Good discussion, everyone! It's good to see people thinking about this.
Just a couple thoughts. First, for what it's worth, Center of Mass (CM) and Center of Gravity (CG) really are the same thing, for all practical purposes.
Second, I'm intrigued by this quote from TomB:
|So in other words, the goal is to use the CM to control the pressure.
Tom--you've brought up what may be at the heart of one of the deeper-rooted philosophical differences that cause much disagreement here at EpicSki, regarding technique. Is technique an end in itself, such that our movements are measured in terms of their technical correctness against a standard of some preferred technique? Or is technique merely the tool we use to accomplish a task, and movements are measured in reference to their effectiveness toward that end?
I strongly lean toward the second answer, personally. Which means that, to me, we most definitely do not use the CM to control pressure--we use pressure to control our Center of Mass! My goal is not to pressure my skis in some particular "correct" way, at least not usually. My goals vary, but they tend to be much more task or outcome-based, rather than technique-based--to ski the path I choose, to control my speed, to get a good time in a race course, or to generate some desired sensation (ie. "fun").
Ric (VailSnoPro) has alluded to this notion as well. "Intent dictates technique" is a running theme of our EpicSki Academy events (including the Eastern Tune-Up and Front Range Workshop at Eldora). The point of pressure on one ski or the other, ultimately, is to accomplish some particular outcome--to "go that way," or to control speed, generally.
And this thought relates to my third point. Remember that "pressure" really refers to a force--as Ric says, a "push or a pull." It is, among other things, the force that pushes us around on the hill, determining our line, speeding us up, and slowing us down. If you want to change direction, you NEED a force to cause it, which generally comes in the form of pressure on the ski(s). This law has been enforced since the reign of Isaac Newton, and it's pretty hard to break it even today.
But, in response to John Mason's post above, it's important to note that "movement" (motion) does NOT require a force. This can include the "crossover" of the CM from one turn to the next. Newton had something to say about this as well--"an object in motion will remain in constant motion UNLESS acted on by an external net force." It is only a CHANGE in motion ("acceleration") that requires force. So, if the feet and the CM are going in two different directions, the crossover can occur without the need to generate any additional force to disrupt the motion of either.
There are times (many) when we do need to change motion, but there are also times when we don't. Shifts of weight (pressure) from one ski to the other do affect the motion of the center of mass, and they are one of the most important tools we have to accomplish that. Likewise, a change in the motion of the center of mass can cause a weight shift--think of a car turning left and right.
The question is--are you looking for the shift in weight as a technical end in itself, or are you more concerned with the result, letting the desired outcome ("intent") dictate the technique? The choice is yours!