Lesson 4: A slippery topic

Class Objective: To understand why certain tuning procedures are done and how to "adjust" your tuning for your ski conditions and ski needs!


I promise this is the last class dealing with "theory" or mental concepts! I generally avoid theories, long winding lectures on.......... but this concept you must know and remember at all times.

Often it is the "small" questions that are vital and crucial!
Such is this question, "why is ice slippery"?


Ask 10 people and I will bet you the 10 will give you the wrong answer.
De Loco and Jamser, ask your teachers , why ice is slippery and I am sure they will give you the incorrect answer!

So let us start this intellectual class with the wrong answer!
Ice is slippery because pressure exerted causes the ice to melt, thus causing water which we all know is "slippery" WRONG!!!!

Please allow me to be "simple" or as the French say "vulgarisé" I will take out long terms, theories, chemical equations and get to essential!

Ice or more precisely water has three states! liquid, solid and gas! Basic high school chemistry! What we have discovered very recently is that ice has "mysterious" properties. (just for skiers)!!!!

You all know the formula for water. The famous H (with two molecules) and O for oxygen!

That H is the key with those two molecules! Those hydrogen molecules have "different" personalities as they get close to the surface. Think of them like adolescent boys when they get near girls! They seem to do "strange" things. So it is with these hydrogen molecules as they get near the top of ice near air! ( I really really am simplifying things here and I am sure some chemist or physicist is tearing his hair out).
Near the top of the ice ( or surface) these hydrogen molecules vibrate more, bounce of each other ( very much like boys) thus causing a very unique and strange layer IN THE ICE! This very thin layer of bouncing hydrogen boys....upps I meant molecules results in "unstable boys....dammmmm I meant molecules!

It is called by people more intelligent than me, "a quasi-fluid layer" That means it is like water, feels like water but is not yet water! Shall I give you that analogy of the adolescent boy ( for Jamser's sake)!
Like an adolescent boy, who acts, feels and may seem to be a man, yet he is not yet a man!

Such is this quasi-fluid layer!

What is important here for skiers and tuners is that this layer makes ice act "slippery"! Those molecules moving about, bouncing off each allow other molecules to "slide" about also! Even when it is -129c.

So if you close your eyes and see a section of ice there is a small microscopic layer that want to get away! That is in motion and ever changing! That is why you can slide!
So next time you ski, thank those hydrogen rebel adolescent molecules! They are the ones giving you all that skiing pleasure!
For the smart readers or those that do not believe me just Google, Somorjai and you will get many articles or refer to New York Times article on , "Why ice is slippery"

What does this mean for ski tuners?

I will often mention this quasi- layer and since I hate repeating myself and have cramps typing this long term, if you do not mind I will label it QFL!

Later you will discover this QFL is vital for structuring and wax selection!

Hope it was not too painful! Hope it was not too "abstract"
Now de Loco and Jamser you can show something new to your teacher because even university lectures still teach that ice is slippery due to pressure!


Now no more theory. Now we get out hands dirty!

Get ready. Soon we will be burning bases. I really mean burning! It will be your homework!

Keep in touch and get those old skis out! Burning time is coming!!!

Ok, I?m sorry, I can?t help it ? I just kinda knew I would be the first to put his hand up in class and look daft ? It must be part of my personality. I apologise to everyone else for slowing up the class, I just can?t get past this bit.

So according to our Hungarian friend there is a QFL at the surface boundary of ice. Whilst I accept this I am struggling to apply this information to my tuning. I am probably the only one in this class who has this particular issue but in general I tend not to ski exclusively on ice. For most of my skiing day I think I am skiing on snow, compressed snow, granulated snow, granulated ice, melting snow, ice or combinations of all the above. Even on the worst days I rarely ski on a smooth sheet of flat ice, there is usually a dusting of snow on the surface.

So make your point, Jan!

Well, if the QFL works because the hydrogen atoms at the surface vibrate at three times those of the atoms within the ice, what happens in a snow crystal (I am so stupid that I don?t even know if a snow crystal is made of ice!) I suspect that the hexagonal structure of the snow crystal is very sharp and that if a QFL existed how would the crystalline structure of the snow interact with the flat surface of the ski? Is the QFL so slippery that even the sharp tip of a snow flake can generate the slipperiness we desire?

The problem is that if I don?t understand this point I can only really use trail and error (or those of the manufactures) to make my waxing choices. Without truly understanding the SCIENCE of the QFL I think I am reduced to the ART of waxing.

Pavel, I am sorry to ask this but I think between us all we should seek the answers!

I look forward to many interesting QFL discussions ?

Jan

Jan I Stenmark wrote:

I look forward to many interesting QFL discussions ?

