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# A Tale of Three Turns - Page 6

Quote:
 Originally Posted by michaelA Rick, I think I've figured out where we've followed diverging paths on this topic - I just need to pull together some graphics to put things in perspective. The highlighted text seems to be where we are not on the same page. I think Gravity can assist this whole thing - the idea I tried to present with the 'Ballistics' concept. Specifically - Take your current visualization and incorporate a slope dropping away from the skier... In this case, if the skier's overall momentum is outward - away from the slope then the slope may be dropping away from the skier slightly faster than the skier is "falling". In short, the distance between the skier's body and the skier's skis is getting greater as they progress into the turn. Does that help? .ma
Quote:
 Originally Posted by Rick With the deep flexion of a retraction transition, straightening of the outside leg requires a lifting of the CM. Gravity is not prone to help a skier do that, and Centrifugal force will only if there is a lateral imbalance, which will also cause a skier to lose edge angle, when at the top of the turn they are trying to do the opposite.
I too agree with MichaelA here. Straightening the outside leg does NOT neccessarily require "a lifting of the CM". I believe both gravity and the perceived centrifugal force from the outside ski engagement, aid the realignment of the CM.. By relaxing and allowing the CM to be pulled across at edge change and then extending the outside leg, the skier will bend the ski supplementing both the pull of gravity on the cm which is already moving on a very similar path, and the turning forces created by bending the ski. Basically the CM is moving laterally not vertically while the legs are extending and retracting underneath the hips.

It is certainly easier the feel than explain but I can see how in comparison in your montage of the aft stance demo, you may feel the need to make a more vertical movement to catch up, where in Bob's montage his movement appears more lateral and linear, demonstrating a higher level of skill and dynamic balance. The skis accelerate out to the side while the cm simultaneously short cuts harnessing both momentum and gravity to compliment the trajectory. voila, dynamic balance.

sorry wife is calling must end now...

b
Quote:
 Originally Posted by cgeib you are demonstrating a skier parked in the back seat at the mercy of the skis sidecut.
Quote:
 Originally Posted by Rick believe it or not, edge angle management is possible from the back seat too.

Quote:
 Originally Posted by cgeib Have I ever said otherwise, Rick?
Oh gee, now where did I ever get the idea you did? :

Quote:
 As you already established no rotary was needed (no pivot then), so you must have hoisted then?:
I'm almost afraid to answer, as you might think I'm throwing stealth "idiot" accusations at you again,,,, but no, I didn't "hoist". IT'S AN AFT DRILL, THEIR IS NO CATCHING UP TO BE DONE.
Quote:
 Originally Posted by bud heishman . It is certainly easier the feel than explain but I can see how in comparison in your montage of the aft stance demo, you may feel the need to make a more vertical movement to catch up b
Bud, please refer the bold print in my previous post.
Fair enough, Rick. I did not say you could not manage the edge, though I did not think you were demonstrating that. You clarified afterwards saying you were driving. I understand where you were coming from though, sorry.

Yes, I recognize it as an aft drill with no catching up to be done, so I'm passing on how the same theory applies on how the catching up is done.
I think that's about enough for me. There's been plenty of clarity in my posts, and people could have found all the answers to their questions and challenges if their motivation was to read my message as a whole and grasp what I was saying, rather than searching desparately for little nit pic, out of context issues to argue with me. Enough time wasted on this one,,, checking out. Carry on kids.
And here are some more pictures of “catching up,” Chris.

Not to belabor what is probably pretty obvious to most people by now, but here is another look at fore-aft movements and rotary movements on a highly tilted axis. Some might think that a half pipe has very little in common with alpine ski technique but, as with the nordic images I posted earlier, there is much to learn here. This is a very short clip of Doug Benson, Freestyle Trainer Accredited instructor with PSIA-Rocky Mountain (also an accomplished alpine skier and snowboarder) in the half pipe at Keystone:

First of all, as Doug goes up the wall of the pipe, he shows an extremely exaggerated view of the “body behind the feet” position that has been much-discussed in this thread (draw Rick's "vertical line test."):

So, is he out of balance? Is he “tail-weighted”? Of course not! These images highlight the difference between analyzing balance statically and in motion. At the very least, they suggest that a slight modification of Rick’s “vertical line test” to the “perpendicular to the slope” test, may describe the situation better in some instances.

