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# Power by nature

I'm sitting here watching the Olympic whitewater C1 slalom event. Very impressive how the athlete harnesses the raging force of the river that surrounds him and uses it to serve him in what appears to be effortless proficiency. This is exactly what we do on skis in our dance with gravity. Any thoughts?
Agreed. Good skiers use the available natural forces to do the work. That's why they don't tire like less skilled skiers, and why good skiers age well in this sport.
Exactly Nolo. Kind of serves as a good model for navigating life, too.
Getting tired is often a result of working against gravity. Knowledge how the ski under your feet are working and an good feeling for your body (center of mass / inertial tensor) are the key to become a better skier. Just my thoughts.
I like the taijiquan term "Borrowing Power".
Inertial tensor--that's a new one! Whatever does it mean?
Quote:
 Originally Posted by nolo Inertial tensor--that's a new one! Whatever does it mean?
I thought I was the only one that didn't know.

My guess is it's the manner in which the body resists the downward and outward forces felt when turning. Sounds good, huh.

Hi,

no education but perhaps a view to the physics of skiing. :

SD, you are already on the right track. While skiing there are two forces at work, gravity and vis inertiae.

We discern two aspects of mass, the weighting mass and the inertial mass. The weighting mass depends on gravity, the inertial mass on acceleration.

The effect of the weighting mass is well known to everybody. You can see it on the scale. The effects of the inertial mass are also always present but we usually don't think much about this. You feel the force in an accelerating or decelerating elevator,car etc. You also feel it while driving a turn with a car. There you don't change your speed but your direction.

At last it means a mass wants to keep speed and direction. Every change causes a force. The centrifugal force we experience during skiing a turn is a direct consequence of this force.

Tech people usually want to compute all kind of physical effects. Unfortunately inertiae is a difficult matter. It depends on shape, weight distribution within the shape and distance from the center of a turn. So there was to find a mathematical term to handle this over all, a 'tensor'. In this case the 'inertial tensor' . It's an abstract term, ugly to handle if you are not used to.

Absolutely useless on the slope 'cause skiers changing shape, mass distribution and the radius of a turn again and again.

But understanding this physical factor can help improving skiing or other sports. As an example, everyone knows ice-skaters speed up a pirouette only by norrowing the turn and centering the mass distribution. Arms to the body or over the head. There is no extra energy push.

The same a funcarver can do to finish a 360. The move of an arm possibly decides wether you get a full 360, a 180 with a pirouette at the end or just lie in the snow.

Of course you still need the strength of your muscles, but there more you are able to work with these forces instead against, the more comfortable skiing gets. Or you can converge to the 'Bode Miller' style, always on the egde (of physics). :

Hope you enjoyed it,

CarvingFan

PS:
For the physicist amoung us, yes, this is not as exact as possible. That would be too much. I've used the term because I don't know a better and more common word for it and I had to serve my sentence to explain.
What kid doesn't learn this by age 5? We just have a name for it now.

To feel this effect, wind yourself up on one of those long chained grade school swings. Start spinning and move your legs in and out....slowing or speeding your spin. You can flatten your body, lean back...all manner of ways to mess with the speed.

And when the swing is unwound, what do kids do? Pull in and make it go faster in the other direction!

Ok, snowfans.....get out on the playground and go for it!
After all the previous talk of physics, we still have a new term!!! I have to admit that that one snuck right by me.

I take it you are speakng of the relationship between our body shape, particularly our upper body position, shape, and respective mass distribution to our gravity line or force vector. Maintaining our core to give our gravity line/force vector something to rely on. I borrowed again from tai chi. Later, RicB
Yes Bonni, you got it. But do you have an explanation why so many grown ups forgot to play the game ?

Yes Ric, but don't forget, I'm talking about two forces. Gravity vanishes when you leave our planet (tell me, if you are on the move) , vis inertiae never leaves you.
Quote:
 Originally Posted by RicB After all the previous talk of physics, we still have a new term!!! I have to admit that that one snuck right by me...
You may have heard of it as the "moment of inertia tensor". The full name is much more commonly used in the US than just the "inertia tensor", which sounds like some concept from general relativity.

