Originally Posted by Jamt
LF. Lets discuss some physics of what could happen when you change CoM/feet relative position.
Assume that you are in balance in the middle of the ski and sideslipping down an ideal slope. The system is in balance, which means that the total turning moment around the ski is zero. If we assume that the ski is infinitely torsionally stiff and straight we have the same edge angle all along the ski if we compare the front to the tails.
With this assumption nothing happens when the CoM is moved, because the turning moment parallel to the slope is the same as the moment perpendicularly to the slope along the ski.
However if the ski is like most skis it will be more torsionally stiff towards the middle of the ski, and many skis are also wider in the front. This means that if you move the weight forward from the center location the torsion twist will be larger in the front of the ski and thus the edge angle will be lower in the front. The ski will slip more in the front.
In reality many other things can happen e.g.
The uphill foot may be further forward and thus the edge angle and relative weight distribution of the upper vs downhill ski will play an important role.
the fore-aft state between the two skis may be different.
Good point, Jamt, about the possibility that ski tips will twist to a somewhat lesser edge angle than the underfoot section of the ski, when you press forward on them (when they are on edge). That's certainly another variable to clutter LiquidFeet's "simple" experiment. And it is highly variable, since torsional rigidity, as well as tip width, vary tremendously from ski to ski. I'm not convinced that it is usually that significant and like CGeib, it does not match my own experience (that my ski tips twist off their edges and release when I shift pressure forward). But then, I tend to ski on skis that are torsionally very stiff. I recognize that it is possible.
Either way, this discussion seems to be trying to take an odd turn. Watching top skiers, we see a lot of turn transitions in which they absolutely do not move forward along the length of the ski in the transition--rather they allow their feet to move ahead of their bodies. And they win (see Hirscher clip, post #6, as well as any number of other video clips, still images, and montages that I and others have posted over the years). This discussion seems to be trying to figure out why it shouldn't be happening, why these top, winning skiers shouldn't be making the movements we see them making--why the "evidence" must be wrong. Instead, I strongly recommend that we accept that what is...is, and try to understand it--even if it appears to conflict with long-held beliefs and doctrine.
THIS is what HAPPENS. Seek to understand WHY!
In any case, LiquidFeet, as you can see, there are many, many variables that can affect the outcome of your "simple" experiment. That's why I suggested that theorizing too much may not reap Truth. When you get down to it, there is not a better teacher of skiing than our skis, snow, and mountains. Shelf the beliefs!
Drills and Progressions to teach the "moving forward at initiation"...correctly!
There are certainly many drills that can help you develop the skill and a sense of how fore-aft pressure management affects ski performance. The aforementioned "falling leaf" drill is a great one--just make sure you "play around" with it and let your skis teach you--rather than forcing them to behave the way you believe they should. 360 degree flat spins (on the snow, not in the air) are another. Do them slowly to increase the need for accurate fore-aft "leverage" to help get them around. (If you spin quickly, you can just throw them all the way around with upper body rotation.) Skiing switch (backwards) will help you find the center. Try (on a very gentle and wide-open groomed hill at first) skiing in a straight run backwards straight downhill, then pivoting your tips 180 degrees down the hill to a forward straight run--you will find that it's almost impossible if you don't get some weight back on your tails. Take some freestyle clinics and learn to "butter." And then, of course, there is the venerable Pivot Slip. "Slip fast--pivot slow," is my mantra. Pivot in slow motion, so you can feel your balancing moves throughout, and to help avoid using upper body gyrations (rotation, counter-rotation, blocking pole plant), which can only throw them around quickly. Remember that an objective in Pivot Slips is to have your skis pivot directly under your feet--not forward of the bindings, or even under the balls of your feet. Your feet should move directly in straight lines down the hill, not swinging left and right of those lines. Have someone you trust watch to make sure you're doing it right (or submit some video here--we'll let you know!).
Another good drill (briefly described earlier in post #62) to feel the effects and find the right movements--a good followup to falling leaf--involves starting in a slow traverse across the hill, weight well forward and pressing on your boot tongues. Gradually--g-r-a-d-u-a-l-l-y--move your feet forward, using whatever combination of ankles, knees, hips, spine, and arms feels right. Keep moving feet ahead beneath your hips and see what happens. As the pressure comes away from your boot tongues and starts to move toward your heels, you will find (although I probably shouldn't tell you and create "beliefs") that you will reach a point at which your ski tips quite suddenly let go, and your skis start gently turning down the hill. Let them go, and then gently steer your skis through the turn completion to another traverse and repeat. Over, and over, and over.... It's quite dramatic and obvious. You may find at first that you end up in "the back seat" as your skis take off down the hill. If that is the case, it is not because you didn't move your body forward along the skis in the transition--it is because you did not move your body sufficiently down the hill--which is a lateral move during the transition, but will result in the proper fore-aft balance later, in the shaping phase.
That moment the skis release and start turning down the hill is what I have called "turn neutral"--the beginning of the turn. Keep practicing these slow movements from a traverse to "neutral" to develop a better and better awareness of what neutral is, and what it feels like. Never begin a turn until you have first found "neutral." Sometimes this will require great patience, and you'll have to resist the urge to throw your weight forward and twist your upper body to "force" the skis to turn (which is the alternative, and what most skiers do all the time). Find neutral, then turn. Again, and again....
Then try linking these turns together, and eliminating the traverse. To do that, you'll have to find "neutral" at the end of each turn, so that you'll already be there when you want the next turn to start. Moving toward neutral as you exit turns is the key to smoothly linked, effortless, "X-Move" transitions. The movements you make to get to neutral are the exact movements you need to simply allow to continue as you enter the new turn. They are the movements shown as the two paths in my animations converge, with the feet moving faster than the center of mass. At neutral, they cross, Base of Support ("feet") directly beneath the CM, and then the paths diverge as the feet move ahead of the feet (across the hill) while the body moves down the hill from the feet to get ahead of them when the new shaping phase begins--"forward in the fourth dimension."
The result will be truly effortless turn initiations--by definition. If "Neutral" describes your position and movements at the moment the turn starts, then it likewise describes a position from which the least possible amount of movement (and effort) is required to get the turn started. If starting the turn involves any effort at all, you simply weren't in Neutral when you tried to start it. And if you have finished the previous turn in Neutral, then everything you need to do to start the next turn, you've already done--every part of you is already in the "right place" and every movement is already in motion. All you have to do is let them continue. Any effort can only disrupt your smooth transition (which is not to say that, in real turns, you may not still need some sort of effort--either because you do did not move accurately to Neutral, or because you suddenly changed your mind and decided to alter the course you had predetermined as you exited the previous turn). For anyone who has never felt this, it will come as a revelation--truly effortless balance, a sensuous floating sensation of freedom and relaxation like you've never felt at the beginning of a turn. (Of course, all of this still relies entirely on having the right intent for turning in the first place--the "GO! Factor," the desire to glide and "go that way," instead of the desire to brake and "control speed" and "stop going this way.")
So, go out and play with this stuff. Let the skis be your teacher! If you really have trouble letting go of your beliefs and expectations, then at least try experimenting with the opposite expectation and see what happens. What I described above is really a "guided discovery" teaching progression, in which the instructor leads the students through specific, prescribed experiences in order to facilitate their personal "discovery" of something new. Guided Discovery is a particularly effective approach when you are trying to "teach" something that may conflict with students' belief system. They don't have to believe you, as they discover the "truth" themselves. Of course, your progression had better work! I have ruined the "revelation" effect here by telling you what I expect you to discover. But go play with it anyway. And give it a try with some actual students--their "discovery" will be your confirmation.
(OK, come on, snow!)