Physics debate

[tkarhu]

https://www.telemarktalk.com/viewtopic ... =80#p54832

The quote above is a good example.

I will wager @lowangle al is an excellent skier. I’m saying that honestly, with out a trace of sarcasm. Yet, he’s at a loss for words explaining how he executes a basic manoeuvre. This doesn’t make him any less good, or any less smart. It just means that, like all of us (and I most definitely include myself in this statement) he’s spent more time doing stuff than thinking about it.

This becomes a problem when it’s time to share knowledge,,which is something that this forum is here to support.

In my experience @lowangleal really does not lack any essential competence in sharing insights about skiing. In many posts, he has explained very clearly, what you should do, when learning a telemark turn. Such understanding has been enough for developing my skills to what I would call intermediate now. Thanks for the insights!

[GrimSurfer]

And what law is that? Hooke’s Law (which doesn’t apply to rubber, which is what the flexor is made of)?

It’s according to Newtons Third Law:

1) We know the force transmitted through the spring/flexor (Tom M has measured this)
2) We know the vector - ie direction - of the force (diagonally towards the front of the skis)
3) Hence, the normal force (equal and opposite) has to be diagonally in the front of the ski (the ski which obviously is flexible to give a perpendicular surface opposite to the vector, to mount a counterforce).
4) This normal force is what we refer to as tip pressure.

In conclusion, the normal force is in its entirety on the front of the ski - and is therefore known as tip pressure. Same goes for the delta, which is measured to 7 lbs.

If you add weight (skier or otherwise) on the ski, that is just additive (which is not to say total normal force exceeds skiers weight).

Interestingly, you can easily verify this by mounting your boots to a nnn-bc or 75 mm binding, and trying to bend the flexor/75mm sole with the ski. You’ll find it’s only possible pressuring the front of the ski..

Agree, in general terms. Differs with the ski. Very camber dependent.

Flat ski, those delta forces aren’t concentrated on the tip. They’re spread out from the binding forward.

Double cambered ski is going to be different. The delta forces will be concentrated in a smaller area.

This is where generalities of physics fail… like simply assuming that all of the forces act on a single point or that those forces are linear (the joining of two data points will always result in a straight line).

The problem with any material being compressed is that there’s no way to know (without measurement) if it is responding in a linear manner to force. Same thing with the boot. This might matter a lot when loading changes.

Also, keep in mind that the loading on the front of the ski just won’t just be a function of flexor deflection. The foot and boot will flex more and more as the flexor is loaded, so the overall % of weight transfer imposed by the flexor will likely become progressively more or less. It depends…

Heck, I don’t know if the channels cut in a NNN BC or the different shapes of the Xplore flexor change the force curves. Somebody designed them, so they are there to fulfill a purpose (fashion? response? weight reduction?).

When we measure things under increasing loads (like I would have proposed in part 2 of the experiment) we’d be able to make some sense of all this.

This could then be used for a more complete comparison between different bindings (repeatable tests provide data that can be compared reliably). It could even reveal why a spring cable system gives a different drive than a rubber flexor system. The forces at any one point in the boot arc might be the same but they could differ considerably outside that point (difference in response).

@lowangle al got into how this works for skis in another thread… bouncing a double camber ski to load it up for turning.

All of what I mentioned can appear like nit picking. It is on a certain level. But them “nits” can go along way in explaining why some bindings and binding configs work well in some areas but not in others. Measuring the different flexors and their impact on force is the start of a process…

If Tom doesn’t do this with the Xplore, I certainly will in the spring /summer with my NNN BC set up. Need time to gather some measurement devices like a matching set of kitchen scales, a luggage scale and order another set of flexors (I have older, hardly used hard flexors and somewhat overused medium flexors).

[CwmRaider]

Heck, I don’t know if the channels cut in a NNN BC or the different shapes of the Xplore flexor change the force curves. Somebody designed them, so they are there to fulfill a purpose (fashion? response? weight reduction?).

Rubber is incompressible, so the channels are there to allow the deformation to be contained. As in a sort of bellows, if you wish.
Yes my physics terminology is bad. Please don't get started.

[GrimSurfer]

Heck, I don’t know if the channels cut in a NNN BC or the different shapes of the Xplore flexor change the force curves. Somebody designed them, so they are there to fulfill a purpose (fashion? response? weight reduction?).