There are simple descriptions of it here1 and here2 .

(gotchya - just kidding about the simple part).

Those are the full technical descriptions. A readable discription is actually here3

Quote:
 Originally Posted by RicB ...I take it you are speakng of the relationship between our body shape, particularly our upper body position, shape, and respective mass distribution to our gravity line or force vector. Maintaining our core to give our gravity line/force vector something to rely on. I borrowed again from tai chi. Later, RicB
To be accurate, a moment of inertia tensor does not per se describe the relationship of the object to the gravity line or force vector. By itself, it only contains the spatial relationship of the individual masses which constitute an object relative to some fixed-in-space coordinate system. One can transform it to reflect the orientation of an object relative to any coordinate system (ie, including the ones you mentioned), but that is not its real role in life.

For multi-particle objects (ie, ones that have angular orientation, not just a point-like position), it serves the same role as the single number "mass" does for point objects. "mass" tells you how difficult it is to get a point-like object moving (ie, accelerating). The "moment of inertia tensor" is a generalization of "mass" tells you how difficult it is to get an extended, irregular object moving and/or spinning around any arbitrary axis or set of axes.

For rotations of many objects about a single axis (eg, pivoting skis on top of a mogul) the "moment of inertia tensor" reduces to nothing more than the usual single number, the "moment of inertia", usually called "swing weight" by skiers.

For the record, let me state that even I see absolutely no need to introduce the full concept to any skier unless he happens to be another physicist (or someone who likes hearing about such things). IMHO, throwing this term around when it is not necessary could easily be construed as being highly pretentious.

HTH,

Tom / PM
Hi Tom,

it wasn't meant pretentious at all. 'Swing weight' is nice term. And thanks for your informations and links. So I can fill up my lack of english words.

CarvingFan
Quote:
 Originally Posted by CarvingFan ...While skiing there are two forces at work, gravity and vis inertiae. We discern two aspects of mass, the weighting mass and the inertial mass. The weighting mass depends on gravity, the inertial mass on acceleration...At last it means a mass wants to keep speed and direction. Every change causes a force. The centrifugal force we experience during skiing a turn is a direct consequence of this force. ... PS: For the physicist amoung us, yes, this is not as exact as possible. That would be too much. I've used the term because I don't know a better and more common word for it and I had to serve my sentence to explain.
CarvingFan - Because you are new to this discussion group, you probably aren't aware that a few weeks ago we just concluded a very lengthy discussion (300+ posts in one thread) of centrifugal vs centripetal forces, "real" vs "pseudo forces", etc. Because of the time and energy this discussion took, I am very hesitant to correct some seemingly minor (but actually fundamentally important) points in the above post. However, because they could mislead / confuse people, I am going to, but I don't intend to enter into a lengthy discussion of these points. If you disagree with what I am about to say, I would simply recommend that you consult a standard textbook of mechanics / dynamics.

"... The weighting mass depends on gravity, the inertial mass on acceleration ..."

Your terminology is non-standard and possibly confusing. I have never heard or seen the phrase "weighting mass" used.

Objects have only one mass. Gravity acts on that mass to produce the effects and sensations of weight, not the other way around. It is the same for the second part of your sentence - forces act on that (single) mass to produce acceleration. The way you phrased your sentence, it sounds like if there is no gravity, there is no (weighting) mass, and clearly this is not true. Mass exists with or without gravity, with or without acceleration.

"... Every change causes a force ..."

This one seeming innocuous little sentence (or its equivalent) can cause a huge ammt of confusion among lay people and is essentially at the heart of the lengthy thread that I mentioned above.

Usually, people say, "every force causes a change in velocity". What this means is that when viewed from an external, non-accelerating coordinate system, forces cause changes in velocity (ie, accelerations).

