Thanks for the thoughtful reply.
BB: "...Why do you think that this move would be important at the initiation, but not later in the turn? Assuming that you are trying to use the ski's sidecut to "decamber" (bend into a reverse arc) and carve a turn, why is the "initiation" any different from any other phase of the turn? ..."
To make what's going on easier to visualize, lets assume we are talking about turns that begin and end up almost perpendicular to the fall line. For such turns, during the initiation phase, any centrifugal force that you may be generating (ie, a force that's always to the outside of the turn & helps decamber the skis) is compensated or even reversed when the the everpresent force of gravity (which is pulling you in the opposite direction, downhill) is added to it. The limiting case of this would be a stationary skier, perpendicular to the fall line, standing on their DOWNHILL edges, as if frozen in a snapshot just after the point of edge change in turn initiation. In this situation, the skis will hardly decamber, if at all.
OTOH, towards the bottom of the turn, gravity and centrifugal force are both pointed in the same direction, down the hill. This combined force pushes the the center of your skis downhill while the snow is pushing the tips and tails uphill into a nice arc.
With more net force decambering your skis at the bottom of a turn than at the top of the turn, if you want to keep a constant radius throughout your turn, you have to help them out at the top with some human powered bending, but you can just let gravity and centrifugal force do the flexing at the bottom of the turn.
BTW, there is a great discussion of this in:
"The Physics of Skiing : Skiing at the Triple Point by David Lind, Scott P. Sanders" http://www.amazon.com/exec/obidos/ASIN/1563963191/qid=995950987/sr=1-1/re f=sc_b_1/104-9339717-9071949
BB: "...Just as forward pressure tightens the bend of the tip of the ski, it also REDUCES the bend of the tail--allows it to straighten out. A straight ski, of course, cannot carve a turn!..."
But ... the most important part of the ski to bend (for a good turn) is the region of highest pressure on the snow. When you are forward, this region will be just forward of your boot. Since this is where the maximum bending occurs, you will get a nice flex in the ski exactly where you need it to occur.
BB: "...So this idea of forward pressure to initiate harkens back to the "old" days when turning meant getting the "skid" started in the initiation phase of the turn, controlling the skid in the "control phase," then stopping the skid in the "completion phase." It made sense to pressure forward to initiate, and roll back, ending the turn with increased tail pressure to dig the tails in and stop the skid. Ball-arch-heel, ball-arch-heel--it was a distinct and effective rhythm! ..."
Oh, yes - I remember it well. It was essentially the only way to bring those long stiff boards around. Don't get me wrong, I was certainly not recommending that people resume pressuring their tips at all turn initiations. Rather, I was pointing out that a short period of forward pressure during the initiation phase could actually help initiate the desired carve and shorten up the overall turn radius. Unfortunately, doing this costs the skier energy, and hence should be reserved for only those situations where it is really important to bring them around fast.
I've never raced, so I don't know if it would be useful there. In my own limited experience, the situation where this seems to be the most useful is if I am slowly coming down a steep pitch, dropping just a few feet with each turn. Then, instead of crossing over perpendicular to my skis, I tend to pull my feet back a bit as I am letting myself fall down the hill, and this definitely shortens up my turns. Now, what I don't know is if the mechanism by which it is shortening my turns is tightening a carve, or I am deluding myself and simply introducing a bit of skidding like the old days.
BB: "...But today's skis allow us to carve more cleanly from start to finish, throughout the turn. To accomplish this, the ski needs to be bent into a smooth, consistent arc from tip to tail, from the start of the turn to the end. The sensation is of remaining in the neutral "sweet spot" of the ski, continuously.
Two important notes, though: First, remaining constantly in this neutral sweet spot hardly means staying in one position! On the contrary, to remain balanced over that one spot, as the skis accelerate and decelerate, turn left and right, tip up and down over bumps, and so on, requires an extremely active and accurate, continuous motion of the body fore-and-aft in relation to the feet.
Second, what I've said here in no way diminishes the importance of developing the skill of "leverage" (purposely adjusting the pressure fore-and-aft along the skis). Whether we want to control the pressure over the sweet spot for a clean, carved turn, or we want to create and control skids, leverage remains an essential skill of skiing. Sometimes we want to carve. Sometimes we want to skid. Skillful control of fore-aft pressure is one of the keys! ..."
I couldn't have said it better myself. Now ...if I could only do what I know I should do, I'd be a good skier instead of just a physicist talking skiing (grin).
[This message has been edited by PhysicsMan (edited July 24, 2001).]</FONT>