What's the Purpose of Separation in a Ski Turn?

[HardDaysNight]

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Well said.

Absolutely. If there’s one thing I love it’s clarity of explication!

 

[Seldomski]

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Well said.

He is correct - one of the greatest impediments to most skier's development is ... poor communication.

 

[Sanity]

You are holding constant something that cannot be... it cannot be the same turn, since the radius and timing changes... so I don't think we can't really compare those apples to those oranges that's the kind of trouble we can get into when we talk more physics than skiing

... what I think you are referring to is, let's take the same radius inclined and angulated, the force vector is pointing more down when angulated, it is an interesting equation, between ski bend at an angle vs force vector and snow hold.

but, since you see closer on that point now, the next interesting part is the torque. even without bringing in the dynamics, the presence of force with an arm and a direction introduces torque. Whether there is rotation or not, is irrelevant:

Torque and Equilibrium

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and this raises a lot of interesting points about why angulation is better, even from a static physics standpoint... there you have the COM to boot vector, the ski edge angle and the width of the ski ! Or course, we're missing the Normal

food for thought. I don't think this point was touched much on before, @Mike King brought it up first... of course, this assumes the idealized case of carving edge locked, but we could easily add a fudge factor for some skidding... or worse, Thor forbid, pivoting

Angulation allows the skier to have the center of mass higher and farther out of the circle at any moment in time compared to a skier without angulation that has the same edge angle. This allows higher edge angles at slower speeds, because the position of the COM with angulation requires less centrifugal force to keep it from falling over.

 

[Mike King]

Angulation allows the skier to have the center of mass higher and farther out of the circle at any moment in time compared to a skier without angulation that has the same edge angle. This allows higher edge angles at slower speeds, because the position of the COM with angulation requires less centrifugal force to keep it from falling over.

That's not my understanding of physics. The inclination of the CoM must be precisely positioned to balance against the force of the turn. The force of the turn is dictated by the radius of the turn, the velocity of the CoM, and the mass of the skier. So while you might generate higher edge angles with angulation, you will also generate more force (tighter radius).

 

[Sanity]

That's not my understanding of physics. The inclination of the CoM must be precisely positioned to balance against the force of the turn. The force of the turn is dictated by the radius of the turn, the velocity of the CoM, and the mass of the skier. So while you might generate higher edge angles with angulation, you will also generate more force (tighter radius).

When you say "the inclination of the COM must be precisely positioned to balance against the force of the turn", I assume you mean properly that centrifugal force must balance with gravity for the skier to be balanced while leaning at an angle. So, yes, faster speed and a tighter turn increases the centrifugal force that equalizes with gravity to stay balanced. But, the mass doesn't matter, because it cancels out when equating centrifugal force with gravity, because both forces depend linearly on mass. But, what does matter is the angle of lean for the center of mass. Gravity gets multiplied by Cos (lean angle) and centrifugal force gets multiplied by sin (lean angle). So, if you decrease your lean, a smaller proportion of centrifugal force is balanced with a larger proportion of gravity. That means to stay balanced the total centrifugal force must decrease. So, for example, let's say a skier has maximum inclination before exceeding the critical platform angle, the edge angle is 30 degrees, and the velocity of v is not fast enough to keep from falling over. If the skier is angulated, then the center of mass is higher and farther outside the circle. In other words, the lean of the COM is less. This means there is less proportion of centrifugal force (sin(angle)) that must be balanced with a greater proportion of gravity (cos(angle)). So, now this skier with velocity of v and edge angle of 30 degrees can keep from falling over, whereas without angulation they couldn't unless they increased their speed. Let's just assume that both scenarios use the same trajectory of edge angles and the same ski technique in all other regards.

 

[geepers]

Absolutely. If there’s one thing I love it’s clarity of explication!

He is correct - one of the greatest impediments to most skier's development is ... poor communication.

Gotta love computer translations....

JAM guy still has a valid point. Although probably better said as something like:
Always be moving in or moving out.
Balance in a ski turn is not a static position.

 

[slowrider]

Flow down the hill.

 

[Chris V.]

In short turns, separation isolates the upper body from ski rotary forces. Meaning, your upper body does not yaw left/right in turns. Essentially separation reduces the rotational inertia that the skis must accelerate/decelerate in each turn.

I say bingo. In other words, the law of conservation of angular momentum means that reducing the mass with angular momentum will reduce the external torque required to change that angular momentum. Hence the effort (which may be in limited supply) required on the part of the skier is reduced, and the forces generated in the ski-snow interaction which may be difficult to deal with and which can potentially lead to breakaway are reduced.

See, a small bit of physics can be a good thing. Just don't get carried away, because the human body is way too complex to model by way of a manageable number of mathematical formulas.

 

[Chris V.]

Still, I'm wondering if the only reason for rotational separation is to achieve greater angulation. Any other reasons?

People have already mentioned a few.

Also, consider the capability of muscles and tendons to store strain energy that can be released and converted to kinetic energy. See for example:

https://journals.plos.org/ploscompbiol/article?id=10.1371/journal.pcbi.1002770

However, this energy must be released quickly or it will be dissipated as heat. Hence it's of the most use in short turns. Releasing this energy in a controlled way, a skier can with reduced effort create a steering angle for the new turn, or simply continue the cycle of separation (or counteraction as some would call it).

 

[Mike B]

I think that many here are probably on the right track. However, physics of snow, ski tune, body function, fall-line changes and INTENT (are you going for it?) all play a part in the physic of conserving decapitation. All of this relates to FEEL. You cant calculate that. You can try to describe it or show it, but it is impossible to calculate.

