Are helmets now compulsory?

mr_poll

Underscore wrote:

dondare wrote:

I don't know if it's risk compensation but it does seem to me that cyclists who wear helmets need them more than cyclists who don't.

Actually one study apparently found that there was a correlation between helmet use and not just a reduction in head injuries but also with a reduction in bodily injuries too. This was put down to those choosing to wear helmets either being more competent or more safety-concious cyclists. Once the figures were normalised for lower limb injuries, the correlation between helmet use and reduced head injuries disappeared...

_

Really? Which study by whom? When? And who funded the study?

All the above are required before you "quote" studies - the study could have been funded by a helmet manufacturer? Also who "put it down to helmet wearers being more competant" - this leap of faith is poor science unless backed with facts. If the sample contained 50% helmet wearing housewives who popped round the corner of their sleepy village once a week with the other 50% being non helmet wearing bike couriers in London it will have nothing to do with competant riding.

I am not saying the study doesnt show something but dont quote something we cant check and verify.

itsbruce

Always Tyred wrote:

itsbruce wrote:

The doctor had a very poor understanding of physics. When a helmet cracks under an impact, it transfers almost all the energy onwards, providing very little protection at all. If it cracked, it failed; your head is still in one piece because the impact wasn't enough to fracture it.;

God, where do we find these people. All it tells you is that the helmet eventually fractured - it says nothing about how energy was transferred up to that point. So it is consistent both with the helmet functioning as intended and with the helmet fracturing prematurely.

Mmm, those statements are obviously made without much knowledge of fracture physics, damage mechanics or the study in question. The paper is "Improved Shock Absorbing Liner for Helmets." by Morgan D.E., Szabo L.S. July 2001. The physics is mostly accessible at A-Level standard. It's a big Internet out there: enjoy.

rjsterry

Australian Transport Safety Bureau says no. (or more accurately, file not found).

itsbruce

Computer says yes

always_tyred

itsbruce wrote:

Always Tyred wrote:

itsbruce wrote:

The doctor had a very poor understanding of physics. When a helmet cracks under an impact, it transfers almost all the energy onwards, providing very little protection at all. If it cracked, it failed; your head is still in one piece because the impact wasn't enough to fracture it.;

God, where do we find these people. All it tells you is that the helmet eventually fractured - it says nothing about how energy was transferred up to that point. So it is consistent both with the helmet functioning as intended and with the helmet fracturing prematurely.

Mmm, those statements are obviously made without much knowledge of fracture physics, damage mechanics or the study in question. The paper is "Improved Shock Absorbing Liner for Helmets." by Morgan D.E., Szabo L.S. July 2001. The physics is mostly accessible at A-Level standard. It's a big Internet out there: enjoy.

Where do we find these people? All it tells you is that the helmet eventually fractured - it says nothing about how energy was transferred up to that point. So it is consistent both with the helmet functioning as intended and with the helmet fracturing prematurely.

(Clearly he didn't understand, so I repeated it. Probably he'll re-state the "fact" that fracture always = premature failure, but it won't make it true).

In NZ, aside from the figures showing a gradual increase in safety over time, with helmet use, absolutely all available evidence unequivocally demonstrates that there is no effect. All of it. Bar none. Any fool can see that. Even the studies that show a positive effect on safety from helmet use are fake. Or wrong. Or actually show something different, if you read them upside down.

itsbruce

Always Tyred wrote:

(Clearly he didn't understand, so I repeated it.

Repeating what you think you know, loudly, doesn't make it correct.

A cycling helmet protects party by reducing the acceleration of impact (by crumpling) and partly by distributing the impact around a larger area of the skull, thus reducing the pressure at any one point. But a helmet that fractures doesn't behave like that. If the foam layer has significant fractures, that means that it didn't crumple (much); instead, it compressed, storing energy rather than absorbing it, and then fractured, releasing it. Not only is the deceleration greatly diminished but the fracture can actually concentrate the impact at particular points.

Just to make it clear, the fact that the helmet stored energy up to the point of the fracture doesn't mean that that energy was cancelled out and is no longer a factor. I can do this in words of one syllable, with stick figure illustrations, if it will help.

Probably he'll re-state the "fact" that fracture always = premature failure, but it won't make it true).

Straw man argument.

Kieran_Burns

No.



What?


I answered the original question. What the hell are you lot ranting on about?

itsbruce

We ran away with the argument while you were trying to get your jeans past your calves...

<ducks and runs>

Kieran_Burns

itsbruce wrote:

We ran away with the argument while you were trying to get your jeans past your calves...

<ducks and runs>

Moo?

always_tyred

itsbruce wrote:

Straw man argument.

Mmm. I don't use straw man in that sense - I use it more as the equivalent of a pseudonym - disguising who you are acting on behalf of.

That's also a strange explanation of the way a helmet works. Storing energy? My understanding is that peak forces are reduced by distributing force over a greater period of time (and, yes, ideally over a greater surface area also). It does this by crushing, just like a car crash structure.

