Physics debate

[GrimSurfer]

All of my arguments have been about NN 3 pin 75mm bindings.

You have been writing about a binding standard. It describes the connection between binding and boot. What you write applies to the binding on the photo, but not all bindings of that norm it seems because the hinge nechanism is not part of the NN 3 pin 75 mm standard. Feel free to correct me if I am wrong.

You don’t understand.

It’s about the cable. It has always been about the cable. I’ve focused on the NN 3 pin 75mm binding because of two things:

1. That’s what started the discussion, so it makes sense to stick to the to the topic for the purposes of consistency; and

2. How the cable interacts with the NN 3 pin 75 mm binding (which is fixed to the ski and has no moving parts other than the bale).

Other bindings, such as those using cable tension and a hinged ramp to help move the boot longitudinally, work differently.

This topic has always been about the NN 3 pin 75 mm binding. People might not like that because it avoids the issue of how these bindings work differently than some may have thought.

This topic is important, if for no other reason than to reaffirm the notion that skills development trumps cable choice.

[fisheater]

@GrimSurfer You could just answer yes or no.

You could just read what’s been posted already. Or you could stay on topic.

All of my arguments have been about NN 3 pin 75mm bindings. I stated this at least twenty times already in this thread, which you would have noticed if you read the thread before commenting.

Does this cable rotate around a pin? (I put arrows pointing to the pivot l

The cable freely rotates. It cannot transmit torque. The only force it transmits are frictional forces, which are scant. Newton’s 2nd Law.




Actually the cable is FIXED TO THE SKI, by way of being fixed to the binding. The rotation is irrelevant.
This is your mis-interpretation of what happens.

[GrimSurfer]

@GrimSurfer You could just answer yes or no.

You could just read what’s been posted already. Or you could stay on topic.

All of my arguments have been about NN 3 pin 75mm bindings. I stated this at least twenty times already in this thread, which you would have noticed if you read the thread before commenting.

Does this cable rotate around a pin? (I put arrows pointing to the pivot l

The cable freely rotates. It cannot transmit torque. The only force it transmits are frictional forces, which are scant. Newton’s 2nd Law.




Actually the cable is FIXED TO THE SKI, by way of being fixed to the binding. The rotation is irrelevant.
This is your mis-interpretation of what happens.

Rotation is relevant to the issue of torque. Torque is force + moment (as in foot-pounds, Newton-meters). If there is free rotation, there is no moment. Why? Because the force is simply creating friction.

The cable is in tension because it is attached to the toe plate. Tension is the symmetrical opposition of force. Therefore, the net external force is zero. Why? Because the forces cancel out. The compression of the boot sole happens because the boot is internal to the system.

If the forces were asymmetrical, the ski would move all by itself if you put a boot in the binding. It doesn’t, of course.

This isn’t about any misinterpretation on my part. It’s what Newton’s 3rd Law actually describes.

[bauerb]

I can't believe this thread is still happening.

[tkarhu]

@GrimSurfer No one else is writing about binding internal forces. Others explain how force is transmitted from skier to snow. So, your Newton’s third law argument is against straw men, in terms of rhetorics. As well you could say that skier pulls earth as much as earth pulls skier (gravity). That is true but not very relevant for learning how to ski.

[GrimSurfer]

@GrimSurfer No one else is writing about binding internal forces. Others explain how force is transmitted from skier to snow. So, your Newton’s third law argument is against straw men, in terms of rhetorics. As well you could say that skier pulls earth as much as earth pulls skier (gravity). That is true but not very relevant for learning how to ski.

It actually is relevant for learning how to ski. Once one accepts that the cable is a skier aid, the goal can be to develop skills so it is no longer needed. We’ll call that skills progression. That saves weight and complexity. Isn’t that helpful?

I mean people talk about boot weight all the time. They also talk about the weight of skis, or construction techniques that reduce weight.

They also talk about fumbling with cables or creating mods to hold cables when not in use… so they don’t break flow.

So is any of this not relevant? Of course it is.


In the vast majority of counter arguments, very few people have ever challenged the physics. They’ve denied it exists. They’ve denied its utility. They’ve dismissed its relevance. But they’ve never actually formed a coherent argument, using physics, to refute the proposition that the NN 3 pin 75mm cable doesn’t transmit force, but is a control element on the force applied by the skier.

So here’s a crazy thought that will bust everyone’s noodle wide open…

Why hasn’t Rottefella marketed a cable system for the NNN BC or the Xplore binding systems? Like, they control the patent on these systems (unlike the NN, which expired years ago).

