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This is UP-UNWEIGHTING - Page 2

post #31 of 155
Thread Starter 
Quote:
Originally Posted by Schussboelie View Post
Nobody is claiming anything else.
No matter what, the turns he is making are done using up-unweighting to unweight the ski's.
Turn of the sound and take out the traverse and you have footage that clearly shows the process of up-unweighting, no more no less.

Nothing is being said about the intention of the video. Can't you really look beyond that?
Thanks for posting! This is exactly the intent of this thread. I have not found any better demo on the net of up-unweighting but if somebody has please post it here.
post #32 of 155
Thread Starter 
Quote:
Originally Posted by jdistefa View Post
.....but wow this post is getting way too complex .
Ha, you are kidding me! This must be the easies and the most basic of all skiing movements next to buckling up your boots and buying a lift ticket .
post #33 of 155
Quote:
Originally Posted by tdk6
All skiing except wedging and arcing needs unweighting. How you do it is a matter of timing and refining your basic up-unweighing movements
Probably should think about this one a little more... Nearly all typical skiing *can* be done without any sort of un-weighting action. It's only when snow conditions and/or terrain interfere with the intent of the skier that the skier needs to add this extra element - like trying to do a pivot in soft snow for instance.

Open Parallel turns can easily be accomplished with no 'un-weighting' at all. In fact, we often teach students to initiate turns while keeping all the existing pressure on their skis as an exercise on mild terrain. It's a matter of using the skis properly. People often need to reduce pressure under their skis solely for the reason that it's the only way they know how to initiate a turn.

On steeper terrain most skiers will probably use some degree of flexion into transition and if we equate any flexing to be a form of 'un-weighting' then I suppose we'd have to it as un-weighting for nearly every turn on steep terrain - even if it's a Wedge Turn.

Quote:
Originally Posted by pdxammo
permit me a small aside here to help me understand . The com is not a point on the body , say the navel , but a dynamic location . So... if the knees were raised the com might move up , and maybe forward despite the torso remaining at the same height , correct?
Now that's mean.

This is delving into the area outside of Rigid Bodies. We often post ideas that rely on Rigid Body dynamics and ignore things like this - but your thought is valid. The CM does change location as we Flex our legs because our whole body becomes shorter. I think this element goes beyond what anyone generally refers to as un-weighting.


jdistefa,
The Center of Mass (generally abbreviated by CM in most textbooks) is a defined location that allows us represent the entire Mass by that given point in calculations rather than having to do calculations against every point in that same Mass.

Center of Gravity (CG) is an almost identical point (for calculation purposes) as the CM when the entire Mass is in a nearly uniform Gravitational Field. For all practical purposes, here on Earth the two points coincide.

For very large bodies (like the Moon) motion characteristics cannot be calculated as precisely using just CM - especially when another large body passes near them (like an asteroid or comet). In this case, part of the Moon is influenced more by the asteroid than by the Earth messing up purely CM related calculations.

Both CM and CG are calculated locations rather than fixed physical locations. CM is the more appropriate term to use in skiing discussions since we are always skiing in a uniform field and we ourselves simply don't have enough Mass to affect other skiers. Use of the term CG is more appropriate when discussing the motion of planetary bodies. And Both CM and CG can be either inside or outside of a given Mass.

.ma
post #34 of 155
Quote:
Originally Posted by michaelA View Post
Probably should think about this one a little more... Nearly all typical skiing *can* be done without any sort of un-weighting action.

Open Parallel turns can easily be accomplished with no 'un-weighting' at all. In fact, we often teach students to initiate turns while keeping all the existing pressure on their skis as an exercise on mild terrain. It's a matter of using the skis properly. People often need to reduce pressure under their skis solely for the reason that it's the only way they know how to initiate a turn.

/ My boldfacing.
post #35 of 155
When a skier allows the legs to be drawn up to the body in flexion as the skis pass underneath , is that up-unweighting (or passive). or is it just when the whole body pops up ala old school style or beginers(active)?

