Everything the Instructors Never Told You About Mogul Skiing

[BeanoNYC]

Well deserved bump here.

I finally got to re-reading this book. It's a great read and I'm looking forward to putting Dan's theories into practice...especially the absorption and extension, which I struggle with. I still can't figure out, however, where the ideal place to turn and pole on a bump is. I realize it's a silly question, but why practice my walking skills when my crawling skills still suck.

 

[bvibert]

I need to find my copy for a refresher before the season starts...

My wife found my copy for me yesterday when she was trying to clean up some of my crap. I'm pumped, just in time for the new bumps at Sundown.

 

[Greg]

I'm pumped, just in time for the new bumps at Sundown.

Indeed. Time for a re-read, methinks...

 

[bvibert]

Indeed. Time for a re-read, methinks...

Are you trying to say I suck, and could use all the help I can get??




...Cause I already know, thanks for that though...

 

[Greg]

Are you trying to say I suck, and could use all the help I can get??




...Cause I already know, thanks for that though...

I meant for me... Get over the martyr routine. You know you're already full of mad steeze... :roll:

 

[jack97]

Here's something to ponder. Although I agree that thinking too much on the slopes can be hazardous to your health, sometimes its good to keep some things in the back of your mind.

I think one of many advices out there is that absorbtion and extension controlls speed by relying on friction using snow contact or using the uphill side to slow you down. Though its good advice, it's part of the story according to the physics. I mentioned a book, Physic of Skiing by Lind over here and at Epic. It can be a tough and boring read, so I just condensed the essentials on the pic below. Basically by moving your center of mass (CM) away from the rotation centers, you will decrease speed. Using Lind's example, say the rotational center is 10 to 15 feet away from the CM, then the reduction in speed is significant when you move the CM by a couple of feet. Note how each absorbtion and extension moves the CM away from the centers. I trust the physics, but I don't trust my body to execute this yet.

see the rotational centers on photo montage below.

 

[Marc]

Here's something to ponder. Although I agree that thinking too much on the slopes can be hazardous to your health, sometimes its good to keep some things in the back of your mind.

I think one of many advices out there is that absorbtion and extension controlls speed by relying on friction using snow contact or using the uphill side to slow you down. Though its good advice, it's part of the story according to the physics. I mentioned a book, Physic of Skiing by Lind over here and at Epic. It can be a tough and boring read, so I just condensed the essentials on the pic below. Basically by moving your center of mass (CM) away from the rotation centers, you will decrease speed. Using Lind's example, say the rotational center is 10 to 15 feet away from the CM, then the reduction in speed is significant when you move the CM by a couple of feet. Note how each absorbtion and extension moves the CM away from the centers. I trust the physics, but I don't trust my body to execute this yet.

see the rotational centers on photo montage below.

Physics is never boring!

That's very cool. Very simplified, but I guess you have to do that when you deal with bio-kinetics.

 

[riverc0il]

meh, physics ain't got nothing on having an "ah huh!" moment when you "know" the physics behind the motion without actually "knowing" the physics. there are all different types of learners, and if you are the type of learner that can learn how to ski moguls by analyzing the physics, more power to you cause that is cool. doesn't work for me though.

i think the physics becomes pretty evident when you are doing something right vs. wrong... you know you are either fighting physics if you are doing it wrong or working with physics if things start to click. i often analyze my skiing from a physics perspective, but only after i have gotten it down and am looking to tweak things. i don't think physics is going to help much if you don't even have the fundamentals down.

fwiw, that montage shows the skier in the moguls in not the best form. holy back seat taking a dump in between A and B! absorption does not mean sit down and take a dump. the forward lean (chest down to the knees!) is also not so hot either. this skier obviously needs to take a physics class from_the_NEK took a video of me skiing some bumps at jay last month, i'll post it in a few...

 

[Greg]

Here's something to ponder. Although I agree that thinking too much on the slopes can be hazardous to your health, sometimes its good to keep some things in the back of your mind.

I think one of many advices out there is that absorbtion and extension controlls speed by relying on friction using snow contact or using the uphill side to slow you down. Though its good advice, it's part of the story according to the physics. I mentioned a book, Physic of Skiing by Lind over here and at Epic. It can be a tough and boring read, so I just condensed the essentials on the pic below. Basically by moving your center of mass (CM) away from the rotation centers, you will decrease speed. Using Lind's example, say the rotational center is 10 to 15 feet away from the CM, then the reduction in speed is significant when you move the CM by a couple of feet. Note how each absorbtion and extension moves the CM away from the centers. I trust the physics, but I don't trust my body to execute this yet.

Physics is never boring!

That's very cool. Very simplified, but I guess you have to do that when you deal with bio-kinetics.

You guys are disturbingly smarter than I am. I can analyze technique until I'm blue in the face; most of it goes right out the window when I'm out on the hill. That's the beauty of Dan's book. Easy read and simple drills that lead to the "Aha" moments Steve is talking about. Once these techniques "click", it's all about repition in an effort to acheive consistency.

 

[andyzee]

So anyone hear from Dan lately, great guy!

