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papa_eos
Jun 7, 2007, 5:49 AM
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Stumbled upon this website with an interesting in-depth
scientific article written in Ireland about what keeps us on the rock.
http://www.theshortspan.com/
(This post was edited by papa_eos on Jun 7, 2007, 5:50 AM)
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bmwman91
Jul 9, 2007, 9:48 PM
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Pretty good read. I found the chalk part to be a tad surprising.
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bent_gate
Jul 10, 2007, 5:53 AM
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Yes, thanks for posting. That is very informational.
There is one small part that I have read several times though, that I still don't get:
http://www.theshortspan.com/ wrote: The only really surprising conclusion is that water has no effect on friction. We know that chalk decreases friction but it decreases friction less than sweaty hands do so it's a necessary evil for most climbers.
So they are saying sweaty hands decrease friction, so how can "water have no effect on friction"?
Their conclusions are correct nonetheless, but can someone explain how that statement doesn't contradict what is obviously known. (That wet hands slip off rock!).
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jakedatc
Jul 10, 2007, 6:07 AM
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That study they quoted was poorly done and had no real cross over to climbing.. if i remember, i think they used a flat piece of rock or whatever.. had the person put their hand on the rock and then they pulled it away.. like <----_____>
but yea.. enough chalk to dry out your skin is good.. way too much chalk either on your hands or on the holds will decrease the friction.. that's why people either "french blow" or clap their hands or whatever to leave just a thin layer.. and why (boulderers mostly) brush the holds after they start getting too chalky.
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Valarc
Jul 10, 2007, 12:49 PM
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article wrote: Friction, as scientists talk about it, applies to two smooth parallel materials sliding against one another. Not one hard, irregular surface (rock) pressing into a soft, supple surface (rubber or skin).
Bullshit. This is the kind of stuff that really irritates the crap out of me. Friction, as high school teachers talk about it, applies to blah blah blah. No real physicist will make the statement that friction is a simple linear relationship, unless they know they are talking about rigid materials in a well-behaved system. Just a few months ago I went to a great colloquium on ongoing research into the microscopic properties of friction. Friction is a whole lot more complicated than "how much surface area is there?", and true scientists are still ACTIVELY researching the topic.
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microbarn
Jul 15, 2007, 6:38 PM
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Indeed the article bothered me too.
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sungam
Jul 15, 2007, 9:30 PM
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More importantly, is the qoute in your sig real? Did Majid really say that???
Sweet catch if he did, dunno how I missed that.
-MagnuS
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theshortspan
Jul 26, 2007, 12:31 PM
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I would welcome any feddback or suggestions for updates to this article.
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rhonius
Jul 26, 2007, 2:04 PM
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I have heard (I don't have the research to back it up) that chalk helps increase the coef of friction between the fingers allowing them to work more as a unit and that provides greater advantage than increasing the coef with the rock.
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microbarn
Jul 26, 2007, 2:41 PM
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and I heard the sky is green
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petsfed
Jul 26, 2007, 2:55 PM
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Valarc wrote: Bullshit. This is the kind of stuff that really irritates the crap out of me. Friction, as high school teachers talk about it, applies to blah blah blah. No real physicist will make the statement that friction is a simple linear relationship, unless they know they are talking about rigid materials in a well-behaved system. Just a few months ago I went to a great colloquium on ongoing research into the microscopic properties of friction. Friction is a whole lot more complicated than "how much surface area is there?", and true scientists are still ACTIVELY researching the topic.
Well, in useful situations (eg car tires, etc) it really is linearly related to surface area. Its the other variables that aren't linearly related to frictional force. Relative velocity, temperature, moisture/lubrication, etc.
If you start zooming in on interacting smooth surfaces to the point that friction that is no longer a linear function of surface area, its less friction and more low strength molecular bonds that form and break randomly (a la quantum mechanics).
Friction itself is mostly based on how much energy is in the system, vs. how much energy it takes to make or break a bond. The energy in the system, of course, is related to a great many things and this is where the research is occurring.
