Below are a series of quotes that I extracted from the EB's tail carving technique thread. These bring up two points that would like to see further comment on but are so lost in that train wreck that comments from others are unlikely.
First is the pervasive myth that toward the end of one of the arcs we call turns gravity and the inertial forces of the turn combine to make the pressure greatest in that phase of the turn.
Second, just how necessary/helpful is a understanding of fundamental Newtonian physics to teaching skiing.
Here is a quote from BB "To get your first pin, you would need to pass a fundamental technical foundations exam, covering physics, biomechanics, snow science, basic understanding of various equipment design and function, and principles of movement analysis." This is what Bob would like to see for a level 1 pin
I'm going to hold off making further comment until I see if there is anyone else interested in commenting.
Gravity and the inertial forces of the turn don't combine at the end of the turn. My guess is that you assume that gravity is pulling you down the hill, it isn't, Dr Maxwell's demons are pushing you down the hill. Inertial forces are also lessened toward the end of the turn because the skier is making less change in the motion of his mass. If you feel the the pressure under your feet is greatest in the last third of the turn then you are probably braking at the end of each turn.
If the above doesn't make sense to you get a basic physics text and research how gravity works (hint, it only pulls us straight toward the center of the earth), and what ground reaction force is. A better understanding of the laws of motion would probably help also.
PS JAMT, hope I got the physics part of that right. If not please set me right my understanding of the subject is that of a well read generalist as apposed to someone who has seriously studied the subject.
Since we ski on a slope gravity will move us down the fall line of the slope unless it is being completely countered by a reactive force, such as the friction from standing on your edges. The steeper the slope the greater percentage of the gravitational force is combined with the centrifugal "force" in the last half of the turn. If we start on a zero degree traverse and start to carve a turn a component of gravity is pulling down slope and the horizontal component of the, so called, centrifugal "force" is working up the hill.
[Note: centrifugal "force" is not really a force, but it feels like it to us because we are turning while our momentum is trying to go in a straight line (this makes it feel like we are being acted on by a force because our body is being diverted and energy is being used to do so)]. So at the top of the turn the horizontal component of the centrifugal "force" is acting in the direction up the slope. The gravitational force is pulling us towards the center of the earth. At this point the horizontal components of these two forces are in opposition. If we don't lean enough we don't compensate for the centrifugal force and if we lean too much gravity will pull us over the other way. This is why initiating a carved turn from a shallow traverse is difficult, especially at slow speed. Once we have gone through 90 degrees and are facing straight down the hill the centrifugal "force" is still acting towards our feet but the down slope horizontal component of the gravitational force is acting at 90 degrees to the horizontal component of the centrifugal "force" so the combined forces are not opposing or combining with each other. As you continue on this same arc into the lower quadrant the centrifugal "force" and the gravitational force start acting more and more in concert and to a greater and greater degree until the the maximum combined "force" is reached at the bottom of the turn. This is why it is harder to hold an edge in the lower quadrant near the end of a turn, and why it helps to weight the tails more then so they don't wash out and result in a skid. The steeper the slope the stronger the gravitational component down slope and the stronger the combined forces (if you kept skiing in the same constant arc at the same speed). Since your speed probably increased when going more directly down the slope as well, with a constant arc the centrifugal "force" will also have increased at the same time it is working in concert with the gravitational force. I hope that is clear and I didn't make too many mistakes that can be niggled over.
This whole paragraph just illustrates that you have no understanding of fundamental Newtonian physics. Without that it is impossible to carry on a discussion. Start by understanding this. There is no such thing as a 'horizontal component of gravity'. Gravity is a simple force that only acts in one way, an attraction between the com of the earth and our body, it acts only in one direction. Would you understand the idea of the vector of the ground reaction force and how it relates to all this. Further, the inertial forces we feel (what you refer to as centrifugal force) are also diminishing in the last third of the turn because we want to make less change in our inertia at that time.
What you wrote was clear enough it was just flat out wrong.
You have complained that others are calling you out without backing up their statements. I'm backing mine up with several hundred years of facts that are called physics.
