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Skate technique USST two cents



 
 
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  #51  
Old January 22nd 04, 01:39 PM
Ken Roberts
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Default Skate technique USST two cents

It's great to see some serious measuring of skating physics -- thanks for
sharing it, Todd.
http://web.mit.edu/afs/athena.mit.ed...i/skating.html

Looks like they've attached a good range of sensors to the skates -- and
also captured and integrated the measurements in a helpful way. It's not
precisely about skiing, but I love inline skates too, so you guessed
right -- I'll be giving them a call. It would be fun to try to get them
working on questions that could result in more specific analysis than their
first experiment (and contrary to their humble assessment, I would be _glad_
for 0.4% accuracy in sensor readings of skating).

I liked the direction of their second experiment on vibration: It would be
great to see some new mechanical approach to making road skating over rough
surfaces more fun.

I think the _technology_ for applying this to XC skis is straightforward.
(I met some mechanical engineers at U of Utah who could have done much of it
ten years ago. Except that they were backcountry skiers -- I had no
interest in XC back then, and no idea there were big-time National-team XC
racers hanging there in Salt Lake.) With the oil money available to the
Norwegian team, I'd be surprised if they haven't already constructed a ski
with force sensors under the binding.

Real-time force-sensor-analysis to help racers find weak spots in their
stroke cycles could become the next "unfair" advantage in World Cup racing.
(Actually I'd guess the bigger paybacks are from time-series analysis of
fore-center-aft foot-pressure distributions thru the stroke cycle of
_Classic_ striding, because of the trickiness of getting both grip and glide
thru the same ski).

3) Build something at least as cool as an SRM.
4) Sell it on the Internet to everyone on RSN.


Good idea -- but I think I'll wait first to see the blockbuster sales
results from Nathan's video and book.

Ken


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  #52  
Old January 22nd 04, 03:22 PM
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Default Skate technique USST two cents

In article , Mark
Drela wrote:
In article ,

(Nathan Schultz) writes:
This fall at a lecture at the CU Engineering department, I had

two experts on physical models of skiing tell me that I push off of my
ski perpendicular to the direction of the ski's travel. I argued that
I was actually pushing more from the side and that one of the most
fundamental errors I see people make in skating is to push "backwards"
or directly perpendicular to the ski.


I know I'm going to catch flak for this,
but these "experts" were essentially correct.


That's what I was thinking too. Assuming you have perfect wax (i.e.,
no friction), the only force the snow exerts on the ski is
perpendicular to the ski (i.e., because it's on edge). Thus,
considering the person/ski as a single body, the only force on the
person/ski is perpendicular to the ski, so the only force that the
person/ski can exert on the snow is also perpendicular to the ski
(Newton's 3rd Law). Interpretation: Pushing perpendicular to
the ski can accelerate you and get you somewhere. Pushing along the
ski simply moves the ski forward or backward relative to the person
(i.e., rotation about the person/ski center of mass).

That last point is very important however. How the person pushes off
the ski (i.e., whether their foot is forward or backward) determines
their body postion and how well they will be balanced when they land
on the other ski, etc., etc. This is the sort of thing that coaches
should focus on.

Cheers,
Brian
 




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