But a half pipe is not fundamentally different from the trough between two (very large!) moguls. Shrink the whole thing down, and the necessity of the forward movement of the feet as you go up the side of the bump becomes obvious. Likewise for the need to pull your feet back, or get your body (CM) ahead of them, on the way down the other side, as Doug also shows:

The interesting question to ask is, what did Doug do to get from way “behind” his feet to way ahead of them? The answer is obvious—he changed the direction his skis were pointing. The relative positions of his feet and CM hardly changed—he’s horizontal, with his feet to the left of his body (from our perspective) the whole time. This is akin to the point Rick has made about how a pivot can affect fore-aft balance, clearly illustrated in the LeMaster sequences of Ted Ligety and Giorgio Rocca. If your CM is behind your feet, all it takes is a 180o pivot of those feet, and you’re ahead of them. I contend that it doesn’t matter whether those skis pivoted, or carved around as in my sequences—the outcome is the same.

Now, imagine two half pipes right next to each other, and think of how you’d have to move to ski from one to the other while keeping your skis on the ground. Here’s a little animation I just made to show just that. Not only does “hips behind feet” not necessarily mean “out of balance,” it is actually often a required relationship to be in in balance:

The “point” between the two troughs (as opposed to a nice, smooth, round bump) exaggerates a couple things, for clarity. First, it shows how the feet move much faster than the CM through the trough, then “wait” at the top for the body, which moves pretty much continuously, to catch up, pass over, and move ahead of the feet prior to diving down into the next trough. Rounder bumps and “virtual bumps” on flat terrain will smooth these movements a bit, but the basic ideas remains the same. Second, the “point” between the troughs completely prevents the skier from levering off his tails to push himself forward.. It’s all balance—and patience—to allow the body’s momentum to continue until it catches the feet.

Some may not see the relevance of bumps and half pipes to this discussion of carved turns on groomed snow, but the relationship should be clear. The ebb and flow of forces in carved turns, as well as the changing speed of the skis as they dive down the hill and carve across (and perhaps even back up) creates virtually the same needs for flexion-extension and active fore-aft balance management, albeit not as dramatically (usually).

One more for Telerod (and any other nords among us). Here’s Patti Banks again, making a telemark turn in the big bumps of Pallavicini at Arapahoe Basin a couple weeks ago:

Once again, you can see the forward motion of her feet beneath her center of mass as they race through the trough, after which they “wait” for her on top of the next bump. Since she is also in the middle of her telemark lead change, it shows her hips and CM well behind her feet. Yet once again, momentum, timing, and balance bring everything back together without any need for an active, muscular “recovery” move to get out of “the back seat.” She’s in balance the whole time!

I should add that, while this aft-looking stance is obviously apparent in the “retraction turns” sequence of me (sequence #2), the same fore-aft movements are happening in the first sequence as well. Without the deep flexion through the transition, the hips do not move as far back, so it does not look as obvious. But look closely—you’ll see it!. (Remember that the hips are NOT the same as the center of mass.)

