 Poster: A snowHead
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| T Bar wrote: |
Still, looked up the speed at which 50% of pedestrains die when hit by a car and this abstract suggests it is between 30 &40 mph.
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Yes, that's a commonly used figure. Still has very little relevance to the head-tree scenario other than suggesting that most impacts are not taken directly on the head. In most pedestrian car impacts, the head impact will almost certainly be a secondary impact after hitting your legs and body first. Hence the higher survivable speeds on average.
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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| T Bar wrote: |
uktrailmonster,
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Still a padded glove makes any impact much less severe than without and the same is true for a helmet.
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Not sure if that is true, I read somewhere that head injuries may be worse in gloved rather than bare knuckle fights because of the greater mass on the end of the arms, though it may be in part due to greater protection of the fists.
Still, looked up the speed at which 50% of pedestrains die when hit by a car and this abstract suggests it is between 30 & 40 mph.
http://www.nhtsa.gov/people/injury/research/pub/hs809012.html |
Not sure what argument you're supporting here.
Head injuries in gloved boxing matches might be worse because the fists are protected which means that fighters can hit harder and more often. It also might be because gloved matches are fought by professionals who hit harder.
With regard to the pedestrian deaths, I'd suggest that very few pedestrians are hit by cars going faster than 40mph because very few cars travel in areas frequented by pedestrians actually travel over 40mph. What's this got to do with anything?
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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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achilles, I'm not rubbishing it, I'm rubbishing the crazy reaction to it on this thread. People with dangerous professions (professional motorsports, armed forces, miners, etc.) also might be of an age where they could have a partner and/or children. I know of over 50 children who have lost their mothers under the age of 40 to cancer in the last couple of years. I was just reacting to the pointless thread drift into yet another helmet debate.
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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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uktrailmonster,
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No we're not talking about exactly the same thing at all, you either haven't read what I said earlier or don't understand it. It's all about how that force is dissipated locally during the impact. The acceleration the force causes in the case of a skier travelling at 15 mph is not critically high. Any talk about brains turning to jelly from the sheer deceleration from 15 mph to zero even in fractions of a second is pure fantasy. It just doesn't work like that and there have been plenty of real life tests to prove it. It was once thought that humans couldn't withstand a deceleration of more than 18G, but after people were found to be surviving all sorts of significantly higher G decelerations in accidents scientists and medics started scratching their heads a bit more and scientfic tests on real humans (not dummies) were carried out. It's now been proven that the real limit is more like 50G. This is totally different to being subjected to a blow on the head where the resultant damage is determined by the force, velocity (i.e. both speed and direction), area and elastic properties of both the impacting object and the target object.
Helmet arguments on public forums always involve bad science and this one is no exception!
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You have definitely miss understood me... I wasn't suggesting that the deceleration would turn anything to jelly. I referred to internal items getting 'squished', I was trying to convey that skiing in to a tree could just as easily result in a ruptured artery or a bone puncture of a vital organ. My original post was just an attempt to (simplistically) illustrate why racers wear helmets when they routinely travel at high velocities.
With regard to the rest of the above, F=Ma i.e. the force is directly proportional to the acceleration (as mass remains constant), you cant have a forces without an acceleration and you cant apply an acceleration to a mass without creating a force. The two jobs of a helmet are to increase the time it takes to go from xm/s to 0m/s (linked to its elastic properties) thus decreasing the acceleration (and by definition the force) and to increase the contact area thus reducing the pressure on the skull making it less likely to depress.
Its not bad science, we are both saying the same thing.
It's nice to bump in to another physics geek every now and again... lets be friends!
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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 don't see any crazy reaction. Just a fairly considered response to what could have been a snuff movie closely related to something almost everyone on this site does (substitute pylons, rocks etc for trees if necessary and loss of edge on ice etc for speed if you can't see the analogues).
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You'll need to Register first of course.
You'll need to Register first of course.
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queen bodecia,
I guess a thread that starts with a video of someone hitting something at speed on skis is pretty likely to result in a discussion on the safety of the sport and all that goes with it (it would be pretty disturbing if people just started positing videos of people getting hurt).
