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# "Less/More Energy From Turn"?

Hi All. I've been reading through the Vail Resorts Alpine Teaching Handbook (2001) and came across a statement I don't understand.

The following is an excerpt from this handbook. The statement in question is highlighted in red. (If any of you have this book, this section can be found on pages 114-116.)

****************************
QUOTE
Objective: Ski braking and gliding short turns on steeps.

Keys To Learning:

-Controlling speed means increasing, decreasing, or maintaining speed at will. Use all your resources:
-Point the skis at different angles across the gravity line.
-Hit your edges at the end of the turn or skid through the end of the turn.
-Round out the tops of the turns.
-Round out the ends of the turns: Play with fish hooks, J-turns, speed checks, etc.
-Manage the energy you feel from the ski/snow interaction, and use it for the next turn. The greater the edge angles, the more energy you feel: Less energy from turn - extend the legs during the Transition to begin initiation. More energy - relax the legs during the Transition to begin initiation, absorbing the energy and then directing it into the next turn.
END QUOTE
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To me, an extension (longer and stronger leg) move will tend to increase the rebound from the ski and a relaxing move (shorter and softer leg) will decrease the rebound, which seems to be the opposite of what's written above.

Maybe by "extension", the writer means something like start your next turn sooner by releasing the edges and moving the cm into the new turn sooner? So extension would really describe the lengthening of the leg to allow the cm to move, while "relaxing" would really mean holding the cm back in the old turn longer and allowing more forces to build?

What am I missing here? These apparent contradictions really get to me. As always, would greatly appreciate any thoughts on how to read/understand this.

Thanks.
If there is-Less energy from turn - extend the legs during the Transition to begin initiation. If there is-More energy - relax the legs during the Transition to begin initiation, absorbing the energy and then directing it into the next turn.
END QUOTE
It is confusing, isn't it? My guess is that what they are referring to is that if you extend your legs, or just keep them "stiff," during the transition, you will experience a strong unweighting action, similar to skiing up and leaping off a bump. If you RETRACT (flex) your legs through the transition, you can absorb much of this energy, and you can then engage your new edges a little earlier by extending into the the turn, AFTER the transition.

This seems to be pretty much what you were saying, DM, when you noted that an "extension move...will tend to increase the rebound...."

I suspect that the "less energy from the turn--extend the legs during the transition to begin initiation..." statement simply refers to the fact that lower speeds reduce the "virtual bump" effect, and that, if you want to redirect your skis prior to reengaging the edges (and thus scrub off some speed), some extension to unweight can be helpful.

The higher the speed, and the tighter the turn radius, the more you will tend to get launched after releasing your edges if you don't flex to absorb the force of the "virtual bump."

This interpretation seems consistent with Miles's take on the passage in question too.

Best regards,
Bob Barnes
Thanks Miles and Bob, that really helped! As usual, I owe you one.
Perhaps someone would care to define what is meant by the expression "energy in the turn." What does it mean to absorb energy, direct energy, or transfer energy?
What kind of energy is involved?

a) kinetic
b) gravitational
c) spring
d) electrical
e) magnetic
f) mechanical
g) heat
h) nuclear
i) light
j) chemical
I would consider it to be the energy stored in reverse cambered skis and in the body's tensioned muscles.

In carved turns there is more stored enery in both the skis and in the muscles resisting the strong deflection by the arcing skis.
(skidded turns create less stored energy and fewer options for it).

But three singular examples of options for stored energy:

It can be "absorbed" by actively retracting and then passively extending the legs so as to minimise the imact of the rebound on the skis or the body.

It can be "directed" by retracting the legs into the transition while guiding the rebound effect of the skis so they quickly cross under and then actively extending the legs as the ski move away from the body's path following the transition.

It can be "transfered" to the body by strongly extending the legs to project the body away from the slope so as to create unweighting.

Skiing takes place in an complex and changing environment of energy composed of forces we control by the shape of our arc's and their speed and gravity which we can but adapt to our purposes.

Far more fun than any indoor physicslab...........

### A++++

I agree with Bud. You should write a book.
Quote:
 Originally Posted by nolo What kind of energy is involved? a) kinetic - Sure b) gravitational - Sure c) spring - Sure d) electrical - Sure e) magnetic - I wouldn't preclude it f) mechanical - Sure g) heat - Sure h) nuclear - Sure i) light - Sure j) chemical - Sure
:
Quote:
 Originally Posted by nolo I agree with Bud. You should write a book.
Thanks, but it might only be 1 page:

"Roll'em, Bend'em, Repeat, and Grin when it feels good!
:
Page 2: When encountering a sudden open water stream at a rate of speed that precludes stopping, jump high!

