Quoted message said: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
Dear Frank,
When a 13-year-old points out that the same hammer blow produces
different effects on a table top, depending on whether it's been
cushioned with a pad, the 13-year-old looks smarter than people
quibbling about his terms and calling him a 13-year-old.
In fact, the 13-year-old is just pointing out this sort of thing:
http://en.wikipedia.org/wiki/Impact_force
I should add that I foolishly forgot that Joe Riel addressed the point
in his usual succinct fashion, clarifying what the 13-year-old was
trying to say about the hammer and the pad:
http://groups.google.com/group/rec.bicycles.tech/msg/b0d5b0fe160759dc
Whether you want to call it peak force, average force, force of
impulse, or anything else, the original point was that a helmet or a
pad does indeed cushion the impact of a crash or a hammer.
Some posters are so caught up in the discussion that they will seize
on the admittedly confused original explanation of the hammer and the
pad instead of addressing the obvious practical point.
I suspect that this evasion is due to their reluctance to grant any
value to helmets, but it makes them look either foolish, frightened,
or unwilling to argue in good faith.
Here's how I'd address the hammer and pad argument instead of
quibbling about semantics.
Yes, helmets can cushion impacts in crashes, just as pads cushion
hammer blows. The peak force is reduced by being spread out over a
longer time.
But . . .
Study after study shows that helmets fail to do what we wish they'd
do. When mandatory bicycle helmet laws cause a huge, abrupt increase
in helmet use, there is no apparent effect on the rate of serious head
injuries and deaths. The hoped-for effect simply doesn't show up.
(Smaller studies, usually comparing badly-chosen groups, _may_ show a
helmet effect, but smaller studies are only useful as far as they
predict what larger studies will show. In crude terms, rolling a
double-six once is not going to be a useful guide to playing
backgammon. To show just how badly designed and interpreted small
studies can be, the most often cited study claiming that helmets
dramatically reduced head injuries also inadvertently showed that
helmets dramatically reduced leg injuries.)
Various explanations have been offered for the helmet failure.
Riders may be risk compensating, meaning that they automatically
increase their risky behavior to maintain the same level of acceptable
risk. The taxi driver study often mentioned in these threads showed
that taxi drivers randomly assigned cars with and without ABS braking
clearly drove faster and closer to other cars when they thought that
they were protected by the ABS.
While insisting that they certainly do no such thing, people will
answer questions that show that they certainly do behave differently
when they wear helmets. Posters here on RBT often expose this behavior
by pointing out that other posters who deny risk-compensation
nevertheless admit that they would ride more slowly and carefully (or
even walk) if they lost their helmet halfway through a ride.
(The hallmark of risk compensation is that almost everyone believes
that _they_ doesn't do it, in spite of clear evidence that they do,
just as almost everyone believes that _they_ have no need of
double-blind procedures. It's those other guys who are human and
fallible, not us.)
Another explanation for helmet failure is that its cushion effect may
be offset by a corresponding increase in actual impacts and rotational
effects. A helmeted head is much larger, so it hits things that the
unhelmeted head misses. When it hits those things, the helmeted head
is rotated with a longer lever arm. More impacts and more powerful
rotations would be a deadly combination, since more and more evidence
shows that rotational injuries, not direct blows, are likely to be the
culprits in typical bicycle crashes.
Yet another explanation for helmet failure is that the cushion effect
may be insignificant. Most bicyclist deaths in the U.S. involve
massive injuries caused by collisions with cars at high speeds, not
the comparatively gentle slip-and-fall impacts suggested by typical
helmet testing standards.
(Consider how rare deaths and serious brain injuries were in
pre-helmet bicycle racing, where simple falling-down crashes were
almost routine. We still speak of "road rash" almost casually. "Car
rash" is quite a different matter.)
In other words, a heavy coat and a hat can cushion you against hail,
just as a helmet can cushion you against minor head injuries. But the
coat and hat offer no more practical protection against bullets and
shrapnel than helmets seem to offer against serious brain injuries and
deaths.
Most anecdotal arguments that a helmet did protect a rider from severe
head injury turn out to be logically flawed, since there's no way to
reproduce the accident without the helmet and it's hard not to draw
shaky conclusions from cracked styrofoam.
But we _do_ have large-scale comparisons. Those dull statistics show
that abruptly raising helmet use from around 50% to nearly 100% with a
mandatory helmet law has no discernable effect on serious injuries.
Here's a typical graph of helmet use rising abruptly from about 60% to
nearly 100% without any significant effect on head injuries:
chapmancentral.co.uk91.4A64!OpenElement&FieldElemFormat=gifOpen ↗
or http://tinyurl.com/23zdsq
You can see the details and similar graphs here:
http://www.chapmancentral.co.uk/web/public.nsf/Documents/maxi-faq-helmets?OpenDocument
We all wish that there was something that we could buy in a store that
would protect us on our bicycles against serious brain injury and
death, but so far there's no practical evidence that helmets offer
that. They may indeed protect against minor injuries.
Luckily, as Frank and others keep reminding us, bicycling is
extraordinarily safe.
Cheers,
Carl Fogel
