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Science of Skiing



 
 
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  #1  
Old December 31st 06, 07:20 PM
Nordic_Addict Nordic_Addict is offline
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Posts: 10
Default Science of Skiing

Hi, I came here about 2 months ago for help on writing a paper. I just wanted to post it to see what you think of it. It exceeds the limit for attachment size, and it is too long to post at once, so I am going to post most of it, then the rest. All of the pictures have been removed, but this is the bulk of it. If you would like to have the real copy to read, I guess I could send it to you via email. Just send me a private message.
I really hope you don't mind such a large post. And please, give comments, suggestions, even insults if you would like to. I just would like some feedback. Plus if you have an idea of how to post it better than I have already, let me know.
Thanks alot,
Isaac

The Science behind Ski Preparation
1.0-Introduction
The world is a blur. All that can be seen is the trail ahead. There is a tree to the left, a rock on the right, and then an uphill straight ahead. The speed just gained from the downhill is quickly dissipated as the fight up the slope begins. Skiers like this one experience many principles of science affecting their speed every day. The first is aerodynamics, which is the resistance in the air. The second is gravity, which increases speed by pulling the skier down the hill. The last are friction and water suction between the ski and the snow, which also play a major role. Of all of these, friction and water suction are the easiest to change. To overcome water suction, a structure can be pressed into a ski. To decrease friction, a skier can wax their ski to the snow and weather conditions. Now technology is making skis go even faster and farther then they have ever gone before. In order to have the fastest skis possible for a race, they must be waxed and structured to the snow and weather conditions.
1.1-Introduction-Types of Skiing
There are two disciplines of Nordic skiing that are used. The first, called classical, is when a skier keeps both skis parallel to each other, and uses kick wax, fishscales, or climbing skins to propel themselves forward. The act of propelling themselves forward is called kicking, and is how skiers manage to go uphill. Kick wax is applied to the wax pocket, a section of the ski that does not touch the snow while gliding across the snow. This wax pocket is the cambered section of the ski. When enough weight is applied to the ski, as in kicking, the wax pocket is pushed to the ground, which allows the kick wax to hit the snow (See Figure 1).

Figure 1
The second style of skiing is called skating. When skiing in the skating style, the motions of a skier replicate that of an ice skater. The skier forms a V with his/her skis, which keeps the skier from sliding back down hills and propels them forward. There are many variations of technique in skating, all of which have to do with when the poles are planted in the snow. Skate skis have a camber made to provide enough of the ski surface to touch the snow to lubricate the gliding process. Skate skis do not have wax pocket, as classic skis do. The camber of a skate ski is much longer than that of a classical ski.
2.0-Ski Construction
A ski base, the bottom of the ski, may appear to be glassy and smooth to the naked eye, but the actual structure is far from the appearance. The base is actually made up of hairs of polyethylene, a compound made up of hydrogen and carbon. A closer look at the ski base would show that it is a series of peaks and valleys, with the hair points as the mountain tops and the “pores” between the hairs as the valleys. When a ski is waxed, the wax fills the pores and covers the peaks. The ski cools, and the pores decrease in size. The wax inside the pores is pushed out, and the excess is scraped and brushed off. This leaves the ski with wax in the pores, in order to protect the base.
“To illustrate this situation, think about gluing sharp shards of glass to your floor and then dragging a soft mat across it. There will certainly be a lot of resistance and there will also be much damage to the mat’s previously smooth surface. Then think about how much easier it would be to drag a large plate of glass across the glass shard-laden floor (Harvey 1)”.
The wax also provides the hydrophobic, or water repelling, properties as well as its lower coefficient of friction.
2.1-Friction
The coefficient of friction is a way to compare the friction created between two surfaces. Given that a ski is properly waxed, the coefficient of the ski base to snow interface is about .05. For comparison, ice on ice is .035, and rubber on cement, like a sneaker on pavement, is about 1.02. The possible coefficient of friction for a ski range from .3 to .001 according to the wax, conditions, and quality of base (Talbot 5). The goal of a ski waxer is to make enough friction to create a layer of water beneath the ski, but to eliminate all of the unnecessary friction.
When a ski rides over the snow, the tiny hairs of the ski rub against the points of the snowflakes, and create friction. This kind of friction is called kinetic friction. There are two types of friction, kinetic and static. Kinetic friction occurs when a ski glides over the snow. When the skier starts to move forward on their skis, they are overcoming static friction, which keeps them stationary. Kinetic friction can be manipulated by using waxes properly, or improperly.


