mastered) which may explain why in contrast to the attitudes of your Mr Fast, mine have looked like the attitudes of Mr Slow (in the Carlo Petrini sense).
You continue to show your ignorance through your posts, and comment on things you know little about. The race orientated instructional model has always been anchored in the development of non-gate fundamental skiing skills. Those who think otherwise (you) do so from a lack personal contact with the race community.

Your post is a prime example of the inaccurate, nonproductive noise meant to draw attention to oneself I've commented on earlier. As PM told you, such behavior only contributes to the confusion of readers who are truly attempting to learn something from the exchanges on this forum.

Give it a rest.
Rick!

Right on! He deserves every bit of it!!!! he is absolutely full of BS!

A-man
so someone putting a point of view you don't like "contributes to the confusion of readers who are truly attempting to learn something from the exchanges on this forum."

Only accepted ideas accepted, a large helping of Freedom Fries all round then, you can have them on me.
A requirement is that the point of view has some basis in fact!
Quote:
 Originally Posted by daslider ...This thread has shown more differences in attitude than in substance ...at least part of that attitude difference is due to different perspectives on ski learning, what may be appropriate for early recreational skiers may differ from what aspiring racers need...

Your posts, including the most recent, continue to trigger some of the most strongly worded responses that I have ever seen on Epic, especially considering that they were made by some of the most knowledgeable and usually patient and level-headed participants on Epic, for example:

Fastman: ...what a load of poetic manure...You continue to show your ignorance through your posts, and comment on things you know little about...

Atomicman ... Rick! Right on! He deserves every bit of it!!!! he is absolutely full of BS! ...

and, from me, Physicsman: ... As in many of his previous posts, the above statements by daSlider once again show a dreadful and complete lack of understanding of some of the most elementary principles of high school physics...Gravity is not, and can not be turned off, re-directed, deflected, sheared, or manipulated in any way at any time, ...There is a big difference between an abbreviated form of an explanation and an incorrect explanation... I really have to wonder how much data you have to come to the conclusion... etc. ...

Given the strong responses which your posts continue to provoke, I think that the difference in attitude between you and "us" is much more fundamental than simply racer vs recreational.

I think that the importance difference is educational and discussion style. From your good writing skills, my guess is that you are well educated, but come from a liberal arts background in which the process of debate is held high in high regard, but the actual technical content of any particular debate is virtually unimportant.

Although I have never met either Fastman or Atomicman, I suspect that they are a lot like myself, nuts-and-bolts type of guys with little tolerance for what we see as ill-informed puffery and word play (ie, the process of debate, with no regard to the content). You seem to think that a debate can go on endlessly, whereas guys like us know when we are outgunned and will shut up and listen to someone more expert on a particular subject. Specifically, you try to continue to debate (in his areas of expertise) a race coach with 30 years experience, and you tried to continue to debate me on physics (with 30+ years continuous professional experience in my own area) until I picked apart enough of your physics gibberish for to to become abundantly obvious even to you that you had no chance of "winning" that debate.

With respect to your thoughts on how the physical world works, I would guess that you have never taken any subject which is axiomatic or essentially axiomatic in nature, e.g., math or classical dynamics. You seem to have no idea how these subjects are structured and best approached, and in this absence of knowledge, obviously feel that minimal-content debate will nicely fill the gap. It doesn't. This is obvious to several of us, but you seem to be completely oblivious of this and perseverate, wasting the time of those of us that want to either learn or share our knowledge.

We find your approach infuriating, and I believe this annoyance is why Fastman suggested, "Give it a rest!". If a student in one of my classes ever acted the way you have, after an appropriate,escalating series of warnings which were ignored, I would have them removed.

Tom / PM

PS - The reason I asked about your background is that even before this most recent flurry of exchanges, I had in mind the possibility you had a strong liberal-arts / debating background, and thought that if this was indeed true and brought to light during a period of relative calm, it would help explain the differences in perspective and help defuse the tensions.
Quote:
 Originally Posted by daslider so someone putting a point of view you don't like...
You still don't get it, do you? In some subjects, "points of view" are not relevant, facts are. Would you think if someone said to the geometry teacher, "My point of view is that the angles of a triangle add to 181 degrees"? This is essentially what you have been trying to do in physics (eg, "Aren't the really heavy g forces you feel at the bottom of a turn actually decelerations as g is diverted sideways?"), in your comments suggesting most ski instruction pros use survival on steep slopes as the metric of technical skiing, as well as elsewhere.

