Feeling the "Push"

[JESinstr]

Just recently in the Fore/Aft Balance and Physics thread, I posted to @karlo regarding the physics of carving.

@LiquidFeet responded:
"JES, you often talk about skiing as something that can best be understood if the skier thinks about how straight line travel (generated by gravity and momentum) and circular travel (generated by the ski-snow interaction) do their thing as we ski. This does not work for me.

Would you find it interesting to start a thread asking the community to tell you what they think these factors mean for a ski turn (straight line and circular travel), and how useful it has been for them to think about them to better understand their skiing? Maybe a large number of people like thinking about that particular interaction and find it illuminating."

I don't know if it will be illuminating but here goes.

The modern shaped ski is a sophisticated, specialized tool whose main design function is to take straight line travel and convert it into circular travel. LF's assertion that forces "do their thing as we ski", appears to ignore the fact that we must have the ability to both control and generate forces that allow us to ski.

The generation of circular travel produces the turning force known as Centripetal Force.
Centripetal Force is an ACCELERATING, INWARD force.
1. "Accelerating" meaning that the force is not constant and will change if not managed.
2. "Inward" meaning your skis, and hence your mass, are being PUSHED toward the center of the circle.
The skier is responsible for the generation of this force. It does not happen without skier input.

The Heart of the Matter:
When creating circular travel (carving), the equal and opposite (outward) force that gets generated is called Centrifugal force. There have been many heated discussions on this topic but my position, relative to skiing, is that Centrifugal (yes it is real) is the feeling (and reality) of our skis and mass seeking escape from the generated Centripetal force in favor of return to the DEFAULT straight line force generated by slope and CONSTANT pull of gravity.

Most lower level skiers relate and react to the DEFAULT pulling force of Centrifugal, because they don't have the knowledge, perception nor ability to truly establish, build and maintain a controlled Centripetal state. These skiers judge and take action regarding their skiing status by trying to sense when their edges are going to begin decoupling from the surface. And why not do so? After all, their view of the world on skis is shaped by the fear of being pulled down the hill.

Along with proper fore/aft balance, we need to build high edge angles through the process of angulation and management of the resulting Centripetal pressure. That's what instructors who want to teach carving need to focus on IMO. Most lower level skiers lead with inclination which severely limits the ability to build and control a powerful, progressive edging process.

When one finally learns to effectively and confidently edge, the FEAR of edge decoupling will be replaced by the PUSH of the skis.

LF also wrote:
"I have line drawings of different types of ideal turns stored in my head, and those simple models depict direction of actual travel. The lines are dark when the pressure is high and light where it's light in these ideal turns. These models take into account degree of turn completion and radius. If I want to make these mental models a little more inclusive, I add width to the tracks where the skis skid/brush across the snow surface. Manipulating those elements in my mental models - radius and shape, degree of completion, pressure, and skid width - pretty much covers all kinds of turns -- for me. "

Wow! talk about complexity! But strangely enough, we have commonality here. I sum that up as the "GO THERE" mentality and I totally subscribe to that. The difference may be that I know that when I "GO THERE", I realize and feel that I am being PUSHED there.

Bottom line, we all have our different ways of perceiving our world, and that is a good thing...most of the time.

Your comments appreciated.

 

[Wilhelmson]

Without trying to justify my own crappy skiing it seems people are paying a bunch of money to fight gravity and turn it into a pretty picture.

 

[Kneale Brownson]

I do not feel that circular travel involves being pushed. But I have no suggested different terminology to describe the push BACK from the snow beneath my skis. I think I direct that push to go where I wish

 

[James]

If you're traveling in an arc, wether carved or skidded, there's centripitel force.
It gets back to the aphorism of "do you turn the skis or do the skis turn you? "
The answer is supposed to be you want to turn the skis and not get "taken for a ride"
However, if the skis don't turn us, what does, magic? Also, going for a ride in a carve is pretty fun.

 

[LiquidFeet]

When I'm carving, I feel the skis bending at the fall line and through apex. I pay close attention to how much bending is happening, and how that's going to affect my line. I look for that diving board spring in the skis, and pay close attention to how deeply that diving board is getting bent. I also pay close attention to turn when I want to let go of the turn, because turn completion helps with speed control and perceived self-preservation. So, for me, the important things when carving are shape and radius, aka line.

I don't think about the snow pushing, it's the ski bending that holds my attention. My focus is on the skis. There are some other things I'm paying attention to, but those are thread-drift material so I won't bring them up. My point is, as a person who already knows how to get my skis to carve, I'm not sure how thinking about the snow on the other side of my bases is going to improve my control over my line.

@JESinstr in that post above, you describe skiers who don't yet know how to keep their skis gripping and moving in the direction they are pointed. I'm now thinking that they are the intended audience for this talk about Centripetal and Centrifugal matters. You said, but not necessarily in this order:

"Most lower level skiers relate and react to the DEFAULT pulling force of Centrifugal, because they don't have the knowledge, perception nor ability to truly establish, build and maintain a controlled Centripetal state. These skiers judge and take action regarding their skiing status by trying to sense when their edges are going to begin decoupling from the surface....Most lower level skiers lead with inclination which severely limits the ability to build and control a powerful, progressive edging process....Along with proper fore/aft balance, we need to build high edge angles through the process of angulation and management of the resulting Centripetal pressure. That's what instructors who want to teach carving need to focus on IMO."

You mention factors in your post (inclination, angulation, progressive edging, fore/aft balance) in addition to Centripetal and Centrifugal matters, so I am betting that you also assume that instructors should focus on all these factors. Here's my question: when you get the chance to teach your students to carve, how much emphasis do you put on these Centripetal/Centrifugal concepts? Do you use those words in your lessons, or do you reserve them for discussions amongst instructors? Does your focus on these two concepts improve your students' carving progress?

I don't get the chance to teach my students to carve very often, or, well, much at all, really. I'm curious. My attempts have always been on purging the embedded pivot. It's quite persistent. Had I chosen to be a race coach for kids in a race program, that pivot issue might be moot. Are you a race coach?

 

[JESinstr]

I do not feel that circular travel involves being pushed. But I have no suggested different terminology to describe the push BACK from the snow beneath my skis. I think I direct that push to go where I wish

I can agree with that perspective

 

[JESinstr]

If you're traveling in an arc, wether carved or skidded, there's centripitel force.
It gets back to the aphorism of "do you turn the skis or do the skis turn you? "
The answer is supposed to be you want to turn the skis and not get "taken for a ride"
However, if the skis don't turn us, what does, magic? Also, going for a ride in a carve is pretty fun.

Totally agree. But I will point out that skidding has to be qualified when used in conjunction with carving. It's ok to skid into a carving state thus continuing the creation of arc. No so good to unintentionally skid out thus destroying the arc.

 

[karlo]

LF also wrote:
"I have line drawings of different types of ideal turns stored in my head, and those simple models depict direction of actual travel. The lines are dark when the pressure is high and light where it's light in these ideal turns. These models take into account degree of turn completion and radius. If I want to make these mental models a little more inclusive, I add width to the tracks where the skis skid/brush across the snow surface. Manipulating those elements in my mental models - radius and shape, degree of completion, pressure, and skid width - pretty much covers all kinds of turns -- for me. "

I’ve read that musicians visualize their music

The generation of circular travel produces the turning force known as Centripetal Force.
Centripetal Force is an ACCELERATING, INWARD force.
1. "Accelerating" meaning that the force is not constant and will change if not managed.
2. "Inward" meaning your skis, and hence your mass, are being PUSHED toward the center of the circle.
The skier is responsible for the generation of this force. It does not happen without skier input.

To me, the physics is simplified by looking at cases in which our com is not deflected, not traveling in an arc. Just let com travel straight down. The apex of the carved turn is within legs’ length, or legs’ reach. Then, the center of the ski’s arc is oneself.

Anything else happening, laterally, with COM is something else, that then adds to what’s going on with the carve. E.g, we might go laterally by using the energy of the ski to rebound laterally. Or, we might simply travel with the ski, yielding a larger turn. But, in conceptualization of the physics and forces of a turn, we would benefit from simplifying.