You said something different: "Every change in velocity causes a force". While this can be true, this only happens when changes in velocity are not visible to an observer (ie, an observer inside a closed box being pushed from the outside). This is what is called an non-inertial (or accelerating) frame of reference, and can indeed can cause this observer to experience very real forces, but these can be difficult for lay people to understand, and hence are sometimes called pseudo-forces.

Unless really needed, analysis of dynamics in such accelerating frames of reference forces is probably best not done. Unfortunately, skiers making turns are always in an accelerating frame of reference and so the issue of what they experience in such a frame of reference must be dealt with. As you point out, this (ie, centrifugal force) is why they feel like they are being thrown to the outside of the turn. A stationary observer looking at the skier from the side of the hill sees the snow pushing on the skier making him/her turn (ie, the centripetal force). Enough said on this. For more details, you may want to take a look at the old thread on this subject.

Tom / PM
Quote:
 Originally Posted by CarvingFan Hi Tom, it wasn't meant pretentious at all. 'Swing weight' is nice term. And thanks for your informations and links. So I can fill up my lack of english words. CarvingFan
Ah, I see we were both writing messages at the same time.

I was pretty sure you didn't mean to sound pretentious, that's why I said something like "could be construed as pretentious".

Your command of English is great - undoubtedly much better than my command of your language. It actually didn't occur to me that you were not a native English speaker. This may explain some of the subtle differences in meaning I brought up in my last message.

Stay around. I hope you will enjoy the discussions on Epic.

All the best,

Tom / PM
Hi Tom,

thanks again, I agree to what you said above. The part of physics, not about my writing abilities.

In fact I wasn't aware of your 'monster'thread. I will read it. Perhaps I will sound like a native american when it's done. :

CarvingFan
powder skiing has only one other athletic base of comparison, in my mind -- and that's whitewater kayaking/canoeing. both are 3-dimensional media, both require mastery of the medium before getting to the "play" levels found at high performance states. the "play" occurs when the athlete is letting the gravity/medium do a lot of the work, and uses the boat & paddle, or skis, to function cooperatively with the medium and gravity.

I didn't reach as high levels in whitewater kayaking as I've reached in alpine skiing, but I can say this for sure: the dynamic power of whitewater is frightening, awesome, and more uncertain than powder snow. I quit kayaking because it scared me at Level IV and higher. powder doesn't scare me the same way.
Quote:
 Originally Posted by CarvingFan Yes Bonni, you got it. But do you have an explanation why so many grown ups forgot to play the game ? Yes Ric, but don't forget, I'm talking about two forces. Gravity vanishes when you leave our planet (tell me, if you are on the move) , vis inertiae never leaves you.
Understood. Just trying out how this applies to me skiing right here on earth.
Thanks PM. As always your keeping us honest. I agree too that I have no more energy for this right now. The term did pick my curiosity after it was drawn to our attention. Later RicB.
Quote:
 Originally Posted by gonzostrike powder skiing has only one other athletic base of comparison, in my mind -- and that's whitewater kayaking/canoeing. both are 3-dimensional media, both require mastery of the medium before getting to the "play" levels found at high performance states. the "play" occurs when the athlete is letting the gravity/medium do a lot of the work, and uses the boat & paddle, or skis, to function cooperatively with the medium and gravity. I didn't reach as high levels in whitewater kayaking as I've reached in alpine skiing, but I can say this for sure: the dynamic power of whitewater is frightening, awesome, and more uncertain than powder snow. I quit kayaking because it scared me at Level IV and higher. powder doesn't scare me the same way.
Man I agree with you there Gonzo. I'm not a kayaker, I'm an open canoeist, but I've been scared in ways on Montana rivers that only equal an avalanche experience on skis. Needless to say, I don't seek those challenges anymore either. Later, RicB.
I've kayaked also, and like you Gonzo my skiing abilities surpass my whitewater skills. Fear levels are totally related to skill levels. The more one exceeds their own perceived competency thresholds the more fear becomes an issue.