2.2-Water Suction
The friction created as a ski moves across snow makes energy in the form of heat. When enough heat is absorbed by the snow, it goes through a change of state, and becomes liquid water. This water is the lubricant that allows a ski to glide across the sharp points of the snow. The presence of water also creates suction on the ski. The layer of water works both with and against a skier.
Imagine putting together two small plates of glass. The plates of glass can be pulled apart quite easily. If you were to add a few drops of a liquid between those two layers, then it becomes nearly impossible to pull them apart without sliding them against each other. In order to eliminate the excess water, there is a grove down the middle of a ski. This groove is not enough to eliminate all of the water suction though.
To aid in shedding extra water, a structure can be pressed into the ski. A structure is essentially miniscule grooves pushed into the ski (See Figure 2 and 3). The water still acts as if it was a lubricant, but the suction created by it is removed. Imagine taking those two same panes of glass, but now one has grooves cut into the surface. The suction created is lessened, but the panels still glide across each other easily. The hardest part in creating a structure is choosing the right one. If the structure created is too deep, then the lubrication of the water is negligible. If the structure is too fine, then there is too much suction left. To have the correct structure, the snow and weather conditions need to be taken into account.
The most relative variable in deciding structure is the amount of water in the snow. The more water in the snow, the deeper the structure. “An effective way of evaluating moisture content of the snow is to look at it carefully. Pick it up and throw it up in the air. Blow on it to see how fluffy and dry it is (Harvey 1)”. The dryer the snow is, the finer the structure because there is lower moisture content. In wetter, heavier snow, deeper structure is needed. Essentially, there are three scales to take into account when deciding on structure, and wax as well. The temperature, moisture content and kind of snow all need to be taken into account. The deepest structure is needed for warm, wet or transformed (older) snow. Finer structure is needed with cold, dry or powder snow. To choose how deep, a ski technician needs to evaluate all three scales, and make a decision based off of experience.

Figure 2

Figure 3
For example, if there were to be cold transformed snow, a medium structure is needed (.75 to 1 mm). The same could possibly used for warmer powder snow. The finest structure is .5 to .75 mm, and the most aggressive is about 2 to 3 mm deep. When the moisture content becomes too much for an aggressive linear structure, then a broken, non-linear structure can be used. A broken structure contains many small pockets instead of long grooves down the ski. Non-linear structures break up the surface tension of the water when there is more of it (Harvey 1). The moistest of all conditions occur with warm new snow, or warm transformed snow. Always remember that when pressing in a structure, err on the conservative side.

Figure 4

Last edited by Nordic_Addict : January 6th 07 at 12:07 AM.
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  #2  
Old December 31st 06, 07:22 PM
Nordic_Addict Nordic_Addict is offline
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And here is the rest. Thanks for dealing with my lack of patience.




2.3-Hydrocarbons
A ski base is made up of a substance called a hydrocarbon. Hydrocarbons can be as simple as propane, or as complex as a ski base. A hydrocarbon is made up of chains of hydrogen atoms connected using carbon atoms. Attached to the tops and bottoms of the carbon atoms are more hydrogen. The longer the chain is, the higher the melting point of the substance. Propane is a chain using three carbons, and therefore burns and melts easy. Polyethylene is what makes up the ski base, and it contains thousands more carbon atoms then propane.