Here's my question: when you get the chance to teach your students to carve, how much emphasis do you put on these C

Referring to inclination, angulation, progressive edging, fore/aft balance. I teach kids. For/aft balance is: stand on your feet like you’re standing on a floor. Progressive edging: not there yet. Inclination: not addressed. Would rather deal with what one should do, not what one should not do, or do less of. Angulation: I ask the kids to imagine a dance floor and to stay upright (above waist) to the floor, while pressuring the outside ski.

 

[James]

To me, the physics is simplified by looking at cases in which our com is not deflected, not traveling in an arc. Just let com travel straight down. The apex of the carved turn is within legs’ length, or legs’ reach. Then, the center of the ski’s arc is oneself.

I still don't get what your talking about. By definition, if you're in a curve you've been deflected. The center of the ski's arc is never oneself. A 10m radius is huge.

 

[JESinstr]

@JESinstr in that post above, you describe skiers who don't yet know how to keep their skis gripping and moving in the direction they are pointed. I'm now thinking that they are the intended audience for this talk about Centripetal and Centrifugal matters. You said, but not necessarily in this order:

"Most lower level skiers relate and react to the DEFAULT pulling force of Centrifugal, because they don't have the knowledge, perception nor ability to truly establish, build and maintain a controlled Centripetal state. These skiers judge and take action regarding their skiing status by trying to sense when their edges are going to begin decoupling from the surface....Most lower level skiers lead with inclination which severely limits the ability to build and control a powerful, progressive edging process....Along with proper fore/aft balance, we need to build high edge angles through the process of angulation and management of the resulting Centripetal pressure. That's what instructors who want to teach carving need to focus on IMO."

You mention factors in your post (inclination, angulation, progressive edging, fore/aft balance) in addition to Centripetal and Centrifugal matters, so I am betting that you also assume that instructors should focus on all these factors. Here's my question: when you get the chance to teach your students to carve, how much emphasis do you put on these Centripetal/Centrifugal concepts? Do you use those words in your lessons, or do you reserve them for discussions amongst instructors? Does your focus on these two concepts improve your students' carving progress?

I don't get the chance to teach my students to carve very often, or, well, much at all, really. I'm curious. My attempts have always been on purging the embedded pivot. It's quite persistent. Had I chosen to be a race coach for kids in a race program, that pivot issue might be moot. Are you a race coach?

Don't short change yourself! You have the opportunity to teach carving the minute you begin teaching the narrow wedge turn.
This is why the 5 fundamentals have been a teaching epiphany to me. They have allowed me teach a single thread of basic technique that spans the beginner to the advanced wannabees.

In fact, I would submit that teaching the basics of carving in wedge formation is the ultimate challenge for the many instructors. The reason being is that early wedge activity is conducted under the force of gravity in terms of keeping balance. Shortening (hence flattening) the inside leg while directing pressure to the outside ski is a very subtle move. That's why I emphasize inside edge of the outside ski as the recipient vs the entire ski.

Nonetheless, if the path of the outside ski shows a circular path, it is carving. Now, do I talk about all this centripetal stuff to the student? Of course not! But it is that knowledge that is a basis for my teachings. I do admit that when the student has built some confidence in what they are achieving, I do try to point out the ski is turning them or as @James says, taking them for a ride.
.

 

[LiquidFeet]

.... Nonetheless, if the path of the outside ski shows a circular path, it is carving....

Your definition of carving is different than mine.

 

[karlo]

I still don't get what your talking about. By definition, if you're in a curve you've been deflected. The center of the ski's arc is never oneself. A 10m radius is huge.

Ok, maybe I just don’t understand what a carve is. Like I said in the other thread, I’ll try to get a video of myself. But, until then, what I mean is that the ski’s are in a curve, not me, at least my upper body. But I also get what you mean. With a 10 m radius, how can the upper body not go laterally for the ride?

Ski’s can’t be carved at a lower radius than stated radius?

 

[James]

Ok, maybe I just don’t understand what a carve is. Like I said in the other thread, I’ll try to get a video of myself. But, until then, what I mean is that the ski’s are in a curve, not me, at least my upper body. But I also get what you mean. With a 10 m radius, how can the upper body not go laterally for the ride?

Ski’s can’t be carved at a lower radius than stated radius?

