GrimSurfer wrote: ↑Mon Jan 02, 2023 9:57 am
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.
