Physics debate

[GrimSurfer]

thanks for answering my questions. Lol. Since you won't answer, I'll make assumptions and the big assumption is that you dont understand telemark skiing and your grasp of critical thinking is suspect. You seem most interested in feeling superior on a public forum and least interested in actual telemark skiing which is what most of us do here, regardless of being "world class skiers" or not.

Your fight is with Isaac Newton… or maybe the Royal Society. It’s not with me. Really, it isn’t.

No, it's with you. Me and IN are good. Let's try this: since you are the only user in the history of this forum to bring up the term "heel control" (do a search if you don't believe me) , maybe you could explain exactly what that telemark sking term means?

OK. Let me give this a “noodle” for a few hours. I suspect that whatever I offer will be pretty much the same that others have already provided on the control aspects of the cable (I felt many of those comments to be quite correct and well thought out).

[GrimSurfer]

I never said that the springs multiply force. But springs return (virtually all) the energy put into them.

Think about the TTS binding (once again, this kind of binding: https://www.voile.com/voile-telemark-te ... -tour.html). If we compare it to your stiff knees, that would mean that there is no spring (cables) in them, but the pins (that are the pivot point) are very rusty and therefore have great friction when the boot is rotated. That means that when the skier would bend the leg and lift the heel, the binding would actually transfer some torque to the ski via frictional forces when the boot is rotating, but once the rotation stops, there would be zero force and zero torque on the binding, as the friction is generating force only when there is moving. The skier would only be able to have some tip pressure during the movement phase, but not at all in a static situation.

However, if we think about a correctly working binding, with virtually frictionless pins and strong springs on the cables, now the energy is stored in the springs, and the loaded springs are able to provide force in the static situation too (when the heel is lifted). No energy is consumed, since nothing is moving, but the springs exert force, equal but opposite, on the binding and the boot. Now this spring force is acting on the lever, which is the binding itself: the length of the lever is the distance between the boot holding pins and the attachment point of the cable. The cable is not a lever, it is only an extension of the spring. As long as the spring is loaded, it is trying to pull the boot heel down, or the binding up. This is what makes both the supporting force on your leg, and the pressure on the ski tip.

When you think about it, there is only two ways to unload that spring: either the boot must come down, or the rear of the binding must come up. So, the spring is trying to make you stand upright again, so it is trying to prevent you from going over the handlebars, while simultaneously it is trying to lift that rear of the binding up, which means that the ski tip would be lowered down, since the fulcrum is on the pins of that binding. That ski tip lowering effect is what people call tip pressure.

I would accept a great deal of what you’re saying… but the issue is that skiing is done with bent knees, bent ankles, flexed metatarsals.

This gets in the way of looking at the ski-binding-boot-skier system as a simple lever. All this bending and dynamic movement is moving mass.

We know that movement can build momentum on flat ground. Leverage won’t do that.

We know that shifting masses either side of normal force (as well as ski edge angle etc), will cause a ski to stop or turn.

But we were not debating how to stop or turn the skis, we were debating on what the heel cable does for the ski.

Yup. Fair enough.

[bauerb]

umm, this is def not a thread that a casual observer should jump into.

[Stephen]

Ironically hilarious.

“No I didn’t.”
Yes, you did.”

This sketch from Monty Python comes to mind. Perhaps most of you know it already but it cracks me up every time.

[Stephen]

umm, this is def not a thread that a casual observer should jump into.

Yes, but if the casual observer has gotten this far, all hope is lost!

[Stephen]

Seriously, is anyone really sure what this is about anymore?
I know, something to do with skis and boots and bindings and snow and the human body, and the immutable forces of the universe, and the “laws” that man has come up with to conceptualize / model / understand all that.

But what exactly?
Or, maybe I’m just not bright enough to keep up.

Don’t you dare answer that…

[Lhartley]

As somebody currently learning the telemark turn I actually appreciate the debate on how the turn is made, it's nice seeing talk about technique and the theory of the turn, even if some of it may be misinformation either way. Nice to see talk about the turn instead of the gear

[lowangle al]

As somebody currently learning the telemark turn I actually appreciate the debate on how the turn is made, it's nice seeing talk about technique and the theory of the turn, even if some of it may be misinformation either way. Nice to see talk about the turn instead of the gear

Don't hesitate to start a thread about whatever technique you are working on. I prefer technique talk over gear talk too.

[GrimSurfer]

Let's try this: since you are the only user in the history of this forum to bring up the term "heel control" (do a search if you don't believe me) , maybe you could explain exactly what that telemark sking term means?

