It's all relativ(ity)
Wow. Centrifugal force exists. No, it doesn't. Yes it does--you don't understand physics. No, it doesn't--you don't understand reality. It's all a matter of perspective, of your frame of reference. It's a pseudoforce--not real. It's something someone just "made up" to make the math work. No it isn't. Yes it is. It's a fake force. It only exists from the accelerated, rotating frame of reference of the skier, but we shouldn't use that reference frame. You're just stupid, and know nothing about Newton's laws. No, you're
stupid, and know nothing about Newton's laws. Oh, forget it--just shut up and ski. Don't just tell me to forget it--this is important and I like to talk about it. OK, but you're stupid. I know you are, but so am I. ....
And so it goes, around and around and around.
This had to come up again, didn't it?
Everyone, please read Tom/PhysicsMan's post in the thread that MichaelA linked to here.
Read Tom's post, #1, and ignore the rest, which sounds a lot like this thread. And read Ghost's posts here--I think he speaks truth!
Of course, I disagree with Tom and Ghost--and a few others here--on one point: while it may be "simpler" to describe and analyze skiing from a "stationary observer's reference frame" (Ghost's "fixed map," in which we define all movements and accelerations as relative to the surface of the earth, and in which centrifugal force does not apply), the undeniable fact is that we each experience
skiing from our own "accelerated frame of reference," in which centrifugal force is very, very real.
So unlike Tom, Ghost, SharpEdges, et al, I think it is often preferable, and in many ways simpler, to describe ski technique from the skier's perspective. (Tom would agree that neither perspective is more "correct" than the other. This is not a matter of "truth" or even opinion--merely one of personal preference.) When I feel a force pulling me toward the outside of my turn, it is real to me, measurable, and something I must deal with. Why should I care that, from your perspective as a "stationary" observer, you can explain these forces another (not incorrect) way?
Motion is relative. Something
must be defined as "stationary"--whether it is the sun, the surface of the earth, the deck of a cruise ship, or your seat in an airplane. Yes, you can be "motionless" while sleeping on an airplane (from your frame of reference), and at the same time be going very fast from the perspective of someone on the ground. Do you walk forward as you head to the tail of the plane--or is it an illusion, and you are "actually" moving backwards at 600 mph? Neither is more or less "real" than the other. Nor is it incorrect to say that you're "actually" going "east," as the earth rotates, from the perspective of someone on the moon. Or that you're really going some millions of miles a minute around the sun....
They're all correct. They're all "real." And yet, motions and acclerations and forces appear very different from each of these perspectives.
Again, the only frame of reference that really matters to me when I'm making a skiing turn is my own. Interestingly, from my own perspective, I'm not moving at all. Not turning, not accelerating, not going from "here to there." Barring a true out-of-body experience, from my frame of reference, I am always "here." (Just ask me--any time! How about right now...yep, I'm here
.) It's only from your
perspective that I can possibly be anywhere called "there."
Why is this important? This frame of reference actually allows me to make sense of the physicist's definition of balance as "equilibrium"--a state in which all forces acting on me add to zero--which they must, of course, since I'm not accelerating, since I am (by definition of my frame of reference) stationary, and always "here." This is the frame of reference from which we--every one of us--experience life. (Yes, the world really does
revolve around me!) This is where balance happens!
Conversely, from a "stationary observer's" frame of reference, I am never in balance--unless I'm standing still, or moving at a constant speed in a straight line. From that perspective, analyzing skiing is all about the unbalanced
motive forces pushing me around the mountain, making me speed up, slow down, and turn. Not unreal, not wrong, but not the self-centered perspective we all know and love!
Some may feel that this "fixed map" perspective is the only "real" perspective, the only one that really makes sense. But from this "stationary observer's" frame of reference, a balanced skier can't turn, and a turning skier is not balanced! That's not the way most skiers talk, is it?
From the frame of reference of the skier--and only from that frame of reference--ski technique is the constant and simple struggle to maintain balance, to keep my equilibrium. I balance the real, measurable
force I feel pulling me toward the outside of the turn (which you may call by whatever name you choose, but it actually has a long and well-established name: it's called centrifugal force) by leaning in against it. (So do you.)
Ahh....what's the point? You either understand this stuff (relativity) and nod, or you don't and it sounds ridiculous. It either makes total sense, or you think I'm nuts to suggest that you could be constantly standing still, while everything else moves about you. (Of course, I maintain that we actually think and speak this way more than most realize. Have you ever felt you were going so fast that the trees "flew by in a blur?" Not so odd, is it?)
It only matters, really, when a misunderstanding goes so far as to make us do things that aren't right--like decide not to lean into a turn because "centrifugal force doesn't exist." If that happens, it really is time to stop thinking about it and to recognize that, understand it or not, from the neck down our bodies know all about it!