From PSIA alpine tech manual. "Extreme movements such as changing your bodys shape can cause the CM to move outside the body . Examples can be seen in watching skiers ski big bumps , make high speed turns or throw off-axis spins in the halfpipe . they put their bodies in positions that are in balance with the external forces working on them , but clearly would not be balanced otherwise ."
Isnt this happening here?
<A href="http://www.myimagehub.com/files/3825/Ski%20Pics/upunweighting.jpg" target=_blank><A href="http://www.myimagehub.com/files/3825/Ski%20Pics/upunweighting.jpg" target=_blank><A href="http://www.myimagehub.com/files/3825/Ski%20Pics/upunweighting.jpg" target=_blank>
post #36 of 155
Thread Starter 
Quote:
Originally Posted by michaelA View Post
Probably should think about this one a little more... Nearly all typical skiing *can* be done without any sort of un-weighting action. It's only when snow conditions and/or terrain interfere with the intent of the skier that the skier needs to add this extra element - like trying to do a pivot in soft snow for instance.
So, how should the skier have turned in the clip according to you?

Quote:
Originally Posted by michaelA View Post
Open Parallel turns can easily be accomplished with no 'un-weighting' at all. In fact, we often teach students to initiate turns while keeping all the existing pressure on their skis as an exercise on mild terrain. It's a matter of using the skis properly. People often need to reduce pressure under their skis solely for the reason that it's the only way they know how to initiate a turn.
What is "using the ski properly"? Explain how open parallel turns can easily be accomplished with no un-weighting at all?

Quote:
Originally Posted by michaelA View Post
On steeper terrain most skiers will probably use some degree of flexion into transition and if we equate any flexing to be a form of 'un-weighting' then I suppose we'd have to it as un-weighting for nearly every turn on steep terrain - even if it's a Wedge Turn.
So you are now saying that on steeper terrain all turns are un-weighted? A bit contradicting to what you stated earlier in your post quoted above: "nearly all skiing......etc "
post #37 of 155
Quote:
Originally Posted by tdk6 View Post
Dont laugh at your dad
I ought to post a vid here and make you laugh as well I got one where he tries to arc and lets his arms go in a 90degree angle from his shoulders to the sides - like a bird And he just skids away : Tried to take his poles from him and he fell
post #38 of 155
Quote:
Originally Posted by tdk6
So, how should the skier have turned in the clip according to you?
Anyway they want to . I've made no determinations on how people should ski - only that they have alternatives to the 'always un-weight' idea. I did not mean to imply any degree of 'wrongness' to un-weighting, just that there are other options that may in many circumstances work better for them.

Quote:
Originally Posted by tdk6
What is "using the ski properly"? Explain how open parallel turns can easily be accomplished with no un-weighting at all?
By tipping the skis and/or twisting them via ILS while Flexing a bit.

This does not require the skier to un-weight at all. These movements (tipping and/or rotating the skis) will initiate a turn with no need to 'lighten' the pressure under either ski. By 'Properly' I mean to the extent that the skier is trying to initiate sans pressure modifications - again, it's not a matter of Rightness or Wrongness - I just mean 'properly' in the sense of accomplishing the desired outcome without intentional reduction of pressure.


Quote:
Originally Posted by tdk6
So you are now saying that on steeper terrain all turns are un-weighted? A bit contradicting to what you stated earlier in your post quoted above: "nearly all skiing......etc "
Nope - that's not what I've said. You've interpreted my words in a way that seems designed to create a contradiction.

On steeper terrain most skiers absorb much of the 'Virtual Bump' in order to avoid the Vaulting Effect that would otherwise ensue due to the forces acting on the skier. Straight legs into transition from a deeply inclined CM position causes the CM to be Vaulted over the feet via straight legs acting like a pole-vault.

The steeper the slope; the more a skier is inclined relative to the slope angle (even when they are standing vertical WRT Gravity while crossing the fall-line at 90-degrees). As the skier moves laterally across the skis the legs must either flex (changing the CM's relative location vs. the Base of Support) or the CM will rise (WRT the Surface) due to Vaulting. That's all I'm saying.

---
pdxammo's question raises the level of uncertainty regarding context. What exactly do we qualify as "up un-weighting"?

If we take 'up un-weighting' to mean any upward movement of the CM (vertically WRT Gravity) then Extending through transition may or may not always qualify as up un-weighting since the skier's CM might always be moving 'downward' relative to Gravity (depends on speed and direction).

