In response to Scientist Bill's comment about the lack of suitability of carving for speed control in steep / narrow places or in traffic, both milesb and CalG both made the very reasonable suggestion of employing short radius turns. Milesb added the term, "carved", and risking putting words in his mouth, probably meant, "as much carving as most recreational skiers can muster in short radius turns".
A string of linked, rapid fire short radius "carved" turns do indeed control speed better than longer radius turns. However, I would suggest that the reason they generally work so well is that for everyone except trained slalom skiers executing their craft on appropriate equipment, the average skier spends a much larger fraction of their short radius turns skarving (ie, partial skidding) than they do when executing linked longer radius carved turns.
Hence, the real reason that short radius turns are effective is pretty much what Scientist Bill suggested - ie, some skidding is usually necessary to control speed.
Another way to think about this question is to consider the average angle of a skier's descent. Lets compare two skiers going down a given run side by side. Lets assume that both are making nice round "sine wave" like turns, but that one is making several short radius turns for each longer radius turn of the other person, and that the maximum angle each skier deviates from the fall line is the same. Obviously, to do this, the "GS skier" will have to use a much wider corridor down the hill.
As both people come through the fall line, their instantaneous angle of descent equals the actual angle of the hill (say, 20 deg). As both people go through the transitions between L & R turns, their instantaneous angles of descent will (both) be some fraction of the angle of the slope, depending on how far away from the fall line they are both turning. This minimum instantaneous angle of descent might only be something of order 10 deg if they turn 45 deg away from the fall line on a 20 deg slope. Now, the important fact is that averaged over one or more complete turns, the average angles of descent of both skiers will be EXACTLY the same (somewhere around 15 deg in the above example). If only pure carving were involved, this would be equivalent to both skiers schussing straight down the same 15 deg slope, and both skiers should reach the same terminal velocity.
However, from experience, we know (as per the suggestions) that skiers making more turns will have a lower speed. The only way for this to happen is because there is excess dissipation of energy involved in the slalom path. The principal reason for this is that a larger fraction of each short radius turn (ie, the early parts) is spent in skidding for most skiers, even when they think of their technique as being pretty close to "pure" carving.
In principle, one could also control speed (on a good snow surface) by doing old school skidding, ie, "sideways drifts in the turns" and "park and ride skarves on the traverses" in the various portions of slow-mo GS-like turns, but this has numerous disadvantages including:
1) uses a wider corridor;
2) requires a larger "skarve angle" (ie, angle of attack) for a given degree of speed control, hence is much less suitable for heavy, rutty, and/or deep snow.
3) is static and doesn't foster the ability to respond to terrain / snow irregularities;
4) looks like static old straight ski technique; and,
5) you can't control "line" as easily/accurately (with a tip of the hat to Bob Barnes).
Because of these issues, I agree fully with the suggestion to employ short radius turns, even though I believe that the underlying reason that this works is usually also skidding. IMHO, effectively, one has two quite different ways to use skidding to control speed for recreational skiers - one more desirable, and the other less desirable.
Tom / PM
PS - I should also point out that in some snow conditions (ie, heavy, moist & clumpy), sideways displacement and compaction of the snow into one or two banked grooves also provides an energy loss (speed control) mechanism similar to skidding, in that (a) it is much more effective in short radius turns (because they develop larger transverse G forces), and (b) sideways motion of the snow is also involved. Again, short turns are better than long turns here as well.
(added in edit) PS#2 - This discussion of speed control is getting quite a bit away from the thread title. Perhaps we should put this in its own thread.
[ April 23, 2002, 08:24 AM: Message edited by: PhysicsMan ]