Physics debate

[Verskis]

The cable almost certainly provides resistance. So what your feeling is likely that, not force.

That "cable resistance" is not a force?

Not a productive force.

Let me put it another way…

My knees are stiff. There is resistance in knee joint articulation. Does this mean I can leg press any better?

You probably have friction in your joints. Friction is a resistive force. You now need to overcome the friction force of your knee with your leg muscles, so you need to use more force to bend your knee, but that does not make for better leg press results, unless you had your knees replaced by frictionless artificial knee joints. Friction converts energy into heat, so it does not return the energy into the original state.

However, the spring force is not friction. Springs return the energy put into them (albeit there is a small friction loss even in the springs), so that is not comparable to the friction in your knees at all.

[GrimSurfer]

Resistance is simply a force working against itself. It isn’t productive in the sense that energy is being expended without mechanical work being accomplished. (That energy is turned into heat)

Ironically, this something most often seen in control systems.

I’ve said all along that a binding cable is a control element. If you’re telling me there’s resistance (which I believe there is… anyone who has ever skied with these bindings can feel the resistance. I have felt it myself), than that points even more in favour of that the cable is a control element.

[エイダン.シダル]

Hi,

I am just starting this new thread so that the “fights” over physics can be discussed in a specific thread and stop derailing other threads. It is really becoming annoying…

Thank you!

Martin

Thank you for trying, but the same character has behaved the same way here as on the other thread, of course. The poster has been registered just over a month, posts over a dozen times a day: all of it unhelpful at best, mostly hostile.

If the moderators don't have a policy to address this, they need one. It's ruining the forum. For now, I suggest that nobody feed the troll, and put them under 'foe' so you don't even see their nonsense.

[GrimSurfer]

That "cable resistance" is not a force?

Not a productive force.

Let me put it another way…

My knees are stiff. There is resistance in knee joint articulation. Does this mean I can leg press any better?

You probably have friction in your joints. Friction is a resistive force. You now need to overcome the friction force of your knee with your leg muscles, so you need to use more force to bend your knee, but that does not make for better leg press results, unless you had your knees replaced by frictionless artificial knee joints. Friction converts energy into heat, so it does not return the energy into the original state.

However, the spring force is not friction. Springs return the energy put into them (albeit there is a small friction loss even in the springs), so that is not comparable to the friction in your knees at all.

Quote right. Springs do return the energy put into them. So they can change an impulse (force) curve. But that curve still sums to zero, so there is no additive force. The net force is still the same.

This is what control elements do. They can limit motion, they can regulate force. They don’t multiply force.

Now some would argue that a cable is a lever. This is incorrect. A lever is a *rigid element* with unequal forces at each end rotating around a fulcrum.

[GrimSurfer]

Hi,

I am just starting this new thread so that the “fights” over physics can be discussed in a specific thread and stop derailing other threads. It is really becoming annoying…

Thank you!

Martin

Thank you for trying, but the same character has behaved the same way here as on the other thread, of course. The poster has been registered just over a month, posts over a dozen times a day: all of it unhelpful at best, mostly hostile.

If the moderators don't have a policy to address this, they need one. It's ruining the forum. For now, I suggest that nobody feed the troll, and put them under 'foe' so you don't even see their nonsense.

Hostile? I haven’t called anyone names. I haven’t called for anyone to be banned. I’ve pointed out factual errors according to the laws of physics.

I understand this is radical stuff in today’s world. But wow, man…

[Verskis]

Quote right. Springs do return the energy put into them. So they can change an impulse (force) curve. But that curve still sums to zero, so there is no additive force. The net force is still the same.

This is what control elements do. They can limit motion, they can regulate force. They don’t multiply force.

Now some would argue that a cable is a lever. This is incorrect. A lever is a *rigid element* with unequal forces at each end rotating around a fulcrum.

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.

[fisheater]

We hold these truths to be self evident. Skis can rise in the snow and cables produce tip pressure. If this doesn't jive with some rules of physics, you must be looking at the wrong rules.

Thank you Allen.
The real lesson is don’t wrestle with a pig, you’ll just end up all muddy and the pig likes it.

[GrimSurfer]

Quote right. Springs do return the energy put into them. So they can change an impulse (force) curve. But that curve still sums to zero, so there is no additive force. The net force is still the same.

This is what control elements do. They can limit motion, they can regulate force. They don’t multiply force.

Now some would argue that a cable is a lever. This is incorrect. A lever is a *rigid element* with unequal forces at each end rotating around a fulcrum.

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.

[wabene]

We hold these truths to be self evident. Skis can rise in the snow and cables produce tip pressure. If this doesn't jive with some rules of physics, you must be looking at the wrong rules.

Thank you Allen.
The real lesson is don’t wrestle with a pig, you’ll just end up all muddy and the pig likes it.

[wabene]

The real question is how can something as magical as surfing be grim? We may have an answer