As someone essentially suggested earlier, you should realize that you continue to make what sound like pronouncements in areas you obviously know next to nothing about. This really annoys knowledgeable people; this confuses less knowledgeable people; and, you WILL continue to be held accountable for such statements. There are lots of people on the internet smarter / more knowledgeable than you, and there are lots of people smarter / more knowledgeable than me who will keep both of us honest. This is one of the beauties of the internet.

Tom / PM
Atomic and Fast Men

'A requirement is that the point of view has some basis in fact!'

Fair enough, I came here to learn, none of us knows it all. Disputing a point of view based on doubtful fact is simple, doubt the fact and provide your correction in what is often called conversation.

If you choose to dispute someone's point of view because you don't consider they are entitled to a point of view (because of your superior qualification and/or experience?) and instead you prefer the ad hominem attack, the messenger shoot and various levels of insult, then that should be called a slanging match.

Which one do you prefer?

As a matter of opinion, if I put up some proposition and it is cogently and persuasively shown to be wrong, isn't that quite a useful exercise for your "readers who are truly attempting to learn something from the exchanges on this forum"?

Dr. Who and the Ancient Greeks had similar words for this kind of exchange and it doesn't seem that bad an idea for such a message board, unless for some reason Epicski prefers otherwise, in which case as a relative newbie I am happy to defer.

263 responses can't all have been wasted time.
Quote:
 Originally Posted by PhysicsMan Would you think if someone said to the geometry teacher, "My point of view is that the angles of a triangle add to 181 degrees"?
I might think his point of view was of a particular triangle on the surface of a particular sphere (such as on the surface of the earth).
Quote:
 Originally Posted by daslider Nice story PM. This latter race-orientated attitude has prevailed until now, but I feel there is scope for a shift towards the other position for early skiers (with the option of moving into race-based teaching once the essentials are well mastered) which may explain why in contrast to the attitudes of your Mr Fast, mine have looked like the attitudes of Mr Slow (in the Carlo Petrini sense).
Surely PM's story illustrates that the discipline of real racing technique (the ability to turn whenever and wherever it may be required of you) is an extremely useful role model for all skiers, racers or otherwise. The only danger is when racing is mis-understood, as by PM's young hothead, ie. "fast skiing = good skiing".
PM

"Aren't the really heavy g forces you feel at the bottom of a turn actually decelerations as g is diverted sideways?"

I should really thank you for the obvious trouble you have gone to, to point out the errors of my ways (for the third time!). In the context of my other posts this didn't seem an unreasonable shorthand for an argument already made at some length, but yes it is imprecise and scientifically sloppy for someone who did both maths and sciences at A level and then a BSc in a field of applied engineering, but that is actually missing the point!!! And if you want to use that as a rod for my back and to invalidate anything else I may say, that's fine, but rather a waste of your time.

I hardly need rehearse here what has been said, but for the record the shorthand version might have read:

"Aren't the really heavy g forces you feel at the bottom of a turn actually decelerations as the effect of g (in accumulated momentum) is diverted into sideways acceleration?"

Still clumsy, and certainly not an on-piste chat line, but its gravitational emphasis comes from an attempt to explain the movement in terms of a gravitational motor force that most people easily grasp (skiing downhill is easier than skiing uphill) that through ski design/body movement can effectively be diverted into sideways movement, controlled then repeated, (thus allowing turns, control and a choice of routes etc,) in a tangible explanation for skiing based entirely on the skier's bodyweight and how he moves it to ski?

Just a subtle difference of emphasis from something that happens to you, towards something that you do.
Quote:
 Originally Posted by sjjohnston I might think his point of view was of a particular triangle on the surface of a particular sphere (such as on the surface of the earth).
As I was typing out the example, I thought to myself, "You don't think anyone would propose spherical trig, do you?" Well, now I know the answer.

Good one!

Tom / PM

PS - Please modify the previous example to read, "In an elementary plane geometry class ..."
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