Paramount

-snip helmet-

Jay Beattie said:

Welcome to hemet threads! Although the posters have changed a little
over the last 10 years, the content and tone have not. In the past,
there has been some useful information exchanged, but that is drying
up as later threads become short-hand for earlier threads. The later
threads skip over the information and go right to the name calling,
particularly when cross-posted to the U.K. groups. This is a rather
tame go-round by recent standards. -- Jay Beattie.

Godwin Time!
Could someone please use 'nazi' as a pejorative so we can move on?

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

Quoted message said:

Ben C said:

On 2007-07-09, [email hidden] <[email hidden]> wrote:

[...]

Quoted message said:

Quoted message said:

Quoted message said:

Actually, discussion on whether helmets reduce "force" or "impact" ARE
technical. Those terms have precise meanings, and they can be used
correctly or wrongly.

What's the technical meaning of "impact"?

Dear Ben,

Technically, impact is the impulse of force. Even your fussiest carbon-
based life-forms tend to use the shorter phrase, even when being as
technical as possible:

"The product of average force and the time it is exerted is called the
impulse of force. . . . The main utility of the concept is in the
study of the average impact force during collisions. For collisions,
the mass and change in velocity are often readily measured, but the
force during the collision is not. If the time of collision can be
measured, then the average force of impact can be calculated."

http://hyperphysics.phy-astr.gsu.edu/hbase/impulse.html#c3

It seems they're basically using "impact" to mean "force" in that
document.

Protecting a table with a foam pad while striking it with a hammer might
be expected to reduce maximum force by spreading the impact experienced
by the table over a slightly longer period of time.

In the basic calculations the impulse is the same in both cases since we
assume the same amount of momentum is transferred from the hammer to the
table.

The foam pad further might reduce the maximum pressure on the table by
spreading the impact (force) out over a larger area.

If you can keep the pressure low enough you can prevent things breaking.
That's presumably roughly how the cardboard boxes eggs are supplied in
are supposed to work.

If you fall off your bike sideways knocking your head on the sharp edge
of the kerb it's possible the helmet could help prevent a skull fracture
in a similar way.

But head injuries are more complex than egg injuries where all we care
about is that the eggs shouldn't break.

Quoted message said:

Browse down that page for an example of a duck (not wearing a helmet)
hitting a jet head on.

The detailed calculator requires the grisly detail of the length of
the duck because the part that goes over the fence last strikes the
600 mph jet slightly later than the beak.

There's even another calculator for glancing rather than head-on
impacts.

(But there's nothing about rotational effect, since the duck is
expected to go splat! in a fashion quite different from a typical bike
crash.)

The assumption is that, since the jet is so massive and the duck's
speed so trivial, we can make a reasonable estimate of impact using
only the jet speed and the duck's mass and length.

Alas, for helmets containing heads, such assumptions don't work well.

While the pavement doesn't dent noticeably and can be ignored, we
can't use the length of the head and helmet, since few bicycle crashes
spread the rider's brains as thinly as impromptu duck paté à la
jetliner.

Yes. It's quite easy to estimate the impulse applied to the head, much
harder to estimate the duration of the impact and how the force varies.
But reasonable to say that the impact might be spread out over space and
time a bit by a layer of styrofoam. How much and how much that helps you
is another matter.

People also sometimes talk about energy absorbed in such collisions,
which is a slightly different metric.

Quoted message said:

There's also that pesky rotational business, which more and more
medical studies suggest causes many bicycling brain injuries.

Yes exactly. Medical studies or not, boxers know that the way to concuss
your opponent is with a blow to the chin causing maximum pesky rotation
of the head.

But I think it's difficult to estimate how much more or less torque you
can expect to receive with or without a helmet. It increases the radius
of your effective head obviously, but it's not that simple.

Quoted message said:

Ben C said:

What's the technical meaning of "impact"?

Technically, impact is the impulse of force. Even your fussiest carbon-
based life-forms tend to use the shorter phrase, even when being as
technical as possible:

Do you have a reference for that definition? Even the web page you
referenced has a quote inconsistent with that here

http://hyperphysics.phy-astr.gsu.edu/hbase/impulse.html#c4

where it says

Jack Elrod in his Mark Trail comic strip (2/27/2000) says "If an
aircraft strikes a big bird at a speed of 500 MPH, the impact will
be about 25 tons." He is pretty well on target, considering the above
model for a headon collision with a medium sized bird.