Some waxes are hydrocarbons, just as the ski is. Three types of hydrocarbon waxes can be found in regular ski wax; synthetic, microcrystalline, and paraffin. Each type of wax has traits that are needed to produce an efficient product. Microcrystalline have higher coefficients of friction, but are more resilient and durable. Paraffin waxes have low coefficients of friction, but are not durable. The main goal of synthetic waxes is to harden the paraffin waxes (Charonnat 1). The traits of the three types of waxes compliment each other and aid in making an effective ski wax.
All other ski waxes are fluorocarbons. The main difference from hydrocarbons to fluorocarbons is that all of the hydrogen atoms have been replaced with fluorine atoms. These fluorine atoms are negatively charged, just as the oxygen in water is. This forces the fluorocarbon waxes to repel the water formed by skiing over snow. This property of wax is called hydrophobia. The negatively charged oxygen in the water pushes away from the negatively charged fluorine atoms, as if they were two similar magnets. The two negatively charged magnets repel each other, and cannot be touched together with out using force. These fluorocarbons are incredibly fast for warm conditions because they repel negatively charged water and dirt particles, as well as their lower coefficient of friction (Charonnat 2).
Most recently, surfactants are being used to create even more repulsion between the ski and the water film underneath it. Surfactants are substances that contain both a water compatible part, and a water incompatible part. These surfactants work in much the same way as fluorocarbons. They push the relatively polar water molecules away using their non-polar molecules (Ski Wax 1). Surfactants are mixed in with hydrocarbon waxes to give them some of the hydrophobic property that occur in fluorocarbons. These surfactants can be demonstrated using a plate of glass. Add a droplet of water onto the level glass surface. When a small bit of liquid soap is added, that droplet will flatten out, as it would if the glass was made up of fluorine atoms (Ski Wax 1).
3.0-Kick Waxes
Kick waxes are used in the classical method to increase static friction. Static friction keeps the ski immobile while the skier kicks, or pushes off. When all of the kick wax is pressed to the snow, the snow crystals become buried into it. Then the skier kicks, and lifts their weight off of the ski, which elevated the wax pocket. Using the wax pocket, kick can be achieved while a skier still has glide. Hard kick wax is applied to the kick zone, the area that is lifted up off of the snow while weight is balanced. The hard wax is then heated up, by using an iron or more commonly, by repeatedly passing a cork over it. Several layers, up to four, are needed.
Instead of longer chains of hydrogen and carbon, there are shorter chains, resulting in a lower melting point. “Because the purpose of the kick wax is to increase friction, the carbon chains are short to make the waxes melting point low and the wax soft to stick (Talbot 14)”. When a ski glides across the snow, the waxes melt slightly, and snow becomes embedded in the wax. This allows for a push forward by the skier.
Kick waxes change as the conditions change. As the temperature rises, the kick waxes become softer and more adhesive. This has to do with the moisture content of the snow conditions. When there is too much water in the snow, the snow does not stick to kick wax. Harder waxes are reserved for days where there is less moisture content, and thus the snow can grip the wax. If the softer waxes were used in colder conditions, then the sharper snow crystals would stick in the ski, and not come off the bottom of the ski (Talbot 14).
Other kick waxes are called klisters. They resemble liquid plastic, and adhere to practically anything that they touch. Klister comes in a toothpaste-like tube, and has to be heated up in order to be applied. Once the klister is on the ski, it must be heated, spread, and heated again. Klister is usually reserved for conditions that do not allow kick from hard wax.
Over two thousand years ago, skis began to be used in Scandinavia as a mode of transportation. They were also used to gather food, and eventually, wars were waged on ski. The sport that has evolved out of this simplistic origin is now much more complex then ever before. No longer is the main aim of skiing to aid in survival, but to be the fastest, the most technical, the most daring. While the latter two depend upon physical and mental prowess, the first is controlled by science.

Works Cited
Charonnat, Noel. “Fluorinated Waxes,” Sierra Nordic. 2005. Focused Web Incorporated. 3 October 2006 http://www.fwpages.com/home/index.ph..._selection=731.

Harvey, Ian. “Waxing for Extreme Cold Conditions,” TokoUS. 14 November 2006. Mammut Sports Group AG. 3 October 2006 http://www.tokous.com/PDF/Articles/W...Conditions.pdf.

Harvey, Ian. “Hand Structure Guidelines,” TokoUS. Mammut Sports Group AG. 3 October 2006 http://www.tokous.com/PDF/Articles/I...20w%20pics.pdf.

Rhyner, Hansueli. Wax Manual. Heber City: Toko, 2006.

“Ski wax,” Wikipedia. 20 September 2006. Wikimedia Foundations Incorporated. 10 November 2006 http://en.wikipedia.org/wiki/Ski_wax.

Talbot, Chris. “The Science Of Ski Waxes,” NENSA. 6 January 2003. NENSA. 2 October 2006 http://www.nensa.net/equipment/TheScienceofSkiWaxes.pdf.

“Toko Tech Manual Nordic 2005/2006,” TokoUs. 2006. Mammut Sports Group AG. 2 October 2006 http://www.tokous.com/Manuals/Nordic...ual%200506.pdf.
  #3  
Old January 2nd 07, 06:34 PM posted to rec.skiing.nordic
Bjorn A. Payne Diaz
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Posts: 104
Default Science of Skiing


Nordic_Addict wrote:
The Science behind Ski Preparation
2.0-Ski Construction
A closer look at the ski base would show
that it is a series of peaks and valleys, with the hair points as the
mountain tops and the "pores" between the hairs as the valleys.


I've never heard anyone say the base is composed of hairs. I think the
base more closely resembles a sheet of plastic (with the pores you
refer to) and often manipulating the surface of the base will produce
peaks, valleys and hairs. See the Swix manuals for micrographs of
petex. (It's been a while since I've looked at the photos.)

