Poster: A snowHead
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According to this report a skier can pull up to 139 G's. Now, a fighter pilot can, I believe, pull about 9G’s or so before he/she starts passing out, and has the assistance of a G-suit to stop him/her from dropping off behind the wheel.
So, why does Herman Maier et al not pass out on the Men's Downhill?!
Without resorting to the instantaneous stopping described in the above report-sounds painful- how many G's can I realistically pull on a fast carve, and should I contemplate getting a G-suit from Snow and Rock?
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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The centripetal force necessary to get round a curve is given by F = mv²/r where m is mass, v is velocity and r the radius of curvature. To get the result in terms of "g's" we need to divide by the natural weight of the object which is given by W = mg, where g is the acceleration due to gravity (9.8 m/s²). Therefore the centripetal force measured in g is given by v²/rg. According to this article, a world cup GS skier will make turns of about 25m radius at about 20 m/s (about 45mph). Plugging these values into the formula gives a force of about 1.6 g. A greater force would be experienced speeding through a compession. Assuming 30 m/s in a tuck and the same curvature, the centripetal force would be about 3.7 g. I'm not sure anyone could emerge upright out of that.
I think forces of 139 g relate to skiing into trees, or the forces on parts of the body when one bit stops suddenly and the rest carries on. I'd say it was definitely in injury or death territory!
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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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139 g is definate injury or death don't forget that at 10 g your body feels like it weighs 10 times its actual weight so a typical 70kg skier might feel like he weighed 700 kg or to put it another way he'd collapse under his own weight, pilots cope because they are sitting in a cockpit and only have to make small movements which I've been told are very difficult at high G, 139 g would make that skier feel like he weighed 9,730 kg, his legs would colapse a lot earlier than that !
I'd guess that at most a skier is unlikely to pull more than 2 or at most 3 G probably at the bottom of a steep dip as they start to go up the other side, even on the fastest stretches of the Lauberhor race last weekend the skiers were only approaching 100 mph assuming a maximum of 50m/s (unlikely but just about possible) and a tight radius at the bottom of a dip of say 10M (much tighter than a normal turn) we get a result of about 2.5 G using the above formula
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O-level (or GCSE for the less crumbly) Physics lesson for the day - part 2.
What speed would you have to drive a car into a brick wall to pull 139G? Assume the bonnet of the car crumples in about 1m. The equation governing this is v*v = 2as (a = acceleration, v = initial velocity, s=distance over which the acceleration applies). 1G = 9.81m/s/s, so v = sqrt( 2 * 139 * 9.81 * 1) = 52m/s = 188kph = 116mph. This would not at first sight seem a sustainable strain to which to subject the body. So I'd not offer any disagreement when
laundryman wrote: |
I'd say it was definitely in injury or death territory! |
It may be that instantaneous Gs could be pulled with slightly less mortal consequences, but I'm not volunteering for the experiment!
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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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Kit Wong, now it should be obvious to anyone who has had the misfortune to find that CNN is the only English language channel in their hotel room that it is a news service staffed by the loony tendency. This is going a bit far though. Using the formulae helpfully provided by laundryman and GrahamN above, I have work out that any skier pulling 139Gs would have a nose about 8 feet long.
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The article does say that a skie rwould reach 139g when doing an instantaneous stop, though. How do you do that, by the way?
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hyweljenkins, with the help of a tree.
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hyweljenkins, as per laundryman's ,comment, in normal ski terms there is no such thing, the shortest stop I've ever managed would be from about 50Mph say 25m/s over a distance of about 5M so using previous formulae it looks like I can pull maybe 6.5 g and from memory it was an emergency and it hurt, I probably wasn't going as fast as I thought though so it may not even have been that high.
So yes 139G is possible I think in an instantaneous stop and in skiing terms the only way you would ever manage that is to hit something solid at high speed, the equivalent would be to be infront of a car travelling at high speed, not usually survivable, but if you did survive very unlikely to be able to walk away
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You'll get to see more forums and be part of the best ski club on the net.
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D G Orf, by the same equation I gave above, and assuming the body could withstand 5cm of distortion without suffering major structural damage, 139G over 5cm is like skiing into a solid cliff face at 25mph. If instead you assume most favourable position of landing feet first on a solid surface, we'd get back to something like the 2ft stop mentioned in the linked article, over which distance 139G translates as a 90mph collision. Not credible that you'd be conscious after either of those. I guess you'd get a similar effect if your chest met a substantial tree in that 25mph collision - with a large number of cracked ribs the best possible outcome. (Other parts of the body would suffer much lower Gs as it gracefully wrapped itself around the tree). So that 139G comment clearly has no relevance to anything anyone could contemplate enduring willingly.