Best regards,
Bob
Nolo,

Based on Arc's list I'd say kinetic and mechanical energy.

Think about the camber in a ski. If you set a ski on top of blocks at either end, then bend the ski down in the middle, you will be storing energy into the ski. If you place an object on top of the bent ski and let it go, the ski will release energy into the object and levitate it (i.e. boing).

When you flex a ski going in to one turn, coming out of the turn you can either let the ski unflex and bounce you into the next turn if you keep your body stiff (similar to what happens to the levitated object example above), or you can flex your body to absorb the ski rebound and not get bounced by the ski.
Where's Physicsman when we need him? I'll agree with Arc that all the other kinds of energy could be occurring here. I'll add that if there's electrical energy and movement, then there is also magnetic energy. I think it was K2, that put a system in their skis to convert vibration into electricity to light a little bulb on their ski. And in the absorb example above, your body and the ski are acting like springs, but at least the springs in your binding will count. I suppose either natural background radiation or the nuclear force in an atom could count as nuclear energy being involved. There's friction between the ski and the snow. Finally, although gravitional energy is the engine behind the whole skiing experience, for this exercise we are not managing that energy. So I'd argue that all the other forms of energy are neglible to the discussion at hand.

Hey Physicsman -> what is the relationship between force and energy?
I hope Physicsman will weigh in!
OK, while ya'll were gettin' energized on this subject, I was out at the movies (a consolation of living in a midwestern city - lot's of theatres). And it turns out that what I saw has some amazing relevance to Nolo's questions about energy.

The film is called "What The Bleep Do We Know?" Here's a little quote from the Seattle Post Intelligencer's review, to give you a taste:

The fascinating, Northwest-made documentary, "What the #\$*! Do We Know?!," explores this phenomenon as well as anything I've ever seen, and makes a strong case that quantum physics will impact our future in ways that are now almost unimaginable.

The film, which was shot in Portland by a trio of filmmakers (two of them from Yelm), tells a light-hearted fictional story and creates a maze of imaginative animation and special effects to illustrate how the heavier thoughts of the science apply to the everyday world.
...

Thus, quantum physics vindicates meditation and even prayer. Indeed, in one experiment in which a large group of meditators tried to see if they could reduce the soaring violent crime rate of Washington, D.C., by 25 percent, they reportedly did exactly that.

In another experiment, a Japanese physicist made a photographic record that proved, to his satisfaction at least, that the blessing of a Zen Buddhist priest changed the molecular structure of the holy water he was blessing.

And, gang, one guess as to what those "blessed" water molecules looked like - snowflakes, of course!!!!

Have any of you seen the movie by any chance? If this sort of thing intrigues you, track down a theatre near you where you can see it: http://movies.yahoo.com/shop?d=hv&cf=info&id=1808578904

I'm still not sure what the sentence in question says----I would also question the previous sentence,

"The greater the edge angles, the more energy you feel".

Holding is holding at any edge angle. It's the reverse camber that creates the energy---as long as there is some resistance of some sort, as "therusty" explained. Put youself between two moguls with no edge angle and give a good bounce and I'll bet you feel considerable energy with no edge angle at all !

And because you asked DM---bet it's a mis-print.
Re the energy:

I heard an explanation that made sense to me. The energy is based on pressure.

-Gravity exerts a fairly constant downward force on our skis.

-Centrifical force (or inertia if you don`t believe in centrifical force, which some don`t).
lines up in the same direction as gravity in the last phase of the turn, so now both forces exert this downward pressure on the skis.

-BUT the snow compresses a bit and then resists these downward forces, pushing back UP against the bases of the skis. So you have both downward forces and an upward force, which in combination, create considerable pressure on the bottom of the skis.

-When the edges are released, the skis no longer "hold" against the snow and the pressure is released quite quickly. This is is what you feel.

The springing back of the skis to a less reversed cambered shape may add to this pressure release, but in this explanation it plays only a minor part.

It makes sense to me.

cdnguy
"The greater the edge angles, the more energy you feel". Hmmm. Lots of room for exceptions here. Let's start with the general case. And let's assume a totally banked skier. In order to stay balanced (key word here) on edge, one would need some speed. The greater the speed, the greater the edge angle possible. The greater the speed, the more kinetic energy one has to feel.

However, when one is angulated and balanced on edge, one has the ability to adjust edge angle and not fall over. If one were to increase edge angle from a merely balanced position, one would tighten the radius of one's turn and feel more energy from that.

Also, as one goes to higher edge angles, the ski becomes easier to bend and one gets more camber energy.

So we can see where the quote comes from, even though there are lots of exceptions.
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