"25 tons" is in units of force, not momentum.

I always thought "impact" was a non-quantitative, purely descriptive
term to describe the event. When someone says the "impact" is some quantity
(or "smaller" or "larger"😉 they are leaving it to the reader to figure
out which quantifiable attribute of the event (e.g. impact force, or
impact velocity, or impact energy) they are talking about.

I could be wrong, though.

Dennis Ferguson

Jay Beattie said:

Welcome to hemet threads! Although the posters have changed a little
over the last 10 years, the content and tone have not. In the past,
there has been some useful information exchanged, but that is drying
up as later threads become short-hand for earlier threads. The later
threads skip over the information and go right to the name calling,
particularly when cross-posted to the U.K. groups. This is a rather
tame go-round by recent standards. -- Jay Beattie.

On the contrary, the helmet posts in u.r.c are much more polite. The lack
of r.b.t.'s two resident buffoons (and their minor camp followers) probably
has something to do with this.

It's also probably worth stating, for the benefit of any r.b.t. readers who
have not also read helmet threads in u.r.c., that not only is the tone more
civil but the majority of opinion there is fact-based, which of course
means also that they come to a conclusion which reflects the fact that the
USofA has so many, many MHLs, while the UK has none.

Dennis Ferguson said:

Quoted message said:

Ben C said:

What's the technical meaning of "impact"?

Technically, impact is the impulse of force. Even your fussiest carbon-
based life-forms tend to use the shorter phrase, even when being as
technical as possible:

Do you have a reference for that definition? Even the web page you
referenced has a quote inconsistent with that here

http://hyperphysics.phy-astr.gsu.edu/hbase/impulse.html#c4

[snip]

Dear Dennis,

Here's what I quoted:

"The product of average force and the time it is exerted is called the
impulse of force. . . . The main utility of the concept is in the
study of the average impact force during collisions. For collisions,
the mass and change in velocity are often readily measured, but the
force during the collision is not. If the time of collision can be
measured, then the average force of impact can be calculated."

http://hyperphysics.phy-astr.gsu.edu/hbase/impulse.html#c3

Feel free to argue with that web site.

Cheers,

Carl Fogel

A Muzi said:

-snip helmet-

Jay Beattie said:

Welcome to hemet threads! Although the posters have changed a little
over the last 10 years, the content and tone have not. In the past,
there has been some useful information exchanged, but that is drying
up as later threads become short-hand for earlier threads. The later
threads skip over the information and go right to the name calling,
particularly when cross-posted to the U.K. groups. This is a rather
tame go-round by recent standards. -- Jay Beattie.

Quoted message said:

Godwin Time!
Could someone please use 'nazi' as a pejorative so we can move on?

Thread Nazi.

Jay Beattie said:

Welcome to hemet threads!

Thanks, but I can't afford more than the standard 5 minutes of abuse,
and I'm sure you have other customers waiting :-)

On Jul 9, 2:36 pm, _ <[email hidden]>

Quoted message said:

Jay Beattie said:

Welcome to hemet threads! Although the posters have changed a little
over the last 10 years, the content and tone have not. In the past,
there has been some useful information exchanged, but that is drying
up as later threads become short-hand for earlier threads. The later
threads skip over the information and go right to the name calling,
particularly when cross-posted to the U.K. groups. This is a rather
tame go-round by recent standards. -- Jay Beattie.

On the contrary, the helmet posts in u.r.c are much more polite. The lack
of r.b.t.'s two resident buffoons (and their minor camp followers) probably
has something to do with this.

Regardless of the civility of the UK groups (which I don't doubt),
cross-posting creates a piling-on in RBT. This includes cross-posting
to the US groups, I might add. It is some sort of negative
synergistic effect.

Quoted message said:

It's also probably worth stating, for the benefit of any r.b.t. readers who
have not also read helmet threads in u.r.c., that not only is the tone more
civil but the majority of opinion there is fact-based, which of course
means also that they come to a conclusion which reflects the fact that the
USofA has so many, many MHLs, while the UK has none.