To summarize, there is clearly much more to fore-aft balance than the distribution of mass about a line in a still image. As you can plainly see in frame 12 of the retraction sequence, the entire ski edge is engaged, even though the pressure is just starting to build up on the skis. It may appear that the outside (uphill ski, mostly hidden from view) tip is off the snow, but I believe it is simply because that ski is bent into reverse camber, yet still quite light on the snow. Or perhaps I am slightly on my tails there, as I drive my body forward and down the hill. Remember that “centered” for me is very much over my heels, and I rarely try to apply pressure to my boot tongues. That’s the sweet spot that allows the entire edge to engage, and it’s where I aim to be during the pressure phase of the turn, which, again, is just barely beginning in frame 12. Frames 9-12 represent pretty much a “float” phase where my legs have actively retracted (flexed), largely to remove pressure from my skis and to allow my CM to flow unimpeded through the transition. For all practical purposes, I’m nearly airborne there and my legs are not supporting my weight, so I’m more concerned with getting everything in the right places for the upcoming pressure phase. It’s much like Doug Benson in the air above the half pipe, getting everything lined up so that he will be in balance when it becomes critical.

Fore-aft balance (fore-aft pressure) depends on body position, accelerations of various body parts, hill angle, snow conditions (who hasn’t gone over the handlebars when your skis hit a big pile of heavy, slow, crud, even if you were somewhat back just prior?), friction (wax and structure), ski performance (gliding or skidding), perspective and viewing angle of the observer, and of course, whether there’s pressure on the skis at all in the first place. We control pressure by blending all these factors, as well as by moving the body fore and aft by flexing and extending various joints (ankles, knees, hips, spine, arms), and through skillful use of rotary movements especially when inclined at high angles.

I’ll close with a few more small animated clips of World Cup and Noram racers doing what they do best, for entertainment and education:

This Finnish racer’s hips touch the snow, yet he floats effortlessly forward and across into the next turn.

Note, in every one of these images, the same obvious movement pattern of feet moving forward of the body through the transition, as the CM travels across and downhill, taking a shortcut to a position well ahead of the feet (downhill and inside the turn).

Best regards,
Bob Barnes
Dangit Bob! Yer supposed ta be in bed by now! Here I am staying up all night putting together something substantial - and you go and sneak in a really well-substantiated 'proof of concept' in the wee hours...!

Oh well - nice post! Maybe I'll just rewrite mine grumble, grumble, grumble and cover things from a slightly different perspective since there's probably still a lot of skeptics out there.

.ma
Quote:
 Originally Posted by michaelA Dangit Bob! Yer supposed ta be in bed by now! Here I am staying up all night putting together something substantial - and you go and sneak in a really well-substantiated 'proof of concept' in the wee hours...! Oh well - nice post! Maybe I'll just rewrite mine grumble, grumble, grumble and cover things from a slightly different perspective since there's probably still a lot of skeptics out there. .ma
Michael, you're kinda cute when you get mad
Quote:
 I contend that it doesn’t matter whether those skis pivoted, or carved around as in my sequences—the outcome is the same.
For me the difference lies in when and how effectively we can get pressure to the skis edges. Leverage is leverage and alignment is alignment, and the two do not always equate to the same thing, and stored energy doesn't always work for us either, it can work against us as well. If I leverage my skis when out of alignment, haven't I compromised the skis ability to fully engage? At least until the Com catches up into alignment.

Everything in skiing is a compromise as I see it. I can be balancing using alignment, and I can be balancing using my momentum with my body in all sorts of weird positions, as I leverage myself into and out of those positions. (think of a cat, or Bode) I can get leverage on the skis through alignment and I can get it without alignment. the difference between can and should maybe.

For me, it all boils down to how and where do I want to spend my energy capital and how much will I get in return? Which allows the body to work with the least amount of unneeded tension? Unneeded tension being a roadblock to versatility, flow and responsive movement. This is where alignment becomes so important. Good alignment reduces the energy and tension needed to maintain balance and create and play with the forces.

To me it is like talking about our eating habits. It is not the 10% we need to focus on, but the 90%.

IMHO, FWIW!

PS, the difference between the halfpipe/bumps, and other skiing is that the snow surface angles just don't change that rapidly. Yes I understand the idea of the virtual bump and all that but I don't believe it justifies any particular posture as a matter of course.
I feel like I should be sending some kind of subscription dues to you Bob! This stuff is priceless though so I guess I can't put a price on it

Another perspective on this topic from a boot fitter, wanna be instructor, is the importance of properly dialed in fore/aft boot and binding alignment which facilitates efficient balancing through transitions like the one being discussed.