 

[LiquidFeet]

^^ @Mike B I admire your autocorrect for its creativity.

 

[Cheizz]

Decapitation in skiing is a real problem. Especially afterwards, when the tune is off...

 

[James]

Best tune for decapitation, 0.3/7 ?

 

[4ster]

Best ski for decapitation...

 

[Mike B]

Geez, these technical threads are getting slow. I think I know why. As I understand it, sometimes the technical acumen can be somewhat questionable on these online forums. I only mention this because, if we are referring to skiing specifically, I believe the correct term is “delamination”. Anatomical separation is going to lead to rapid blood loss and sudden fatality so I do not recommend it, especially during a family vacation. All the average middle class parents with 2.5 children may know what I am talking about. A very messy experience to say the least. Sometimes it can take up to 10 seasons for a skier to delaminate their CoM from their BoS. The key for achieving a quicker delamination is to get a little water seeped into a manufacturing defect void in your construction, which, upon freezing, will further expand the delamination of this bond. When too much delamination occurs, spread an epoxy adhesive between the CoM and BoS and clamp them together in a vice overnight. I know exactly what you are thinking right this second and, yes, it is “OK” to sniff a little during the process. I’ve seen a skier’s entire technique become fully delaminated after a bad impromptu lesson from their suddenly less significant other, in which case a little needle and thread on the chairlift will do wonders. There is also the term, ski “decapitation”, where the binding comes off altogether. Now, “skier” decapitation, a form of anatomical separation mentioned above, involves low lying branches camouflaged with snow and stretching across the line of a skier who is not good at vertical separation resulting in cranial separation which, again, is correctly referred to as decapitation in this and other circles. When people tell you that you need to get your sh*t together, this is probably what they are talking about and, unless you are a skier, there’ll be nothing you can do about it.

No auto correct needed.

 

[François Pugh]

Best ski for decapitation...

Maintaining sharp edges on Machetes is a difficult task over time (due to the steel cap).

 

[Yo Momma]

We are witnessing the next gen of skiers where the rule book has gone out the window. Call them hacks, park skiers, trick skiers, etc... It's where the sport is growing w/ our youth. Many are skiing "switch" just as much as forward. How do the rules apply when skiing switch where safety requires that you develop a dynamic flow with in an almost locked in, rotated upper body position as you generally look over the shoulder of the ski that is furthest back. Just curious as to how one would analyze these movements and maybe shed some light on the physics and analytics of this genre. I have never seen any deep technical discussion about the art of skiing Switch.

 

[Disinterested]

We are witnessing the next gen of skiers where the rule book has gone out the window. Call them hacks, park skiers, trick skiers, etc... It's where the sport is growing w/ our youth. Many are skiing "switch" just as much as forward. How do the rules apply when skiing switch where safety requires that you develop a dynamic flow with in an almost locked in, rotated upper body position as you generally look over the shoulder of the ski that is furthest back. Just curious as to how one would analyze these movements and maybe shed some light on the physics and analytics of this genre. I have never seen any deep technical discussion about the art of skiing Switch.

It exists, and you can describe it in the same language as alpine skiing. It's not necessarily the most efficient way to ski forwards but I agree that understanding how doing freestyle in general takes you out of the fundamentals can be a good way to adjust your thinking about skiing in general. Anyone who wants to be an examiner or RMT in PSIA has to do it and I think there's probably more good freestylers out there in the ski nerd squad than you'd think.

 

[4ster]

Many are skiing "switch" just as much as forward. How do the rules apply when skiing switch

Better learn good separation of the head.
I don’t ski switch much mostly because it hurts my neck!

 

[James]

We are witnessing the next gen of skiers where the rule book has gone out the window. Call them hacks, park skiers, trick skiers, etc... It's where the sport is growing w/ our youth. Many are skiing "switch" just as much as forward. How do the rules apply when skiing switch where safety requires that you develop a dynamic flow with in an almost locked in, rotated upper body position as you generally look over the shoulder of the ski that is furthest back. Just curious as to how one would analyze these movements and maybe shed some light on the physics and analytics of this genre. I have never seen any deep technical discussion about the art of skiing Switch.

Better learn good separation of the head.
I don’t ski switch much mostly because it hurts my neck!

Well that’s telemarkers for you- everything is wrong, and ugly… (All the grace of a Minion with concrete shoes on.)

In switch alpine the outside ski is ahead usually, not behind.
But some just pick a shoulder and look over that way, not changing between turns. So ski lead is pretty constant, but amount will change. Depends on which side they like to spin from, and maybe how shallow the turns are. But the finer points are beyond me, and if competing you need to spin both ways.


Even starting the world record, 138.62 km/hr (86mi/hr), though later he gets pretty even.

Fun video-

But a lot of things in freestyle/park have movements that are I suspect, just for moving. For some reason, it is better for us to be moving in order to react, than not. Even if it’s the wrong way. Think of tennis players returning serves st 130mph. They jump up just before the movement one way or another. This logically makes no sense.

I played with this subway surfing last week. (Where you try to balance standing without holding on.) You have better balance moving around constantly, before the action needed to balance, then standing there “ready”, attempting to anticipate. Even if you!re moving in the opposite direction. It’s freakish.

So if you're constantly about to jump, spin, or perform some maneuver, they’ll be a lot if movement. Then style and idiosyncrasies come into it.