When a
ski is waxed, the wax fills the pores and covers the peaks. The ski
cools, and the pores decrease in size. The wax inside the pores is
pushed out, and the excess is scraped and brushed off. This leaves the
ski with wax in the pores, in order to protect the base.
"To illustrate this situation, think about gluing sharp shards of glass
to your floor and then dragging a soft mat across it. There will
certainly be a lot of resistance and there will also be much damage to
the mat's previously smooth surface. Then think about how much easier
it would be to drag a large plate of glass across the glass shard-laden
floor (Harvey 1)".


I don't understand the point behind the quote.

The wax also provides the hydrophobic, or water repelling, properties
as well as its lower coefficient of friction.
2.1-Friction
When a ski rides over the snow, the tiny hairs of the ski rub against
the points of the snowflakes, and create friction.


It seems misleading to say "hairs."

2.2-Water Suction
In order
to eliminate the excess water, there is a grove down the middle of a
ski. This groove is not enough to eliminate all of the water suction
though.


The groove is mainly for adding stability to the ski's tracking. I
don't think it's purpose is for reducing suction.

If the structure created is too deep, then the lubrication
of the water is negligible.


Structure is something upon which the snow crystals can drag (before
melting). So too much structure increases drag due to crystal shear. If
the snow is very wet, that won't matter. If it's just a little wet,
then it will matter (you can add too much structure.) Added structure
also makes for extra surface area, and the extra surface can be a
problem if the snow is dirty. Dirty wax makes for added resistance and
reduced suction doesn't compensate for the added resistance of the
dirty wax...at least for long. (My opinion.) Then we're into this ripe
area of no-wax that Kuzmin talks about.

A lot people talk about trying to "shed" water with non-linear
structure, but I have a feeling the non-linear structure is effective
because it's better at aerating the water layer (and preventing
suction.)

Jay

  #4  
Old January 2nd 07, 09:39 PM posted to rec.skiing.nordic
Ken Roberts
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Posts: 243
Default Science of Skiing

Isaac "Nordic_Addict" wrote
The Science behind Ski Preparation


Well you've taken the plunge into the game of trying to explain things. It's
a fascinating game -- or several games -- and for explaining skis and skiing
it's a big + very complicated game.

I put it on a website as well
(http://nordicskiprep.tripod.com/)


Unfortunately that link didn't work for me today. Perhaps what's on that
website addresses some of the points I raise below.

2.0-Ski Construction
. . . (sentences of explanation) . . .
This leaves the ski with wax in the pores, in order to protect the base.


If that's really the purpose of those details of ski construction, the
reader might wonder why it wouldn't be simpler just to construct the ski
base as a smooth chunk of extruded plastic with almost no "pores" -- which
then wouldn't need so much "protection".

I would think the paper could benefit from a discussion of these questions:
Are there some cross-country ski bases which do not have pores? Roughly
what's the percentage of skis sold in the world (or USA or Canada) which
have few if any pores? (and what about the word "sinter")

The base is actually made up of hairs of polyethylene


Some readers might imagine that "hairs" would tend to penetrate down into
the snow and _increase_ friction -- good for the grip zone of the ski, bad
for the glide zone. Seems like the reader would want an explanation of
either: Why hairs really do not increase friction, or Why it somehow makes
sense for ski base manufacturing or preparation processes to allow hairs to
appear in the glide zone despite the likely increased friction.

There are two types of friction, kinetic and static . . .
. . . Kinetic friction can be manipulated by using waxes properly, or
improperly.


Actually there's (at least) one more type of friction which is important for
skiing (especially skating): "plowing".
"Plowing" friction is because the ski digs down into the snow. Waxing or
base structure has very little effect on it. What does affect the amount
of "plowing" friction are things like: (a) how well the ski's overall
stiffness and flex pattern match the skier's weight and explosiveness versus
current snow conditions; and (b) subtleties of edging and fore-aft and
side-side force distribution of the ski-skater's forces and torques applied
thru the foot and binding.

... Kick wax is applied to the wax pocket,


This makes it sound like the two boundaries of the "wax pocket" are simply
obviously defined -- and that a Classic skier would (or should) never apply
wax outside those two boundaries. I think it's more complicated than that.

a section of the ski that does not touch the snow while
gliding across the snow . . . When enough weight is applied
to the ski, as in kicking, the wax pocket is pushed to the
ground, which allows the kick wax to hit the snow


This makes it sound to me like whether the grip zone contacts the snow is
"binary" question: either it does or it doesn't -- rather than a matter of
degree, with a varying amout of pressure across different sections of the
grip zone. Also the textbook explanation of static friction implies that
you're not going to get much grip friction if you only press the wax pocket
enough to put the kick wax into contact with the ground. To get useful grip
you have to go beyond mere contact, to applying serious pressure against the
snow surface. (Not to mention subtleties like packing the snow down firmly
enough so the surface layer doesn't just shear off).