As I have said before, I believe that the stiffer the boot you choose to ski, the more important it is to dial in the fore/aft angles precisely so that you are not compensating your body position just to find your neutral balance but rather using the boot as a tool to recenter to a balanced neutral position that the boot places you in.

I am pretty sure that Bob Barnes has had his boots dialed in precisely to his morphology and has taken into consideration the angle created by the binding, the zeppa (boot board), and forward lean, and even the footbed.

A good skier is very perceptive to any small change in this fore/aft plane. As little as 1.5 mm shim under the heel or toe is perceptable by an expert skier and will make a noticable difference.

My point is, if Bob's boots were not balanced he would have difficulty making such dynamic and well balanced turns as illustrated in this thread.

bud

Thanks Fastman for debating your views with us. Sorry if you got frustrated or felt attacked, because I don't think anyone's intent was to discredit you, just have a healthy debate!! You are certainly one of the folks here I would be honored to ski with one day! respectfully, bud
BB, great animations, as ever.

Quote:
 Originally Posted by Bob Barnes/Colorado At the very least, they suggest that a slight modification of Rick’s “vertical line test” to the “perpendicular to the slope” test, may describe the situation better in some instances.
Perhaps we should even go one step further and say "perpendicular to the skis". Someone could be on a very steep slope but if their skis are momentarily in a shallow traverse, the actual inclination angle of their skis is not that great. As they move into the next turn, of course that angle will steepen quickly.

I couldn't find a great photo sequence showing this effect: this one is not bad (courtesy of Mike Saemisch) and shows it a bit:
http://homepage.mac.com/saemisch/Bes...uence2-tb.html
Quote:
 Originally Posted by RicB PS, the difference between the halfpipe/bumps, and other skiing is that the snow surface angles just don't change that rapidly.
Following on from my last post, one point to remember: with someone doing short turns on the steeps, the snow angle wouldn't be changing rapidly, but the inclination angles of their skis would be.
When we speak of objects as being 'Perpendicular', 'parallel', 'above', 'below', 'vertical', 'horizontal', (etc.) we should not confuse visual relationships with their dynamic relationships.

For instance we frequently say something like "The skier is 'over' his skis..." but what does this really mean?

- Does it mean 'vertically' with respect to the Horizon?
- With respect to Gravity?
- How about perpendicular to the slope?
- Or maybe perpendicular to the rock wall next to them?

It's true that Visual Relationships often conveniently 'line up' in some way with underlying dynamical relationship - but it's also true that they frequently don't.

Visual relationships by themselves are simply too incomplete to accurately analyze the dynamics of an amorphous entity like a skier in ever-changing motion.

Even if we talk about Balance in General with respect to a skier in a video, we fall far short of an accurate assessment and get into heated arguments about whether the presented skier is, or is-not 'in balance'. Preconceived ideas placing too much relevance on visual relationships are generally responsible for such arguments.

It's much more accurate to analyze a skier's balance by evaluating the alignment(s) of their supportive structure(s) between all relevant Forces and the respective Mass supported by each structure.

Even if we choose to regard the whole skier as a rigid object (to simplify discussions) we still need to consider all the relevant Force Vectors acting on the skier, not just the ones that are easy to figure out.

.ma
Quote:
 Originally Posted by Martin Bell Following on from my last post, one point to remember: with someone doing short turns on the steeps, the snow angle wouldn't be changing rapidly, but the inclination angles of their skis would be.
The underlying concept here (the virtual bump) is crucial to the application of the technique being described.

The rapidity of ski-inclination-angle of which you write is directly relevant to the shape of the 'virtual bump' - something we skiers actually control by managing the curvature of our turn. The larger the radius; the larger the effective virtual bump will be. A smaller radius produces a virtual bump with a steeper 'drop-off'.

