Crash and helmet

[mattheus]

Sounds very dull ....

NO IT DOESN'T!!!!!!

(Sorry I'll stop now.)

Peace brother

But I hope you can see why a helmet compulsionist, using misunderstandings of physics he *claims* to have learned at university, beating me over the head with his proofs that helmets saved his life (and most of the western world's) MIGHT sometimes provoke a reaction from some of us. That is very different from the response I give to a friend/colleague politely asking me: "So Matt, do you think I should get a helmet now I'm getting into cycling?"

[jois]

Do you have a citation - on THIS thread - for your first claim?

"... some of the assertions being made, e.g. that if your head is about to be hit hard by a blunt or sharp object, then having a helmet on your head won't offer any protection"
Who said this?

(I'm choosing not to quote the individual posts, as that would send each poster a notification which increases the likelihood that we'll end up regurgitating dormant discussions. I've stated the page number so you can find them.) The following posts in this thread have questioned whether helmets provided any benefit in cases where the impact had enough force to significantly damage the helmet itself. My point is that Joe Public would read this type of thing and say "what sort of person would not strongly prefer a helmet to a bare head when being exposed to such a high impact?" which detracts from your credibility and distracts from the very strong argument that can otherwise be made against mandatory helmet use:

“And you got concussion anyway, which is a failure too. So the helmet could have provided some benefit, but the evidence is far less impressive than if neither of those things had happened. And it also fits with no benefit at all.” Page 2. 7th post, made in response to someone recounting their experience of an off-road impact with a metal post which resulted in their helmet being smashed in two.

“Until you remember that all except a few full face MTB helmets are only tested for standing falls onto flat surfaces or kerb edges. The old test of falling onto a stone has gone. Other things like typical rough surfaces have never been tested. And if a helmet hits something like a stone, or walnut, it may well fail and split. Just as well none of the helmets talked about here split, isn't it?” 2nd page, 9th post, made in response to my assertion that the helmet’s role in the above accident was clearly better than nothing.

“I see a LOT of pictures of cracked helmets - so remember this is barely absorbing any energy at all. Think of car CRUMPLE zones - they are not made out of brittle materials, deliberately!” You, page 8, referring to the same incident whereby the helmet smashed after impact with a metal post.

“I'll try to put this simply; if you crack a protective helmet, it has not reduced* the decelerations involved. It is not crumpling. A thick cushion would be better protection. In fact thick cushions would be good protection for your head against blunt trauma, even though I haven't seen any tests for me to quote at you *Or perhaps only negligibly!” You, page 8

“You can flash your credentials all you like: I do know how energy conversion works (you're not the only cyclist that went to school my friend), and I know that a cracked helmet isn't doing a lot for you.” You, page 10.

Well a split helmet has used energy to split and thereafter deformed to absorbe more energy. To say it's done nothing is inaccurate.

Perhaps not very much is closer to the mark. Enough to make an actual difference to the extent of your injuries ? Don't know , depends on a lot of things.

You can't expect motor cycle helmet level of protection from something that doesn't weigh and cost the same as a motorcycle helmet. Both of which can be a great deal.

To be clear I'm not recommending helmets. I generally don't wear one unless I'm going out with the intention of being a bit silly off road, in which case I put on a full face downhill hat. It's saved me from many abrasions non of which would be considered life threatening, but who knows next time I might hit a big lump of stone

This started when I managed to knock myself out cold on my own in the middle of nowhere. In the dark on a freezing night. Thought " that was a bit stupid" "won't do that again"

My particular hang up with cycling equipment is wearing leather gloves after I watch a friend grind his little finger down to the second knuckle. He was doing most of 50mph, but still!

[DevonDamo]

But I hope you can see why a helmet compulsionist[/i]

I know better than to get involved in someone else's argument, but I thought that guy's point was limited to the physics of energy dissipation etc? I didn't notice anything about him being pro helmet laws. But either way, you could still argue your case even if it could be shown that helmets had a 100% success rate at preventing any injuries. Head injuries from cycling are, apparently, quite rare, whereas strokes, diabetes, heart attacks etc are all too common.

[Mike Sales]

One has to wonder why the road safety intervention whose "benefits are too modest to capture, compared with other strategies" is the one most favoured by motorists, to the extent that the AA has given out free helmets. If you object to bad driving when lidless, your bare head is often mentioned.
The objections from drivers to the proved effective measures have been enough to often defeat schemes for safer cycling lanes.

[mattheus]

But I hope you can see why a helmet compulsionist[/i]

I know better than to get involved in someone else's argument, but I thought that guy's point was limited to the physics of energy dissipation etc? I didn't notice anything about him being pro helmet laws. But either way, you could still argue your case even if it could be shown that helmets had a 100% success rate at preventing any injuries. Head injuries from cycling are, apparently, quite rare, whereas strokes, diabetes, heart attacks etc are all too common.

Yep, good points. Bear in mind that:
- he was strongly pro-compulsion in another thread (Cyprus law discussion?)
- I'm interested in the science of all this! So I cannot help challenging bad science when I see it. mea culpa.
- you WILL find me citing the bigger issues, I promise. I just don't mention them in every helmet thread on every forum everywhere ...

[dmrcycle]

Sounds very dull ....

NO IT DOESN'T!!!!!!

(Sorry I'll stop now.)

Peace brother

But I hope you can see why a helmet compulsionist, using misunderstandings of physics he *claims* to have learned at university, beating me over the head with his proofs that helmets saved his life (and most of the western world's) MIGHT sometimes provoke a reaction from some of us. That is very different from the response I give to a friend/colleague politely asking me: "So Matt, do you think I should get a helmet now I'm getting into cycling?"

The problem is people don't understand the laws of physics and believe they know best. The people who know best about helmet impacts are the engineers and scientists who design helmets. Its not a scam the manufacturers are pushing to reduce injury is it?. You claim that conservation of momentum is true even if energy is lost as heat. That is 100% not true and not what is in Newtons laws which specifically apply to an isolated system and do not consider losses. When you apply your brakes you lose momentum which is the product of mass x velocity. Momentum is not conserved in that case. The brakes don't move and take up the momentum lost from the moving bike. That momentum is lost as the kinetic energy is converted to heat in the brakes, momentum is not conserved. You may be confusing energy with momentum as there is always conservation of energy as kinetic energy in a helmet collision is converted to heat during the deformation of the helmet. Conservation of momentum and conservation of energy are different. In any solution to reducing an impact you need to convert the kinetic energy into another form like heat, sound or light. A helmet cracking does this as it absorbs the energy impact by deforming the material producing heat and reducing the momentum of the head.

[Mike Sales]

The problem is people don't understand the laws of physics and believe they know best. The people who know best about helmet impacts are the engineers and scientists who design helmets.

You and they, give no consideration to what is really the most important factor producing "accidents". Human behaviour. We would all prefer to avoid being hit to a collision which a helmet might ameliorate.
Why is it that road users impact each other?
The benfits of helmets are "too modest to capture, compared with other strategies."
All this arguing about an unproved measure serves as an excuse and a diversion from those strategies which have been shown to actually produce a safe cycling (and walking) environment.
An early poster in this thread would refuse to ride with an unhelmeted rider! I have ridden with helmeted riders who I took care to keep out of the way of, because their riding was dangerous.

[mattheus]

Oh dear, how wrong can one be.

Would you like have to go at the "physics" above, or should we just leave it there, and hope no-one ever finds it and believes it.

[dmrcycle]

The problem is people don't understand the laws of physics and believe they know best. The people who know best about helmet impacts are the engineers and scientists who design helmets.

You and they, give no consideration to what is really the most important factor producing "accidents". Human behaviour. We would all prefer to avoid being hit to a collision which a helmet might ameliorate.
Why is it that road users impact each other?
The benfits of helmets are "too modest to capture, compared with other strategies."
All this arguing about an unproved measure serves as an excuse and a diversion from those strategies which have been shown to actually produce a safe cycling (and walking) environment.
An early poster in this thread would refuse to ride with an unhelmeted rider! I have ridden with helmeted riders who I took care to keep out of the way of, because their riding was dangerous.

I was just correcting the physics. Human behaviour is not something I have a qualification in so I will leave that to experts.

[Mike Sales]

The problem is people don't understand the laws of physics and believe they know best. The people who know best about helmet impacts are the engineers and scientists who design helmets.

You and they, give no consideration to what is really the most important factor producing "accidents". Human behaviour. We would all prefer to avoid being hit to a collision which a helmet might ameliorate.
Why is it that road users impact each other?
The benfits of helmets are "too modest to capture, compared with other strategies."
All this arguing about an unproved measure serves as an excuse and a diversion from those strategies which have been shown to actually produce a safe cycling (and walking) environment.
An early poster in this thread would refuse to ride with an unhelmeted rider! I have ridden with helmeted riders who I took care to keep out of the way of, because their riding was dangerous.