But, for the benefit of the new-comers, you should distinguish
between: (1) arguments concerning the protective effects of helmets,
and (2) arguments concerning MHLs. I think even the UK groups agree
that helmets prevent certain types of injuries but generally conclude
that there is a net loss of ridership which results in increased
morbidity from disease -- or there is increased risk-taking, or both.
I wonder whether in the US there would be the same loss of ridership
considering the tendency in this country to wear helmets when doing
any athletic activity. In other words, helmets are part of our culture
but not part of yours.

Also note that the UK is the size of my state, Oregon. It is not
surprizing that the United States has many more MHLs. We have more of
every type of law -- almost. We do not have a television licensing
law. Because of my fact-based opinions, I have been successful in
preventing an MTL (mandatory television license) law in Oregon. -- Jay
Beattie.

Andrew Muzi said:

Godwin Time!
Could someone please use 'nazi' as a pejorative so we can move on?

If you wear this for fashion and/or head protection while cycling, you
are a Nazi: <http://www.ahgmilitaria.com/Medals/GermanPolice2.jpg>.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

--
Posted via a free Usenet account from http://www.teranews.com

Michael Warner said:

Jay Beattie said:

Welcome to hemet threads!

Thanks, but I can't afford more than the standard 5 minutes of abuse,
and I'm sure you have other customers waiting :-)

Man - "Look! I came here for an argument."
Mr. Barnard - "Oh! I'm sorry, this is abuse."

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

--
Posted via a free Usenet account from http://www.teranews.com

Quoted message said:

Dennis Ferguson said:

Quoted message said:

On Jul 9, 11:38 am, Ben C <[email hidden]> wrote:
> What's the technical meaning of "impact"?

Technically, impact is the impulse of force. Even your fussiest carbon-
based life-forms tend to use the shorter phrase, even when being as
technical as possible:

Do you have a reference for that definition? Even the web page you
referenced has a quote inconsistent with that here

http://hyperphysics.phy-astr.gsu.edu/hbase/impulse.html#c4

[snip]

Dear Dennis,

Here's what I quoted:

"The product of average force and the time it is exerted is called the
impulse of force. . . . The main utility of the concept is in the
study of the average impact force during collisions. For collisions,
the mass and change in velocity are often readily measured, but the
force during the collision is not. If the time of collision can be
measured, then the average force of impact can be calculated."

http://hyperphysics.phy-astr.gsu.edu/hbase/impulse.html#c3

Feel free to argue with that web site.

Ah, okay. I just didn't see "impact" being defined as "impulse of
force", or anything else, in there. I still don't, actually, but that's
okay.

Dennis Ferguson

Quoted message said:

Ben C said:

What's the technical meaning of "impact"?

Dear Ben,

Technically, impact is the impulse of force.

Sorry, not so.

As someone else posted, "impulse" has a definite technical meaning,
and is a measurable (or calculable) quantity with units of pounds
times seconds.

But impact is a soft "general" term, not numerically defined and with
no units of measurement. An impact refers, in a general sense, to an
event involving the application of a force for a small amount of
time. This normally happens through a collision. But "impact" does
not equal "impulse."

Quoted message said:

"The product of average force and the time it is exerted is called the
impulse of force. . . . The main utility of the concept is in the
study of the average impact force during collisions. For collisions,
the mass and change in velocity are often readily measured, but the
force during the collision is not. If the time of collision can be
measured, then the average force of impact can be calculated."

Note that in that paragraph, they're using impact as an adjective (not
a noun) to specify a certain force - that arising between colliding
objects.

Quoted message said:

For the curious, here's a link to one helmet test, with heights,
weights, and what the head forms actually hit:

http://www.smf.org/standards/b/b90astd.html

http://www.smf.org/standards/pdf/b95rev.pdf

And of course, Snell does its part to perpetuate the idea that cycling
is dangerous. Their point number one: "1. Bicycling imposes risks of
death or permanent impairment due to head injury."

Yes, and so do thousands of other activities. What is the _level_ of
bicycling's risk? Is it worse than, say, walking down stairs?