Nothing stops us from progressively tightening our turn radius at turn entry - thereby re-shaping the 'backside' of the Virtual Bump to suit our re-balancing needs (increasing the time available for re-orienting our body for instance).

.ma
I'll offer a different point of view on what I am seeing in Bob's montages and also in what I am reading in Bob's posts regarding the fore/aft issues.

First, I would suggest that Bob never really got forward in any of the frames shown in the montages (Note, I'm not saying Bob is incapable of getting forward, just suggesting that he didn't get there in the turns he posted).

Quote:
 Originally Posted by Bob Barnes/Colorado Or perhaps I am slightly on my tails there, as I drive my body forward and down the hill. Remember that “centered” for me is very much over my heels, and I rarely try to apply pressure to my boot tongues. That’s the sweet spot that allows the entire edge to engage, and it’s where I aim to be during the pressure phase of the turn, which, again, is just barely beginning in frame 12.
Second, I would suggest that there is a possible contradiction in the bold portion of the description above. When a skier drives their body forward and down the hill shouldn't the pressure point move from the heel (which I would suggest is back rather than centered) to somewhat forward of the arch (not so far forward that a pivot point is created under the ball of the foot) and then back towards the heel again as the turn is released?

Third, wouldn't the sweet spot be the mid point of the ski or a bit forward of the midpoint (both of which are farther forward than the heel)?

If we take another look at the montages of Bob we can see that he is making nice carved turns (perhaps some of the turns could have used more angulation, but nice turns non the less). So, is anything missing in the demonstrated turn mechanics? If Bob were to take these same turns to a hard surface that was steeper (lets say a dark blue or black run) what would happen? My guess is that after 5 turns he'd be zooming and that he'd continue to accelerate with each additional turn. Why do I think this is the case? Because the skiing mechanics demonstrated don't show a forward movement of the CoM which is a key component of creating the big bend required for speed control on steeps.
Quote:
 Originally Posted by Max_501 I'll offer a different point of view on what I am seeing in Bob's montages and also in what I am reading in Bob's posts regarding the fore/aft issues. First, I would suggest that Bob never really got forward in any of the frames shown in the montages (Note, I'm not saying Bob is incapable of getting forward, just suggesting that he didn't get there in the turns he posted). Second, I would suggest that there is a possible contradiction in the bold portion of the description above. When a skier drives their body forward and down the hill shouldn't the pressure point move from the heel (which I would suggest is back rather than centered) to somewhat forward of the arch (not so far forward that a pivot point is created under the ball of the foot) and then back towards the heel again as the turn is released? Third, wouldn't the sweet spot be the mid point of the ski or a bit forward of the midpoint (both of which are farther forward than the heel)? If we take another look at the montages of Bob we can see that he is making nice carved turns (perhaps some of the turns could have used more angulation, but nice turns non the less). So, is anything missing in the demonstrated turn mechanics? If Bob were to take these same turns to a hard surface that was steeper (lets say a dark blue or black run) what would happen? My guess is that after 5 turns he'd be zooming and that he'd continue to accelerate with each additional turn. Why do I think this is the case? Because the skiing mechanics demonstrated don't show a forward movement of the CoM which is a key component of creating the big bend required for speed control on steeps.
With the tipping I also think that it would be difficult to carve on a hard surface period let alone a WC surface.

Maybe if your balance point is your heel then it requires you to rotate the femur in order to engage the tip
Max,
The Core Concept we've been trying to explore here is not easy to 'show clearly' in an image or sequence. Much of the resistance and contention in this thread has come about specifically because the elements we typically "see" gloss over the dynamics otherwise unseen.

In any image Bob presents you and I can easily find tiny inconsistencies where the perpetrator of the turn has left visual evidence of imperfection or perhaps merely some other intent. None of those skiers were specifically trying to demonstrate a pure example of the technique we're talking about.