1.0-Introduction


It's good to provide context and limit scope for an explanation of "science"
claims. But this Introduction section contains several statements which are
more general than is needed to provide context, claims which in themselves
seem debatable -- and so would require further "introductions" to clarify or
justify them. e.g. Is it true that the only variations in skating technique
are about when the poles are planted? Whether true or not, there's no need
to raise a question like that in order to provide context for the main
focus of the paper on ski preparation -- so why not instead make narrower
claims in the Introduction which do not even raise that question and perhaps
distract the reader from the focus of the paper to follow. Like just say
something like: "There's lots of variations in skating techniques, but most
of them don't seem to matter much for ski base preparation."

(Though for Classic I would think that the variations in techniques expected
to be used in a race _do_ make a difference for ski base preparation.)

Ken


  #5  
Old January 3rd 07, 12:32 AM
Nordic_Addict Nordic_Addict is offline
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First recorded activity by SkiBanter: Sep 2006
Posts: 10
Default

Quote:
Originally Posted by
Actually there's (at least) one more type of friction which is important for
skiing (especially skating): "plowing".
"Plowing" friction is because the ski digs down into the snow. Waxing or
base structure has very little effect on it. What does affect the amount
of "plowing" friction are things like: (a) how well the ski's overall
stiffness and flex pattern match the skier's weight and explosiveness versus
current snow conditions; and (b) subtleties of edging and fore-aft and
side-side force distribution of the ski-skater's forces and torques applied
thru the foot and binding.
[color=blue
[i]

This makes it sound like the two boundaries of the "wax pocket" are simply
obviously defined -- and that a Classic skier would (or should) never apply
wax outside those two boundaries. I think it's more complicated than that.

a section of the ski that does not touch the snow while
gliding across the snow . . . When enough weight is applied
to the ski, as in kicking, the wax pocket is pushed to the
ground, which allows the kick wax to hit the snow


This makes it sound to me like whether the grip zone contacts the snow is
"binary" question: either it does or it doesn't -- rather than a matter of
degree, with a varying amout of pressure across different sections of the
grip zone. Also the textbook explanation of static friction implies that
you're not going to get much grip friction if you only press the wax pocket
enough to put the kick wax into contact with the ground. To get useful grip
you have to go beyond mere contact, to applying serious pressure against the
snow surface. (Not to mention subtleties like packing the snow down firmly
enough so the surface layer doesn't just shear off).

(Though for Classic I would think that the variations in techniques expected
to be used in a race _do_ make a difference for ski base preparation.)

Ken
First, I would like to thank you for the feedback.
Ken- I have never heard of "plowing" friction. It sounds more about how force is applied downward as opposed to how energy is created by moving across. It is not entirely relevant to ski prep, but it is to me as a skier. I may look into it for myself.
About the wax pocket. I know that the "boundaries" of the kick zone are not stationary. I can explain it more, but I was simply trying to explain it in layman's terms.
The kick wax- I go on to explain how kick wax works later on. "When a ski glides across the snow, the waxes melt slightly, and snow becomes embedded in the wax. This allows for a push forward by the skier." I may move the explanation up, but the sentence in question was in the introduction; i was trying to give an overview.

Jay-I have always been taught that the ski base has tiny fiberous hairs. Maybe I should change the way I word it so that it does not seem as if the whole ski is made up of hairs. Hairs are created by us, the skier and ski prep person, if we are not paying attention. I'll go into greater detail.
I think that the reason of the quote was to give a visual of what it is like to ski over snow without wax.
I did not know that about the groove, but when I think about it, it makes total sense. No alpine skis (that i know of) have a groove,and they too must have water created as a ski rides over the snow. and alpine skis are wider and thinner, so they would not need support, as you say the groove is for.
Also, I have heard about friction points when talking about structure. I did not know enough about it to explain it though, so I left it out, and substituted it with what I assumed was correct. Not the best idea I guess.
Isaac
EDIT: I realize that I was wrong about the hairs; they are produced when you are not taking proper care for your skis. Thank you for pointing it out.

