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# Let's get PHYSICS-cal - Page 2

Does a learning skier south of the equator turn more easily to the left while those north of the equator the right?

http://www.eoht.info/page/Human+molecular+spin

If your doing the bicycle back pedaling  move in moguls, does the gyroscopic effect help turn your skis and legs when you tip them or try and stop your turn?

Quote:
Originally Posted by fatoldman

Bob,

This brings up a couple interesting questions. If you are at a standstill in a wedge stance will a weight shift by itself produce movement? Will the act of flattening one of the skis (releasing) by itself produce movement? Assume you are on a slope not a flat for this.

I think the answers to these questions will say a lot about why I teach what I do in this 'go' sport of skiing.

fom

Lets get PHYSICS-cal

If you are in a standstill wedge position torso pointing straight down in the fall line....

....an active weight transfer (angulation) will not produce any forward motion if done moderately.

....a passive weight transfer (inside ski tipping) will produce a forward edge locked motion in the direction the new outside ski is pointing with released ski skidding over the snow sideways.

Quote:
Originally Posted by bud heishman

Sorry, not Bob here but I think we both know the answer to your query

Assuming we are standing stationary across the fall line in a wedge, an active weight transfer will not in and of itself produce movement or a turn initiation.  To the contrary, beginning from the same position, by releasing the edge grip of the down hill ski will produce forward movement, tips to seek the fall line and consequently cause a more passive weight shift to the outside ski and a turn.   One is a Don't go movement and the other is a "GO" movement.

TDK6 is still stuck in the 60's

You probably mean 2060's

Bud, Go- and Don't Go there movements are not very PHYSICS-cal IMO. Regarding active vs passive weight transfer..... there are no scientific proof of one being better than the other. Every statement made is only based on own subjective opinion. The results of movements on the other hand are not debatable.

Quote:
Originally Posted by Ghost

If your doing the bicycle back pedaling  move in moguls, does the gyroscopic effect help turn your skis and legs when you tip them or try and stop your turn?

Interesting..... yes the gyroscopic effect produced by lightning fast back pedaling in bumps prevents the skier from deviating out of the zipper line.....

Suggestion to the OP:  start a new thread with the thread title specific to your targeted topic.  This one is crashing (circling under the influence of magnetic forces?)

Quote:
Regarding active vs passive weight transfer..... there are no scientific proof of one being better than the other.

As always, I suggest that it is not a question of "good or bad," or "better or worse," but merely a question of cause and effect--in this case, a simple matter of physics. In an open stance (that is, both feet not in the same place, and the wider the separation, the more the effect), any active weight transfer (muscularly driven extension or flexion of one leg more than the other) will produce a lateral force on the center of mass. In other words, an active weight transfer will disrupt the motion of the body, altering its path.

Sometimes we need to alter our path through the transition, of course, so active weight transfers are a critical skill to develop. Sometimes we don't need to alter our path in the transition, so an active weight transfer should not be our "default" movement. My personal preference, for what it's worth, is to exit the shaping phase of my turns with my body (CM) traveling in the direction, and at the speed, it needs to be going through the transition--and the same with my feet, on their separate path and speed that crosses the path of my body. If I do that right, I have no need to use my muscles for anything during the transition, other than to guide my skis as needed during this phase (when they are obviously not carving). That's my ideal--my preferred "default" movement pattern--reserving active weight transfers for any situation that requires them. In "real" skiing, that could be many situations indeed, but it does not change the fundamental principle that my default is a passive weight transfer, with my CM flowing unimpeded and undisturbed from one turn to the next.

Best regards,

Bob

and Physics professors think centripetal force is dark magic.

Oddly, I was just thinking about how the body moves down the hill and trying to create an analogy. I was considering the way the wind makes waves to the way the skis divert the paths of the feet and body vs forklifts moving crates around. The idea being that there can be tremendous power from seemingly indirect or less tactile means, It's a work in progress...

Quote:

Originally Posted by Bob Barnes

As always, I suggest that it is not a question of "good or bad," or "better or worse," but merely a question of cause and effect--in this case, a simple matter of physics. In an open stance (that is, both feet not in the same place, and the wider the separation, the more the effect), any active weight transfer (muscularly driven extension or flexion of one leg more than the other) will produce a lateral force on the center of mass. Are we considering flexion of the old outside leg an active weight transfer?  In other words, an active weight transfer will disrupt the motion of the body, altering its path. If flexion of the old leg is an active transfer is it not a part of a "basic turn"? or is the suggestion that the travel of the CoM over the body through asymetrical leg lengthening/shortening  has already occurred by the time we have reached transition?

