Where Instructors go Wrong

[Mike King]

And you can alter the lever arm through which it is applied.

Exactly!

 

[Mike King]

Well, that's because centrifugal force doesn't exist.

Depends on your perspective.







Or frame of reference...

 

[mister moose]

It's an 'apparent' force. If you're a sailor, you'll know this as true wind direction vs. apparent wind.

No, this is apparently going to add to someone's confusion. In sailing, apparent wind is what is coming over the deck, it is a vector sum, the vector addition of the boat's velocity and the wind velocity. Both are readily observable. Centrifugal force is an imaginary force that is only viewed in a rotating reference frame, which I'm pretty sure is what @Mike King meant when he said "It depends on your perspective. " Centrifugal force is not readily observable outside the specialized rotating reference frame. You may "see it" but your friends watching you do not.

Two quick examples:
1) Swing a potato on a string. There is no outward force, the only force applied is you pulling inward on the string to keep the potato orbiting.
2) Let go of the string. If Centrifugal force was present, the potato would fly out away from you, radially, in the direction the string was pointing at the instant you let go. But it doesn't go that way. It goes tangentially, 90 degrees to the string. Which is the direction the potato was going at that instant you let go.

"Centrifugal force" is the feeling of your direction being changed in a rotary motion. You are feeling the resistance of your own inertia. Inertia: not a force.

Bonus round: Coriolis force.

But all of this this is why I said don't make it hard. Focus on what we do in skiing that works. I think comparisons to leaning a bicycle or a race track banked turn is something readily understood and doesn't devolve into a chalkboard discussion filled with lines, arrows, and Greek letters.

 

[mdf]

Major sidetrack, but of course centrifugal force exists. Just like gravity, another "apparent" force that only appears in non-inertial reference frames.

 

[François Pugh]

Gravity is an apparent force, because, apparently I'm being pulled towards the centre of the Earth. Electricity and Magnitism are two other apparent forces, weak and strong nuclear forces, and any other forces you may care to point out. Apparently, Coriolis force exists too. What makes these forces real? Their observed effects, which are necessarily described in a particular reference system. Denying one based on the observations from a point of view of a different reference system than the reference system for which the force is real is either lack of knowledge and understanding, or deliberate obfuscation.

People who argue that such apparent forces do not exist reveal their inability to switch between reference systems. Just like people who argue that the sun (and other stars) comes up in the east and settles in the west versus the earth rotates on it's axis. Both points of view are valid, but one makes the math easier.

 

[mister moose]

People who argue that such apparent forces do not exist reveal their inability to switch between reference systems. Just like people who argue that the sun (and other stars) comes up in the east and settles in the west versus the earth rotates on it's axis. Both points of view are valid, but one makes the math easier.

Yes. Keep in mind I did not say it didn't exist, I said it was imaginary, ie to suit the reference frame. It exists as an observable force in that reference frame. But it does not exist outside of that reference frame.

You hint at an elevated understanding of generalized coordinates. I like to say you can stick the thumbtack (the origin) at a location and description of your choosing. Most people don't get that.

Gravity is an apparent force, because, apparently I'm being pulled towards the centre of the Earth. Electricity and Magnitism are two other apparent forces, weak and strong nuclear forces, and any other forces you may care to point out. Apparently, Coriolis force exists too. What makes these forces real? Their observed effects, which are necessarily described in a particular reference system. Denying one based on the observations from a point of view of a different reference system than the reference system for which the force is real is either lack of knowledge and understanding, or deliberate obfuscation.

Except gravity and magnetism et al transcend your choice of reference frame, centrifugal force does not. That's the difference.

 

[mdf]

Actually, the separation of the Maxwell tensor into magnetism and electricity depends on your reference frame.

 

[François Pugh]

As the Beatles (not the first to do so) said, "Nothing is real." It's all imaginary, a model to explain observations and make predictions, but that doesn't matter, as long as it works. When it doesn't work well enough for our purposes, we will invent a new force or matter or something else that makes it work.

 

[Chris V.]

How about...we just point out to students that they'll go straight if they don't resist that momentum, and if they resist it correctly their skis WANT to turn?

 

[fatbob]

Where instructors go wrong? Arguing about frames of reference and relativity. 90% of your clientele have buggered off to the bar by then......

 

[François Pugh]

Where instructors go wrong? Arguing about frames of reference and relativity. 90% of your clientele have buggered off to the bar by then......