Last edited by Nordic_Addict : January 3rd 07 at 02:23 AM.
  #6  
Old January 3rd 07, 01:39 PM posted to rec.skiing.nordic
polarpoler
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Posts: 15
Default Science of Skiing

One comment, Nordic, about grammar - watch the 'agreement' between
nouns and their pronouns ("To decrease friction, a skier can wax their
ski ....") 'Skier' is singular, 'their' is plural; so that means you
either have to state 'a skier can wax his ski' or 'skiers can wax their
skis.' I'd avoid the 'his/her, he/she' method of solving this
problem.
Burgess

Nordic_Addict wrote:
Hi, I came here about 2 months ago for help on writing a paper. I just
wanted to post it to see what you think of it. It exceeds the limit for
attachment size, and it is too long to post at once, so I am going to
post most of it, then the rest. I put it on a website as well
(http://nordicskiprep.tripod.com/) All of the pictures have been
removed, but this is the bulk of it. If you would like to have the
real copy to read, I guess I could send it to you via email. Just send
me a private message.
I really hope you don't mind such a large post. And please, give
comments, suggestions, even insults if you would like to. I just would
like some feedback. Plus if you have an idea of how to post it better
than I have already, let me know.
Thanks alot,
Isaac

The Science behind Ski Preparation
1.0-Introduction
The world is a blur. All that can be seen is the trail ahead. There
is a tree to the left, a rock on the right, and then an uphill straight
ahead. The speed just gained from the downhill is quickly dissipated as
the fight up the slope begins. Skiers like this one experience many
principles of science affecting their speed every day. The first is
aerodynamics, which is the resistance in the air. The second is
gravity, which increases speed by pulling the skier down the hill. The
last are friction and water suction between the ski and the snow, which
also play a major role. Of all of these, friction and water suction
are the easiest to change. To overcome water suction, a structure can
be pressed into a ski. To decrease friction, a skier can wax their ski
to the snow and weather conditions. Now technology is making skis go
even faster and farther then they have ever gone before. In order to
have the fastest skis possible for a race, they must be waxed and
structured to the snow and weather conditions.
1.1-Introduction-Types of Skiing
There are two disciplines of Nordic skiing that are used. The first,
called classical, is when a skier keeps both skis parallel to each
other, and uses kick wax, fishscales, or climbing skins to propel
themselves forward. The act of propelling themselves forward is called
kicking, and is how skiers manage to go uphill. Kick wax is applied to
the wax pocket, a section of the ski that does not touch the snow while
gliding across the snow. This wax pocket is the cambered section of the
ski. When enough weight is applied to the ski, as in kicking, the wax
pocket is pushed to the ground, which allows the kick wax to hit the
snow (See Figure 1).

Figure 1
The second style of skiing is called skating. When skiing in the
skating style, the motions of a skier replicate that of an ice skater.
The skier forms a V with his/her skis, which keeps the skier from
sliding back down hills and propels them forward. There are many
variations of technique in skating, all of which have to do with when
the poles are planted in the snow. Skate skis have a camber made to
provide enough of the ski surface to touch the snow to lubricate the
gliding process. Skate skis do not have wax pocket, as classic skis
do. The camber of a skate ski is much longer than that of a classical
ski.
2.0-Ski Construction
A ski base, the bottom of the ski, may appear to be glassy and smooth
to the naked eye, but the actual structure is far from the appearance.
The base is actually made up of hairs of polyethylene, a compound made
up of hydrogen and carbon. A closer look at the ski base would show
that it is a series of peaks and valleys, with the hair points as the
mountain tops and the "pores" between the hairs as the valleys. When a
ski is waxed, the wax fills the pores and covers the peaks. The ski
cools, and the pores decrease in size. The wax inside the pores is
pushed out, and the excess is scraped and brushed off. This leaves the
ski with wax in the pores, in order to protect the base.
"To illustrate this situation, think about gluing sharp shards of glass
to your floor and then dragging a soft mat across it. There will
certainly be a lot of resistance and there will also be much damage to
the mat's previously smooth surface. Then think about how much easier
it would be to drag a large plate of glass across the glass shard-laden
floor (Harvey 1)".
The wax also provides the hydrophobic, or water repelling, properties
as well as its lower coefficient of friction.
2.1-Friction
The coefficient of friction is a way to compare the friction created
between two surfaces. Given that a ski is properly waxed, the
coefficient of the ski base to snow interface is about .05. For
comparison, ice on ice is .035, and rubber on cement, like a sneaker on
pavement, is about 1.02. The possible coefficient of friction for a ski
range from .3 to .001 according to the wax, conditions, and quality of
base (Talbot 5). The goal of a ski waxer is to make enough friction to
create a layer of water beneath the ski, but to eliminate all of the
unnecessary friction.
When a ski rides over the snow, the tiny hairs of the ski rub against
the points of the snowflakes, and create friction. This kind of
friction is called kinetic friction. There are two types of friction,
kinetic and static. Kinetic friction occurs when a ski glides over the
snow. When the skier starts to move forward on their skis, they are
overcoming static friction, which keeps them stationary. Kinetic
friction can be manipulated by using waxes properly, or improperly.