---
Watching a skier on video we can "see" their speed but we cannot "see" their momentum - but you would likely agree that momentum plays an important role in skiing, wouldn't you?

That is the inherent difficulty when offering up images that incorporate the dynamics described, but all we can really "see" are the structural relationships and extraneous elements. We nitpickers can't help but Key on the suggestive little contrary tidbits because that's what we can see.

If we were debating the aerodynamics of a skier and airflows around them we'd likely end up with an all out war.

Quote:
 Originally Posted by Max_501 ...the skiing mechanics demonstrated don't show a forward movement of the CoM...
If you look thru the text of his last post you'll find a description in there of an alternative to 'moving the CM forward' in relation to the feet - namely that he took a common 'shortcut' to get his CM and feet into proper position. Of course, doing so requires the dynamic application of 'Active Rotation' - and I'm pretty sure HH tore those pages out of all your text books.

As to the questioning of Bob's exact technique in individual images and whether or not the same exact technique as shown on easy terrain applies equally well to cliff skiing, I'll leave all that to Bob.

.ma
Quote:
 Originally Posted by Martin Bell Following on from my last post, one point to remember: with someone doing short turns on the steeps, the snow angle wouldn't be changing rapidly, but the inclination angles of their skis would be.
True enough Martin. But how do I manage this effectively? By keeping more perpendicular to the skis with my alignment, and drawing the feet back under the hips, not by allowing my hips to get way behind the feet by over flexing the knees. But you know that Martin.

Is the difference in the path of the CoM and the feet different enough to make up all the difference? From my own experiences, I have my doubts. There still needs to be some recentering energy utilized to get things back to alignment. IMHO
Quote:
 Originally Posted by michaelA Max, The Core Concept we've been trying to explore here is not easy to 'show clearly' in an image or sequence.
Good point Michael. Maybe for these discussions we need to see the video with the montage.
Quote:
 Originally Posted by michaelA The Core Concept we've been trying to explore here is not easy to 'show clearly' in an image or sequence.
Are you suggesting that you can't look at a nice photo montage like the ones that Bob put up and analyze the location of the CoM through the turn?

Quote:
 Originally Posted by michaelA If you look thru the text of his last post you'll find a description in there of an alternative to 'moving the CM forward' in relation to the feet - namely that he took a common 'shortcut' to get his CM and feet into proper position.
If you read the text I posted you'll see that I suggest he did not get his CoM forward (the method of getting it forward was not addressed). Also, he specifically said "as I drive my body forward and down the hill"
Still formulating a response, please continue talking amongst yourselves. My response will address the vertical line thing which I missed, coming late to these threads but I assume I touched on similar ideas in my post concerning the seated position. That post lead to a little moving picture with knees behind the feet in the bumps eventually leading to a moving picture of knees BENEATH the feet in (out of) the halfpipe.

I think Martin Bell is on to something, and Cgieb touched on it earlier, we need to look at perpendicular to the surface or to the skis. In the stills from the 1/2pipe you will see the boots deeply flexed in the first shot and backwards flexed on re-entry. Although Bob Barnes says he appears to be leaning back going up the wall and catching up coming back down the wall, I see the opposite. He is too far forward going up and too far back coming in. I would like to see closer to boot neutral at both points. It takes a lot of force to bend boots backwards like that. That's not catching up.