Lets not confuse what's discussed on an internet forum at the end of a long off-season with what's discussed with ski instructor's students on the hill!

 

[Mike King]

Where instructors go wrong? Arguing about frames of reference and relativity. 90% of your clientele have buggered off to the bar by then......

You are wrong. 99.995%.

 

[mdf]

You are wrong. 99.995%.

Based on the posters in this thread, I think 90% is closer to the correct number.

I first time I ever sailed, my friend explained how the force on the keel and the force on the wind form a resultant that lets you go upwind. I thought that was very cool. So I took the Sailfish out, decided it was time to come about, jibed and promptly capsized.

 

[peterm]

I've taken a ton of lessons, both private and group, at US resorts over the past seven years and thus feel somewhat qualified to answer the OP's question/assertion of "Where instructors go wrong".

I'll start by saying that more often than not I'll enjoy the lesson and get something out of it, or at least feel like I did. And I don't really think the amount of theory is much of an issue. Maybe that's because I'm pretty good at absorbing information and either filing it away for later, or just tuning out it if it sounds like too much detail .

Here's my list of things that instructors could do better:

- Take a critical look at the student's equipment. I skied in boots that were too big and too soft for a few seasons. Not a single instructor mentioned this. My skis also weren't ideal, again never mentioned. And lastly, my poles were too long. Well one intructor did say my poles looked a bit short, so I guess that's something

- Not enough use of video. Out of 30+ lessons I recall exactly one where video was used. Not good enough.

- Lack of race style training. I have no interest in being a racer, but I know the clock doesn't lie. What better way to improve fundamental technique than to take multiple runs through a short race course, it only needs to be a half dozen easy turns, trying to improve ones time? Mixing this with a bunch of coaching and video analysis would cut through a lot of the BS and get to the heart of what needs to be improved with your skiing.

- Excessive possivity. Sometimes I know I'm doing some dumb sh*t with my skiing, but the instructor is still a box of birds. I guess that's better than the instructor getting frustrated, but it can make it hard to get accurate feedback. I wonder if tipping culture is part of it? I've actually had the idea of giving my tip at the start of the lesson so we can dispense with the niceties! I really need to try that next time.

Some of the problems go away if you're able to take several lessons with the same instructor. Once a bit of a relationship forms everything tends to work better.

 

[Chris V.]

Although...one has to be careful about telling a seven day a year skier that he needs to spend $1600 and three days of his life getting new gear. Similar considerations surround the positivity thing. Walking the tightrope!

 

[mdf]

Although...one has to be careful about telling a seven day a year skier that he needs to spend $1600 and three days of his life getting new gear. Similar considerations surround the positivity thing. Walking the tightrope!

The dynamics can be very different in a multi-day lesson. That's what is so great about them.

 

[Philpug]

When Instructors go Wong

 

[Mike King]

Based on the posters in this thread, I think 90% is closer to the correct number.

I first time I ever sailed, my friend explained how the force on the keel and the force on the wind form a resultant that lets you go upwind. I thought that was very cool. So I took the Sailfish out, decided it was time to come about, jibed and promptly capsized.

Clearly, you are part of the .005%...

 

[oldschoolskier]

Instructors go wrong when they teach only the way they know how to teach verses teaching the way the student learns. Granted the methods you mention are ways to teach but you are also assuming that is the way every student learns which will fail in many cases. There are students that are very analytical and if you teach with Bruce Lee's method, it will fall on deaf ears.

There are many ways to learn, therefore there needs to be many ways to teach.

Just stumbled onto this thread @Philpug you nailed it. Any instructor, coach, teacher, mentor fails when they fail to adjust to the student. Those that are most flexible are remembered to be inspirational and have the greatest impact. Those that can do this and have exceptional skills to match are simply the best.

Every now and then I have to remind myself to be flexible (and I think we all do) to prevent being caught in a rut.

 

[James]

And lastly, my poles were too long.

Hah. The resistance to pole length is unbelievable. Everyone apparently learns at birth about the right angle arm standing upright.
Go outside this length thinking and most are convinced you’re insane.

It’s worse for kids. I’ve had kids show up with poles at least 10 inches too long. Usually I’ll just get a “meh”. Even kids with adjustable poles don’t want them adjusted because a parent adjusted them and that’s the right way.

Seems kids get vaccinated on pole length early and are incredibly resistant to change.