Snell: "Um - we'll get back to you on that after we design and test-
market our stair helmets."

Quoted message said:

Note that such drop tests ignore the rotational problem--the severed
fake head in a helmet is simply dropped straight down onto various
anvil forms. Since few bicycle crashes involve a lack of forward
motion, this has been criticized as well-meant, but unrealistic.

I still recall the first article I read on the then brand-new Snell
bike helmet standard. That measly standard (an attempt to protect
against a stationary topple) was immediately criticized as uselessly
small. The response: "It's all we can do. Anything that would
protect against stronger impacts would be unwearable."

And therefore, un-sellable, which is the REAL priority.

- Frank Krygowski

Jay Beattie said:

Quoted message said:

On Jul 9, 11:15 am, Jay Beattie <[email hidden]> wrote:

Quoted message said:

Quoted message said:

Welcome to hemet threads! Although the posters have changed a little
over the last 10 years, the content and tone have not.

Quoted message said:

Well, it _is_ discouraging when people will post to these threads for
10 years without bothering to read any of the science that's available
on the subject!

Quoted message said:

Try www.cyclehelmets.org, Jay.

Frank, I was reading that [censored] before I even started posting to this
group. It was a work requirement -- particularly those studies
showing that helmets reduce focal injury (such as skull frature). I
had a spate of fork failure cases 10-15 years ago involving helmetless
bohemians who smacked their noggins (fractures, stitches mostly -- and
MBI). I talked to real MD/PhD biomechanics about the protective
benefits of bicycle helmets -- in those cases and several others.

With respect: There's been much learned in 10-15 years. IIRC, at
that time there were few in America questioning the actual level of
risk of head injury, and thus the need for any type of head
protection. Also at that time there were no scientific studies
showing that mass uptake of helmets produced no detectable benefit.
Furthermore, there were (IIRC) no studies noting that rotational brain
accelerations were much more damaging than linear ones.

I believe that if you could persuade your biomechanics specialists to
look impartially at the current evidence, and examine the current
state of the debate, they'd be much less pro-helmet. Certainly, when
free debate has been possible in Great Britain, the decision by
experts went against helmets. (Only tricky political moves ever
changed that.)

Quoted message said:

Note that wearing a helmet is often a credibility booster for the
plaintiff in MBI cases. I have had to look at a fair number of cracked
helmets and had to endure plaintiffs and their lawyers pointing and
saying "ahah, there, you see -- it was a serious impact. It cracked
the helmet." It's like body damage in an auto case. We never even get
in to the evidentiary value of helmets on this NG. I suppose if you
don't wear a helmet, you get a laceration or a skull fracture -- which
is even more dramatic evidence of impact, but then the jury goes "why
weren't you wearing a helmet"? Wear a helmet.

What you're saying, in essence, is that those evaluating the legal
situation believe that cycling is dangerous, and that helmets are
wonderfully protective and necessary. In other words, they've bought
into the propaganda, just as you seem to have. Sorry, but that's not
news - and it does NOT prove the propaganda is correct.

The evidence I've seen indicates quite clearly that cycling is NOT an
unusual source of serious head injuries. It also indicates that
helmets are NOT particularly effective in mitigating those few serious
head injuries that do occur. IOW, the best evidence shows helmets are
an ineffective solution to a largely nonexistent problem.

If you're going to take part in these discussions, you really should
examine the evidence.

- Frank Krygowski

Quoted message said:

Quoted message said:

Ben C said:

What's the technical meaning of "impact"?

Dear Ben,

Technically, impact is the impulse of force.

Sorry, not so.

As someone else posted, "impulse" has a definite technical meaning,
and is a measurable (or calculable) quantity with units of pounds
times seconds.

But impact is a soft "general" term, not numerically defined and with
no units of measurement. An impact refers, in a general sense, to an
event involving the application of a force for a small amount of
time. This normally happens through a collision. But "impact" does
not equal "impulse."

[snip]

Dear Frank,

Sorry, but sites like hyperphysics end up saying:

"The main utility of the concept [impulse of force] is in the study of
the average impact force during collisions."