Tell me, in your parallel physics multiverse, what's the difference between storage and release, and dissipation (over a larger surface area)? Where is the energy of a correctly functioning helmet released to? Does it all go back out? Perhaps its released as a "boing" noise

itsbruce

Always Tyred wrote:

That's also a strange explanation of the way a helmet works.

That's because it isn't; it's an explanation of how it fails.

Tell me, in your parallel physics multiverse, what's the difference between storage and release, and dissipation (over a larger surface area)?

Dissipation happens in two ways:

1. When the Styrofoam crumples; the energy of the impact is transformed into heat as molecular bonds are snapped. But there is less crumpling in a fractured helmet, so that effect is reduced.
2. By sending a shock wave reverberating through the structure of the helmet, disippating energy over time - only that is interrupted by the fracture.

Dispersal of the energy over a wide area of the skull isn't dissipation - the overall acceleration to the skull is not reduced, just the pressure on any one part of the skull. And in a helmet that fractures, this doesn't happen in the same way; impact energy can be concentrated at or near the point of fracture. Think of the whiplash effect of a taut cable that snaps under tension.

Where is the energy of a correctly functioning helmet released to?

1. By crumpling, into the helmet (as heat).
2. By reverberation, into the helmet (again, as heat) and the surrounding air.
3. By direct transmission (compression then expansion), into the skull.

In both cases, most of the energy is transmitted directly to the skull. The helmet compresses and expands and transmits the energy on - if you think that reduces the impact on its own, I invite you to swim in a pool while I toss grenades into it at the other end. The difference in the functioning helmet is that a) a portion of the energy isn't transmitted and b) that the remaining force is spread over a larger area, reducing the pressure on the skull.

Spreading the force doesn't actually reduce the acceleration. This is another reason why the benefits of helmets can be said to be overstated; the risk of fracture is reduced, but the risk of brain damage is largely unchanged; most of the energy dissipation happens as deceleration within the skull.

(Edited for typos)

always_tyred

I don't know where to begin. Breaking chemical bonds? No - lets just print this out and leave it on university noticeboards through out the land for a laugh.

My helmet makes me safer by expanding into my skull. Sure there aren't massless, noiseless weight lifters inside each polystyrene bead taking the strain?

Dude, be careful not to believe everything you read. If you can't tell the different between tennis balls and testicles, keep it to yourself.

tailwindhome

*A new argument has entered the room*


Me "You have to wear your helmet"

Daughter, age 7 "But I don't want you"

Me " No helmet. No bike ride"

Her " But...."

Me " No buts. No helmet. No bike ride"

Her " But it has Barbie on it. I don't like Barbie any more"



As you were,

I'm sure you were reaching a conclusion........

always_tyred

itsbruce wrote:

Spreading the force doesn't actually reduce the acceleration. This is another reason why the benefits of helmets can be said to be overstated; the risk of fracture is reduced, but the risk of brain damage is largely unchanged; most of the energy dissipation happens as deceleration within the skull.

(Edited for typos)

Aaaah, he's mmmmmmad sir.

You have 10 lego bricks. Imagine you don't wear a helmet, and your impact takes a brick-lengh of time. The total force is fully 10 bricks high! Wow.

Imagine you wear a helmet and it spreads the imact over 3 brick-lengths, but you still have 10 bricks' energy to dissipate. Now, the peak force is 4 bricks, and you don't suffer brain damage.

That's the general idea of a helmet. No chemical bonds. No storing energy in the skull. No heating (well, not much anyway).

Btw - if you drop a grenade in a swimming pool, the force will be transmitted through a medium far less compressible than air. As such, the shock wave will be travelling much faster and will hit you with a far higher pile of lego bricks.

(The colour of the bricks doesn't matter, but the whole thing doesn't work so well with the space-ship shaped ones).

I'm going to sleep now. This is a waste of time.

always_tyred

TailWindHome wrote:

*A new argument has entered the room*


Me "You have to wear your helmet"

Daughter, age 7 "But I don't want you"

Me " No helmet. No bike ride"

Her " But...."

Me " No buts. No helmet. No bike ride"

Her " But it has Barbie on it. I don't like Barbie any more"



As you were,

I'm sure you were reaching a conclusion........

Does this mean that you are stuck wearing a barbie helmet? Waste not want not. I'm sure it suits you.

itsbruce

Always Tyred wrote:

I don't know where to begin. Breaking chemical bonds?

Molecular. The breaking and/or excitation of molecular bonds causes heat. This isn't even A-Level physics. Basically, dissipation = energy turned into heat. As opposed to the transmission of force through an object, where molecular bonds are compressed and then expand. That's GCSE physics.

You haven't made a single coherent argument, just pulled silly faces in response.

tailwindhome

Always Tyred wrote:

Does this mean that you are stuck wearing a barbie helmet? Waste not want not. I'm sure it suits you.

Poor

lost_in_thought

<serious suggestion alert>

TailWindHome - get her to do a collage on it of her favourite thingo. I'm sure one of the physicists/chemists/whateverists here will be able to explain in full the effect of pritt-stick on a helmet.

tailwindhome

lost_in_thought wrote:

<serious suggestion alert>

TailWindHome - get her to do a collage on it of her favourite thingo. I'm sure one of the physicists/chemists/whateverists here will be able to explain in full the effect of pritt-stick on a helmet.