The halfpipe stickman is doing what it takes to roll out of the pipe but not what it takes to lauch and re-enter. To roll out you would collapse like that, to re-enter you must extend as you ski up the wall. His boot doesn't budge, so little stickman has to fold at the waist to roll out of the pipe. To achieve the same result, I need to flex my ankles cause my belly is too big to bend like that. That whole post was great though, really well presented and interesting. Luckily I can't log on at work, but I sometimes lurk and I was surprised to find I could watch that little movie of the pretty bumpin' telebabe on my blackberry and it filled the screen. Sweet!
Quote:
 Originally Posted by michaelA When we speak of objects as being 'Perpendicular', 'parallel', 'above', 'below', 'vertical', 'horizontal', (etc.) we should not confuse visual relationships with their dynamic relationships.
Of course, no doubt. Good point.
Quote:
 Originally Posted by volklskier1 Maybe for these discussions we need to see the video with the montage
I agree that video would be nice, but only if the video were made with an intent to specifically demonstrate the ideas being presented. Still, even video is a visual media and cannot show momentum except thru the interpretation of collisions.

Bob clearly went fishing for transitions that exhibit elements of the described mechanics. I'm quite sure the mechanisms described could be used in a pure form but suspect we all use them in one partial form or another. There's no real-world requirement on skiers that they implement any particualr technique in a pure and isolated form.

And yes, if we'd like to undermine the validity of the concept or simply draw attention away from the primary presentation into unimportant minutia we can certainly do that with video also.

The concept it rock solid. Providing the descriptive mechanics, not quite so easy.

.ma
Quote:
 Originally Posted by michaelA The concept it rock solid. Providing the descriptive mechanics, not quite so easy..ma
Please summarize "the concept" for me. I got lost.
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 Originally Posted by telerod15 ...we need to look at perpendicular to the surface or to the skis...
This can be a useful starting 'Line' for analysis but with motion involved, must always be modified to accommodate acceleration. (and I rarely use the word 'always')

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This will be a bit of a sidebar but it might help explain why the dynamics are more important than the image. I wont bore everyone with non-essential math and will stick with the simplicity of a rigid skier going straight down hill...

If we ignore friction we can say that a skier pointed downhill on any slope will be accelerating down the slope and we can easily calculate their rate of acceleration.

On a 20-degree slope their skies (without friction) will accelerate forward at 11.00 fps^s. (feet per second squared)

If a rigid person is held leaning 'forward' at 20-degrees then released, the CM of that person will instantly begin to accelerate 'forward' (in the direction perpendicular to the 20-degree tilt). Not surprisingly, the acceleration forward (at their CM) will be at a rate of 11.00 fps^2.

This is why we hear so often that to be 'in balance' the skier needs to get perpendicular to the slope - so that the forward acceleration of their CM will match the forward acceleration of their skis. If both accelerate in the same direction at the same rate then, over time, neither the CM nor the skis will get ahead of the other. This provides an easy-to-check visual relationship - the one we all argue about.

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But this 'ideal' relationship isn't really correct because we left out Friction.

Friction of the air slows down both the skier's acceleration and that of their skis. More importantly, Friction from the snow (kinetic friction, snow-compression, snow-displacement) prevents much of the acceleration that would otherwise occur. Sticky snow and deep snow add quite a lot of friction at the skis.

This is the dominant reason why a skier in Powder needs to be 'further back' than when they're on the groomers. Yes, ski angle within the snow also matters for support and control - but the main reason the skier's body (CM) must be aligned further 'back' is the fact that their skis are not accelerating forward nearly so much. They must 'balance' the rate of CM-acceleration with that of ski-acceleration.

If they choose to keep their skis on a 'plane' within the snow they may also happen to be 'standing perpendicular' to their skis, though not to the slope they're on.

This simple example shows how drawing visual lines can help instructors - we use them as a handy 'rule of thumb'. but any good instructor modifies what they see with what they know is also happening beyond this simple 'visual report'.

When we get into complex movements that include momentum, rotations and ballistic paths cosmetic lines become a hinderance to the conveyance of ideas.

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In short, drawing Lines based on "Visual Geometric Convenience" is fine so long as we don't take cosmetically chosen Lines to be directly meaningful to the Forces surrounding the action we've drawn them on. Such lines give us a place to start and a place to work from but are not intrinsically relevant.