Yes you do.
One ski carve- on green terrain put one ski very far on edge. With the other leg in a wide stance, it's just supporting a bit, it's basically flat.
Now, just ride that ski on edge in the natural arc of the ski/edge angle. Do whatever you need to do with the body to support staying on edge. Eg, counter balance/angulate.

You will carve an arc. At some point flatten the ski being edged and edge the opposite one. There you go, a simple carved turn.

These videos are interesting. Really zero physics despite the title. However, here's one of the best speed skiers in the world, Kjeitil Jansrud, talking about how different skiers bodies will affect the ski differently. Thus they need different setups.

 

[Chris V.]

A word about terminology.

Physicists use the word "acceleration" differently from most people. Acceleration doesn't just mean speeding up. It can mean that, or it can mean something else. Acceleration is the rate of change of velocity of an object. Acceleration is a vector quantity. It has magnitude (a scalar quantity) and direction. Therefore, it can be a straight line speeding up or slowing down, or it can incorporate a change of direction. When a skier is turning, he's accelerating in the direction of the turn. An object's acceleration is the net result of all forces acting on the object. Acceleration is not itself a force.

See https://en.wikipedia.org/wiki/Acceleration .

 

[Chris V.]

When one finally learns to effectively and confidently edge, the FEAR of edge decoupling will be replaced by the PUSH of the skis. ...I sum that up as the "GO THERE" mentality and I totally subscribe to that. The difference may be that I know that when I "GO THERE", I realize and feel that I am being PUSHED there.

Might this be summed up by saying that we want to replace pushing on the skis with letting the skis push on us, and directing the energy of that push?

 

[Steve]

@JESinstr I think you and @Doby Man both take a very high level conceptual approach in your writing and I for one learn from it.

I've skied with him and the general, conceptual matters discussed make for some great skiing, All of his COM/BOS/Vector complex writings were simplified once into the concept of thinking of a joystick on a game controller and thinking of your body/force vector as that stick. When skiing "push the stick." This simple focus has helped me in my skiing many times.

My point is that awareness of circular travel to me is also a useful concept. Do I think about it when I ski (and I think about a lot of different things from time to time when I ski) - no. I sure feel it though.

 

[François Pugh]

I just want to say that @JESinstr and @Doby Man 's models of skiing take a little effort to get into, but the effort is worth it.

 

[karlo]

A word about terminology.

Physicists use the word "acceleration" differently from most people.

See https://en.wikipedia.org/wiki/Acceleration .

Yes!

when I "GO THERE", I realize and feel that I am being PUSHED there.

Which is the way we feel acceleration. Far easier to be talking about what we feel than physics.

I think I direct that push to go where I wish

Yes! That push from the turn can push us, our COM, laterally. Or, if we choose to release from that push, the push can push our skis, along with our legs, into the next turn. Whichever the case, we have choices. We can choose when we rengage the ski relative to our COM. WE can choose what part of the ski to engage first, the tip, or further back from that. It’s that moment of transition in which we have the greatest amount of choice, as well as influence on what will happen in the next turn. Once ski’s are engaged, we still have choices, but more limited, limited by what terrain and gravity allow while maintaining balance. Which brings the question, what choices do we have at point and what effect will that have on both result and subsequently available choices.

don't think about the snow pushing, it's the ski bending that holds my attention

Pretty much the same as thinking about the push. When the ski unbends, it will push. And, even when bent, it is pushing.

Anyway, I like this idea of talking about the push. It’s somrrhing folks can feel.

 

[LiquidFeet]

When the ski unbends, it will push. And, even when bent, it is pushing.
Anyway, I like this idea of talking about the push. It’s somrrhing folks can feel.

Karlo, I think this thread is addressing the snow pushing up at the ski, not the ski pushing down on the snow, or the ski pushing back up at the skier.

 

[geepers]

Karlo, I think this thread is addressing the snow pushing up at the ski, not the ski pushing down on the snow, or the ski pushing back up at the skier.

For every action there is an equal and opposite reaction - Isaac Newton

So, does it matter which way we think about it?

Except I don't like the word "pushing" as it implies an action on the part of the skier which is likely to lead to 'exciting' outcomes.