Jan

I couldn't follow that either. There's a terminology problem firstly which it looks like you corrected. H2O is a molecule, the hydrogen component is at the atomic level not the molecular. A quasi-fluid layer is caused in ice when the molecule vibrates. This is really due to the lattice structure of an ice crystal, basically at the core of the crystal any given ice/water molecule has multiple bonds with other molecules and is stable, towards the outside there's fewer bonds so those molecules vibrate more as temperature rises. This is obviously related to the transformations you get in snow conditions from powder to neve when the snow's been in the sun or air temperature's gone up and down. There's some wrinkles to that, certain structures of ice crystal are inherently more stable than others, some reflect light radiation differently and impurities in the ice impact it etc etc.

The lower the temperature the thinner the QFL layer becomes, at some point it becomes mono-molecular, ie one molecule thick but that's pretty damn cold. QFL just explains why ice is slippery, the old theory says the weight of the skier exerts enough pressure to melt some snow/ice which forms a lubricating layer or that frictional melting occurs as the ski travels.

Interesting stuff but I don't quite connect it with wax; qfl, frictional or pressure melting all imply pretty much the same thing for wax anyway, ie the ski is travelling on a thin film of water. The thickness of the film depending on temperature. All of which only tells us that waxes need to deal with different temperatures so as a result we get some universal waxes for a big range of temperature and some specific waxes for certain temperature ranges.

You both present excellent points.
First let me please ask you to always ask questions for clarification. As stated in the intro if you did not get it , and both of you are smart skiers then "others" who are more shy did not!

Allow me just a few "moments" of thought on how to approach the subject and present it from another angle!

Both of you also presented the topic and the criticism of my presentation very well since you touched on at least two topics which in this Tuning 101 course may "confuse" the students. That said , the issues are relevant. The questions deserve an answer and clarification.

Just to leave you with some food for thought here are two issues; the molecular level of that zone and the varied ski conditions.


The molecular level issue.
Off the top of my head,one example comes to mind that Ise will relate to. If ever you have taken a course in avalanche identification and avoidance you will surel accept that the cornerstone to moder procedure is thye concept of "sheer zone"! That unstable layer hidden!

Can you accept that at molecular level such a zone also exists!

As far as Jan's comments let me please consider how to answer him since the class is listening and I do not want to "change" the focus from ski tuning to our discussion!
I may send you Jan some results undertaken by the American Ski Team with an embedded laser beam in a ski to determine some parameters you refer to. I must contact author of study for permission to "pass along information".

Pavel

I have had some time to think of the issues you both presented. I had two thoughts at same time once I had read both comments.
What to answer,,, ie content and how to answer,,ie context!

Let me explain. The goal of this course is to introduce basic ski tuning to skiers who want to go more than ski shop tuning. They want to understand how to tune fro recreational skiing. The course outline presents this.

I teach at a university several graduate courses relating to evaluation. it is my passion like skiing is my passion. I am not sure which is dominant! Often I say I do the formal teaching to pay for my addiction. In that context the course content is published by the university and I must follow this content in order for students to obtain Masters or Phd. I have a legal duty to present to students what is published and I do! How I do it is my choice and often I am considered a "little" too entertaining or "off the wall"!

I choose to share with others my experiences as a ski tuner via this medium. The site administrator accepted to provide space. It is free and so we have in class a great divergent group in age, ethnicity, competence and education. The youngest is 14 and the oldest did not give me his age so you can appreciate that I am constantly trying to use the KISS principle ( Keep It Simple Stupid). I do not want the class to "stumble" over micro- issues! I do not want class to focus on me! I do not want to be the "expert" because I am not!
I just want to present how I tune skis and then let students accept or reject this or that procedure for them!

I am trying to reach all the class, thus I do not want to have a "class discussion on important "technical" point that will be discussed in ski tuning 364. Already I am hesitating to present the topics; variance , distribution and sampling which must be presented once we get to wax selection and factors related to this selection.

I think you understand now the context part of the answer.

Now for the content part.
Both comments are central to ski tuning. I am not an engineer or chemist or physicist. However my peers are and I am know to ask irrelevant questions which they think are not that important until they think more about it. I will give you both more detailed answers, I promise to even send you either PHd thesis or published articles. Just give my time.

Also I will send them via PM since I do not want to have this discussion in class. I found in other sites that it creates a long cyber-technical debate which in effect deals with the issue, "how many angels are on a head of a pin"! Besides I am sure there are skiers who are more intelligent than I who have the technical knowledge and vocabulary to clarify the two issues you mentioned.

In conclusion, I will find some sources and "experts" who will answer your issues and I will send via PM or snail mail relevant information.

Please continue making comments. That is how our brains stay sharp and young! Please keep responding, that is why this site is far superior than others since it respects divergent thought!

Respectfully,
Pavel