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microbarn
Jul 26, 2007, 3:03 PM
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petsfed wrote: Valarc wrote: Bullshit. This is the kind of stuff that really irritates the crap out of me. Friction, as high school teachers talk about it, applies to blah blah blah. No real physicist will make the statement that friction is a simple linear relationship, unless they know they are talking about rigid materials in a well-behaved system. Just a few months ago I went to a great colloquium on ongoing research into the microscopic properties of friction. Friction is a whole lot more complicated than "how much surface area is there?", and true scientists are still ACTIVELY researching the topic. Well, in useful situations (eg car tires, etc) it really is linearly related to surface area. Its the other variables that aren't linearly related to frictional force. Relative velocity, temperature, moisture/lubrication, etc. If you start zooming in on interacting smooth surfaces to the point that friction that is no longer a linear function of surface area, its less friction and more low strength molecular bonds that form and break randomly (a la quantum mechanics). Friction itself is mostly based on how much energy is in the system, vs. how much energy it takes to make or break a bond. The energy in the system, of course, is related to a great many things and this is where the research is occurring.
Perhaps in dry friction, but this is not clearly dry lubrication. The fact that sweat is present and that people's fingers deform easily brings in Partial Elastohydrodynamic Lubrication, and there certainly is research occuring in this area. I should have some more results this afternoon....
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cracklover
Jul 26, 2007, 4:41 PM
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theshortspan wrote: I would welcome any feddback or suggestions for updates to this article.
This was the one useful thing I got out of the article: In reply to: rubber is different. Because the friction coefficient tends to increase with velocity (up to a point), and is very low for zero velocities (in fact, some researchers doubt whether there is actually a true static friction for rubber at all)
Thanks for that! Though, could you not find a better source for the frictional properties of rubber than an astrophysicist? But, having thrown out this claim, you don't speak at all about how this very odd characteristic of rubber might actually influences the friction of shoes on rock.
A few other issues. You claim that all climbing shoe rubber was designed to have maximal friction between 0-5 degrees centigrade, and propose an explanation for this. Do you have any documentation for either the claim of either the best rubber temperature for one shoe, the supposed fact that all climbing rubber behaves in that same way, or the supposed fact that it was done explicitly for the reasons you claim?
You say: "We have contours in our skin's surface called friction ridges that help the hand to grasp" So you claim that the ridges in skin increase friction, but in other materials, the smoother the better. You make no effort to explain why skin might be unique in this way, or to give any expert opinion on it (not even an astrophysicist).
You claim that a new shoe will always do better than an old shoe on an edge, and, at least your picture suggests, the sharper the edge on the shoe, the better. This does not match my climbing experience exactly, and it would be easy to show instances where the shoe with the sharper edge should (and, IMO, does) do worse.
One example. Let's say this is a small (on the order of 1 millimeter) edge:
In the picture, I'm blowing it up for the sake of seeing what's going on.
In the picture on the left, we have a sharp-edged shoe. Beyond a shadow of a doubt, in this case, the edge of the rubber would shear off, and the foot placement would fail. However, in the picture on the right, as the climber is able to paste her shoe into the edge, using more force, and deforming the shoe around the edge, the rounded edge of the rubber is able to deform around rock. With the force getting loaded *into* the rubber, the rubber is less likely to shear, and the foot placement is more likely to stay put.
A second example- Let's say it's a sloping ledge:
In the picture on the far left, we have one possible solution for the climber with a new sharp edge on their shoe. But this may put the weight way out too far. So what if they try to bring the foot more in line? You get something like the middle picture, with a lot less surface area. Finally, on the right, the climber with the rounded shoe is able to get both a bit better surface area, and the force directed more down into the rock, rather than being pushed too far back.
Lastly, in the section titled: "The mathematics of smearing", this obviously bears little relation to either reality, or to the description of rubber you'd given earlier.
But thanks for giving lots to think about and discuss!
Cheers,
GO
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microbarn
Jul 26, 2007, 5:22 PM
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theshortspan wrote: I would welcome any feddback or suggestions for updates to this article.