Someone said that it wouldn't have happened if the piste hadn't been groomed. I guess that would slow people down, but I personally wouldn't be in favour. I actively seek out challenges to improve my skiing so I like moguls and steep runs where I cant (don't have the ability to) ski fast, but I also love the feeling of cruising down a blue with the wind in my face.
I know its unlikely to happen but are less meticulously groomed pistes the way to go?
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| Bambi on ice wrote: |
| I know its unlikely to happen but are less meticulously groomed pistes the way to go? |
Somebody posted something recently (from a US site, so apologies for the jargon, but I'm sure it applies here too) that went along the lines of:
The people with money who go skiing are the Babyboomers.
The Babyboomers have dodgy knees.
The people with money who go skiing don't like bumps on their slopes these days.
Slopes have no bumps.
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FFS if you don't want to wear a helmet then don't. But get off your high horses already. This is ridiculous.
Sometimes I wonder why I bother checking snowheads. Oh yeah I remember its all about the holidays.
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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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I do find myself questioning what sort of person videos such an incident and posts it on the internet. This whole thread is a bit like rubbernecking at a car crash.
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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if farlep99 is right about the video not shot at Sugarbush's Sleeper run at the North Lynx Peak then the video is likely a hoax and we all waste time to talk about it. May be the whole thing has been doctored to show something unreal, say the speed of the skiers or even the impact.
If we treat the Sugarbush report and the video unrelated then we could explain the following
(1) The Sugarbush Sleeper run as depicted here does not run directly below the chairlift but the run of the video clearly shows it is. If the video were authentic then the Sugarbush spokesman must have told lie or could not get the fact right.
(2) The chairlift nearest to the Sleeper run is the Gate House Express Quad. The name implies it is a 4 seater and the trail map indicates this too. As far as I could make out the chairlift in the video is a 2 seater on the side where the video was taken. On the return side the empty chair has only one drop down T bar enough for the foot rests of only two passengers. Thus the chairlift of the video does not match the information gave by the Sugarbush resort spokesman.
I believe the report from the newspaper is true as more than one newspaper reported the same death. This leads me to suspect the authenticity of the video as its accompanying information does claim the accident took place in Sugarbush and the same video also appears in the Youtube. If the video was not taken from Sugarbush but used for such a purpose then the motive is clearly intended to trick the readers.
Last edited by snowHeads are a friendly bunch. on Wed 8-02-12 20:21; edited 1 time in total
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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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| Tirol wrote: |
Not sure what argument you're supporting here.
Head injuries in gloved boxing matches might be worse because the fists are protected which means that fighters can hit harder and more often. It also might be because gloved matches are fought by professionals who hit harder.
With regard to the pedestrian deaths, I'd suggest that very few pedestrians are hit by cars going faster than 40mph because very few cars travel in areas frequented by pedestrians actually travel over 40mph. What's this got to do with anything? |
I am not particularly trying to support any argument. The cars/ pedestrians although not a perfect analogy was the best analogy to the skier hitting a tree in finding the kind of speed at which death becomes likely. It is an area in which there have actually been some studies so we can find some facts to base an argument on rather thab making guesses as to the forces necessary to kill someone.
From memory the argument about the gloves is that the greater mass enables the fist ot create a greater force causing rotation of the head and it is this that creates the problems in boxing, I don't think the actual studies have been done comparing the injuries just that experts looking at the damage done have surmised that gloves may increase the danger of brain damage.
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I know its unlikely to happen but are less meticulously groomed pistes the way to go?
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Just to reiterate an earlier post, this is an almost 100% artificial surface. There's been a serious snow-drought in NE US this year (actually it's been weak out west too). Artifical snow has to be groomed, otherwise it just turns to a sheet of ice. It's icey enough when it's actually groomed. It would literally be a sheet of ice with no grooming. The artifical snow doesn't behave like natural snow that can be left untouched.
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You know it makes sense.
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Why people hate a meticulously groomed piste? As soon as it is open to use it can no longer be meticulously groomed.
Also I like to know if a piste is classified by colour according to its difficulty would this not be based on the freshly groomed condition? In a heavy snow fall the piste is a lot harder to ski and can resemble to the ungroomed condition even it has been meticulously prepared.