It's your own fault when they do.

For they will

God help us all, they will.

diplomacy

so it seems like we have thrown enough internet at each other to answer the initial question: cycle helmets are not compulsory. the BBC IS compulsory but is, in this case, wrong. there is a general consensus that helmets should not be made compulsory, because of the negative effects that would have on general population health, traffic and pollution - from the ensuing reduction in casual cycling.

BUT the big question remains: are you safer on your bike with a melon?

yes, you would have a reduction in control from having one arm clasping the melon, but wouldn't that make you ride more cautiously? and in the case you did fall one arm at least would be kept to your body, reducing the risk of broken fingers or wrist. not to mention the positive kinetic attenuation properties inherent in the melon - as mentioned previously they are intended to fracture when dropped. they are nature's crumple zones.
i haven't done any research into this, but it is obviously correct.

and what about compulsion? they could be subsidised, and the positive benefits to general health of the fresh fruit could be significant. not to mention for melon farmers.

poster ideas for promotion:

life's more mellow with a melon
go velo go melon
the melon - it makes sense. & salads.
who's fruity? - just take it!
every time you ride, have a melon at your side
you came off, because you didn't mel-on

surely?

itsbruce

diplomacy wrote:

BUT the big question remains: are you safer on your bike with a melon?

yes, you would have a reduction in control from having one arm clasping the melon, but wouldn't that make you ride more cautiously?

It'd certainly make drivers give you more space.

always_tyred

lost_in_thought wrote:

<serious suggestion alert>

TailWindHome - get her to do a collage on it of her favourite thingo. I'm sure one of the physicists/chemists/whateverists here will be able to explain in full the effect of pritt-stick on a helmet.

It will make the helmet sticky. And increase drag.

Collages are known to increase drag also. I think Zipp make dimpled time trial collages, but they are carbon and very expensive.

always_tyred

itsbruce wrote:

Always Tyred wrote:

I don't know where to begin. Breaking chemical bonds?

Molecular. The breaking and/or excitation of molecular bonds causes heat. This isn't even A-Level physics. Basically, dissipation = energy turned into heat. As opposed to the transmission of force through an object, where molecular bonds are compressed and then expand. That's GCSE physics.

You haven't made a single coherent argument, just pulled silly faces in response.

Just so you know, I've got a few degrees in chemistry. This never made me any good at chemstry, but I know enough to find you funnny and to distinguish between chemistry, physics and a room full of chimpanzees with typewriters.

At least you have conviction.

WesternWay

Always Tyred wrote:

Just so you know, I've got a few degrees in chemistry.

You should try for one in maths.

N.B. I haven't been reading this thread, so I'm not having a pop.

Kats

:idea: Helmets are not a legal requirement.
To make sure a retraction is broadcast, so please let the BBC know your thoughts...

yourlondon@bbc.co.uk

Underscore

mr_poll wrote:

Really? Which study by whom? When? And who funded the study?

wikipedia wrote:

In another study, helmet users also seemed to be protected against severe injuries to the lower body; "helmet non-use is strongly associated with severe injuries in this study population. This is true even when the patients without major head injuries are analyzed as a group".[43] It is possible that at least some of the 'protection' afforded helmet wearers in previous studies may be explained by safer riding habits rather than solely a direct effect of the helmets themselves.[51]

See here to follow up the references.

_

itsbruce

Always Tyred wrote:

Just so you know, I've got a few degrees in chemistry. This never made me any good at chemstry, [/quote]

If it taught you to laugh at the idea that some of the force from an impact is converted into heat, then it never made you much good at anything else.

always_tyred

itsbruce wrote:

Always Tyred wrote:

Just so you know, I've got a few degrees in chemistry. This never made me any good at chemstry,

If it taught you to laugh at the idea that some of the force from an impact is converted into heat, then it never made you much good at anything else.[/quote]
Do you seriously think its a significant effect? Compared to bulk transfer of momentum, its going to be negligible.
Do you even know what heat is?
What are they teaching children these days?

MonkeyMonster

I think this argument has gone well past the 5 minute allocation you paid for. Please desist and go next door for complaints or one door on for being hit on the head lessons.

that is all.

dondare

itsbruce wrote:

Always Tyred wrote:

I don't know where to begin. Breaking chemical bonds?

Molecular. The breaking and/or excitation of molecular bonds causes heat. This isn't even A-Level physics. Basically, dissipation = energy turned into heat. As opposed to the transmission of force through an object, where molecular bonds are compressed and then expand. That's GCSE physics.

You haven't made a single coherent argument, just pulled silly faces in response.

Breaking and/or exciting bonds requires energy. Heat will not be released.

Molecular bonds are neither compressed nor expanded when force is transmitted through an object. (Unless you are classing the weak interactions between molecules as bonds, rather than the stronger forces that hold the molecule together.)