If I have made any errors in what I have said I'm sure JAMT or one of the other physics gurus here will call me on it (not absolutely sure I'm using the term inertial forces correctly). What I am sure of is that what I have written is much closer to reality than the junk science you are coming up with.
PS Unless you show the ability to accept facts and learn from them I'm done here.
The the skier being acted on by the gravitational force is being diverted down the fall line by the slope. That is happening and our edges are resisting that motion. That is what I was trying to get accross, but perhaps not using the correct terminology. Your contention that the force is not so great in the lower quadrant is simply because you changed the rules of the game by changing the arc of the turn in the lower quadrant. Of course, if you are not going to complete the turn, the closer to the fall line you end the turn the less of the inertial force that is going to be added to gravity in that quadrant. What you originally said in your first sentence is wrong. The "forces" that need to be resisted do work in directions that are additive in the lower quadrant. You wrote: "Gravity and the intertial forces of the turn don't combine at the end of the turn". if you are sticking with that statement, please explain why it is so much more likely for your skis to skid out of a carve at the bottom of a turn (of fixed radius) than during other parts of the turn (which was what I was originally trying to get accross, albight in my bumbling manner). You seem to be trying to deny this even occurs.
Likely my last response. My skis are not more likely to skid out in the bottom of the turn even though I am reducing the edge angle progressively through the last third of the turn. Why no skid? Because the forces are naturally diminishing in the bottom of the and I am using the skills I have developed to diminish them even further. I in fact often diminish them to the point that I float through the transition.
It also appears that you seem to think that turns are of constant radius. They aren't. Rather than being the half circle most people think of them as they are closer to a parabolic shape. I'm sure that a half circle turn is possible but it would be the ultimate in a park and ride turn and even then the pressure felt under my feet would be greatest at the apex of the turn and would diminish through the final third.
I engaged here because I thought that perhaps you might actually be interested in learning but it turns out that you are after all just another species of troll and I just don't have a billy goat handy.
The physics stuff is getting ridiculous. I don't see the relevance and a lot of it is wrong.
Maybe he'll come out and talk about it, cause I don't get it, but Jamt has talked about we don't accelerate at the end of a turn.
Also, forces are often the greatest at the bottom of a turn because of the direction change across the slope. Even if one ends up on the heels at the very end, just before one is often the most forward- flexed into the boots, of the whole turn.
It's not required to know the physics of what one is doing. Does an ice skater know all about conservation of angular momentum and whatever else is involved in a routine? Does someone doing tricks off jumps know the physics of the spins? Does one need to know the physics of a frisbee to make a good throw? (Is it even understood how it flies?)
More interesting is the physiological part of being either too back or too forward.
The aft technique we see with the posted montage of Ligety in slalom is possible only because he's able to pivot the skis quickly and have them switch sides. You couldn't do that in a gs type turn because there's too much distance to the next gate and you're going too fast.
"Also, forces are often the greatest at the bottom of a turn because of the direction change across the slope.'
At the bottom of the turn we have already made most of our direction change (unless your goal is to ski back up the hill) so the forces are less than they were a split second before in the pressure/shaping phase of the turn.
Sorry for harping on this but it is one of my pet peeves. I hear this repeated every season and it just isn't true, both the physics of the situation and modern ski technique combine to make the last third of a normal turn a period of diminishing pressure. The first third has increasing pressure the middle third is max pressure (for that particular turn) because that is where the greatest change of direction occurs. These comments are in respect to a transition to transition turn model.
As to the question of the relevance of understanding the physics behind skiing. It's true that you don't need to know the physics to learn to ski or to teach it. But, understanding the physics of the situation has helped me and others I know to make sense of why we do what we do on skis and often why my students are not progressing to their goals. Also, a flawed understanding can easily lead to flawed technique.
It totally depends on the shape of the turn.
If you're intent on showing people this then you should post some diagrams and photos. Otherwise "end of turn", "bottom of turn", "direction change" are all vague and subject to interpretation. If a gate is in the middle of a turn that's quite different than if one turns down at the gate.
Sorry, but I'm not buying what you said just on the words. There's too many types of turns. You're going to have to show me.