I was just correcting the physics. Human behaviour is not something I have a qualification in so I will leave that to experts.

I am afraid that the real problem of cyclist head injuries is not to be solved in the field in which you are qualified. We really need to look elsewhere for an answer, and all this discussion on helmets is an irrelevance and a diversion which serves best the interests of those who would prefer not to give up any convenience for the sakes of our safety.

[dmrcycle]

The problem is people don't understand the laws of physics and believe they know best. The people who know best about helmet impacts are the engineers and scientists who design helmets.

You and they, give no consideration to what is really the most important factor producing "accidents". Human behaviour. We would all prefer to avoid being hit to a collision which a helmet might ameliorate.
Why is it that road users impact each other?
The benfits of helmets are "too modest to capture, compared with other strategies."
All this arguing about an unproved measure serves as an excuse and a diversion from those strategies which have been shown to actually produce a safe cycling (and walking) environment.
An early poster in this thread would refuse to ride with an unhelmeted rider! I have ridden with helmeted riders who I took care to keep out of the way of, because their riding was dangerous.

I was just correcting the physics. Human behaviour is not something I have a qualification in so I will leave that to experts. But the important factor for me is as go mountain biking as well as road cycling and I don't want to be more careful, I want to protect my head and a helmet is the best way to do so. Arguments about individual risks and statistics of a large group and its effects on human behaviour are separate. I even prefer a helmet as its bright yellow and I'm more easily seen and therefore avoid impact in the first place.

[Mike Sales]

But the important factor for me is as go mountain biking as well as road cycling and I don't want to be more careful, I want to protect my head and a helmet is the best way to do so. Arguments about individual risks and statistics of a large group and its effects on human behaviour are separate. I even prefer a helmet as its bright yellow and I'm more easily seen and therefore avoid impact in the first place.

Using a helmet to extend your safe performance in an area which you chose to engage in for fun is fine. Climbers wear helmets when exposed to falling rocks, and yachtsmen wear lifejackets in the circumstances they see as risky. Riding to work, school or the shops should not be an adventure sport.
But to advocate cycle helmets as a solution to the problem of dangerous roads is not good enough. Even if helmets were a guaranteed way to avoid head injury, it would still be unpleasant, at the least, to be hit by a motor.
As I keep saying, wearing a helmet might just ameliorate some of the effects of a collision, but roads ought to be safe enough for all to use without fear, and helmets not only fail at this, but actually are an alibi for doing nothing else. Cyclists' skulls are not the problem, inadequately restrained motors are. Most road victims are not cyclists and it is wrong that such a large portion of our common public space is unsafe for all.
The decrease in vulnerability given by helmet wearing is not enough to encourage many parents to allow their children to ride to school. I rode to school and regard this as the beginning of the lifelong freedom of the road that bikes have given me.
The visibilty of a helmet argument is tenuous. Many hi-viz vehicles are hit by reckless drivers. Any benefit must be marginal, given the difference in size between the back of a helmet and the back of a motor vehicle.

[mattheus]

I was just correcting the physics.

<COUGH>

[buryman]

Oh dear, how wrong can one be.

Would you like have to go at the "physics" above, or should we just leave it there, and hope no-one ever finds it and believes it.

Momentum is one of the fundamental conserved quantities no matter what energy conversions are taking place.

[dmrcycle]

Oh dear, how wrong can one be.

Would you like have to go at the "physics" above, or should we just leave it there, and hope no-one ever finds it and believes it.

Momentum is one of the fundamental conserved quantities no matter what energy conversions are taking place.

No absolutely not the case, thats conservation of energy. Momentum is only conserved if there are no other forces acting. Newton stated that is the case.
See
http://teacher.pas.rochester.edu/PHY_LA ... _Laws.html

Quote
Friction between moving bodies and their surroundings means there is an external force acting on them, so that conservation of momentum is not applicable.

Confusion between conservation of momentum and conservation of energy is what is the issue here. I can appreciate it might have been some time from school level physics but the information can be looked up. In a collision energy is conserved momentum is not unless its a perfect situation (similar to two billiard balls). If there is friction, deformation, heat, sound etc then conservation of momentum does not apply. The momentum (mass x velocity) is not the same after the interaction. Think about it, otherwise we would all be bumping around never stopping transferring 100% of our momentum between things we touch. Nothing slowing down. When energy is absorbed and converted from kinetic energy to heat (aka braking) it cant be conserved as you slow down and have less momentum. This is basic school level stuff.