I don't think the operator sets out to groom a piste meticulously because the grooming is often done after the resort has been closed when it is dark so the operator rarely has the chance to examine his work or go back to give it another pass if the result not perfect enough.
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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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My god the title was a question, and I hardly see anyone able to answer without going on about helmets!
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Poster: A snowHead
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| Bambi on ice wrote: |
With regard to the rest of the above, F=Ma i.e. the force is directly proportional to the acceleration (as mass remains constant), you cant have a forces without an acceleration and you cant apply an acceleration to a mass without creating a force. The two jobs of a helmet are to increase the time it takes to go from xm/s to 0m/s (linked to its elastic properties) thus decreasing the acceleration (and by definition the force) and to increase the contact area thus reducing the pressure on the skull making it less likely to depress.
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You've got that the wrong way round. You can't have an acceleration without a net force acting on a mass, but you can certainly apply a force without any acceleration of mass. You don't apply accelerations, you apply forces which may or may not lead to accelerations depending on the situation. You can push hard against a brick wall (applying a force) but neither the wall nor you accelerate as the force and reaction cancel each other out. A bit of a digression I know, but since we were talking about the physics involved we might as well get it right.
The more relevant calculation to make during a collision is the Impulse involved i.e. change in momentum. F.t = m.dv Impulse is derived directly from Newton's second law but is more useful in this case as it is more practical to calculate the Force of a collision from the change in velocity (dv) and time taken for that change. Impulse itself also conveniently combines the magnitude and duration of a collision Force into a single representative number i.e. the higher the Impulse the more it will hurt!
So going back to helmets then, in a collision with a tree the overall Impulse invloved in the collision will be totally unaffected by whether or not you are wearing a helmet. You still decelerate from 15 mph or whatever speed to zero in a few fractions of a second. But the critical thing at that kind of speed is not really the overall magnitude of the Impulse (which would be pretty harmless in terms of damage from the pure acceleration) but the way energy from the force of the impact is distributed. If the whole force of impact is applied directly as a point contact on your head then you are for sure dead, helmet or not. But if, as is far more likely, that same force of impact is applied across multiple points on your body, then the damage will be spread out across all those points. The purpose of a helmet, as you say, is to distribute the force of any head impact over a larger area and absorb energy through plastic deformation. But a helmet doesn't really act like a crumple zone on a car as you are implying above and in your earlier post. A crumple zone on a car significantly reduces the acceleration of the occupants inside, whereas a helmet doesn't significantly reduce the acceleration of your head when you hit a tree. The deflection of the helmet is too small to work in that way. You'd need an airbag to do that kind of thing.
Finally just to re-iterate, the impact force is not determined by the acceleration as you have stated a couple of times already. The impact force is determined by the momentum and the resultant acceleration depends on the elastic properties of the colliding objects. Getting this the right way around is quite fundamental. If you could apply an acceleration and generate a force I'd be seriously impressed!
Sorry to bore anyone without a physics background.
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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| kevindonkleywood wrote: |
Almost all bumps to the head are not direct impacts at high speed but falls with the head hitting the ground.
If a racer lets go, their horizontal speed has little to do with the impact force their head hits the ice. That impact is determined by the vertical height from which their head falls. Even when travelling at fairly high speeds the actual impact velocity with the ground is fairly low and well within the specs of the helmet design. |
Are you sure of that? If you catch an edge, say a back edge while snowboarding, you will continue moving in the direction of travel but you will also have decelerated a significant amount before your upper body impacts the surface... a significant portion of that deceleration will have been translated into angular velocity - so yes, there is some acceleration of the head as you fall, but also the fact that your body had a kickstart spinning around either its' center of mass (if your edge dislodged and you're flying through the air) or around your feet (board just stuck in something) means your head will be traveling south a great deal faster than if you had just fallen from a standing start.
I'm guessing at the Physics involved (A-Level physics only I'm afraid, so educated guess, but barely) but also speaking a little from experience. I've fallen many MANY times on my board and bumped head, but never as fast as a few weeks ago building speed into a flat when I rotated backwards and hit the rear of my head on the snow... without a doubt considerably more force than I've ever experienced in a slower fall, left me somewhat dazed and mildly concussed.
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FAQ
so we can be tolerant and rational about peoples strange behaviour 
