 Poster: A snowHead
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| Masque wrote: |
| In our case it seems that the physicists amongst us are making the analogy that we're all just dead weights on the end of a virtual string. |
...only in respect of trying to clear up misconceptions propagated earlier in the thread - including some of your own  (e.g. posts prior to Sat 15:03, regarding variable radius turns). I would like to draw the honourable member's attention to the last para of my post of Thurs 21:06 (edited time), well before he raised that point himself, also Fri 12:49, Sat 14:37, 15:26, 17:37, Sun 0:30, where I raised precisely this point. There've just been no equations to describe the motion as they're a bit difficult to formulate!
I personally think that the amount of energy stored in the ski board is a minor perturbation on the whole motion - just see how little effort is required to put bend even a race ski into a carve position...not much is the answer (I've just tried it), and it would have precious little effect on the motion of an adult's bodyweight.
Easiski has just raised a point I was thinking about on the train this afternoon - friction. So team, your next mission  should you choose to accept it is to determine the lowest friction route down the mountain.
1) Going onto your edges puts the smallest amount of the ski onto the snow, so may seem the lowest friction solution. From what I remember from A-level though the frictional force is proprtional to the normal force, given the same coefficient of friction. The normal (downward) force is still your bodyweight, so this would keep the same frictional force if the coefficient of friction is the same. But that coefficient is probably reduced due to the lower surface area.
However, this does also put the highest pressure on the snow, and gouges the deepest tracks (which requires energy expenditure to deform the snow). Counteracting this though is that the track from the flat ski is wider, so may produce a similar amount of deformation of the snow - shallower and wider vs deeper and narrower.
The other counter-argument is that it looks to me as if downhill skiers glide out straight sections of the course on flat skis. If it were lower friction to sit on the edges wouldn't it be faster to sit on the edge (alternately left and right) and make shallow slalom turns doen the course? The fact that they don't makes me think that sitting on the edge is NOT the fastest configuration.
2) The commentator on today's Super-G made a comment about one skier getting too far forward on his skis in the glide, so slowing him down. I guess we've all felt this - you glide faster if you take the pressure off the tips of the skis and sit a bit on your tails. I wonder whether this is related to the ski planing over the snow (air trapped under the tip of the ski forming a bit of a cushion for the ski to ride on?), which could make a big difference to the frictional effect.
3) Now for friction through the air. This is probably the dominant frictional effect when the skier is travelling at a fair speed. Ski racers generally seem to have a wide stance when in a tuck. This is largely in order to maintain lateral stability. However I've noticed myself that if you narrow the stance in a flat glide so that your feet come pretty much together then you do go marginally faster. So there's then the question do two separated poles (your legs) cause more, less or the same air resistance as if they are brought together such that they form effectively a single bow-wave through the air.
I should say up front I have no further insight on any of this beyond I've written above, and my physics runs out here. Any aerodynamicists around?
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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I would say that as skis work by spreading your bodyweight over a large surface area so reducing friction, having your skis flat would have the least resistance.
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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GrahamN, Do you want to include the molecular level cavitation per m² in the base structure? (assuming correct preparation). Of course you will have to set a 'standard' snow temperature and density
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You need to Login to know who's really who.
You need to Login to know who's really who.
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| Kramer wrote: |
| I would say that as skis work by spreading your bodyweight over a large surface area so reducing friction, having your skis flat would have the least resistance. |
Yes - the goal in speed events is to spend as little time as possible on your edges. Sometimes in the technical events where racers are under the impression that they have put in a fast time and haven't, subsequent analysis of their runs show that they were too "hard on their edges", too aggressive.
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