I feel totally at ease doing things on skis that would terrify most skiers, yet feel anxious and unsure in some whitewater that others of greater skill would feel totally relaxed. In both environments, snow and water, we are dancing with very powerful forces that have the potential of hurting us very badly; even killing us.

That's the draw though. We do it for the rush; to walk on the edge of danger and feed on the adrenalin. There's a downside to elevating our competency though. The better we get at something the more we must push the envelope to experience the same level of excitement, and in doing so we intensify the repercussions of making a mistake. Fall making snowplow turns and you might twist a knee. Fall while making a 60 mph SG turn on a narrow, tree lined trail and you might die.

That's the game we choose to play though. Fear or fun: it's all about how well we can dance with nature.

### Say What?

Quote:
 Originally Posted by SnowDog Fear levels are totally related to skill levels. The more one exceeds their own perceived competency thresholds the more fear becomes an issue.
Sounds like a bunch of psychological mumbo jumbo to me.
Totally consistent with what I said before. Improve the skills and the fears over performing relatively simple tasks magically disappear.
Snow Dog, you're right on the money with that. I like skiing fast, not reckless fast and not edge-of-control fast, but I enjoy the buzz of adrenaline and the thought of "just how much faster can I go and still feel like I"m in control."

the problem with whitewater wasn't so much my skill level -- I progressed reasonably quickly but not prodigiously and surely not falsely. I was paddling Class III+ and IV- after two seasons. I don't think that's quite piddle-paddle, it's surely not V and VI water -- but to me, Extreme Skiing Comps are V and VI water analogs, not double-diamond runs or untracked backcountry bowls.

snow is more predictable in its movement against you. that's the basic thrust of what I'm saying. water is forever dynamic, impossibly hyperlaminar,and that's what makes it scarier. it's much more unpredictable. IMHO, top boaters just don't mind the unpredictability, and in fact in a way crave it.

are we saying the same thing?
Quote:
 Originally Posted by gonzostrike I was paddling Class III+ and IV- after two seasons. I don't think that's quite piddle-paddle, it's surely not V and VI water -- but to me, Extreme Skiing Comps are V and VI water analogs, not double-diamond runs or untracked backcountry bowls. are we saying the same thing?
I think we probably are Gonzo.

Even with competency, each person has his own acceptable fear level tolerances. To use your comparison (which I like, by the way); when we get up to V-VI whitewater, Extreme Skiing Comps or 90 mph Downhills even the knowledge of competency won't necessarily placate.

At these levels of intensity there is some degree of awareness of danger in all but the insane. Few, short of the extremely gifted, have the skills to perform at these levels with little chance of making a mistake. That fact, combined with the knowledge of the consequences of making a mistake at levels of performance make the risk beyond the tolerance of most.

As to the differences between the nature of the forces encountered on snow and water: I can see what your saying. On snow you move over the ground, and on water the ground moves you. I wonder, even though the river is inconsistent and ever changing, whether after a lot of time on the river one would begin to become very familiar with all the various hydro patterns and gain confidence in being able to spontaneously handle them as they're suddenly encountered? Just speculation, I haven't attained that level myself.
Just started surfing this last summer & was discussing this with Man from Oz(Philay now) ... The snow feels relatively safe compared to the sea - because the sea is just SO unpredictable....

He has been surfing for years but tells me that it never feels as safe - you have to always have so much respect for the sea....
He tells me I will never get close to the same level in surfing as on snow - harder to predict....(Remember i can't react in the same way as normal)
he says my addiction to surf may change after my first drowning experience :
SnowDog,

during my 2d season I helped teach a beginner's class at Univ MT with two other folks (the real teachers, I was a fetcher basically), one of whom is a top pro freestyle kayaker. She said she craves the buzz of the water's unpredictability. of course, she has skills that would make most boater's eyes bulge.