Even if the skier doesn't Flex at all the CM might not actually rise above its previous level since their feet are constantly dropping to a lower level at the same time - just depends on how rapidly they're dropping downslope vs how quickly they're turning.


If we take upward un-weighting' to mean a changing distance between CM and the Surface of the snow then a skier can still avoid it by simply keeping their CM at the same approximate 'level' WRT the surface - by Flexing through transition and extending into Apex.

Still, I suspect most of us exhibit a bit of lightness into turn entry on steeper slopes simply because of our speed and the Virtual Bump effect being greater than our limited inseam length can absorb. But if we make any effort to ski differently, it will work the way we want it to work.

---
Hmmm.. I wonder if people are confusing the deliberate reduction of accumulated pressure vs. the constant management of pressure.

In the former, a skier is deliberately reducing pressure and in the later the skier is simply maintaining a constant degree of pressure. In other words, pressure is not allowed to build up from Apex to Finish only to be released/reduced dramatically during transition and turn entry. Instead, a constant rate of pressure is maintained throughout the turn. Personally, I don't think of this as any sort of deliberate un-weighting movement to a given purpose.

.ma
post #39 of 155
A few points:

First - not sure why you think the article is gone...I can still see it....in 2 places in fact. If it is infact gone, please let me know and I will try and repost it.



You can define things how you like but since you are using CSIA videos you should use CSIA definitions:

These are:

Weighted: A ski that is supporting the skiers mass plus turning forces is said to be "weighted". ie: when turning

Unweighted: A ski that only the skiers mass and no turning forces on it is said to be "unweighted". ie: at transition

Down unweighting: A skier is said to "down" unweight when the COM moves down in the transition RELATIVE to where it was in the body of the turn....this is virturally impossible to do in high performance skiing.

Up unweighting: A skier is said to "up" unweight when the COM moves up in the transition RELATIVE to where it was in the body of the turn....this is by far the most common way we turn.


Schoubollie: You asked how is it possible for the COM to rise if the legs dont extend? Well the height of COM is considered from the SNOW...not the feet....hence when you are inclining in the turn your COM is closer to the snow...if you are really cranking it, and inclining alot your COM will be very low....WC racers will be inches from the snow....then as you "cross over" you cease to incline at the transition....this sends your mass up....like a pole vaulter....with your legs acting as the pole...


A good thread on this topic is here....

http://forums.epicski.com/showthread.php?t=44885
post #40 of 155
Quote:
Originally Posted by tdk6 View Post
Ha, you are kidding me! This must be the easies and the most basic of all skiing movements next to buckling up your boots and buying a lift ticket .
Too funny.
post #41 of 155
Quote:
Originally Posted by SkiDude72
Down unweighting: A skier is said to "down" unweight when the COM moves down in the transition RELATIVE to where it was in the body of the turn....this is virturally impossible to do in high performance skiing.

Up unweighting: A skier is said to "up" unweight when the COM moves up in the transition RELATIVE to where it was in the body of the turn....this is by far the most common way we turn.
Skidude, in these definitions is 'Down' a reference to Gravity or to the Net Force direction in a turn?

In my thinking, I "un-weight" whenever I actively retract my feet - even if I were to do this at the Apex of the turn.

I guess I think of Un-Weighting itself as an act of actively reducing the current level of pressure under one or both skis regardless of how that pressure came to be there.

Adding the concept of 'Down' or 'Up' un-weighting to this suggests active retraction of the feet for the 'Down' version and some kind of 'Launching' mechanism for the 'Up' version to create the implied pressure reduction. This mechanism can be either a leg extension or using the Virtual Bump or some physical bump.

Is it the same in Canada?

.ma
post #42 of 155
Quote:
Originally Posted by michaelA View Post
Skidude, in these definitions is 'Down' a reference to Gravity or to the Net Force direction in a turn?

In my thinking, I "un-weight" whenever I actively retract my feet - even if I were to do this at the Apex of the turn.

I guess I think of Un-Weighting itself as an act of actively reducing the current level of pressure under one or both skis regardless of how that pressure came to be there.

Adding the concept of 'Down' or 'Up' un-weighting to this suggests active retraction of the feet for the 'Down' version and some kind of 'Launching' mechanism for the 'Up' version to create the implied pressure reduction. This mechanism can be either a leg extension or using the Virtual Bump or some physical bump.