Sometimes we need to alter our path through the transition,Would you please define a couple examples? of course, so active weight transfers are a critical skill to develop. Sometimes we don't need to alter our path in the transition, so an active weight transfer should not be our "default" movement. My personal preference, for what it's worth, is to exit the shaping phase of my turns with my body (CM) traveling in the direction, and at the speed, it needs to be going through the transition--and the same with my feet, on their separate path and speed that crosses the path of my body. If I do that right, I have no need to use my muscles for anything during the transition, other than to guide my skis as needed during this phase (when they are obviously not carving). That's my ideal--my preferred "default" movement pattern--reserving active weight transfers for any situation that requires them. In "real" skiing, that could be many situations indeed, but it does not change the fundamental principle that my default is a passive weight transfer, with my CM flowing unimpeded and undisturbed from one turn to the next.

Best regards,

Bob

Posted by tdk6

....an active weight transfer (angulation) will not produce any forward motion if done moderately.

....a passive weight transfer (inside ski tipping) will produce a forward edge locked motion in the direction the new outside ski is pointing with released ski skidding over the snow sideways.

While this could be created with additional movements and intensity I don't think this would be the result of the movement suggested.

Originally Posted by Bob Barnes

Quote:
Regarding active vs passive weight transfer..... there are no scientific proof of one being better than the other.

As always, I suggest that it is not a question of "good or bad," or "better or worse," but merely a question of cause and effect--in this case, a simple matter of physics. In an open stance (that is, both feet not in the same place, and the wider the separation, the more the effect), any active weight transfer (muscularly driven extension or flexion of one leg more than the other) will produce a lateral force on the center of mass. In other words, an active weight transfer will disrupt the motion of the body, altering its path.

Sometimes we need to alter our path through the transition, of course, so active weight transfers are a critical skill to develop. Sometimes we don't need to alter our path in the transition, so an active weight transfer should not be our "default" movement. My personal preference, for what it's worth, is to exit the shaping phase of my turns with my body (CM) traveling in the direction, and at the speed, it needs to be going through the transition--and the same with my feet, on their separate path and speed that crosses the path of my body. If I do that right, I have no need to use my muscles for anything during the transition, other than to guide my skis as needed during this phase (when they are obviously not carving). That's my ideal--my preferred "default" movement pattern--reserving active weight transfers for any situation that requires them. In "real" skiing, that could be many situations indeed, but it does not change the fundamental principle that my default is a passive weight transfer, with my CM flowing unimpeded and undisturbed from one turn to the next.

Best regards,

Bob

I think I get what you mean, Bob, but the way you've stated it above could be confusing.  It might read as saying you do not flex one leg while extending the other during the transition, which of course you don't mean.

What I think you mean is that you prefer to shape turns so that there is no dramatic "hucking the body over the skis" going on due to leg length changes.

Your preferred turn has the body traveling on a smooth sinuous line that is narrower than the line the feet and skis follow.

These two lines, the body's line of travel (COM if you prefer) and the feet/skis' line of travel, cross each other at transition without drama.

The body experiences no big ups and downs, no decisive forwards and backs, no flamboyant lefts and rights, as it moves along.  It flows smoothly while the skis flow smoothly under it.

Have I got that right?

Quote:
Originally Posted by LiquidFeet

I think I get what you mean, Bob, but the way you've stated it above could be confusing.  It might read as saying you do not flex one leg while extending the other during the transition, which of course you don't mean.

What I think you mean is that you prefer to shape turns so that there is no dramatic "hucking the body over the skis" going on due to leg length changes.

Your preferred turn has the body traveling on a smooth sinuous line that is narrower than the line the feet and skis follow.

These two lines, the body's line of travel (COM if you prefer) and the feet/skis' line of travel, cross each other at transition without drama.

The body experiences no big ups and downs, no decisive forwards and backs, no flamboyant lefts and rights, as it moves along.  It flows smoothly while the skis flow smoothly under it.

Have I got that right?

But that's exactly the point of the "do nothing" turn. Which is part of Bob's "Do Nothing" clinic.

If you manage the body properly, in the right circumstance, there is no active flexing or extending. You just go over and change edges and you're in the new turn. You had to do nothing other than get yourself in the right place at the right time going in the right direction. Which is something for sure.