Feel free to draw distinctions without numbers or explanations in the
original question about helmets hitting the ground.

But that's what's so unimpressive about this portion of the thread. A
number of posters are stating that the wrong terms are being used, but
none have bothered to address the example.

I note that the hyperphysics people put up examples with numbers and
calculations and even calculators

Put together an example with some numbers to show what you mean, and
perhaps hyperphysics (and other sites and RBT posters like me) will
appreciate that you have a point about the helmet hitting the ground,
rather than a quibble about the language.

Frankly, I've been surprised that posters who usually use numbers,
equations, and examples suddenly stopped using them in this particular
portion of the thread.

Cheers,

Carl Fogel

Michael Press said:

In article
<[email hidden]>,

Quoted message said:

You complain about people who say you're not very intelligent. But do
you ever stop to think that you're the ONLY one who can't grasp that
Usenet shows context in prior posts? Despite having it explained to
you literally dozens of times?

When you are using google groups
you are not necessarily fully adhering to
Usenet standards and usage.
gg shows context through a web interface
and does not always quote context in replies.

??

Google groups does quote context in replies, just as it did this
time. At worst, one might have to click "Show quoted text" - or, in
"Sort by reply" mode, simply re-read the previous post or two.

I'm using Google Groups, and I have no trouble at all following
context. And I note, Bill Sornson does not appear to be using Google
Groups. His newsreader is almost certainly more capable, so he should
have no excuse whatever for his (pretended?) inability to remember
context.

He's the only person I've ever encountered who is offended by the
standard, recommended practice of trimming posts. Or who pretends he
is.

- Frank Krygowski

Quoted message said:

Quoted message said:

Quoted message said:

On Jul 9, 11:38 am, Ben C <[email hidden]> wrote:

Quoted message said:

Quoted message said:

> What's the technical meaning of "impact"?

Quoted message said:

Quoted message said:

Dear Ben,

Quoted message said:

Quoted message said:

Technically, impact is the impulse of force.

Quoted message said:

Sorry, not so.

Quoted message said:

As someone else posted, "impulse" has a definite technical meaning,
and is a measurable (or calculable) quantity with units of pounds
times seconds.

Quoted message said:

But impact is a soft "general" term, not numerically defined and with
no units of measurement. An impact refers, in a general sense, to an
event involving the application of a force for a small amount of
time. This normally happens through a collision. But "impact" does
not equal "impulse."

[snip]

Dear Frank,

Sorry, but sites like hyperphysics end up saying:

"The main utility of the concept [impulse of force] is in the study of
the average impact force during collisions."

Again, "impact" is being used as a specifying adjective. To rephrase,
their sentence could read: ""The main utility of the concept [impulse
of force] is in the study of
the average force during collisions." It would lose no meaning
whatsoever.

"Impact" is different from "impulse." The second term is
quantifiable. The first term is merely descriptive.

Admittedly, this is a fairly minor point. In a similar manner, many
lay people use the word "strain" when they really mean "stress," and
I'm sure similar discrepancies arise in other fields. But when folks
trained in the discipline see the misuse, they interpret it as a
warning that the user probably isn't very expert in the topic.

- Frank Krygowski

Quoted message said:

...But when folks
trained in the discipline see the misuse, they interpret it as a
warning that the user probably isn't very expert in the topic.

More likely, they wave the specialized jargon around in front of them
like some kind of disinfectant spray to ward off any further
intrusions from 'non-experts.'

Robert

Quoted message said:

Quoted message said:

...But when folks
trained in the discipline see the misuse, they interpret it as a
warning that the user probably isn't very expert in the topic.

More likely, they wave the specialized jargon around in front of them
like some kind of disinfectant spray to ward off any further
intrusions from 'non-experts.'

That wasn't terribly forceful, but it sure had impact.

Heh.

Quoted message said:

Quoted message said:

...But when folks
trained in the discipline see the misuse, they interpret it as a
warning that the user probably isn't very expert in the topic.

More likely, they wave the specialized jargon around in front of them
like some kind of disinfectant spray to ward off any further
intrusions from 'non-experts.'