In slalom, usually there isn't much of a carved arc to the turn, it happens late and down near the gate. So just in that example, what you've said is not totally correct.
Exhibit A. Most force at bottom of turn. edit: I should clarify in that I consider the "turn" starting at image 3 or just after really. In the previous turn, prob max force is before image 2. At 2 she's starting to come out of the turn.
I'll use your photo to try to make my point. Notice that in images 1,5,6 there is substantial spray coming off the skis, the pressure is so great the the snow surface is breaking down. In image 2 the arced ski is holding a carve with little or no snow spray, this indicates to me that the pressure has diminished and the snow surface can now support the load without breaking down. In my way of looking at a transition to transition turn images 1,5,6 all occur in the pressure/shaping phase, image 2 would be the last third of the turn and the unseen image 4 would be the first third.
Turn shape, intent and other factors certainly effect where pressure occurs in relation to the slope/fall line, but from my frame of reference every turn/arc shows the increasing pressure, max pressure, decreasing pressure profile.
One last point. Breaking the turn into thirds like this can be misleading because in respect to time the thirds may not be equal. In a slalom turn the first and last thirds will be of very short duration in respect to the pressure phase, in a Super G turn they may be of greater duration than the pressure phase.
Well I call 1+ (between 1 and 2) and 6 the bottom of the turn. So we agree! (prob not...)
If I break the turn into thirds it's distance, not time. I'm not confused about that. However, the distance is the arc they've moved on since transition. There may be almost no pressure for the first third or even half.
But this is all vague. Let's go get some diagrams.
Different turns, different max forces in different parts:
Look at the middle one. Now, I'd call that max pressure at "the bottom" but maybe you wouldn't and maybe it's not exactly. If you take the most extended position, the go four back, that's probably where max force is. That would be 18 images from the bottom. Do we agree on that? (maybe it's 18.5?) Now if you call that the middle third, and I call it the bottom third, there's the problem.
Slope pitch and turn shape make a big difference.
That's the point. People were doing just fine falling off bridges before Newton. You don't need to know the gravitational formulas. It's a safe bet that 90% of the population does not. But they're doing ok.
Now if they want to fly to the moon it's a different story if they're going to do the project. If someone else does it, no problem.
Besides, what is gravity? Beyond the formulas, how would you explain it? Are you going to use Relativity?
I'm saying it's fine to know about those forces, but it has little to do with saying someone's technique is "wrong". Because, probably you got the physics wrong in saying it for one thing. (I wouldn't say that to Jamt...)
For another, in a way it doesn't matter all that much.
Someone does something. Does it work or not? How are you going to say it works? That's the question.
Using Physics to "prove" it doesn't work, when they are already doing it, is weird.
If someone's technique is "faster", then race. If it's a style, then there's really nothing you can say to prove it's no good.
Look, feet glued together pushing the tails out, butt wagging makes some people happy going down the hill. They think it's great. Maybe they're stuck in the past, or just don't care and really like it.
Are you going to use physics to "prove" it's not good? I'd love to see that one.
Of course you might say well in such n such a situation you can't do x, like a high speed carve. That might be true, but they don't care. Now what?
Now if you tell them that physiologically, if they constantly weight their quads they have less balance response etc... That could make a difference. That's more a "proof" then any physics you could throw at it.
However, if they're doing it all day and are still fine with it, then whatever, they're ok. It might drive you nuts, but they like it so there's nothing to do.
Some runners that win have inefficient techniques but they're used to it. You could take it away, change it, and they might get better. They might get worse. They might not want to bother.
Take baseball hitting. Some styles are so bizarre you wonder how they hit the ball. They do, and they're good at it. You wouldn't teach someone that, but there it is, it works for them. They're in the major leagues and doing well.
I'll respond this evening when I have a little more time but for now one question. What criteria are you using to identify the 18th image as the one with max pressure? I ask because the better I understand your thinking the better I can frame my response to you.
Here is a quote from BB "To get your first pin, you would need to pass a fundamental technical foundations exam, covering physics, biomechanics, snow science, basic understanding of various equipment design and function, and principles of movement analysis." This is what Bob would like to see for a level 1 pin! This is from the Pass rates on level 3 exam thread.