OK. Let me give this a “noodle” for a few hours. I suspect that whatever I offer will be pretty much the same that others have already provided on the control aspects of the cable (I felt many of those comments to be quite correct and well thought out).[/i]


I’ve been invited to comment on what I mean by heel control in the context of telemark skiing. There are two parts to this “heel control” which is what I believe cables on 3 pin bindings are bringing to skiing and “telemark skiing”, which is style of skiing that can be practiced by people wearing 3-pin bindings and boot systems.

What follows is restricted to what I’ve described above. It does not have anything to do with other equipment variations in bindings or boots.

I would like to preface my comments by saying that any reference to principles or laws of physics isn’t arrogance. On the contrary, it is my humble and complete acceptance of the superb work of others. So here goes…

This is a typical three pin binding and cable.

My crudely drawn red line is roughly the point where the rat trap locks down the duckbill. This is the furthest forward pivot point around which the can boot rotate around the longitudinal axis of the ski. Why? Because the rat trap (which is the exact term used by the inventor) and three pins bind the boot to the ski at this point.

The crudely drawn green line shows the rotational axis of the cable system. Most, but not all, cables use springs to maintain cable tension. For reasons I have already explained using the laws of motion, this arrangement does not apply any force to the ski. It’s purpose is to act as a control mechanism on the movement of the boot.

How does it do that and why does it matter to telemark skiing?

Before getting to that, we need to consider the human foot…

The human foot evolved from a climbing/grasping appendage to one suitable for walking. It retained a lot of flexibility but it’s musculature adapted to walking. So the phalanges shrunk and lost strength and the metatarsals gained considerable strength. This had a profound affect on the way the human foot functioned (i.e. transmitted force).

The main force bearing and force transmitting elements of the human foot are the ball of the foot (the point that lies between the phalanges and metatarsals) and the heel. Of these, the the ball of the foot is the forward most force transmitting element.

The phalanges (toes) can transmit force but they’re not all that good at it. Their primary function is balance control.

This is why a person can retain an ability to walk (transmit force to the ground) without toes, but lacks the ability to do so smoothly.

Big deal… So what?

Let’s look a three pin boot (not necessarily the one any of us would use for telemarking, but the angle of the photo is useful)

The forward most pivot point of a 3 pin binding is where the rat trap holds the duckbill. The flex of the sole of a boot has some give and flex, but the pivot point is still well forward. This is why boot soles show fatigue failure at that point.

This pivot point is not ideal because it is well forward of the ball of the foot. It is also well forward of the phalanges, which we know aren’t designed to transmit force (they control balance).

Cables shift the pivot point of the boot backwards, closer to the ball of the foot. They do this by controlling the centre of pressure of the boot relative to the ski by creating unequal forces on the sole of the boot…

The rat trap holds the toe. The point of greatest deflection of the boot is at the toe. The cable’s pivot point is roughly in line with the ball of the foot. Tension in the cables move the boot’s centre of pressure forward to somewhere between the rat trap and the cable pivot point.

This slight shift in pressure point helps the foot to transmit force more effectively onto to ski (through the binding). The force isn’t greater (force is still a function of skier mass and loading (“stomp”), but it’s application is now through the ball of the foot instead of the phalanges (which contribute to balance way more than the transmission of force).

So what about the heel? In an ideal world, the foot wouldn’t twist while skiing. But it does. So does the boot… especially in a 3 pin boot which NEEDS a flexible sole in order to “kick”. This flexibility is a problem. It is mitigated but not entirely eliminated by cables, which act as “stays” used to limit the lateral flex of a sailboat mast.

Unfortunately, their placement isn’t ideal. This is because the only practical place to attach them is to the trailing edge of the binding. They still play a role in heel control through resistance.

We all know that telemarking requires heel lift because there is only so much flexibility in the calves and Achilles’ tendon to accommodate how far we sometimes need to bend the ankle. Bending one’s knees to get weight over the front of the ski for balance and control puts our lower leg at an acute angle. The heel must lift to accommodate this in order to execute a telemark turn.

Even though the cable angles are not ideally placed for lateral control, they are designed to resist unequal side loading. This is why the back of cable straps aren’t simply wire… there is either a small clip or channel that helps centre the cable at the back of the boot. Again, it’s an aid, not a perfect solution.

This is what happens when a binding made for one particular purpose (classic XC skiing) is modified for another purpose altogether (telemarking).

Anyhoo… those are my thoughts on the matter. What I’ve offered in terms of the cable NOT transmitting force to the ski are supported by the laws of motion. What I’ve offered in terms of the cable using tension to change the manner in which the boot and foot apply pressure to the ski don’t (as far as I can tell) violate any of these laws.

Lots of words, lot of pictures. Freely given. How readers wish to apply it is entirely up to them.

[lowangle al]

GS, I'd like to hear more about that heel control too. It would be worth the embarrassment to find out what's missing in my technique. Between that and my skiing in jeans it might be too much to handle. If you can embarrass me I'll let you know the top two things that will embarrass you.