2.2-Water Suction
The friction created as a ski moves across snow makes energy in the
form of heat. When enough heat is absorbed by the snow, it goes
through a change of state, and becomes liquid water. This water is the
lubricant that allows a ski to glide across the sharp points of the
snow. The presence of water also creates suction on the ski. The
layer of water works both with and against a skier.
Imagine putting together two small plates of glass. The plates of
glass can be pulled apart quite easily. If you were to add a few drops
of a liquid between those two layers, then it becomes nearly impossible
to pull them apart without sliding them against each other. In order
to eliminate the excess water, there is a grove down the middle of a
ski. This groove is not enough to eliminate all of the water suction
though.
To aid in shedding extra water, a structure can be pressed into the
ski. A structure is essentially miniscule grooves pushed into the ski
(See Figure 2 and 3). The water still acts as if it was a lubricant,
but the suction created by it is removed. Imagine taking those two
same panes of glass, but now one has grooves cut into the surface. The
suction created is lessened, but the panels still glide across each
other easily. The hardest part in creating a structure is choosing the
right one. If the structure created is too deep, then the lubrication
of the water is negligible. If the structure is too fine, then there
is too much suction left. To have the correct structure, the snow and
weather conditions need to be taken into account.
The most relative variable in deciding structure is the amount of water
in the snow. The more water in the snow, the deeper the structure. "An
effective way of evaluating moisture content of the snow is to look at
it carefully. Pick it up and throw it up in the air. Blow on it to
see how fluffy and dry it is (Harvey 1)". The dryer the snow is, the
finer the structure because there is lower moisture content. In
wetter, heavier snow, deeper structure is needed. Essentially, there
are three scales to take into account when deciding on structure, and
wax as well. The temperature, moisture content and kind of snow all
need to be taken into account. The deepest structure is needed for
warm, wet or transformed (older) snow. Finer structure is needed with
cold, dry or powder snow. To choose how deep, a ski technician needs
to evaluate all three scales, and make a decision based off of
experience.

Figure 2

Figure 3
For example, if there were to be cold transformed snow, a medium
structure is needed (.75 to 1 mm). The same could possibly used for
warmer powder snow. The finest structure is .5 to .75 mm, and the most
aggressive is about 2 to 3 mm deep. When the moisture content becomes
too much for an aggressive linear structure, then a broken, non-linear
structure can be used. A broken structure contains many small pockets
instead of long grooves down the ski. Non-linear structures break up
the surface tension of the water when there is more of it (Harvey 1).
The moistest of all conditions occur with warm new snow, or warm
transformed snow. Always remember that when pressing in a structure,
err on the conservative side.

Figure 4




--
Nordic_Addict


  #7  
Old January 3rd 07, 02:49 PM posted to rec.skiing.nordic
[email protected]
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Posts: 565
Default Science of Skiing

His usage is correct. This is among a number of grammatical rules we
grew up with that have changed. See
http://merriam-webster.com/dictionary/their and the Usage link.

rm

"polarpoler" wrote:

One comment, Nordic, about grammar - watch the 'agreement' between
nouns and their pronouns ("To decrease friction, a skier can wax their
ski ....") 'Skier' is singular, 'their' is plural; so that means you
either have to state 'a skier can wax his ski' or 'skiers can wax their
skis.' I'd avoid the 'his/her, he/she' method of solving this
problem.
Burgess

  #8  
Old January 3rd 07, 04:23 PM posted to rec.skiing.nordic
Ken Roberts
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Posts: 243
Default Science of Skiing

Isaac Nordic_Addict wrote
About the wax pocket. I know that the "boundaries" of the
kick zone are not stationary. I can explain it more, but I was
simply trying to explain it in layman's terms.


OK that makes sense. And explaining things "in layman's terms" is very
valuable (and difficult) task.

But then how about do not title your paper "The Science ... "
Because most "laymen" will not read something called "The Science".
.. (and Wow, not just "some science" or "some scientific concepts behind",
but _The_ Science. Sounds like the text needs to be copied onto a sheet of
platinum and stored in a special room in the museum.)

Maybe instead you could try a title like, "How three hours of mildly
carcinogenic labor beforehand could save you thirty seconds of time out
skiing", with subtitle "and leave your ever-supportive Significant Other
grateful for an extra three hours of peace + quiet".