Rubber is incompressible, so the channels are there to allow the deformation to be contained. As in a sort of bellows, if you wish.
Yes my physics terminology is bad. Please don't get started.

The compressibility of rubber goes from had (Indian rubber) to soft (gum rubber). Synthetic rubbers are all over the map. Deformation is a sign of flexibility. Breakage is a sign of inflexibility.

Agree on the bellows (and shapes). It’s probably there so that the durable rubber used for the flexor can flex better.

[TheMusher]

And what law is that? Hooke’s Law (which doesn’t apply to rubber, which is what the flexor is made of)?

It’s according to Newtons Third Law:

1) We know the force transmitted through the spring/flexor (Tom M has measured this)
2) We know the vector - ie direction - of the force (diagonally towards the front of the skis)
3) Hence, the normal force (equal and opposite) has to be diagonally in the front of the ski (the ski which obviously is flexible to give a perpendicular surface opposite to the vector, to mount a counterforce).
4) This normal force is what we refer to as tip pressure.

In conclusion, the normal force is in its entirety on the front of the ski - and is therefore known as tip pressure. Same goes for the delta, which is measured to 7 lbs.

If you add weight (skier or otherwise) on the ski, that is just additive (which is not to say total normal force exceeds skiers weight).

Interestingly, you can easily verify this by mounting your boots to a nnn-bc or 75 mm binding, and trying to bend the flexor/75mm sole with the ski. You’ll find it’s only possible pressuring the front of the ski..

Agree, in general terms. Differs with the ski. Very camber dependent.

Flat ski, those delta forces aren’t concentrated on the tip. They’re spread out from the binding forward.

Yeah here we agree! Tip pressure is not necesssarily a very precise term - front pressure is probably more descriptive.

This was all theoretical of course, assuming you had only one scale in the front.
Where on the front of the ski the pressure hits in reality obviously depends like you indicate on a multitude of factors relating to the terrain, ski and its properties, binding mouting point, flex location, binding resistance, etc etc. At this point we probably need a rocket surgeon..

Indeed would also be interesting to compare the resistance "curve" of xplore flexor to a hardwire cable with regular 75 soles, like I think you propose.

[GrimSurfer]

Precisely, Sir!

[bauerb]

you ever seen one of those threads titled "How to make Telemark Skiing more popular"? ...this is the exact opposite of that thread. .. "How to make telemark skiing sound insanely complex and basically impossible short of a theoretical computer simulation"....

[CwmRaider]

Heck, I don’t know if the channels cut in a NNN BC or the different shapes of the Xplore flexor change the force curves. Somebody designed them, so they are there to fulfill a purpose (fashion? response? weight reduction?).

Rubber is incompressible, so the channels are there to allow the deformation to be contained. As in a sort of bellows, if you wish.
Yes my physics terminology is bad. Please don't get started.

The compressibility of rubber goes from had (Indian rubber) to soft (gum rubber). Synthetic rubbers are all over the map. Deformation is a sign of flexibility. Breakage is a sign of inflexibility.

Agree on the bellows (and shapes). It’s probably there so that the durable rubber used for the flexor can flex better.

Do we use the same definition of compressibility?
https://en.m.wikipedia.org/wiki/Compressibility
I meant relative volume, or density, change as a function of pressure, not how easily it deforms.
I'm pretty sure that the compressibility of rubber is negligible for in the pressure range in binding bumpers. So when you compress the rubber piece in one direction, the material wants to be squeezed out in another direction. I *think* it is logical that channels mitigate this effect.
Edit: for reference, rubber is about as incompressible as liquid water.

[Peter P]

you ever seen one of those threads titled "How to make Telemark Skiing more popular"? ...this is the exact opposite of that thread. .. "How to make telemark skiing sound insanely complex and basically impossible short of a theoretical computer simulation"....

Screen Shot 2023-01-05 at 9.49.34 AM.png

This is awesome in general, but "Fig Newton" put it over the top for me.

[TallGrass]

Duuuuuude.... I was AT that concert!

I have not read all 21 pages of this Physics Debate because I know if it's about Physics it doesn't take 21 pages.