Is it the same in Canada?

.ma
No it seems our terms differ here.

Down or up refers to the direction in which gravity acts. We refer to any act of increasing or reducing pressure on the skis through extension or retraction or flexion/extension as "pressure control".

Pressure control is one of our 5 fundamental skills.

The term "up-unweighting" has become rather confused. Many people take it to mean that you are actually "hoping" off the snow....while I can see the logic in this definition, it is not what the CSIA uses.

In Canada we generally speaking advocate "up-unweighting" for all turns in all conditions....however this term is really meaningless...as you can extend your legs to up-unweight...you can flex your legs to up-unweight...or you can keep them still and up-unweight...all on a groomed run...
post #43 of 155
Quote:
Originally Posted by Skidude72 View Post
In Canada we generally speaking advocate "up-unweighting" for all turns in all conditions....however this term is really meaningless...as you can extend your legs to up-unweight...you can flex your legs to up-unweight...or you can keep them still and up-unweight...all on a groomed run...
Do we?

I hate to belabour this topic, since it is hurting my head, but do we "up-unweight" on:

- the steeps?
- in all moguls?
- in transitions where the gate is set on a knoll?
- in high velocity, high loading slalom turns, when running the line deep?

Hmm.

And apologies to MichaelA - in the midst of trying to keep it simple on post #30, I was also keeping it (strictly speaking) wrong .
post #44 of 155
Quote:
Originally Posted by jdistefa View Post
Do we?

I hate to belabour this topic, since it is hurting my head, but do we "up-unweight" on:

- the steeps?Yes.
- in all moguls?Yes.
- in transitions where the gate is set on a knoll?Yes.
- in high velocity, high loading slalom turns, when running the line deep?Yes.

Hmm.

And apologies to MichaelA - in the midst of trying to keep it simple, I was also keeping it (strictly speaking) wrong .
Answers in blue.

I'll try to get some examples for ya.

steeps:
http://www.youtube.com/watch?v=mKhg-...eature=related

moguls:
http://www.youtube.com/watch?v=scLlZ5E-zCQ
Note: Here that the COM actually has very little COM movment either up or down...but in larger bumps I think you will find that since you transition on the bump that your COM will infact rise.
Like this:
http://www.youtube.com/watch?v=Wh4OlRf1P8U&NR=1
(sorry about the music)


Transition on a knoll...best I could find
http://www.ronlemaster.com/images/20...sl-1-1-SR.html

Slalom turns:
http://www.ronlemaster.com/images/20...2006-sl-1.html
better one
http://www.ronlemaster.com/images/20...r-pc-sl-1.html
this is GS but shows the concept well
http://www.ronlemaster.com/images/20...-pc-gs-1b.html
another good slalom shot...and steep!
http://www.ronlemaster.com/images/20...c-sl-2-wm.html
last one
http://www.ronlemaster.com/images/20...r-pc-sl-1.html

If you look you can find examples of where the COM stays level...but hard to find examples of where it drops....either it is level or goes up.....more perfomance means greater inclination which means a lower COM..which means your COM must go up in the transition so your feet and skis fit under you....
post #45 of 155
Quote:
Originally Posted by Skidude72 View Post
Answers in blue.
Hmm, all the time in all those conditions, eh?

I happen to disagree with you on the basis of both practice and observation, but would be very interested in having you explain your thinking.

Are you suggesting that active retraction or avalement is up-unweighting?
post #46 of 155
Quote:
Originally Posted by jdistefa View Post
Hmm, all the time in all those conditions, eh?

I happen to disagree with you on the basis of both practice and observation, but would be very interested in having you explain your thinking.

Are you suggesting that active retraction or avalement is up-unweighting?
Well hang on....I did say "generally speaking"...sure there are exceptions....but as a general rule...yes, you will up-unweight.

Active retraction can be up-unweighting.....or it can be down-unweigthing....

I understand that "avalement" litterally translates to "down unweight"....but the bend and stretch turn which I beleive you are referring to...if done correctly is down-unweighting...however if you are referring to the action of extending in the fallline and flexing the transition...then as I said before...yes, that can be up-unweigthing too.

