Physics is at the heart of many sports and recreational activities and it is puzzling that so much of the passion and advice expressed in this forum rarely gives even lip service to the fundamental forces that cause us to formulate our skiing movements.
So I begin with a thread on gravitational and centripetal force. Comments are appreciated.
The second we begin moving and put a (shaped) ski on edge we are creating an arc (circular path), and so begins dynamic changes in our body's relationship with gravitational force to deal with the onset of centripetal force.
Now someone may pull a Hillary Clinton here and say: "WHAT DIFFERENCE DOES IT MAKE!" But it does and here's why.
Gravitational force is our weight (mass*force of gravity). This force pulls us toward the center of the earth. When we are standing or sliding on our skis, this force is pulling your feet down and away from the BOTTOM of the ski. Why? Because your mass is aligned vertically.
Centripetal force is a force which keeps a body moving with a uniform speed along a circular path (arc) and (believe it or not) pushes from the edge of the ski up the radius of the arc and through your body towards the center (furthest point from the ski along the radius).
With gravitational force, we deal with an axis which is ALLWAYS constant and vertical. From the moment we learned to walk our ability to balance has been relatively easy because we stand erect and our mass is skeletally aligned with gravity.
With centripetal force things get more complicated and precise. Upon entering a turn, we deal with a RADIUS (but you can think of it as a tilt-able axis if you like) which is always subject to change based on the angles of your skis, velocity and mass.
In the context of centripetal force we are balancing AGAINST the skis not on them. (Aside: for all those who use the words "Weighting your ski"...STOP IT!!!)
NOW HERE'S THE NUGGET...
As a turn is enacted, your mass is no longer aligned VERTICAL to gravity. Instead, it is parsed by your body hinges and "strung out" along a non-vertical radius. We therefore we need to create angles to reach an alignment that provides optimum balance, edging and pressure throughout ALL phases of the turn. As instructors, we really need to understand these physics fundamentals because this is where the real teaching happens.
Hopefully you have notice that I have not provided any instructional or movement tips here because that was not my intent. It is simply to make some room for the physics that drive the methods for this great sport.
As a shout out, please take a look at HeluvaSkier’s frame by frame video posted here http://www.youtube.com/watch?v=RR8yG5WjkBA&list=UUixIAgNEt4KwY1YHrin7l6Q
You can see the centripetal radius in action. Depict a straight line (radius) from his outside foot up through the inside shoulder and watch how he moves, creating a “flowing” tilt of the radius from side to side. Notice how the radius (axis) becomes vertical and gravitational as he passes through the neutral zone.
Thank you for your time.