I think it's definitely relative to the individual athlete, but I think that many top "high risk" athletes have a MUCH higher tolerance for what's not within their control. on the other hand (my hands) predictability is fun as it sets the groundwork for what playing I do -- whether on skis or on my mtn bike. reaction to the unpredictable is what's scary, but really only when the reaction is wrong! when it's working, it's the source of adrenalin. my mental calculus couldn't get past the river death scenario.
Quote:
 posted by SnowDog: Posted August 6th Quote: Originally Posted by LisamarieIn my case, the misalignment is due to a mental stateNo kidding. Man, talk about an energy leak,this thread is an energy leak. What the hell is this, the Sigmund Freud School of skiing? Can the psycho babble, spend the extra time learning to ski, and much of your little female emotional stuff will take care of itself.Heck, three hundred pound puff muffins can rip if they know how to ski. It ain't about fitness, it's about skill, and until you quit yappin and get out there and learn you’re going to be leaking energy and girly tears all over the slopes.

Quote:
 Originally Posted by SnowDog posted August 18th: I've kayaked also, and like you Gonzo my skiing abilities surpass my whitewater skills. Fear levels are totally related to skill levels. The more one exceeds their own perceived competency thresholds the more fear becomes an issue. I feel totally at ease doing things on skis that would terrify most skiers, yet feel anxious and unsure in some whitewater that others of greater skill would feel totally relaxed. In both environments, snow and water, we are dancing with very powerful forces that have the potential of hurting us very badly; even killing us. That's the draw though. We do it for the rush; to walk on the edge of danger and feed on the adrenalin. There's a downside to elevating our competency though. The better we get at something the more we must push the envelope to experience the same level of excitement, and in doing so we intensify the repercussions of making a mistake. Fall making snowplow turns and you might twist a knee. Fall while making a 60 mph SG turn on a narrow, tree lined trail and you might die. That's the game we choose to play though. Fear or fun: it's all about how well we can dance with nature.
"Suck up, Mr. CandyAss.....quit yer whining and learn to whitewater in whatever medium you choose and your little MALE EMOTIONAL stuff will take care of itself." -Me, pretending to be you

How ridiculous you sound! How your story changes from annoyance with the fears of others to tolerance of your own fears.

Exposed before your peers.....tear down the wall.
Quote:
 Originally posted by SnowDog, A.K.A. "Mr. CandyAss" Heck, three hundred pound puff muffins can rip if they know how to ski. It ain't about fitness, it's about skill, and until you quit yappin and get out there and learn you’re going to be leaking energy and girly tears all over the slopes.
Yeah, but an increased fitness level helps greatly! I may not be that "three hundred pound puff muffin", but I am a person of size, so I am speaking from experience. I know that my skiing would be greatly improved if I were smaller. I have taken off some pounds, it used to be horrible, I could hardly buckle my own boots (I couldn't reach them) so I bought rear entry with one buckle just so I could continue to ski. They are gone now and I have "real" ski boots.

I've been told that I am a good skier, I don't think so, but others do. I've been told that I float right over the snow and am very smooth. I often feel clumsy and uncoordinated.

I think that MENTAL attitudes and FEAR play a large role in the whole picture too. I used to totally freak when my friends would turn down diamonds and double diamonds. I would avoid them thinking that I could not ski them. Then one day, when I was participating in an NSP ski clinic at a larger NE mountain. I was unfamiliar to the area and did not know the trail names or ratings. All day I skied on Blacks and double blacks. At the end of the day, when we were in the wrap-up session I mentioned to the person next to me that I was glad they had stayed on the blues all day, they were harder than the blues I usually ski. She laughed and looked at me and as she pulled the trail map from her pocket said, "we didn't go on any blues all day, this is where we were skiing, that lift only accesses blacks." I was in shock, but from that day on I never feared trying a black. I have come across some that I have a tough time on though.

Ok, I know...I have opened myself up to criticism about my size and ski ability, that's ok, I am secure with myself now and can handle it.
You ARE a smooth skier, skierteachljp, I've seen ya a number of times!

Lucifer's Leap didn't scare us. I know one that did.

Roberto's.

It no longer scares me. We'll ski it this winter, mmmmkay?
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