Is it that they don’t understand how a cable actually works? Or is it because they recognize it is about control (not force), and they already addressed the issue with bumpers and flexors?

Has nobody ever made this connection? Anyone? Or do you think Rottefella doesn’t know exactly what it is doing with successively more modern binding systems?

Or, as Johnny said:

People stuck in the past and older technology will never be able to see and even apprehend new innovations and progress, blinded by their own ignorance and their retarded last millennium beliefs. But one day, sooner or later, in a life-changing enlightening moment, these non-playing characters will come to realize the truth. And sadly, at this point, they will start regretting their entire life...

[leon]

Does this cable rotate around a pin? (I put arrows pointing to the pivot point)

E023EAD0-C92D-404D-9568-23825EEDCAC0.jpeg

Why yes, it does. What a frackin revelation.

Interesting discussion… still.

Yes, the cable rotates around a pin, BUT those cable pins are not on the 3-pin line (or tech toe pin line). @GrimSurfer Does the “torque” on the ski or the lack thereof from the cables depend on the relative positions of the boot pin line (3-pin or tech pins or whatever point allows rotation of boot with respect to ski) and the cable pin connection? As a non-physicist, it makes intuitive sense that if rotation occurs at the same point as the cable attachment then torque is not generated. If on the other hand, a pulling force is applied at a point on ski other than the pivot point between ski and boot, then a torque would be applied to the ski by the pulling force.

Am I getting this correct? If not where is my logic running counter to physical laws?

[GrimSurfer]

Does this cable rotate around a pin? (I put arrows pointing to the pivot point)

E023EAD0-C92D-404D-9568-23825EEDCAC0.jpeg

Why yes, it does. What a frackin revelation.

Interesting discussion… still.

Yes, the cable rotates around a pin, BUT those cable pins are not on the 3-pin line (or tech toe pin line). @GrimSurfer Does the “torque” on the ski or the lack thereof from the cables depend on the relative positions of the boot pin line (3-pin or tech pins or whatever point allows rotation of boot with respect to ski) and the cable pin connection. As a non-physicist, it makes intuitive sense that if rotation occurs at the same point as the cable attachment then torque is not generated. If on the other hand, a pulling force is applied at a point on ski other than the pivot point between ski and boot, then a torque would be applied to the ski by the pulling force.

Am I getting this correct? If not where is my logic running counter to physical laws?

It’s a reasonable question… and yes, there is likely some minuscule torque. But that torque will be limited by the stiction of the cable (which isn’t much) and the flex of the cable/spring (which is considerable). This issue is whether it is sufficient to change work*.

Now let’s compare this with the torque generated by the skier’s foot, backed by ~50kg or so. It’s likely to be insignificant. Still worthy of measurement… but it would require a very rigorous experiment to define because the generated torque is likely to get lost within the margins of error of most tests.

If we were to compare this to the resistance applied against the skier’s boot, I’m fairly certain this force would be several orders of magnitude higher. Why? Because this is its primary function. That’s why you can buy cables with different springs but there is a lot of consistency in the cable mounting points (relative to the duckbill placement) on NN 3 pin 75mm bindings.

You see, this is all about applying tension to the boot, thereby changing its response to skier input. This is one characteristic of a basic control system. (Response is one, another may be range of motion though I’m not sure if the cable works effectively in this way.)

* work being a specific term used in the field of physics that describes something which, in a general sense, can change the magnitude of force or direction of motion.

[tkarhu]

Ok, we have tested free pivot vs cable on our physics apparatus. Video proof uploaded to YouTube.

@leon you can see the torque on the video. There is no need to intellectualize, when you can test and observe. Video observations should apply to most 75 mm nn 3 pin bindings, when cable attachment point and boot / binding bending point are at similar locations.

Thanks for the discussion.

[Telerock]

Perhaps we need a force diagram. Most engineers and physicists would do that to provide a visual representation where the applied forces and opposing forces can be set equal.
I am not volunteering to draw one, perhaps someones sister /daughter would do that on a bar napkin?
What I gathered from the video test (thanks to the patient lady tester) is that when locked down toes, with spring loaded heel bindings, there is minimal forward force applied by raising the heel. Not quite sure what was changed for the second test, but she clearly slipped foreward when raising the heels; may be a balance thing?
PS: I think some compassion, understanding and repetition may be necessary due to the length of this discussion. I would not expect the newcomer to this thread to read through the entire 45 pages.