Bottom line:

if your mass goes up...you are up-unweighting
if your mass goes down...you are down-unweigthing

It is not necessarily related to whether you are flexed or extended.
post #47 of 155
Quote:
Originally Posted by Skidude72 View Post
Answers in blue.

I'll try to get some examples for ya.

steeps:
http://www.youtube.com/watch?v=mKhg-...eature=related

moguls:
http://www.youtube.com/watch?v=scLlZ5E-zCQ
Note: Here that the COM actually has very little COM movment either up or down...but in larger bumps I think you will find that since you transition on the bump that your COM will infact rise.
Like this:
http://www.youtube.com/watch?v=Wh4OlRf1P8U&NR=1
(sorry about the music)


Transition on a knoll...best I could find
http://www.ronlemaster.com/images/20...sl-1-1-SR.html

Slalom turns:
http://www.ronlemaster.com/images/20...2006-sl-1.html
better one
http://www.ronlemaster.com/images/20...r-pc-sl-1.html
this is GS but shows the concept well
http://www.ronlemaster.com/images/20...-pc-gs-1b.html
another good slalom shot...and steep!
http://www.ronlemaster.com/images/20...c-sl-2-wm.html
last one
http://www.ronlemaster.com/images/20...r-pc-sl-1.html

If you look you can find examples of where the COM stays level...but hard to find examples of where it drops....either it is level or goes up.....more perfomance means greater inclination which means a lower COM..which means your COM must go up in the transition so your feet and skis fit under you....
Nice pictures.

Having stood on the hill this season for training and race runs at Alta Badia, Val Gardena, St. Anton, and Whistler, I can assure you that I witnessed down unweighting being used as both a tactic (for terrain & timing) and recovery move (oops) on several occasions in several different events.

Although I agree with you that up-unweighting (in all its variations) is the primary form of pressure control for edge change, I think that relative movements of the COM exist along a spectrum that elite athletes use to get the job done in a specific context/situation. I hate generalizations .

Regards,
Matt
post #48 of 155
Quote:
Originally Posted by jdistefa View Post
Nice pictures.

Having stood on the hill for training and race runs at Alta Badia, Val Gardena, St. Anton, and Whistler this season, I can assure you that I witnessed down unweighting being used as both a tactic (for terrain & timing) and recovery move (oops) on several occasions in several different events.

Although I agree with you that up-unweighting (in all its variations) is the primary form of pressure control for edge change, I think that relative movements of the COM exist along a spectrum that elite athletes use to get the job done in a specific context/situation. I hate generalizations .

Regards,
Matt
Good post, totally agree.

I have no doubt down-unweighting exists...or can be done...or is done...in the situations you describe and others, but I would suggest that when done a "setup" move is required..ie: you need to come from a tall stance with low edge angles....not suggesting that is bad...but that it is contrived...and not part of the normal flow that the everyday skier would use.

I think we pretty much agree on this topic.
post #49 of 155
Thread Starter 
michaleA, thanks for your valuable input here. Im going to comment on your great posting and try to dig a little bit deeper. Dont take any of what I say as offensive, Im simply trying to question as much as possible in order to learn more.

Quote:
Originally Posted by michaelA View Post
Anyway they want to . I've made no determinations on how people should ski - only that they have alternatives to the 'always un-weight' idea. I did not mean to imply any degree of 'wrongness' to un-weighting, just that there are other options that may in many circumstances work better for them.
Why do you want an alternative way? What are the skiers options in this particular clip?

Quote:
Originally Posted by michaelA View Post
By tipping the skis and/or twisting them via ILS while Flexing a bit.

This does not require the skier to un-weight at all. These movements (tipping and/or rotating the skis) will initiate a turn with no need to 'lighten' the pressure under either ski. By 'Properly' I mean to the extent that the skier is trying to initiate sans pressure modifications - again, it's not a matter of Rightness or Wrongness - I just mean 'properly' in the sense of accomplishing the desired outcome without intentional reduction of pressure.
Ha, "by flexing a bit"!!!!! Sounds like pressure reduction.......

Quote:
Originally Posted by michaelA View Post
On steeper terrain most skiers absorb much of the 'Virtual Bump' in order to avoid the Vaulting Effect that would otherwise ensue due to the forces acting on the skier. Straight legs into transition from a deeply inclined CM position causes the CM to be Vaulted over the feet via straight legs acting like a pole-vault.
Bump: terrain obsticle shaped as a bump over which one can ski and get a push upwards which can be used for unweighting to reduce pressure under the skis which makes turning easier. The technique here is to run up the side of the bump with legs extended in order to get some upwared lift but then flex to absorbe the rest of the bump. Cue here is to get sufficient lift at the base of the bump and flex the rest. Great bump skier have a great feel for just how much is needed. As the bump rises underneath the skis the bump skier flexes but not as fast as the bump pushes upwards causing a slight upward motiong that can be absorbed later on. Less flexing more push up. More flexing less push up. BTW, is this up-unweighting or down-unweighting?
Virtual bump: skier uses the exact same movements but without the bump. This would not be possible without an upward force of some sort because you cannot cheat gravity. You are in your quote above suggesting we "absorb" the virtual bump in order to avoid the vaulting effect. Sounds like leg retraction and flexing which causes a pressure reduction underneath our skis which is the same as unweighing.

Quote:
Originally Posted by michaelA View Post
The steeper the slope; the more a skier is inclined relative to the slope angle (even when they are standing vertical WRT Gravity while crossing the fall-line at 90-degrees). As the skier moves laterally across the skis the legs must either flex (changing the CM's relative location vs. the Base of Support) or the CM will rise (WRT the Surface) due to Vaulting. That's all I'm saying.
You might not be aware or your intention might not be unweighting but that is what your flexing through the transition causes. And whether you are aware of it or not it helps you with turning.

Quote:
Originally Posted by michaelA View Post
pdxammo's question raises the level of uncertainty regarding context. What exactly do we qualify as "up un-weighting"?

If we take 'up un-weighting' to mean any upward movement of the CM (vertically WRT Gravity) then Extending through transition may or may not always qualify as up un-weighting since the skier's CM might always be moving 'downward' relative to Gravity (depends on speed and direction).
This is not true since its not a question of skiers CM moving in direction of the center of the earth or not. Its allways in reference to the surface resisting gravity, the slope in this case. The only exeption would be free falling and I dont se the guy in the original clip doing that.

Quote:
Originally Posted by michaelA View Post
Even if the skier doesn't Flex at all the CM might not actually rise above its previous level since their feet are constantly dropping to a lower level at the same time - just depends on how rapidly they're dropping downslope vs how quickly they're turning.
See above comment.....

Quote:
Originally Posted by michaelA View Post
If we take upward un-weighting' to mean a changing distance between CM and the Surface of the snow then a skier can still avoid it by simply keeping their CM at the same approximate 'level' WRT the surface - by Flexing through transition and extending into Apex.
Well, he could technically avoid a certain definition but it would still be unweighting because a he would be flexing through the transition.

Quote:
Originally Posted by michaelA View Post
Still, I suspect most of us exhibit a bit of lightness into turn entry on steeper slopes simply because of our speed and the Virtual Bump effect being greater than our limited inseam length can absorb. But if we make any effort to ski differently, it will work the way we want it to work.
The lightness is unweighting. Ski differently.... why/how?


Quote:
Originally Posted by michaelA View Post
Hmmm.. I wonder if people are confusing the deliberate reduction of accumulated pressure vs. the constant management of pressure.
This starts to sound interesting....

Quote:
Originally Posted by michaelA View Post
In the former, a skier is deliberately reducing pressure and in the later the skier is simply maintaining a constant degree of pressure. In other words, pressure is not allowed to build up from Apex to Finish only to be released/reduced dramatically during transition and turn entry. Instead, a constant rate of pressure is maintained throughout the turn. Personally, I don't think of this as any sort of deliberate un-weighting movement to a given purpose.

.ma
Stating that anybody could ski with constant pressure under skis is questionable. On snow tests with measuring instruments under footbeds show that there is a great ammount of pressure change in dynamic skiing.
post #50 of 155
Thread Starter 
Quote:
Originally Posted by Skidude72 View Post
You can define things how you like but since you are using CSIA videos you should use CSIA definitions:

These are:

Weighted: A ski that is supporting the skiers mass plus turning forces is said to be "weighted". ie: when turning

Unweighted: A ski that only the skiers mass and no turning forces on it is said to be "unweighted". ie: at transition

Down unweighting: A skier is said to "down" unweight when the COM moves down in the transition RELATIVE to where it was in the body of the turn....this is virturally impossible to do in high performance skiing.