I'll grant you this: When a few people have spent years studying
things like impulse and momentum or stress and strain, and they're in
a technical discussion involving such concepts, it can be very
annoying to have a cocksure no-nothing wander in and try to redefine
fundamental terms. This is why 13-year-olds aren't usually allowed in
research labs.

Usenet runs by different rules, of course, and most technically
trained people here are patient and kind to non-techies. But there
are reasonable limits to that patience.

- Frank Krygowski

Quoted message said:

Jay Beattie said:

On Jul 9, 8:43 am, [email hidden] wrote:

Quoted message said:

Quoted message said:

On Jul 9, 11:15 am, Jay Beattie <[email hidden]> wrote:

Quoted message said:

Quoted message said:

> Welcome to hemet threads! Although the posters have changed a little
> over the last 10 years, the content and tone have not.

Quoted message said:

Quoted message said:

Well, it _is_ discouraging when people will post to these threads for
10 years without bothering to read any of the science that's available
on the subject!

Quoted message said:

Quoted message said:

Trywww.cyclehelmets.org, Jay.

Quoted message said:

Frank, I was reading that [censored] before I even started posting to this
group. It was a work requirement -- particularly those studies
showing that helmets reduce focal injury (such as skull frature). I
had a spate of fork failure cases 10-15 years ago involving helmetless
bohemians who smacked their noggins (fractures, stitches mostly -- and
MBI). I talked to real MD/PhD biomechanics about the protective
benefits of bicycle helmets -- in those cases and several others.

With respect: There's been much learned in 10-15 years. IIRC, at
that time there were few in America questioning the actual level of
risk of head injury, and thus the need for any type of head
protection. Also at that time there were no scientific studies
showing that mass uptake of helmets produced no detectable benefit.
Furthermore, there were (IIRC) no studies noting that rotational brain
accelerations were much more damaging than linear ones.

I believe that if you could persuade your biomechanics specialists to
look impartially at the current evidence, and examine the current
state of the debate, they'd be much less pro-helmet.

<snip>

He has, particularly with rotational injury and helmets. He is
against boxing helmets. He has nearly 200 published articles (not
including books), he was on the teaching staff at Harvard and MIT. He
has a PhD. He is not an internet expert. This is what he does for a
living. He qualifies as an expert in court. Do you?

Quoted message said:

Quoted message said:

Note that wearing a helmet is often a credibility booster for the
plaintiff in MBI cases. I have had to look at a fair number of cracked
helmets and had to endure plaintiffs and their lawyers pointing and
saying "ahah, there, you see -- it was a serious impact. It cracked
the helmet." It's like body damage in an auto case. We never even get
in to the evidentiary value of helmets on this NG. I suppose if you
don't wear a helmet, you get a laceration or a skull fracture -- which
is even more dramatic evidence of impact, but then the jury goes "why
weren't you wearing a helmet"? Wear a helmet.

What you're saying, in essence, is that those evaluating the legal
situation believe that cycling is dangerous, and that helmets are
wonderfully protective and necessary. In other words, they've bought
into the propaganda, just as you seem to have. Sorry, but that's not
news - and it does NOT prove the propaganda is correct.

The evidence I've seen indicates quite clearly that cycling is NOT an
unusual source of serious head injuries. It also indicates that
helmets are NOT particularly effective in mitigating those few serious
head injuries that do occur. IOW, the best evidence shows helmets are
an ineffective solution to a largely nonexistent problem.

If you're going to take part in these discussions, you really should
examine the evidence.

I have. I just disagree with you and do not accept epidemiology as
the be-all and end-all of a biomechanical inquiry -- or the more
particularized inquire of whether I should wear a helmet. A helmet
does protect against certain injuries. That is a fact. Am I likely
to suffer those injuries? Yes, because I have several times in the
past. Am I part of the population that would benefit from a helmet?
Yes. Do I need to wear one all the time. No. Do I take more risks
when wearing a helmet? No, because I don't like hurting any other part
of my body. Do I care about MHLs? No because they do not apply to me,
except to my benefit. Do I care if MHLs reduce the number of
cyclists? No, because there are too many cyclists who get in my way,
and I like having the road to myself. Do I care if you wear a helmet.
No. There you have it. EOM. -- Jay Beattie.