Quote:
Originally Posted by Tog
....

But that's exactly the point of the "do nothing" turn. Which is part of Bob's "Do Nothing" clinic.

If you manage the body properly, in the right circumstance, there is no active flexing or extending. You just go over and change edges and you're in the new turn. You had to do nothing other than get yourself in the right place at the right time going in the right direction. Which is something for sure.

I'm sorry, Tog, but I don't see it that way.  When I ski, I do have one leg long and the other short, and somehow they switch.  I take full responsibility for that switch.

Do you really ski without flexing and extending your legs alternately?  Of course not.  It is misleading to people reading this thread to say you don't do anything with your legs at transition.  Unless you really don't, and keep both legs the same length while motorizing your turns with your upper body.  I know that is not the case.

Making the "passive" alternating flexing and extending of the legs sound like you don't do anything with those legs is misleading.  I'm not arguing with how the turns happen; just how this process is being verbally presented.

Perhaps going into what you mean by "If you manage the body properly" would be more informative than saying what you don't do with the legs.
Quote:
Originally Posted by LiquidFeet

Suggestion to the OP:  start a new thread with the thread title specific to your targeted topic.  This one is crashing (circling under the influence of magnetic forces?)

oh come on LF, it said physics, how can you really grasp anything only looking through one set of lenses, I don't know squat about how electromagnetic force influences human movement, they exist and are stronger than gravity, so they must play some role, anyone?

Well there's a difference between flexing actively and extending actively. If you're on a slope in a turn the inside leg will be shorter than the outside.

The statement was about the transition though.

"It might read as saying you do not flex one leg while extending the other during the transition, which of course you don't mean. "

That statement appears to be saying actively flexing/extending at transition. The "Do Nothing" transition is not actively doing either. There are other types of course. So I do those too.

Even with the do nothing transition, I would actively flex the inside during the turn if so needed.

Try it.

edit;

Quote:
Originally Posted by LiquidFeet
I'm sorry, Tog, but I don't see it that way.  When I ski, I do have one leg long and the other short, and somehow they switch.  I take full responsibility for that switch.

Try recruiting gravity and momentum for the switch, that's the point. Just like psiman. You explained the rest with the alternate lines of feet/body. There may be an up/down component and there may also be an active component, but the basic transition he's talking about there's not an active move to flex or extend.

Edited by Tog - 3/19/14 at 8:50am
Quote:
Originally Posted by LiquidFeet
Do you really ski without flexing and extending your legs alternately?  Of course not.

LF, you are missing the word "active".  Your car almost certainly does not have active suspension, but in the transition in the middle of an S-curve, one side is extending the other is retracting.

Try recruiting gravity and momentum for the switch, that's the point.

Oh, Tog, please.  It takes leg action to do this.  Release is necessary.

It doesn't happen by itself, even when you direct the skis uphill under you at the end of your turn.

So, how does psiman make a turn?

Thank God I am not PSIA man.

Notice that PSIA man's inside "shoulder" moves laterally, which moves the whole inside half, which gets the equivalent on-snow effect of a long leg and a short leg.  This entity has no knees, no ankles, no hips, no movable spine. Gravity does this with the non-sentient toy because it has that nice heavy shield hanging from the rod up there where its shoulders are, because someone pushed it off to begin with so it has momentum, and because there are loose joints up at the shoulders.  Gravity pullls on that shield, the joints at the top allow the lateral movement, and over the toy topples, into the next turn.  I'm sure Bob designed the parts just so, in order to assure turns that work.

Yes, a person can motorize a turn by laterally moving the new inside shoulder into the next turn, and not ever mess with flexing a leg at the hip, knee, or ankle.  You can even do it by moving the hip itself over, and skip that whole thing about working from the snow up using ankles and knees.

A person can also motorize a turn passively just like PSIA man, harnessing gravity and momentum, by stiffening all the joints of the body while leaving only the one PSIA man has up there where the rod is (shoulder) nice and loose.  Once those other joints are stiffened, you, impersonating PSIA man, once someone pushes you off, can allow gravity to pull your body down the hill passively from one turn to the next, until at some point your body falls over because the timing isn't just right.  Please watch to the end of this little pirated video for that finale.

Try it, Tog.  Stiffen yourself up and allow gravity to laterally move your inside shoulder down the hill enough to produce PSIA man's edge angles, not bending your knees nor ankles nor hips. Report back on how great that feels.