I really don't think you want this feedback. I don't think you deserve to have your work ripped apart, and a lot of it is pretty reasonable... BUT who could turn down a chance to argue on RC.com???? (not me  )
Full Disclosure: My research concentrates on controlling partial elastohydrodynamic lubrication of roller bearings. While I have done work on friction, my research concentrates on modeling the friction for control rather then for physical descriptions. I have never gone out of my way to read about rubber friction.
We are working on a macro scale, so I guess it is ok to use the Coulomb law. This law is not the best model of friction any more. However, you have to make an assumption somewhere to simplify things and arrive at simple rules. The validity of this assumption could be my biggest complaint.
In reply to: The frictional force is always exerted in the opposite direction to the object's movement or potential movement.
In reply to: The rougher the surfaces the higher the value.
In reply to: As regards our hands we are only interested in static friction as once the relationship becomes dynamic you have slipped and are mat bound.
In reply to: Rubber generates friction in 3 ways
In reply to: Wear - Imagine the resistance generated by shaving a thin layer of rubber from your shoes this is a macro version of friction due to wear. This isn't a good thing and costs us a fortune.
In reply to: Similarly climbing shoe manufacturers design their shoe rubber to work best in a specific temperature range (0-5° centigrade), below this the rubber is harder and won't mould well to the shape of the rock and above this the rubber will be too soft and will deform too easily. This why climbing shoes work best in the cold.
very cold temperatures - stiffer and acting more like hard metals in friction properties (second lowest friction)
'optimal' temperatures - malleable, but limiting wear (reasonable friction)
high temperatures - more malleable, but much greater wear (excellent friction)
very high temperatures - rubber begins to break down (lowest friction)
In reply to: New shoes are better at edging for two reasons, firstly the rubber is harder before it is worn in and secondly the edge of the shoe is better defined so the contact area is larger.
I am not following your 'bulk effects' section. The statements about the energy loss far away from the contact area is not connected to the rest of the section. I don't think this statement needs to be included. To maximize friction, you want to maximize the hysteresis loss while minimizing distance of deformation or travel. Not a real clear connection, huh? Finally, you aren't making any kind of a connection to how temperature changes the hysteresis. I agree that rubbers are sensitive to temperatures, but I don't think bringing hysteresis into the discussion validated this.
In reply to: We don't climb in the wet so climbing shoes are threadless to maximise grip.
It is my belief that hands that are too cold have poor friction because they don't conform as well. However, I think climbers combat this kind of cold naturally by heating up their hands. I think warming up the muscles in the hands plays a more important part in climbing at cold temperatures then the stiffness of the skin.
I don't want to waste even more time today reading the other paper you referenced. However, based on what you wrote, I agree that there are problems in applying the other paper's findings blindly to climbing. Did they include dirt? I think this would change things a lot.
My personal opinion of chalk is that it is most useful in the gym. Holds in the gym already have the layer of dirt, chalk, and grime on them. Another layer doesn't change things a lot, and the alternative is to have very wet hands making the dirt turn into mud. This effect could happen outdoors, but this is less of a problem there.
Your descriptions of granite and sandstone textures does not agree with my experience, but I guess you are kind of referencing this when you show the grain sizes in your pictures.
In reply to: for a smoother rock type the temperature will need to be higher for the same shoes to work optimally.
Overall, it seems as though you started with the conclusion that friction is better in the cold, and then you brought up parts of friction theory to validate this. I do not believe that enough information is known about friction to arrive at this conclusion. I believe there are more important factors that help us send in cold weather.
I am sorry I can't give as many hard and fast rules about friction as you, but as we gain more knowledge we realize how little we actually understand.
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theshortspan
Jul 27, 2007, 9:46 AM
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Thanks to you all for your replies. I appreciate them. My motivation for writing the article was a get a better understanding to friction for myself and to maybe share some of it. It isn't an scientific paper and I'm not a scientist.
Obviously you guys know a lot more about friction than I do, I will go through all the above next week and make some improvements to the article, I will be back with questions.
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microbarn
Jul 27, 2007, 10:32 AM
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theshortspan wrote: Thanks to you all for your replies. I appreciate them. My motivation for writing the article was a get a better understanding to friction for myself and to maybe share some of it. It isn't an scientific paper and I'm not a scientist. Obviously you guys know a lot more about friction than I do, I will go through all the above next week and make some improvements to the article, I will be back with questions.
yea, I didn't write out my response before because I knew you weren't going for scientific.
I will gladly check out your update and answer questions, but I think we might end up without a definitive guide to friction.
Rubber and skin interactions are freaking complicated, and they don't simplify extremely well.
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microbarn
Jul 27, 2007, 10:41 AM
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cracklover wrote: This was the one useful thing I got out of the article: In reply to: rubber is different. Because the friction coefficient tends to increase with velocity (up to a point), and is very low for zero velocities (in fact, some researchers doubt whether there is actually a true static friction for rubber at all) Thanks for that! Though, could you not find a better source for the frictional properties of rubber than an astrophysicist? But, having thrown out this claim, you don't speak at all about how this very odd characteristic of rubber might actually influences the friction of shoes on rock.
Perhaps that Prof will be following this discussion and post for himself.
Assuming he isn't here to respond for himself:
In the context of the article, I thought the Prof wrote that as an example of how difficult it is to describe rubber interactions. I think this boils down to another reason Coulomb friction is not a good model to use. I don't think it tells you much if anything about climbing friction.
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skinner
Jul 28, 2007, 3:24 AM
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elastohydrodynamic lubrication
Sounds like something that prevents condom breakage.
Seriously.. interesting thread though.
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microbarn
Jul 31, 2007, 12:56 AM
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Those that are interested are probably watching this thread.
The history channel had a Modern Marvels show called "Sticky Stuff" taht had a bit on Stealth Rubber from the inventor.
http://www.history.com/...amp;episodeId=233156
Perhaps anyone missing it can catch a rerun.
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skinner
Jul 31, 2007, 5:48 AM
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microbarn wrote: Those that are interested are probably watching this thread. The history channel had a Modern Marvels show called "Sticky Stuff" taht had a bit on Stealth Rubber from the inventor. http://www.history.com/...amp;episodeId=233156 Perhaps anyone missing it can catch a rerun.
History Channel
Modern Marvels: Sticky Stuff
Saturday, August 04
TVPG | cc
4 pm MST
6 pm CST
7 pm PST
7 pm EST
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paulraphael
Jul 31, 2007, 5:38 PM
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petsfed wrote: Valarc wrote: Well, in useful situations (eg car tires, etc) it really is linearly related to surface area. Its the other variables that aren't linearly related to frictional force. Relative velocity, temperature, moisture/lubrication, etc. I don't believe this is true at all. Bicycle racing tires that are an inch wide, and provide barely over a sqaure inch of surface contact for both wheels combined, can routinely produce coeficients of friction greater than 1.0 on dry pavement. Well in excess of what most cars can produce, in spite of many times the surface area. This was explained to me by a tire engineer as a factor of the cars leaning to the outside (the car's body and each tire individually) increasing pressure on the outer edge of the tire until mechanical deformation actually reduces the friction properties. Wide tires are just one of many engineering solutions to keeping the pressure from peaking to this point. The most useful piece of information I found in the article is that coeficient of friction is too complicated to calculate by theory and must be experimentally measured. I'll remain skeptical of all these conclusions until i see a test done with good methodology that shows more contact area of a rock shoe actually producing more friction. My casual experience certainly doesn't bear it out, even thought that's what I was originally taught.
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climbordie7
Jul 31, 2007, 6:12 PM
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this is the most drawn out conversation about friction i have ever read, actually its the only but ehat ever. yall have fun debating whether this is an accurate article or didn't have enough research to matter. lol
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paulraphael
Jul 31, 2007, 6:37 PM
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what's the matter? this thread rubbing you the wrong way?
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