 

[riverc0il]

from_the_NEK took a video of me skiing some bumps at jay last month, i'll post it in a few...

not as much mogul footage on here as i thought and the bumps are soft, small, and powdery, but what the hay... jay peak 12/30/06.

 

[Greg]

not as much mogul footage on here as i thought and the bumps are soft, small, and powdery, but what the hay... jay peak 12/30/06.

Codec error... :-?

 

[jack97]

That's the beauty of Dan's book. Easy read and simple drills that lead to the "Aha" moments Steve is talking about. Once these techniques "click", it's all about repition in an effort to acheive consistency.

Woa guys, I 'm not trying to take away from Dan's book. It's a great "how to" book, one of the best imo. I just want to point out why the absorbtion and extension works, the other factors involved. For me, I need to know why before I dive into a situation or an approach. Others don't need to, cool with me.

 

[jack97]

fwiw, that montage shows the skier in the moguls in not the best form. holy back seat taking a dump in between A and B! absorption does not mean sit down and take a dump. the forward lean (chest down to the knees!) is also not so hot either. this skier obviously needs to take a physics class from_the_NEK took a video of me skiing some bumps at jay last month, i'll post it in a few...

Actually compare this to the montages from Skiers Edge by Lemaster, he looks reasonable. The wc bumpers LeMaster shot all took deep squats, almost sitting back. They recover by bringing his foot underneath for good aft/fore balance, some calls this foot containment others calls this backpedaling. Since a deeper absortion is proportional to lower speed, it makes sense.

 

[riverc0il]

Actually compare this to the montages from Skiers Edge by Lemaster, he looks reasonable. The wc bumpers LeMaster shot all took deep squats, almost sitting back. They recover by bringing his foot underneath for good aft/fore balance, some calls this foot containment others calls this backpedaling. Since a deeper absortion is proportional to lower speed, it makes sense.

why would a WC bumper do something that causes lower speed? :???: for a non-WC bumper such as a recreational skier, the trade off in balance and position seems to great a compromise for lower speeds. contact with the snow including a high degree of rotary motion and twisting from the waist would be a preferable method used to slow down speeds through increased snow contact. you could never convince me that that much back seat and waist bend is a good thing in any skiing circumstance regardless of lie of the slope.

 

[jack97]

That's very cool. Very simplified, but I guess you have to do that when you deal with bio-kinetics.

Glad you liked it, Lind made some simplified assumptions, like neglecting the force normal to the surface. It makes the derivation easy and provides less algebraic clutter. As is negligible at higher speeds. I think the point he was trying to show was that you can change your rotational speed by moving the center of mass. He shows this by using a "pumping to increase speed" example; increasing rotational speed by moving the CM closer to the rotational center. Racers leverage this idea and thats why they can increase speed in their turns. I just took Linds approach and turn it upside down to show how you can decrease speed.

 

[riverc0il]

Codec error... :-?

heh! this is exactly what i was worried about when i decided to use the xvid codec. this should fix it:
http://www.xvid.org/Downloads.15.0.html

 

[awf170]

heh! this is exactly what i was worried about when i decided to use the xvid codec. this should fix it:
http://www.xvid.org/Downloads.15.0.html

I have xvid and still doesn't work. :???:

 

[jack97]

why would a WC bumper do something that causes lower speed? :???:

They may lower their speed to setup for the aerial tricks. Usually, they have to do two, once they get done with it, they fly, hardly use any A&E.

Don't take the WC bumper montage as literal for recreational use, I'm just pointing out how important A&E is to them and the physics behind it. BTW, I saw the freestyle coach at Okemo, lots A&E. Whether a recreational skiers wants to do that way, it's up to them.

 

[Marc]

You guys are disturbingly smarter than I am. I can analyze technique until I'm blue in the face; most of it goes right out the window when I'm out on the hill. That's the beauty of Dan's book. Easy read and simple drills that lead to the "Aha" moments Steve is talking about. Once these techniques "click", it's all about repition in an effort to acheive consistency.

It's all a conservation thing, Greg. In this simplified case, if the two centers of rotation are about the same average distance from the skier, than, neglecting ski friction and wind resistance, angular momentum can be conservied.

Think about spinning around in an office chair. You put your arm out and your rotation rate slows down, you pull your arm in and your rotation rate speeds up. Why? Because the angular momentum, which is the linear momentum by the radius of the CM of mass, stays the same unless acted on by outside torque. So if the radius at which the center of mass stays the increases, to conserve angular momentum, the linear momentum must decrease, which means linear velocity decreases, which means angular velocity (rotational rate) decreases. It actually depends directly on your moment of inertia, which can be subsituted, more or lass with the center of mass just for an easier visualization here.

The approximation is a rough one for bump skiing, but it's there. And it's neat to know why. Points A and B in that photo represent the center of the rotation (the shaft of the office chair). When you absorb going into a bump, you are moving your center of mass away from A, same as when you put your arms out in the chair. To conserve your angular momentum, your linear and angular velocity decrease.

Make sense?

:dunce: