I thought about this when you implied it in one of your other posts. I completely get that being gentle and gradual on the edges is necessary for ice. This is because static friction is generally higher than kinetic friction (I know we're always moving, but the analogy applies to holding an edge or skidding). You don't want to push too quickly and break from one mode of friction to another mode. But, I just don't buy that you can reduce pressure to change the transition point between the skidding phase and the carving phase (i.e. critical edge angle). This particular angle is not going to vary that much with the skier's weight. Sure, a heavier skier has more pressure to apply and thus greater friction, but they also have more momentum, so the two largely cancels out. What's worse is if you purposely reduce your pressure, then you've reduced your friction, but you can't change your mass, so your momentum is the same. Therefore, reducing pressure typically makes grip less. I think the idea is that you float through the skidding phase. Applying pressure during the skidding phase will just make more skidding, and so you hold the pressure for the carving phase when the ski can edge lock with higher angles. So, it's not that you're changing the critical edge angle by reducing the pressure, but instead you skip carving during this phase and apply steering as Jamt described.
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What's essential for carving on hard snow?
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I thought about this when you implied it in one of your other posts. I completely get that being gentle and gradual on the edges is necessary for ice. This is because static friction is generally higher than kinetic friction (I know we're always moving, but the analogy applies to holding an edge or skidding). You don't want to push too quickly and break from one mode of friction to another mode. But, I just don't buy that you can reduce pressure to change the transition point between the skidding phase and the carving phase (i.e. critical edge angle). This particular angle is not going to vary that much with the skier's weight. Sure, a heavier skier has more pressure to apply and thus greater friction, but they also have more momentum, so the two largely cancels out. What's worse is if you purposely reduce your pressure, then you've reduced your friction, but you can't change your mass, so your momentum is the same. Therefore, reducing pressure typically makes grip less. I think the idea is that you float through the skidding phase. Applying pressure during the skidding phase will just make more skidding, and so you hold the pressure for the carving phase when the ski can edge lock with higher angles. So, it's not that you're changing the critical edge angle by reducing the pressure, but instead you skip carving during this phase and apply steering as Jamt described.
Thread Starter
TS
I wish this image of carved tracks were on hard snow, but maybe it can help clarify what happens in transition anyway.
The following two images showing why a PLATFORM ANGLE of 90 degrees or less is necessary for grip
are courtesy of Bob Barnes. Notice that platform angle is between the ski and the skier. The images
show why edge angle to the snow is irrelevant to ski grip, contrary to what many skiers believe.
The following two images showing why a PLATFORM ANGLE of 90 degrees or less is necessary for grip
are courtesy of Bob Barnes. Notice that platform angle is between the ski and the skier. The images
show why edge angle to the snow is irrelevant to ski grip, contrary to what many skiers believe.
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I love reading about the physics of skiing, but there is a point where applied to human movement analysis the physics become muted. Physicists need to work out a repeatable problem to an exacting level. Human movement patterns are anything but exacting within one human from movement to movement, let alone within any two humans, or within the rest of the 7 billion of us for that matter. So, @skier arguing that he read in The Physic of Skiing that there is a minuscule amount of skidding within the transition phase of "all" skiers and there is no such thing as a "pure" carve is mostly insignificant arguments when applied to the real world of skiing by humans on variable snow surfaces. If one were designing a robot to ski on a consistent surface, then perhaps an examination at the micron level would matter, but maybe not even there.
There are two different uses of the term critical edge angle floating around. I hope I describe it correctly, one is the angle where all the forces align to maintain balance while carving. This is not what I meant when I brought up this term. There's another use of the term which seems to be less common. Allegedly, when someone starts a turn, initially, the ski will carve somewhat and slide somewhat. This is called the skidding phase in the Physics of Skiing. As the edge angles increase, the amount of carving will increase, and the amount of skidding will decrease. At some angle, the turning will be predominantly carving, i.e. edge locked. I believe this angle is what Jamt referred to as the critical edge angle and is how I was using the term. So, initially, for low angles, there is no pure edge locked carving. It's not until the edge angles reach a certain value where it's more approximately edge locked. I was also reading today, how the physics is different for soft snow, so that could be the disconnect. RR tracks in soft snow is one idea, but purely carving on hard snow is where the skidding phase has more relevance and must be dealt with appropriately. So, it may be that steering at the top of the turn is part of what's necessary to carve well on hard snow.
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Thread Starter
TS
I think on hard snow, it's not minuscule. It's maybe useful to think about, because the best carve on hard snow may need some steering at the top of the turn, but yet many endorse the tipping only mantra. If you look at world cup, they do a ton of redirecting at the top of the turn. Is it really helpful to believe that we should work to eliminate that from our turns on hard snow just because RR tracks on soft snow show a minuscule amount of skidding? See, doesn't that sound more useful when you take the physics talk out of it? Physics and ski forums, bad mix. Physics and designing skis, great mix. Physics and learning to ski, depends on the person.
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It's the angle between a duck's legs.
Thread Starter
TS
This just doesn't sound right. Deeply not-right.
So I'm struggling to figure out what you're talking about, assuming it matches your experience in some way and has truth in it.
Oh. I see your last post now. Whatever.
I believe Bob Barnes had a gif of this diagram. It would be useful here.
