Another good shot:
NoCleverName wrote:Fran?ois wrote:On a flat slope all of gravity is straight into the snow, and it's easy to turn a tight turn. On a 90 degree cliff face NONE of gravity is pushing into the hill and you cant carve anything
Au contraire, mon ami. Yes, gravity plays a part, but you can't count out the component vectors of the centripedal force that is causing the turn (i.e. the continuous inward-pointing force that causes you to follow a curved course). The centripidal vector is right up from the ski top thru your leg straight thru the Cg. The two components of the vector are (1) in shear to the surface and (2) normal to the surface. Shear force tries to break away while normal force presses you deeper into the surface. So all those g's you feel in the turn go towards (a) trying to breakaway and (b) digging deeper into the snow. Add in the gravity vector (itself having shear and normal components) and you get the final vector diagram.
At slope angles less than 45 deg the components of the gravity vector predominate "normal" to the surface (helping edge grip), but beyond 45 deg the shear vector get bigger than the normal vector and gravity is working against edge grip. In any event, it's the total shear strength of the surface that's going to determine whether or not you stay upright. But again, you've got to combine all the forces, not just gravity
Said in a simpler way: if "flatter" surfaces allowed "tighter" turns, auto race tracks wouldn't have banked corners.
(As a review, a vector is an arrow whose direction points along a force and whose length is proportional to the strength of that force. The components of a vector may be considered to be the two vectors that form the sides of the rectangle that has the original vector as its diagonal. If the rectangle is drawn so as one of its sides "lies on" a surface, then the "component vectors" measure the individual forces parallel and normal to that surface (this is called a "vector diagram"). Don't bother to bring up vector diagrams on the E..c forum, they'd rather believe in magic, instead).
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Fran?ois wrote:NoCleverName wrote:Fran?ois wrote: vertical component of that centrepedal force is equal to the gravity force
NoCleverName wrote: Nah, a centripedal force on a flat surface doesn't have a vertical component, it's all inward pointing towards the center of the turning circle
Enough of this polluting this thread! But it's been fun.
When I was director of training at Winter Park, I had a whole fleet of PSIA trainers and examiners on my staff. They were constantly skidding and pushing the skis in the upper part of the turn. I told them to stop pushing the feet out to the side. They told me that they were instructed to get angles by getting the feet out away from the body as far as they could. I responded by telling them that you don?t get angles by pushing the feet away, you develop angles by tipping the feet and dropping the body into the arc. This was a huge deal. After some further coaching they began to understand and realized PSIA had been telling them everything backwards.
Harald wrote:Just wanted to clarify this point. When you can't see the forest for the trees you take after and talk about the nuances, not the glaring problems.
This example tells the story: Part of a long post I put up earlier.When I was director of training at Winter Park, I had a whole fleet of PSIA trainers and examiners on my staff. They were constantly skidding and pushing the skis in the upper part of the turn. I told them to stop pushing the feet out to the side. They told me that they were instructed to get angles by getting the feet out away from the body as far as they could. I responded by telling them that you don?t get angles by pushing the feet away, you develop angles by tipping the feet and dropping the body into the arc. This was a huge deal. After some further coaching they began to understand and realized PSIA had been telling them everything backwards.
This is a major technical misunderstanding within PSIA. Do they repair or fix the damage? No they talk about whether or not we use steering in PMTS. This is again, I keep using this when referring to PSIA ?Ridicules?. Whether or not we use steering isn?t the issue, the issue is, if you are teaching it and it?s screwing up your own best skiers and teachers, why don?t you address it? They are a baffling organization and I know they have a back door escape just as esoteric in definition as the rest of their explanations of technique they don?t use. They can't even tell you what they do use and its affects.
By the way Level 6 in the PSIA progresion still has a wedge. And you have to practice it if you take a lesson from level 2 through 6 to perfect it before you can move on to parallel. We've come a long way baby.
Fran?ois wrote:NoCleverName wrote:And I will stop polluting the thread now too.
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