Ken


  #9  
Old January 3rd 07, 05:24 PM posted to rec.skiing.nordic
Bjorn A. Payne Diaz
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Posts: 104
Default Science of Skiing

If I remember correctly, this is a high school project. As such, I
think we can cut him some slack. Trying to communicate the ideas behind
waxing is tough for the well informed, and most limit the discussion to
the mantras (from wax clinics) that are presented as the dogmas
professed by Ph.D.s in waxing. So I'm impressed you took on the project
and got this far.

I _believe_ (this means I don't know) that the polymer of petex
(polyethylene) is made into something like very small pellets, and
these small pellets are then pressed together under heat and pressure
to make a sintered base. I don't think individual polyethylene chains
(hairs) are pressed together to make a sintered base. Since you've gone
that direction, it is probably worth doing a little research to figure
this out.

For your paper, I wouldn't worry too much about the various aspects of
ski construction (camber, pressure distribution, width) that make for a
fast ski. This would also exclude the "plowing" idea, good skis to
prevent suction, etc. It's just a really tough subject and anything you
write probably has exceptions, or worse, is just wrong.

BTW, there are skis that are extruded plastic, and I bet in dirty, wet
conditions (no wax conditions), extruded bases could glide well. Also,
I think a fine layer of wax rests on top of the ski, and too much
emphasis has been placed on the wax in the pores rather than how thick
the layer of wax is. (I'm kind of going against the existing thoughts
on waxing here. I'm just throwing this out there as a mental exercize.)

Jay

  #10  
Old January 3rd 07, 06:49 PM posted to rec.skiing.nordic
Bob L
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Posts: 6
Default Science of Skiing

Nordic Addict wrote:
The goal of a ski waxer is to make enough friction to
create a layer of water beneath the ski, but to eliminate all of the
unnecessary friction.


Very ambitious paper. Good luck.

I'd take issue with the idea (which is a very often
repeated) that a layer of water is somehow helpful to skiing. Water
is always bad,
creating added resistance. At a molecular level, ice consists of a
rigid
lattice beneath its surface, but at the surface the unattached ends are
free to
wiggle, wobble and rotate in a way that is described as fluid. Fluid
is used
in a general sense, not to be confused with a phase change to liquid
water.
It is an inherent property of the water ice crystal, and can be
observed by electron scattering.

Here are some notes I copied off the web a while back. The question
of why
snow crystals are slippery is essentially the same as why ice is
slippery, but
snow involves some added complexity because of the structure and
moisture
involved.

From Science Now, online journal of AAAS/Science Mag


9 December 1996
Getting a Grip on Ice
Ice has always been a slippery subject. As simple as an ice cube may
seem, scientists have long been baffled about why its surface is so
slick. But an upcoming paper in Surface Science may give researchers a
firmer grasp of ice's surface subtleties by hinting that its outermost
molecules behave like a liquid.

That would give the surface layer drastically different properties from
those of the bulk of the crystal, says Gabor Somorjai, a surface
chemist at the Lawrence Berkeley National Laboratory. The liquidlike
layer could explain, for instance, why it is more fun to skate on ice
than on concrete. According to Somorjai's colleague, Michel van Hove,
the popular conception that ice's slipperiness comes from
pressure-induced melting is wrong. "It doesn't work out," says van
Hove. "You put data into the formula, and there's not enough pressure."
The slippery layer, he says, is there to start, even at very low
temperatures.

Somorjai and van Hove discovered this layer when they probed the
surface of thin layers of ice with low-energy electron diffraction, a
technique that uses electrons to determine the surface structure of a
crystal in the same way as x-ray diffraction reveals the crystal
structure of a solid. The researchers expected to see the scattering
signature of the first three layers of ice molecules, but they only saw
two. After determining that the invisible top layer did, indeed, exist,
the researchers hypothesized that its water molecules were vibrating
three or four times faster than those in the lower layers--blurring its
diffraction pattern to invisibility. Although the water molecules are
bound in the lattice like a solid, says Somorjai, "the vibrational
amplitude is like a liquid."

Besides making ice slippery, says Somorjai, the liquidlike layer could
help explain how ice crystals in the upper atmosphere help catalyze the
chemical reactions that deplete ozone. The finding, says Steve George,
a chemist at the University of Colorado, "illustrates how we don't
understand the simplest things we know about."
----
See also http://www.edwardwillett.com/Columns/ice.htm and some strange
ideas on ski electrodes

----
Bob L

 




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