Sorry I couldn't find Bob's official PSIA man video.

Edited by LiquidFeet - 3/19/14 at 9:39am

Psiman is basically a parallelogram tipping this way and that. The mass of the middle goes over tipping the sides of the parallelogram which tip the skis. The only thing that controls the turn is the skis in the snow tipping. Same thing can be done with humans.

Hopefuly Bob will be back to explain it better.

There needs to be a release yes. The body going over tips the skis. If the body is not in the right spot, it's still too far uphill, even flexing the downhill leg won't do anything.

You can demo from a standstill. Stand across the hill with some pitch. Move the body/pelvis directly downhill. Won't take much and the skis release. If you're countered when doing it the tips will go down and you'll have half a turn. We argued about this in the traverse thread.

This is fun but I need to go do some work.  Enjoy!

With some angulation you will vault somewhere after the fall line without making any release effort (relaxing is not an effort). DIRT of movements will determine what "somewhere is".
I think what Bob is talking about is the "zone" or "flow" you get when float through transition with a weightless feeling and you turn effortlessly because every body part is just where it should be due to small "passive" movements. In spite of this the turns are very powerful.
This is what dynamic skiing is about. If you are static then yes you must flex or extend something to move into the next turn. It looks easy and when your in the zone it feels easy, but there is a lot of mileage behind.

For the sake of accuracy, releasing is an effort. It is called eccentric contraction from a muscle recruitment perspective. Eccentric contraction is a muscle "exerting force" that is less than the force being exerted on the body by an external force. Because the muscle force is less than the external force it allows body movement in the direction of the external force. Like lowering a weight or walking "down" a flight of stairs. In both of these examples we are also creating directional control of the body through by this eccentric effort. So yes flexing is less effort than extending, but it is still effort. Extending is concentric contraction, which requires that our muscles exert a force greater than the external force, resulting in body movement in the opposite direction of the external force. Like lifting a weight or walking up a flight of stairs. Most people have a harder time controlling eccentric contraction movements because most people never train eccentrically. This is why people get sore walking down hill for extended periods.

From a skiing perspective it seems to challenge skiers more to manage pressure through flexion than by extension. Ask a group of ski instructors to demo pressure control and they will all start doing leapers, hop turns, or dolphin turns. Seldom will anyone demo flexing to release, retraction turns, or absorption. Because it requires finesse, touch, and feel, it seems to be a more challenging skill to develop.

I like to say "More movement = less effort", particularly when we move with the forces versus against them. And just like going down a flight of steps, when flexing to release, we exert directional control over our body from one turn to the next by applying DIRT to the eccentric effort. For those who don't know what DIRT stands for it means duration, intensity, rate, and timing.

RicB, It could be eccentric where the muscles are doing work while they are lengthening vs. shortening but it could also be a total relaxation "replemont" or it could be an active retraction "availment".  I believe Bob was focusing on a brief period during edge change of total relaxation permitting the inertias of the the feet and the CoM to continue on their respective paths until such time when we want to begin to redirect again.

If Bob were to enact a "total relaxation" wouldn't he fall down?

I believe I said "BRIEF", meaning a very short period of time during the transition.  Bob may describe it better.  It is the toss or release in the medicine ball graphic.

Quote:
Originally Posted by Bob Barnes

As always, I suggest that it is not a question of "good or bad," or "better or worse," but merely a question of cause and effect--in this case, a simple matter of physics. In an open stance (that is, both feet not in the same place, and the wider the separation, the more the effect), any active weight transfer (muscularly driven extension or flexion of one leg more than the other) will produce a lateral force on the center of mass. In other words, an active weight transfer will disrupt the motion of the body, altering its path.

Sometimes we need to alter our path through the transition, of course, so active weight transfers are a critical skill to develop. Sometimes we don't need to alter our path in the transition, so an active weight transfer should not be our "default" movement. My personal preference, for what it's worth, is to exit the shaping phase of my turns with my body (CM) traveling in the direction, and at the speed, it needs to be going through the transition--and the same with my feet, on their separate path and speed that crosses the path of my body. If I do that right, I have no need to use my muscles for anything during the transition, other than to guide my skis as needed during this phase (when they are obviously not carving). That's my ideal--my preferred "default" movement pattern--reserving active weight transfers for any situation that requires them. In "real" skiing, that could be many situations indeed, but it does not change the fundamental principle that my default is a passive weight transfer, with my CM flowing unimpeded and undisturbed from one turn to the next.

