 Poster: A snowHead
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| RachelQ wrote: |
| Wear The Fox Hat wrote: |
| women are better |
Couldn't agree |
Well, that's your opinion. 
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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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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| Spyderman wrote: |
Always cofused me the speed thing, as to why one person will be faster than another in a straight line. I can understand the ski prep bit, the need to have flat skis and fore/aft posture.
What confuses me is why men are faster in a tuck than women? Women are more aerodynamic, smaller shoulders and heads, less frontal area. Breasts that stream airflow over their knees. Smaller frame and generally wedge shaped when in a tuck. |
OK, here goes (with the usual assumptions and simplifications implicit in this kind of thing):
The force leading the skier down the hill is of course gravity, or the component of it that acts along the slope:
F(g) = m.g sin X ;
where m is the skier's mass, g the acceleration due to gravity and X the angle of the slope.
There are two main forces counteracting this: friction of the skis on the snow, and air resistance (drag).
The friction component is given by:
F(f) = mu.m.g cos X ;
where mu is the coefficient of friction between the two surfaces.
The drag component is given by:
F(d) = (C.A.D. v^2)/2 ;
where C is the drag coefficient, A is the skier's frontal area, D is the air density and v^2 is the skier's velocity, squared.
The net force down the hill is:
F = F(g) - F(f) - F(d)
So,
F = (m.g sin X) - (mu.m.g cos X) - (C.A.D.v^2)/2
Now, the net force creates the acceleration, F = m.a (Newton's 2nd law)
So,
m.a = (m.g sin X) - (mu.m.g cos X) - (C.A.D.v^2)/2
we get acceleration by dividing both sides of the equation by m:
a = (g sin X) - (mu.g cos X) - (C.A.D.v^2)/2m
Note that the skier's mass only appears in the drag term, as a denominator; the bigger the mass, the less the effect of drag and hence the greater the acceleration.
In practice, the effect will not be as big as all that, because the skier's frontal area will also, other things being equal, increase with mass. However, for people of different size but the same shape, A will increase as the square of a linear dimension (say height), whereas mass will increase as the cube of a linear dimension. So, the drag term will be somewhat smaller for the bigger/heavier skier.
Here endeth the first lesson. 
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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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I need a beer after that. 
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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laundryman, except that the drag term is not Coulomb friction but fluid resistance to do with the lubrication and adhesion of your skis with the melted snow (water) they are gliding on...
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You'll need to Register first of course.
You'll need to Register first of course.
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David Murdoch, indeed, I presented a simplification. However, the effect you mention is to do with what I called the friction term not what I called drag, ie. air resistance. I believe that my analysis is sufficient to show that a heavier skier will go faster. However, I also suspect that increased mass leading to increased pressure would also reduce the surface friction due to increased "lubrication". So, the fatties win all round.
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I can confirm that one of the small pleasures in skiing is effortlesslessly gliding upright past less lardy specimens on cat tracks while they are in a frantic tuck. Even more pleasing if they are in the "calling Mars" position.
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| fatbob wrote: |
| I can confirm that one of the small pleasures in skiing is effortlesslessly gliding upright past less lardy specimens on cat tracks while they are in a frantic tuck. Even more pleasing if they are in the "calling Mars" position. |
one of my small pleasures is tuckrolling past lardies attempting to skate along cattracks 
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You'll get to see more forums and be part of the best ski club on the net.
You'll get to see more forums and be part of the best ski club on the net.
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FAQ
) that as a lardy I'm faster and more well lubricated than the average lightweight skier. Although after a lunchtime genepi I could have told you that without the math 