One reason your feet slip off foot holds
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I was watching a climbing partner climb and slip off holds. After watching closely I noticed something subtle about his footwork. I think I know why and talk about it in this video. |
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oh, I thought we were going to talk about my affinity for eating bbq while climbing again. |
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Funny how ice climbing, you want to drop your heels to have the secondary points purchase the ice. Is your friend an ice climber by any chance? |
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One reason why *my* feet slip off holds, is because my footwork sucks! =) |
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It's an interesting video, but it does over simplify the problem a little since you seem to always be assuming that your center of gravity is directly over the point of contact and that no other holds are involved (if either of these weren't the case, F_1 would be less than your body weight). |
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one of the really tough things (i think) is that in order to increase F_n on vertical to overhanging terrain, you will have to somehow pull more with your arms. the more you try to push your feet into the wall to get a better angle, the more it is going to push you outward. on jugs this is easy, but when you have poor handholds this gets really hard to do. the really hard part is determining the minimum amount that you need to pull with your arms, or the maximum amount or angle that you can push with your feet. |
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does this 'heals up' idea apply to slab climbing? I usually find that I get more purchase on smears and technical small holds on slabs with my heal slightly dropped. |
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Nice idea for a discussion Don. |
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maineah wrote:does this 'heals up' idea apply to slab climbing? I usually find that I get more purchase on smears and technical small holds on slabs with my heal slightly dropped.As I mentioned, the video oversimplifies the physics such that it's not really relevant in a lot of situations. Slab climbing is one of those. What the video is actually comparing is a stance on a surface perpendicular to the force of gravity VS a stance that is angled. When the surface is perpendicular to gravity, zero friction is required so the coefficient of friction isn't important. When the surface is angled, there are horizontal forces at play that require friction to hold the foot on the hold. With slab climbing, assuming the rock is featureless and the same angle everywhere, you don't have much choice in terms of the direction of the forces as you'll have the same angles pretty much any way you stand. In this case, what you want to do instead is increase the coefficient of friction. This can be done by increasing the contact area between your shoes and the rock, which is easily done by lowering your heel to allow more of your shoe to touch the rock. |
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Ian Stewart wrote: As I mentioned, the video oversimplifies the physics such that it's not really relevant in a lot of situations.The video oversimplifies climbing (that shouldn't surprise anyone). In friction slab you try to maintain your center-of-gravity right over your feet (your ass end up sticking out slightly) for the maximum amount of friction. What slim is saying is on a slopping foothold, if your hand holds allow inward pull, then it becomes a delicate balance between the strain of pulling inward with your hands to shift your your center-of-gravity over your foothold, which increases friction and allow more weight to be taken off your hands in the downward direction. An extreme example of this is liebacking a crack. |
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reboot wrote:What slim is saying is on a slopping foothold, if your hand holds allow inward pull, then it becomes a delicate balance between the strain of pulling inward with your hands to shift your your center-of-gravity over your foothold, which increases friction and allow more weight to be taken off your hands in the downward direction. An extreme example of this is liebacking a crack.Getting your center of gravity over a hold does NOT increase friction. Increasing the coefficient of friction and/or increasing the NORMAL force, the force perpendicular to the surface, increases friction. If you have a sloping foot hold, putting your center of gravity directly above the hold provides LESS friction than if you were to angle your body so your feet are pushing into the surface at a 90 degree angle. Maximizing the friction on a purely slab climb would actually require your center of gravity to be BEHIND you such that you are pushing in 90 degrees to the wall. But since there's nothing for your hands to hold on to, the furthest you can lean back is having your center of gravity over your feet. A layback is an example where you DO have something to lean back on to get your center of gravity away from the wall to push in to it. |
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Ian Stewart wrote: Getting your center of gravity over a hold does NOT increase friction. Increasing the coefficient of friction and/or increasing the NORMAL force, the force perpendicular to the surface, increases friction. If you have a sloping foot hold, putting your center of gravity directly above the hold provides LESS friction than if you were to angle your body so your feet are pushing into the surface at a 90 degree angle. Maximizing the friction on a purely slab climb would actually require your center of gravity to be BEHIND you such that you are pushing in 90 degrees to the wall. But since there's nothing for your hands to hold on to, the furthest you can lean back is having your center of gravity over your feet.I guess I wasn't clear when I said "over", it included going behind (outward) from the foot. And yes, perpendicular to the foothold provide the most amount of friction. But most of the time in climbing, creating the most amount of friction for your feet is secondary to reducing the overall pull force (measured at the muscles/tendons) required by your hands, and those 2 factors often conflict. |
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Glad to have spurned lots of discussion. Yes, the video only applies to a very specific situation. Got me thinking about making others that cover laybacks, slabs, stemming. Would that be interesting to this group? |
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I don't buy the "heel up" analysis. |
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Don McGrath wrote:spurnedDoesn't mean what you think it does... |
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Love the discussion... |
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Ian, increasing the surface area with between your shoe and the rock on a slab, does not increase the frictional force. |
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Don McGrath wrote: Maybe I'll make a short video about how this works in the case of a slab. DonThat would be cool |
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If you want to make the point that dropping your heel too much might make your foot slip off a sloping hold, best to leave it at that. The pseudo-science adds nothing to it. |
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lol and now it's not there |
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Don McGrath wrote:Ian, increasing the surface area with between your shoe and the rock on a slab, does not increase the frictional force. Ff=Fn*u=m*g*u ...no A When you increase the contact surface area, all it does is spread the force Fn over a larger area, decreasing the force per unit area, but the total Fn force stays the same. Therefore Ff stays the same. In reality, it often does help to increase the surface area of your shoe on the slab. I think this is because a) it's a more relaxing position and b) the surface is not totally uniform and you may catch a crystal or rougher spot, which increases the frictional force. Just clarifying this. Maybe I'll make a short video about how this works in the case of a slab. DonYou're right. It's been a while since I took physics and I oversimplified things, too. I'm pretty sure all of these equations must assume that the bodies are completely rigid; that is, they don't deform at all. With the rubber on climbing shoes, that is not the case. In reality the rubber on a shoe deforms a LOT. Because of this, your (b) point is partly correct in that increasing the contact area increases the shoe's ability to deform around the rock and provide more traction. This doesn't change the coefficient of friction itself, but all those deformities mean that there will be many other forces acting on the shoe than just that of friction (eg. there will be many small "normal" forces in many different directions, not just one). So instead of thinking as slab as one featureless surface, you should instead think of it as many many many small holds (that you can't see) that the rubber can deform around...you're not standing on one slab, you're standing on thousands of mini holds. |