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GrahamN, yep definately, though I wonder about extream skiers when they do those high cliff jumps, what sort of G do you reckon they take when they land at the bottom ?
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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D G Orf, the biggest variable there will be the incline of the landing zone. Splatting onto level ground will be different to landing on a 45 deg. slope that gradually flattens out.
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And love to help out and answer questions and of course, read each other's snow reports.
And love to help out and answer questions and of course, read each other's snow reports.
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laundryman, yes I realised that, likewise the distance of the drop will to a certain extent have an effect, and the depth of powder snow in the landing zone
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D G Orf, I suppose the boys and girls who do that kind of stuff intuitively take these factors into account. Come to think of it, those of us who don't follow our intuition as well!
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You know it makes sense.
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It would have been better to past the whole sentence, the discussion woudl have benefitted from that...
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In hockey, for instance, a two-foot quick stop exposes a player's lower extremities to about 15Gs — where one G equals the force of gravity. For a downhill skier making an instantaneous stop or catching an edge, the force can be as high as 139Gs. That's a lot of force to place on your joints and ligaments, especially your knees.
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My take is that the writer and the doctor discussing this are talking in extremes, I have never seen an "istantaneous stop" in any downhill skier, beside when one catches an edge, it tends to take off or fall or wahtever, thus diminishing the g forces.
Bottom line, take all news with a grain of salt (lot of)
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Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
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Yep catching an edge could momentairily exert massive forces on a skier but it would only last for a tiny period of time, after that in most downhills the skier takes to the air before doing multiple cartwheels into the nearest crash netting
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Poster: A snowHead
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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Paul Roberts, well they do have to turn occasionally
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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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Going by the article, it suggests that 139Gs are possible when catching an edge. Surely catching an edge will not provide the instantaneous stop that would result in that number of Gs? After all, catching an edge does not cause a full stop but merely redirects the forces as Matteo suggests. I equate it to hitting a car head-on when on a motorbike. When done at approx 30mph (and the car at about 20mph) the motorbike does not stop but continues into the car - about 70cm in a Fiesta. As the bike decelerates, I continue my trajectory (because there's no way my grip is that good) until I too impact with the car, head-plant on the bonnet and continue forward and slightly sideways until I land on the floor. I don't know what forces are involved (I was never very good at physics) but I don't see that the Gs can be that great as the end result was no injury . The bike, on the other hand, did not do so well . The point being that there is always somewhere else for the force to go. Now, if I were to hit something relatively immobile like a brick wall or, worse, a big tree, then that would be a different matter.....
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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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I emailed the Mayo Clinic about their figure of 139G. I don't think they got the point that although a skier *could* experience 139G, it's unlikely that many will, and those that do wouldn't experience it for very long simply because they'd have just skied (at 65mph) into a pistenbully and would be a few millimetres thick.
Their response said
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G = .0333 X (miles per hour, squared) divided by Distance (in feet)
The skier is estimated at 65mph and the stop, instantaneous.
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Using their figures that works out as
G = (0.0333 x 4225) / 0
You can't divide by zero, so forget the last bit.
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hyweljenkins, maybe if he skied into black hole? Black holes on the piste are certainly a problem that should not be ignored. Should we cover that problem in this thread or open a new one?
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Based on Laundyman's initioal calculation I assumed they had missed the decimal point out (1.39G) but looking at their reply to hyweljenkins, it seems to be a nonsense. How can they just ignore the fact that stopping in 0 zero feet gives a division by zero? They'd need to frig it and supply a minute distance (as would actually be the case) and get a huge number, which would be occur for a very short amount of time as the velocity would very quickly reduce to nil (or even a negative number - resulting in an increase in the distance value).
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There is no such thing as an intantaneous stop, as that would mean exerting an infinite force on the body in motion, which would require an infinite amount of energy, which is not possible. Also I think that they've got their physics wrong. I'll have a think and get back to you.
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Their calculation is bassed on someone stopping in 11.85 inches. (using their formula)
Edit:
D'oh, that's wrong!
hold on, working out the right answer!
Edit 2: 1ft 0.14 inches
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Wear The Fox Hat, in that case, as has been said, the amount of G pulled is probably the least your worries, and would very quickly drop below 139.
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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skanky, I know that if I went from 65mph to stationery in 30cm, that I wouldn't completely stop. I can assure you that my bowels would be moving...
(which reminds me of the joke, which has the punchline "pass me my brown trousers")
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