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Wendy

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I see what you mean. Yeah, i'd still say it was inclination even though they could be sliding straight downhill leaning uphil. So, perhaps gravity should be added to the def.


Well the com is not a bodypart and maybe outside the body. Think of a boomerang. The com is in space, not in the object.
In general though, the com is where the most mass is. So let's say around the belly button. Simply banking, you're just letting your body fall inside the turn. Com will still be roughly belly button. Arms don't have much to do with it, but since they have mass, yes they will slightly influence where the com is.

But the banker didn't get inside the turn by using her arms! Stand near to a wall and fall into it withthe bodystraight. Do you use your arms for that? Well... in that case you might sice there's no turn force or slope. But you would have to push off a column or something to propel you.

It's not really important to know exactly where the com is, unless you're going to do calculations. Just knowing what it is and what affects the position of it is fine.
Look in the feet pullback thread on moguls. There's some gifs there that show com outside the body at times.

Yeah, I understand the COM is not a body part...it’s often outside the body. (I’ve taught physics ). The diagrams make sense to me; it’s the semantics that are confusing.
 

Jamt

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Most definitions or inclination and angulation have their pros and cons. The one I like the most is the one used by Reid and others, as shown below. The advantage is that edge angle=inclination+hip angulation+knee angulation.
Inclination and angulation definitions.PNG
 

LiquidFeet

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Well there you go.
Without that set of diagrams, it's easy to get confused about the exact meaning of inclination.

But we don't want to have to remember and reference those diagrams.:eek:
What-oh-what is a ski instructor to do???????
 
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Nancy Hummel

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Well there you go.
Without that set of diagrams, it's easy to get confused about the exact meaning of inclination.

But we don't want to have to remember and reference those diagrams.
What-oh-what is a ski instructor to do???????

Avoid jargon that can be interpreted differently or explain your understanding of terms when you use them.
 

Chris Geib

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Angulation/Inclination has certainly stirred a bit of thought!

With all due respect to the tech manual which you quoted in your opening post, shouldn't it be "relative to gravity"? Just look where the angle is identified in @James 's diagram above.

It might be helpful to think of inclination as a term defined relative to gravity and angulation as a term that isn't.

Don’t overthink it karlo, that’s the danger come exam time. Yes the mass is inclined in your photo (may be a tad hip-dumped?), but jesinter and James are merely saying that the line of action between the bos and the cm need not be of a centripetal origin, eg, you could be leaned in and skidding straight down the fall line, with no turning. An interesting point indeed.


zenny


Inclination is dependent on turn forces.

Angulation is in spite of turn forced


Don't forget that angulation changes where your center of mass is. So if your traversing across an icy slope, you move your hips into the hill, that's inclination and angulation, and then say lean out with your upper body over the outside ski. That changes where the com is and the line of action to your edge. The result is likely more edge angle, but more importantly, more downward component of force to the edge. (Not sure how to phrase it) Upshot- your edge, the downhill ski, holds better as you traverse across the ice.


Now @Jamt or @cgeib should review that.

Eh, I think the traverse is a tough one. The BoS is going to typically be both skis with some bias toward the downhill ski, thus the line of action resolves generally between the feet, but closer to the downhill ski. So, when you lean out over the downhill ski, do you incline? Or, simply align your CoM more (or directly) over that ski? What if you pickup the uphill ski and traverse only on the downhill ski. What if you step up onto the uphill skill and motor along with the downhill ski lifted off the snow.

Traversing across the slope with some edge angle to the slope - inclined?

Ever stand balanced on the uphill ski only on a steep slope? Would we be inclined when doing this?

What if stopped standing sidewise stationary on both skis on the side of a slope - inclined?

How about doing a stivot entry to the top of a turn? Turn forces? Centripetal forces? Inclined?

Hockey stop? Are there “turn forces”? Does the skier incline?

Turn neutral? (see description below) Imagine completed C or S shaped turns. Inclined?

Inclination is beginning to seem akin to expert skiers and porn! …not easily described but all claim to be able to recognize it when they see it ogsmile


Bob Barnes said:
NEUTRAL:
An attitude or position when not turning—uncommitted to turning, but prepared to move any direction. In linked contemporary turns, “neutral” occurs at the inflection point where one turn ends and the next begins, marked by the edge release. As it is the moment a turn begins, “neutral” is a position from which the least possible amount of effort or movement is required to start the turn. It is the key to the apparently effortless, gliding, smoothly linked turns of experts.

Characteristics of neutral in turn transitions include 1) edge release, but skis not necessarily flat on the snow; 2) center of mass directly over feet, with balance favoring the downhill foot and centered beneath the ankle, shins centered in the boot cuffs; 3) legs rotated to some degree in the hip sockets, resulting in some lead of the uphill ski and uphill half of the body (“counter”).

Note that other definitions of “neutral,” such as “rotary neutral” (skis pointing straight ahead with no lead), “edge neutral” (skis flat on the snow surface), and “pressure neutral” (balance 50-50 on both skis) also occur in basic turns, but (contrary to popular opinion?) they all occur at some point after the turn begins. They do not occur at “turn neutral,” where the old turn ends and the new turn begins.
 

James

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There is still some angulation there, He's not a stick. If only inclining you can't hold an edge.