What some people still don't get is that the critical angle is a function of the direction of the net applied force, including gravity and centripetal. The critical angle is not some constant angle like 10 degrees that you are below until you tip the skis past. Looking at the above diagram it should be clear that all you have to do to not skid is push the ski more into the groove than out of the groove. At transition the ski need provide no turning force; there is no need for any out of the groove force. You meet the critical angle requirement with 0 tipping angle.
It gets even better if you have released the centre of mass from the last turn before the skis.
Maybe you have been taught and repeated that you have to smear first and then carve for so long that you can beleave nothing else, but it's not true. You can do that if you choose, but there's a better way.
Right, that's what makes the conversation interesting. How many carving threads have you participated in? Lots. You want to just keep rehashing the same old ideas over and over? If you were a beginner skier looking for advice on how to carve, I wouldn't even begin to break ranks, but you've been around the block and are ready for entertaining controversial ideas that go beyond the simple physical models. I'm just pointing to respected people that have a different take on things, but I didn't invent these ideas. So, it's better for you to PM Jamt or something like that, if you want to dig in deeper. I think there's enough evidence there not to dismiss these ideas just because it's not the mainstream mantra, but certainly it's not beyond any doubt.
You're talking about something different. It's an unfortunate double use of the term. I was never taught to smear first.
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Do I have any videos of me partially skidding or applying rotary force at the top of the turn? LOL, I wish I didn't, then I would be the world's expert. Do I have any videos of anyone on ice not partially skidding or applying steering? Please show me the way. Though, I doubt we'll agree. Razie is clearly using rotary at the top of his turns, but not all of us agree on that, so I don't think we'll solve this with a video challenge. I don't have any personal ski videos that are relevant to this conversation, otherwise I'd be happy to post. I think in all of my videos, I'm on mogul skis. And yah, they don't cleanly carve the top of the turn in pretty much any condition. Now don't start bashing mogul skiers, Josh, we have feelings too, and we are occasionally found on other types of skis.
My bad; I got the impression you thought a skidding phase was required at the start of all carved (OP definition) turns. Regardless of definitions of critical angle, all one has to do is insure skis are not required to provide more sideways force than the downwards force on them permits without the ski being pushed up out of the groove the tips cut.
Last year at A-Basin I was told about the benefit of an OPTIONAL small rotation right at transition on steep, manky snow. You have to get to a true neutral (front-back and side-to-side) for it to work. Rotate your skis maybe 10 or 20 degrees and then tip. So I played with it and it was eye opening.
What problem does it solve? Sometimes in that kind of snow I edge too hard in the bottom of the turn, the whole length of the ski digs deeply into the heavy snow, and it becomes diffictult to get out of my own rut and start the next transition. That little rotation speeds up the start of the turn and helps get speed control going at the top of the turn. In turn, that lets you avoid such a hard finish to the turn and you don't dig in as deep. And the next transition is smoother.
I didn't remember to experiment with this move on firm snow this fall -- I'm guessing there won't be much benefit there.
What problem does it solve? Sometimes in that kind of snow I edge too hard in the bottom of the turn, the whole length of the ski digs deeply into the heavy snow, and it becomes diffictult to get out of my own rut and start the next transition. That little rotation speeds up the start of the turn and helps get speed control going at the top of the turn. In turn, that lets you avoid such a hard finish to the turn and you don't dig in as deep. And the next transition is smoother.
I didn't remember to experiment with this move on firm snow this fall -- I'm guessing there won't be much benefit there.
The Physics of Skiing says that a skidding phase is required at the start of all carved turns, and this is the concept of the Critical Edge Angle as used by Jamt. I don't know whether it's true or not. I was taught to tip the skis and carve which is largely what I do on groomed runs unless I'm specifically practicing techniques that use rotary.
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The last image relates to people who have trouble side slipping and get the uphill ski caught on the uphill edge. It can still have an angle of less than 90. Or, they let the uphill ski hang back then develop a < 90deg angle on the downhill edge and catch that.
If one is trying to carve arc to arc, then that's different then intentionally skidding/steering the beginning of the turns. If the micro skidding you claim exists while attempting to carve arc to arc, there's nothing to worry about since nothing can be done about it. Trying to skid/pivot/steer at the beginning of a turn is a whole different matter.
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Skis, and especially ski tips are flexible. Done right, the ski tip cuts a clean groove as it moves forward and the rest of the ski follows. This requires pressing the edge into the snow and allowing the bending to take place from leading edge on back only as the ski advances along the path. The bending does not require a skidding phase displacing the edge from its grove; a fresh groove of increasing curvature is continually being cut with no skidding as the ski moves forward.
I'm not worried about it. I think you can ski either way. But, Razie and Jamt bring up a good point. It's generally easier to keep from skidding, than it is to stop skidding once you start skidding. So, if you apply too much pressure in the early phase of the turn, according to this skidding phase (in the book, for hard snow, it's not considered minuscule) then you'll be predominantly skidding at first, and then have to edge lock from a skidding mode. Where as if you hold that pressure by floating, then redirect, you'll have more pressure to apply to the beginning of the carve phase without initially skidding at first. At least, that's somewhat how I believe I read Jamt explain it at some point.
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