Physics debate

[Verskis]

First of all, thanks @Stephen for trying to be constructive. I guess you are right that we are mostly debating pretty simple things here because we cannot explain those things properly.



Then, to the fun part (the physics debate)

And here comes the same statement repeated 100 times

Yes, as the same statement still holds true. Tip pressure is generated, Newton's laws are not violated.

Where does the pressure come from?

If the forces on the cable are equal and opposite, there is no torque (thrust and direction). There is only tension.

Your car’s springs are currently in tension. Look out the window. Do you see it jumping up on its own? Of course not. The mass and the resisting force are equal. The springs are in tension.

That pressure comes from the skier's leg, the only energy source in the system.

The basic system is that the skier is pushing against the ground via the boot, binding and the ski, and the ground is pushing back on the skier, as the Newton's 3rd law states. The binding springs (or NNN BC flexors, or Duckbill stiffness in plain 3-pin bindings) makes it possible that the skier generated force on the ground is not only the normal force (perpendicular to the plane of the ski bottom surface), but there can also be lengthwise torque applied to the ski.

Now, if the spring tensioning device would be mounted to the ski so that it would take the counterforce from the ski (for example if the ski boot would be rotated forward and then kept in that position by strapping it to the front part of the ski, think Voile straps going around the cuff of the boot and the bottom of the ski), then it would be a closed system and it would not generate any external tip pressure on the ski, as the Voile strap is taking all that tip pressure (it would only try to bend the ski and rip the binding out of the ski, but it would not generate any external torque on the ski), but now the reaction force to the skier comes from the ground (or snow), not the ski itself, so it is not a closed system inside the ski/binding, you have to take the skier and the ground into account also.

[Verskis]

You can make an experimental test about the tip pressure: take one ski (with a binding), one boot, two scales, and some Voile straps.

First put the ski on the scales, and tension the binding springs with the Voile straps like on the bottom picture. You will see roughly 50/50 split of the weight on the scales. Tensioning the Voile strap (and thus tensioning the binding springs) more does not affect the readings on the scales at all. This is your closed system.

Then take the Voile straps out, and push the boot with your hand (to tension the binding springs), like on the top picture. Now it is not a closed system inside the ski/binding/boot anymore, and you will see the front scale will get more weight than the rear scale. That's the tip pressure. You will be able to adjust the weight split between the front and the rear scales with your hand, you can for example get the 30%/70% split like in the picture.

[Verskis]

If you would try to make the above experiment with a truly neutral binding, like a TTS pin binding with the cables detached, you would not be able to produce any tip pressure by pushing the boot, until the range of movement in the binding runs out.

[TheMusher]

Just came here to praise the artistic paint masterpiece with attention to anatomic detail, notwithstanding it's content which I can't verify.

Here's what our new friend ChatGPT says:

And notably:

[TheMusher]

Also, is perhaps @GrimSurfer overlooking the energy expended to exert forces by man himself?

Certainly a long-distance runner or mountain climber is not a closed system relying only on gravity to move himself forward or upward.

In physics, Hooke's law states that the force exerted by an extended coil spring (read: telemark binding) is directly proportional to its extension.

I'm not sure why its debatable that the telemark binding exerts force? Just ask your calf (ref expended energy).

Question I presume is what is the practical significance of that force. It definitely "pulls" the back-part of the ski towards the skier, and is only doable if the skier puts weight on its foot ball to counter that force. I believe this is what is commonly refered to as "tip pressure".

[Crayefish]

Has anyone considered that skiing, and in fact the entirety of the 'physics' discussed here, is just an illusion as a result of the holographic principle?

Makes all these arguments totally moot if this and the whole universe is all just a holographic projection of some distance two dimensional surface.

[tkarhu]

I might be an absolutist, but I’m am consistent.
First, it is my view that the cable does not (in itself) transfer any force that does not cancel itself out between the boot and the binding.

Thanks for the conversation, and patience all seem to still have some. I ski NNN-BC only, but think I now after reading understand what a cable would do. It lets a skier to lean forward against the spring without falling on one’s nose. Further, that lets you edge your rear ski more.

So @GrimSurfer seems to be right that the binding does nothing. It lets a skier do things. Well that is quite obvious actually. Yet for a skier a binding feels active, when it actually just returns some energy you put on it. Would it help further conversations here, if GS would use the concept of active binding in same meaning how most others use it here? That would not be necessary technically, but would certainly clarify & help human communication.

[Verskis]

Here is one more experiment. Upper picture has the binding with springs (this could be again substituted with NNN BC with flexor, Xplore with flexor, 3-pin with bending duckbill (the duckbill is a torsional spring)).
Lower picture is exactly the same situation with horizontal force (hand) pushing the boot forward, but the binding is now just the toepiece of a TTS binding (=same as alpine touring tech binding toe part) with very low friction pins as a pivot point. With that binding, you are unable to affect the readings of the scales, as the springless binding does not transmit any torque to the ski.

[wabene]

When I stated this,

"I meant this statement which I don't agree with.

"The forces are equal and opposite. There is no net torque. The forces cancel at the boot/binding. Nothing is transmitted to the ski other than the skier’s mass." ,

I was not clear enough. I agree with much of what GS said except, "Nothing is transmitted to the ski other than the skier’s mass" . This is the part I disagree with, I believe the cable does multiply and transmit a force. Simply the only point in contention and one never acknowledged by GS.

[mca80]

My education has included quite a lot of physics (Master of science in technology). How about you?

The argument from authority is a logical fallacy. Not to say you don't know what you're talking about, but whether or not one holds X Y and Z degrees is irrelevant to a proposition's truth or falsehood.