Up unweighting: A skier is said to "up" unweight when the COM moves up in the transition RELATIVE to where it was in the body of the turn....this is by far the most common way we turn.
Thanks for the definitions. I have no gripes with these.... the only objection I have is that I dont like the CM movement direction determining if its UUW or DUW. I have allways thaught of muscle movements determining if its unweighting or or not because I think of it as a movement performed by the skier. This is the way its defined in austria and many other countries as well. Can you allso explain what CSIA calls a ski that bears less weight than skiers mass?

What I think is pritty cool here is that even though we have different definitions the skiing is exactly the same. No matter what we say or do the skier in the clip will still be doing the same thing over and over and over...... !
post #51 of 155
Constant pressure isn't possible.
At the end of a turn, close to perpendicular to the fall line gravitational and rotational forces are added in pretty much the same direction.
IIRC pressure ia a function of surface and applied force.
The surface pretty much remains teh same but the forces applied directly through teh ski down on teh surface change greatly.

As I always understood it (though this may be a dated theory) up-unweighting is caused by raising the CM relative to the surface up until you stop moving it up actively. At that point inertia (one of Newton's laws) makes your CM wanting to move up more thus creating an upward force and pressure release on the surface.
Downward release is done by retracting and immediately releasing pressure before gravity catches up and pulls you down again. The CM does not necessarily have to move down but usually it will as a result, after the unweighting.
So not only do I discern a difference in CM movement direction, there is also a clear distinction in the timing of the unweighting.
Up-unweighting comes after the CM movement, down-unweighting before and stops as soon as the CM movement stops.

I'll comment more later, gotta get back to work...
post #52 of 155
If you think of the mechanisms and timings I described above you could even downunweight while the CM is moving, just as long as teh CM is moving slower than the ski's, hence creating a pressure drop.
It's hard for me to picture the opposite though, up-unweighting while the CM is moving downwards (relative to the surface).
post #53 of 155
Thread Starter 
Quote:
Originally Posted by Skidude72 View Post
Good post, totally agree.

I have no doubt down-unweighting exists...or can be done...or is done...in the situations you describe and others, but I would suggest that when done a "setup" move is required..ie: you need to come from a tall stance with low edge angles....not suggesting that is bad...but that it is contrived...and not part of the normal flow that the everyday skier would use.

I think we pretty much agree on this topic.
Exactly!

Down-unweighting is actually the same as up-unweighting. Insted of extending at the transition you extend earlier as you come through the low C part of the turn. Ski rebound gives you a lift that you can then down-unweight against as you come through the transition. This is the way advanced skiers turn when they are linking turns and it makes their skiing efficient and smooth. In moguls you use bumps to provide you with that lifting force.
post #54 of 155
It's also a much faster way to unweight.
Pressure release is immediate.
That's why it's being used so abundantly in bumps, there is often no time to up-unweight and to get the CM to move up all that distance (created by the bump + the active movement by the skier).
It's used in powder too because up-unweighting is hard to control/create against a non-solid surface.
post #55 of 155
Quote:
Originally Posted by michaelA View Post
If we take upward un-weighting' to mean a changing distance between CM and the Surface of the snow then a skier can still avoid it by simply keeping their CM at the same approximate 'level' WRT the surface - by Flexing through transition and extending into Apex.
I would call that down-unweighting.
post #56 of 155
Quote:
Originally Posted by Skidude72 View Post
Schoubollie: You asked how is it possible for the COM to rise if the legs dont extend? Well the height of COM is considered from the SNOW...not the feet....hence when you are inclining in the turn your COM is closer to the snow...if you are really cranking it, and inclining alot your COM will be very low....WC racers will be inches from the snow....then as you "cross over" you cease to incline at the transition....this sends your mass up....like a pole vaulter....with your legs acting as the pole...
I agree that the CM can move up with the legs flexing however in my book the technique you described does not qualify as up-unweighting.
post #57 of 155
Thread Starter 
Quote:
Originally Posted by Schussboelie View Post
Constant pressure isn't possible.
At the end of a turn, close to perpendicular to the fall line gravitational and rotational forces are added in pretty much the same direction.
IIRC pressure ia a function of surface and applied force.
The surface pretty much remains teh same but the forces applied directly through teh ski down on teh surface change greatly.

