Originally Posted by jack97
car's mass is somewhat intact and is nearly impossible to move its mass to shift its axis of rotation. The more appropriate analogy is a (steerable) sled going downward on a slope with a man/woman sitting on it, where that person can lean to either side to shift its COM and move the axis of rotation.
That's the thing jack, you are not moving the axis of rotation, you are moving some of the mass at the radius, which could effect the moment of inertia. In a typical ski turn, the axis of rotation is a point in the snow at the center of the turn radius.
The ball and string anology to moving your CoM would be changing the length of the string.
It gets more complicated though because in skiing there is no string. At each instant our skis interact with the snow and provide external forces in myriad of ways depending upon how we manipulate them, which continuously diverts the direction of travel, much like the string does to a ball on string, but we are continuously able to manipulate that interaction.
If your skis are carving the axis of rotation is pretty far away from the body. If your tails washout the axis of rotation is probably right around the tips of the skis.
If you actually start to spin out of control the axis of rotation could be within the body of the skier itself.
Perhaps this is the distinction I am trying to convey. when the axis of rotation is within the skier's CoM then an actual moment of inertia will be formed within the skier itself, which equates to the skier spinning. When the axis of rotation is outside the skier, then the skier no longer has their own moment of inertia that can perpetuate spinning, the skier becomes like a ball on the end of a string which is only rotating and turning by virtue of continuous external forces making it happen. By this analysis makes the skier just a lump of mass in a larger rotational system, that is rotating around some theoretical center point by virtue of the ski to snow external forces.
I don't know what language will explain this distinction, but there is a distinction and it matters a lot in skiing. Maintaining yourself as a ball on the end of a string rather then becoming yourself the center of the circle is the difference between turning and spinning. And since there is no string, it's manipulated in real time by our edges. Turn off the edges and a non spinning skier will continue straight. if the axis is within the skier and they are spinning then turn off the edges and the skier keeps spinning. That is the distinction. I am not sure what is the correct physics terminology at this point according to you PhDs to note this distinction.