Best regards,

Bob

Active weight transfer does two major things: it teaches the student pressure control and angulation. At wedging speeds tipping your upper body towards the outside of the turn at initiation out over the outside ski does not disrupt the motion of the body that much since speeds are very low and the movement is not very big. Lets say the turn radius is 5m and you move your CoM 10cm.... we are talking 2% gross deflection.... not major. And if you look at the CoM path from above it would still draw a very smooth and natural round line down the hill. What is of upmost importance however is that you get used to balancing over your outside ski and learn pressure control and angulation. Once you start skiing parallel and carving you are well set up if these skills are familiar. I'm convinced that you cant effectively teach the fundamentals of skiing and wedging without an active weight shift. If you don't, your students will start rotating to tighten up the turn radius. Best way IMO is to teach an active weight transfer followed by inside ski tipping. Or simultaneously. No leaning on the inside ski, no rotation or banking but instead angulation, outside ski pressure, inside ski tipping, turn radius control and path open to expert skiing without any bad movement patterns or bad habits to unlearn later. The biggest issue is in my opinion how to get rid of micro wedging. Back in the old days this was solved by making a clear distinction between wedging and parallel skiing and movements easy to see and understand. Today the trend has been the complete opposite. This leads IMO to "masking" so called "bad movements". We are taught to be like magicians. Simply tip that inside ski.... still there is a lot more going on because simply tipping that inside ski does not produce a turn according to physics except @ some very favorable conditions.

Quote:
Originally Posted by tdk6

No leaning on the inside ski, no rotation or banking but instead angulation, outside ski pressure, inside ski tipping, turn radius control and path open to expert skiing without any bad movement patterns or bad habits to unlearn later. The biggest issue is in my opinion how to get rid of micro wedging. Back in the old days this was solved by making a clear distinction between wedging and parallel skiing and movements easy to see and understand. Today the trend has been the complete opposite. This leads IMO to "masking" so called "bad movements". We are taught to be like magicians. Simply tip that inside ski.... still there is a lot more going on because simply tipping that inside ski does not produce a turn according to physics except @ some very favorable conditions.

Who here is associating a weight shift, passive or active, with "leaning on the inside ski", rotation and banking?  How could these things be associated with a weight transfer to the outside ski?  Wouldn't they indicate the opposite?  I continue to believe that you don't understand the mechanics of a passive weight shift?

Quote:

If Bob were to enact a "total relaxation" wouldn't he fall down?

-Liquidfeet

Not completely relaxed as in a sack of potatoes. If one stops walking down the street, are they relaxed?

Fall down - yes. Down the hill.

But all that implies it's an active relaxing instead of a continuous flowing. There may be some relaxing of muscles at some point somewhere, but it's not an abrupt happening at transition. (As in relax or flex the outside/downhill leg)

Explained here. (Psiman is the clue to this. It's very similar)

Quote:

Originally Posted by Bob Barnes

Quote:
Regarding active vs passive weight transfer..... there are no scientific proof of one being better than the other.

As always, I suggest that it is not a question of "good or bad," or "better or worse," but merely a question of cause and effect--in this case, a simple matter of physics. In an open stance (that is, both feet not in the same place, and the wider the separation, the more the effect), any active weight transfer (muscularly driven extension or flexion of one leg more than the other) will produce a lateral force on the center of mass. In other words, an active weight transfer will disrupt the motion of the body, altering its path.

Sometimes we need to alter our path through the transition, of course, so active weight transfers are a critical skill to develop. Sometimes we don't need to alter our path in the transition, so an active weight transfer should not be our "default" movement.

My personal preference, for what it's worth, is to exit the shaping phase of my turns with my body (CM) traveling in the direction, and at the speed, it needs to be going through the transition--and the same with my feet, on their separate path and speed that crosses the path of my body. If I do that right, I have no need to use my muscles for anything during the transition, other than to guide my skis as needed during this phase (when they are obviously not carving).

That's my ideal--my preferred "default" movement pattern--reserving active weight transfers for any situation that requires them. In "real" skiing, that could be many situations indeed, but it does not change the fundamental principle that my default is a passive weight transfer, with my CM flowing unimpeded and undisturbed from one turn to the next.

Best regards,

Bob

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