As I always understood it (though this may be a dated theory) up-unweighting is caused by raising the CM relative to the surface up until you stop moving it up actively. At that point inertia (one of Newton's laws) makes your CM wanting to move up more thus creating an upward force and pressure release on the surface.
Downward release is done by retracting and immediately releasing pressure before gravity catches up and pulls you down again. The CM does not necessarily have to move down but usually it will as a result, after the unweighting.
So not only do I discern a difference in CM movement direction, there is also a clear distinction in the timing of the unweighting.
Up-unweighting comes after the CM movement, down-unweighting before and stops as soon as the CM movement stops.

I'll comment more later, gotta get back to work...
You are absolutely correct conserning Newtons laws and how they apply to skiing. Let me add that unweighted state of being in case of up-unweighting becomes present during the time period of CM upward movement slowing down, stopping and then accelerating back down again and catching up with gravity while unweighted state of being in case of down-unweighting becomes present durning CM acceleration and catching up with gravity. Very short in other words.
post #58 of 155
Come to think of it a lot has changed though.
I think in advanced skiing it might indeed not be about unweighting anymore, it's more about pressure control and edging.
I do however believe a lot of people use the old up-unweighting technique, not to unweighting but to flatten the ski's so they can change edges.
Nevertheless, there is always gonna be a pressure shift from the old to the new outside ski in transition.
I think moving the body over the ski's will relate closer to up-unweighting whereas moving the ski's under the body (both in regard to the surface) will resemble down-unweighting more.
post #59 of 155
Quote:
Originally Posted by tdk6 View Post
Thanks for the definitions. I have no gripes with these.... the only objection I have is that I dont like the CM movement direction determining if its UUW or DUW. I have allways thaught of muscle movements determining if its unweighting or or not because I think of it as a movement performed by the skier.
Interesting that you think of it as a movement. The CSIA views it as an outcome. By viewing it as an outcome, then we gain consistency in our approach to skiing from beginner to intermediate to expert. This consistency aids instructors understand skiing, and takes the guess work out of how/when/quantity and whether the skier needs to be extending, or flexing as they approach the transition....as you are managing an outcome.....

If you define "up-unweighing" as movment....how do you evaluate its effectivness? What are you shooting for? How do you know when to reduce the extension, or even start flexing? What do you base it on?

With the CSIA approach you have a well defined goal....and then a variety of ways of achieving it.

Your definition, along with Schusbollie's of UUW and DUW seems to be equivalent to the definitions of flexion and extension....why have 2 terms for the same thing?


Quote:
Originally Posted by tdk6 View Post
This is the way its defined in austria and many other countries as well.
Interesting,I trained under an Austrian Statlicha (sp? for those who dont know, that is the highest level in Austria) for an entire year, and I dont recall that being the case...infact I believe they define it exactley as I do, however I could be wrong, if there is an authority here on that I would be interested to know.

Quote:
Originally Posted by tdk6 View Post
Can you allso explain what CSIA calls a ski that bears less weight than skiers mass? !
We call that unweighted....however it can be up or down...and achieved in a variety of ways...additionally if the skis bear the entire of the skiers mass...but no more...that is also considered "unweighted"....when you add turning forces to the skiers mass, the ski is considered to be "weighted".

Quote:
Originally Posted by tdk6 View Post
What I think is pritty cool here is that even though we have different definitions the skiing is exactly the same. No matter what we say or do the skier in the clip will still be doing the same thing over and over and over...... !
This is true...but the question is...if we were looking to improve this skier...would we come to the same recommendation?
post #60 of 155
Quote:
Originally Posted by Schussboelie View Post
I agree that the CM can move up with the legs flexing however in my book the technique you described does not qualify as up-unweighting.
So you agree that the skiers weight is moving "up"....yet you still call it "down unweighting"?:

Seems really bizzare.
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