Physics debate

[fisheater]

Stephen, the best way to look at binding activity is from a historical perspective. I think, and I could be corrected, but the first binding I skied that gave me that different, “active” feeling was the Rainey Super Loop. The original Scarpa T-1 had been out, you had this powerful boot, skied by good skiers shins to boots, and expecting to pressure the front of the ski. There were a lot of good skiers coming to Telemark from an Alpine skiing background.
I think it’s still about that high resistant spring tension. The typical boots used with a highly active binding are 3 and 4 buckle boots.
When I read about guys that ski this gear, it seems a big reason why guys skiing strong boots, but short skis for maneuverability, prefer more neutral bindings, is to prevent sticking the tip on the inside ski.
Bottom line is binding activity on 75 mm cable and NTN is quite subjective.

[fisheater]

Cable is attached to heel, cable is attached to ski in a more forward location, Heel is lifted spring is compressed, pressure is applied to the lifting heel, therefore by physics as quoted by @GrimSurfer equal pressure is applied to that mor forward location on the ski
The front of the ski is pressured

Please tell me where my understanding of physics is wrong.

You can’t, you just ignore it

[Stephen]

I have said, and continue to say, that the *cable* does not apply any force to the ski. Doing so would violate a law of motion.

The interaction between the cable and the binding sums to zero. That happens in accordance with a law of motion (the 3rd one).

I don’t think anyone would argue that with you. You’re talking about a closed system. The caulk in my caulking tube stays there until the caulking gun forces it out. Duh.
But again, I think the single point of contention is where a cable binding can allow a skier to apply force to the front of a ski that he WOULD NOT be able to apply without the cable.
Possibly it was a matter of semantics all along, and you were talking about one thing (your closed system loop) and others were talking about the binding applying force to the front of the ski, when maybe that was loose language, since the binding can’t do anything on its own.
The thing is if you stick to literal, without seeking to understand, it can end up like this.
That’s my spin on it.

[beeeweee]

I’m surprised I managed to read through this whole thread. At the risk of getting muddied, I’ll put my thoughts out there.

Herein is the disconnect with GS’s understanding of the mechanics of the problem.

I have said, and continue to say, that the *cable* does not apply any force to the ski. Doing so would violate a law of motion.

The interaction between the cable and the binding sums to zero. That happens in accordance with a law of motion (the 3rd one).

This isn’t so much a physics problem as it is a mechanics problem. Draw a free body diagram that includes the forces and torque applied by the boot, binding, cable, ski, and snow surface, and you’ll notice a few things missing in the picture.

The act of lifting your heal with your boot introduces both a force and a resulting torque on the system. This torque is counteracted by the snow surface against the front of the ski, which is a force. This is basically what some folks here are trying to describe which is that the cable allows enough mechanical leverage to pressure the front of the ski when applying a torque about the toe of the boot.

This can also be empirically verified with a simple experiment with two scales.

Put on your boots, attach boots to binding of ski, place two scales under one of your skis with one scale in front of the balance point and one scale behind the balance point. Move the scales such that the scales read roughly similar amount for weight while standing straight up without lifting your heal. Then get into the telemark turn position and lift your heal and notice how the front scale has more weight (force) applied compared to the rear scale.

[wabene]

Why would people want to ditch the cables for k & g on the flats if there wasn't resistance to lifting your heal? What is the purpose of springs if there isn't resistance provided? Since the pin line and cable attachment are offset, there are two separate fulcrums that operate on different axes. That is why when you lift your heal, resistance is created resulting in the opposing force pressuring the tip. At least that's what makes sense to me. The axis of the cable is closer to the ball of foot aiding in flexing that part of the boot.

When you lift your heal more force is applied to the front of the ski. This will not happen without your foot moving, but it certainly is the cable applying the extra force. Every conversation doesn't have to lead to some kind of theoretical blabbering.

I posted this on Saturday approximately 16 freaking pages ago and in my opinion says all that needs to be said about this. I would guess that the vast majority here would agree.

[wabene]

Remember last year when the fit young, I think, Norwegian guy showed up posting videos of himself skiing all over mountains on Gammes in just his shorts? That firestorm blazed brightly, but was over quick That one, I thought was funny.

[Verskis]

I have said, and continue to say, that the *cable* does not apply any force to the ski. Doing so would violate a law of motion.

The interaction between the cable and the binding sums to zero. That happens in accordance with a law of motion (the 3rd one).

Goddamnit, do I have to repeat all the posts I have made about the topic so far?
Once again, you forget that the spring is creating torque to the ski (via the lever presented in your binding picture with the red and green lines), and the ski boot.

[GrimSurfer]

I have said, and continue to say, that the *cable* does not apply any force to the ski. Doing so would violate a law of motion.

The interaction between the cable and the binding sums to zero. That happens in accordance with a law of motion (the 3rd one).

Goddamnit, do I have to repeat all the posts I have made about the topic so far?
Once again, you forget that the spring is creating torque to the ski (via the lever presented in your binding picture with the red and green lines), and the ski boot.

The spring is in tension. It is held at opposite ends by the boot and binding, which are locked together at the duckbill. The force in one direction is exactly the same as the force in the opposite direction.

If those forces were not equal, you’d move automatically on level ground. Without having to do anything.

This does not occur.

None of this changes when you raise your heel. The boot and binding are still locked together. The spring increase in *tension*. Tension means that the forces are equalized in opposite directions. Compression? Same thing.

When the heel is lifted, the only thing the tension of the cable does is act on the boot. Whatever torque is generated by the differing rotational paths prescribed by the rat trap and cable attachment allows the centre of pressure exerted by the skier to move further back (from the tips of the toes to the ball of the foot).

The skier is transmitting all of the pressure to the ski. The only thing the cable is doing is helping that pressure to be applied closer to the point on the foot where the skier can more effectively apply it. The ball of the foot.

This allows the skier to exert more effective application of his/her mass.

[Verskis]

Newton's 3rd law states that for every force there is an equal but opposite counterforce. That one you've got right. But now you have to learn to apply that law.
Spring is not violating the 3rd law, it is pullin the boot heel and the binding with equal but opposite forces. These forces generate torque to the boot, and the binding. Boot torque generates force to the shin of the skier (think tall plastic boots, so it is easier to mentally get the image), the skier leg is pushing against the boot with an equal but opposite force, 3rd law not violated here. The binding torque tries to rip the rearmost binding screws out of the ski, but let's assume the screws can handle that, so the ski core holds the screws with an equal but opposite force. Once again, no laws of Newton were violated.
Since the binding is screwed rigidly to the ski, the torque generated to the binding is torqueing the ski too, trying to sink the front part of the ski deeper in the snow. So ski is pushing against the snow with some force. This force of course has the counterforce, the snow is supporting the ski with an equal but opposite force. Newton can rest in his grave, we are still abiding his 3rd law when skiing.

[wabene]

And here comes the same statement repeated 100 times