.ma
Quote:
 Originally Posted by whygimf Please summarize "the concept" for me. I got lost.
Heh - not surprising. We keep getting distracted and caught up in our underwear.

The Basic Technique:
- The skier is making a medium radius carved turn. It needn't be perfect.
- Moving into transition, the skier Flexes low (sometimes into a nearly seated position).
- From this low position, the skier's upper body crosses over their skis, and out into the void. (they 'go weightless' - or largely so).
- As the skier's body moves across and down the slope, they engage the skies and allow mostly centripetal force to turn the skies. Leg-length adjustments and active rotation may be used to keep the skis properly tracking.
- At no time is any significant portion of the skier's weight supported against Gravity - nor does it need to be since their upper body is following a ballistic trajectory that does not bring it 'downward' against the snow.
- Because no real support against Gravity is required, the skier can be in what is visually a 'Backseat' position without the usual consequences.
- A Balanced orientation of CM over Base-of-support is only needed when the skier's Mass is once again being meaninfully supported by their feet against Gravity.
- Any 'Backseat' or 'leaning back' position seen during transition is converted to inclination by the time the skier's weight is back onto their feet.
- Any Lateral re-orientation directed downhill at transition is converted into the Fore/aft position by the time weight is again on their feet.

The Objectionable Concept:
- A skier is not necessarily 'Out of Balance' simply because the bulk of their body Mass Visually appears behind their skis based on the cosmetics of a geometrically convenient reference Line.

Does that help?

.ma
Quote:
 When we speak of objects as being 'Perpendicular', 'parallel', 'above', 'below', 'vertical', 'horizontal', (etc.) we should not confuse visual relationships with their dynamic relationships. For instance we frequently say something like "The skier is 'over' his skis..." but what does this really mean? - Does it mean 'vertically' with respect to the Horizon? - With respect to Gravity? - How about perpendicular to the slope? - Or maybe perpendicular to the rock wall next to them?
Why leave out the idea of the forces we are creating, managing, and releasing? Isn't the "ideal alignment" of our structure perpendicular to the skis center, which is under the front half of the foot? DavidM used to refer to this as positional gravity. We all know what it feels like I guess. For me the plane of the snow and the plane of the skis should ideally correspond, and if we want to generate forces with entire ski edge then shouldn't the ideal alignment be directed down through the middle of the ski?

I too would like a good summary of the concept being presented recently. Lots of words have been written though.

This all started with three turns and the difference in movement patterns between these, including the pluses and minuses of the three turns. So far not a single thing has been written to change my mind on my initial summary.
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 Originally Posted by michaelA The Objectionable Concept: - A skier is not necessarily 'Out of Balance' simply because the bulk of their body Mass Visually appears behind their skis based on the cosmetics of a geometrically convenient reference Line. Does that help? .ma
So that's what this has been about? It's been a long thread for me. I've had to read sentences over and over and I still don't have a clue what they mean. Sigh. Sorry for the interruption. Carry on.
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 Originally Posted by Max_501 Are you suggesting that you can't look at a nice photo montage like the ones that Bob put up and analyze the location of the CoM through the turn?
No, I'm suggesting that we can't clearly "see" Momentum nor Acceleration.

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 Originally Posted by Max_501 If you read the text I posted you'll see that I suggest he did not get his CoM forward (the method of getting it forward was not addressed). Also, he specifically said "as I drive my body forward and down the hill"
Max,
Bob put forth a considerable effort to fully describe and document with images a variety of very important concepts beneficial to all instructors, coaches and skiers.

I think you're just caviling.

.ma
Quote:
 Originally Posted by michaelA ... This is why we hear so often that to be 'in balance' the skier needs to get perpendicular to the slope - so that the forward acceleration of their CM will match the forward acceleration of their skis
I was nodding my head, thinking "yeah, that seems to make sense" about most of what you'd written till I got to this post. You seem to be saying that how you hold your body will, in and of itself, change how it accelerates. Surely that is not what you meant?:
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