No. Completely absurd.
Well, you're actually right! Sorry I dismissed it as absurd. Essentially when I said that I operated in the "I've always thought..." mode which has no bearing on reality.

If one is technically only inclining, like a stick, (which you said and I ignored), you can not get less than 90 deg of platform angle on the outside ski. Thus it won't hold. The inside would, but we're not talking about skiing on the inside ski. One would need a little...angulation in the system to get below the critical edge angle of 90deg. It's not much, but more than a rigid stick could manage.

Here's the diagram. (Illustrator wishes to remain anonymous)
image.png

So on a 65mm ski we, the stick figure, need to find 4.2 deg of angulation in order for the ski to hold.
Arrrgh! This critical edge angle stuff is so non-intuitive. At least to me.

So, @Jilly , you were right!
 
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Jamt

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Well, you're actually right! Sorry I dismissed it as absurd. Essentially when I said that I operated in the "I've always thought..." mode which has no bearing on reality.

If one is technically only inclining, like a stick, (which you said and I ignored), you can not get less than 90 deg of platform angle on the outside ski. Thus it won't hold.

If 50% of the weight is on the inside, and/or if you are just landing (upwards acceleration), the ski will still hold, but not for long.

Edit, soo starting a turn with little to no angulation is not a big problem, but later in the turn it is usually not a good idea.
 
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James

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If 50% of the weight is on the inside, and/or if you are just landing (upwards acceleration), the ski will still hold, but not for long.
How do we get that?
Hmmm.. So hop turn strategy could work.
Do you have a title link, or just the name, for the Reid book?
 

Jamt

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How do we get that?
Hmmm.. So hop turn strategy could work.
Do you have a title link, or just the name, for the Reid book?
The word landing just means the CoM is moving up and down through the turn, not necessarily a full lift off the snow.

The Reid phD thesis is downloadable from here : https://brage.bibsys.no/xmlui/handle/11250/171325

It is a bit long but very good read.
 

Chris V.

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The Reid phD thesis is downloadable from here : https://brage.bibsys.no/xmlui/handle/11250/171325

Plenty to chew on here. Thank you. "[O]ur scientific understanding of how the underlying mechanics of alpine ski racing technique relate to performance is surprisingly weak." That's sobering.

Attempting to distill this discussion, these basic points SHOULD be unquestioned:

o A skier must have inclination to keep from tipping over while turning. If the skier is standing still and in balance, the center of mass will be vertically over the base of support (for which we can just substitute "skis" :D). The force of gravity acts on the COM in the vertical direction; hence, the snow pushes up on the skis in the vertical direction. If the skier is moving and making a turn, the COM must be inclined from the vertical, relative to the skis, in the amount and in the direction needed to counterbalance the force of the snow pushing up on the skis during that turn. This force results from a combination of centripetal force and the force of gravity. The result of correct inclination is dynamic equilibrium, or dynamic balance.

o Skiers naturally incline without even thinking about it. A skier who doesn't incline tips over very quickly, and tends to learn from that experience. Inclination is natural and indispensable in other everyday activities, such as running and bicycling. We all learn it from an early age.

o Angulation alone, if angulation is defined as a realignment of body parts that does not move the location of the center of mass, is not effective to create the dynamic equilibrium necessary to counteract the combination of gravity and centripetal force. To get dynamic equilibrium, the COM must be inclined from the vertical.

o If the skier's posture is such that while at rest the skis are flat, then inclination alone while moving will result in ski bases that are at a 90 degree angle to the direction of inclination.

o Bases and edges held at a 90 degree angle to the direction of inclination will not furnish adequate grip in real-world skiing conditions.

o Therefore, angulation is needed to create a more acute angle between the edges and the direction of inclination, increasing grippiness.

o Therefore, to create good ski performance, the skier needs to employ a combination of inclination and angulation. (Which I think the Five Fundamentals have something to say about.)
 

Doby Man

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The video below is a good comparison of angulation and inclination from the mechanics of the same skier and how they are both used in for both large and small radius turns. More inclination than angulation in SL (crossunder) turns and more angulation than inclination in GS (crossover) turns. Whatever the mix of each that is determined by the size of the turn, inclination always comes in first and then blends into angulation as the path of the CoM is directed over the path of the skis in a manner that allows the turn to happen on all accounts. Because inclination gives the skier more stacking power to manage the larger forces of higher speeds, it is a huge tool for the speed disciplines. Because angulation provides more redirection for the smaller forces of slower speeds, it is a more valuable tool for the more technical disciplines. How angulation and inclination are used in conjunction with each other is a prime example of skill blending. The primary attribute to skill blending is not so much about the blending of the movements themselves but rather the timing those movements are based on. That said the difference between the crossunder and crossover are just as much about the mechanics of inclination and angulation as it is about the timing of that blend.

In the video below, we can see how there is more time and space to use more inclination when granted by speed and allowed with more time and space in large crossover turns.

We can see how because there is not enough time and space in small turns, the skier is forced to tip the legs without tipping the upper body (crossunder) to help achieve the same tipping angles.

We can see how that what inclination is used is facilitated at the beginning of the turn primarily disappears with counterbalancing of the upper (angulation) through the end of the turn. See how inclination turns into angulation and never the other way around.

Inclination is used to stack the skeleton against the general centripetal forces of the turn and angulation is used to direct the force vector of that stacking to the outside ski.

 

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