Warning: H*lm*t content

Euan Wrote:
"Claes" == Claes
writes:


Claes It seems that statistics can not solve this one. How about a
Claes simple test. You wear nothing on your head, I smack a
Claes baseball bat on your head, just hard enough to crack you
Claes scull, then we do a test with your head again, healed up and
Claes all, and smack at the same force, you think you head would
Claes not crack this time?

You would have to have a very fine gradient in the velocity of the
baseball bat.

Bicycle helmets absorb kinetic energy (KE). The formula for KE is:

KE = 1/2 * M * V^2

It's tempting to think that a bicycle helmet that's rated for a 1
km/h
impact will take 19km/h off of any impact speed and make a difference.
This isn't the case.

Let's say the mass is 10kg and the velocity is 19km/h. The kinetic
energy is 1805.

Now let's take an impact at 40km/h. The kinetic energy is 8,000.

So we take away the 1805 from the 8,000 which leaves 6,195.

Re-arranging the equation a bit we can find out how much speed the
helmet's taken off the impact. The effective speed of the impact is
35.2km/h.

The higher the impact speed, the more ineffective the helmet is an
it's
an exponential curve. At 60km/h the effective speed of impact is
56.9km/h. At 80km/h the effective speed of impact is 77.7km/h

I ride consistently at speeds over 35km/h. A collision at that speed
whilst wearing a helmet would make the collision speed 29.39km/h. I
don't think that's going to make a huge difference to the extent of a
head injury incurred, but that's a personal judgement.

Add in the fact that I weigh considerably more than 10kg and tha
makes
a helmet almost irrelevant.
--
Cheers | ~~ __@
Euan | ~~ _-\,
Melbourne, Australia | ~ (*)/ (*)

This doesn't smell right - surely it is the distribution of the energ
of an impact through time and across an area that determine th
likelihood of damage. You have shown that the distribution of energ
through time is little changed, especially for higher speed impacts
but not shown that energy is dissipated across a wider area of th
head. For example, a 20kg plate can be supported by balancing it o
your head, but put a nail in the centre of the plate and you'll pierc
a nice hole in your head if you try to balance it in the same way. Thi
example says nothing about velocity, but something about th
distribution of force...

Ritc

--
ritcho

Euan Wrote:
"Claes" == Claes
writes:


Claes It seems that statistics can not solve this one. How about a
Claes simple test. You wear nothing on your head, I smack a
Claes baseball bat on your head, just hard enough to crack you
Claes scull, then we do a test with your head again, healed up and
Claes all, and smack at the same force, you think you head would
Claes not crack this time?

You would have to have a very fine gradient in the velocity of the
baseball bat.

Bicycle helmets absorb kinetic energy (KE). The formula for KE is:

KE = 1/2 * M * V^2

It's tempting to think that a bicycle helmet that's rated for a 1
km/h
impact will take 19km/h off of any impact speed and make a difference.
This isn't the case.

Let's say the mass is 10kg and the velocity is 19km/h. The kinetic
energy is 1805.

Now let's take an impact at 40km/h. The kinetic energy is 8,000.

So we take away the 1805 from the 8,000 which leaves 6,195.

Re-arranging the equation a bit we can find out how much speed the
helmet's taken off the impact. The effective speed of the impact is
35.2km/h.

The higher the impact speed, the more ineffective the helmet is an
it's
an exponential curve. At 60km/h the effective speed of impact is
56.9km/h. At 80km/h the effective speed of impact is 77.7km/h

I ride consistently at speeds over 35km/h. A collision at that speed
whilst wearing a helmet would make the collision speed 29.39km/h. I
don't think that's going to make a huge difference to the extent of a
head injury incurred, but that's a personal judgement.

Add in the fact that I weigh considerably more than 10kg and tha
makes
a helmet almost irrelevant.
--
Cheers | ~~ __@
Euan | ~~ _-\,
Melbourne, Australia | ~ (*)/ (*)

You argue ****e again I think.
If you come to a dead stop a 50 km/h, the helmet will not save you
agreed. But that was never the case. You fronting with a car or truck
helmet will probably not save you either. The MAJORITY of accidents, i
Sweden at least, are single accidents. The only force absorbed is hea
towards the ground. Lets assume head hits the ground at a VERTICA
speed of 20 km/h as stated before, and suddenly, the helmet make
sense.

You weighing more than 10 kgs is not relevant either in most cases
Your body is not a stiff metal rod connected to your head. You will no
transfer the energy the same way so your example is ****e once again.

Your head weighs about 5 kgs. We can argue for ever about how th
kinetics work, but that will not help. From sweden there is statistics
and we do NOT have a helmet law, that 40 % of the cycling accidents ar
head injuries where helmets COULD help. The MAJORITY, of accidents ar
single accidents too. That is sweden, so it seems like helmets coul
help. No

--
Claes

Euan wrote:
"Bob" == Bob writes:
Bob Everyone do what they want, legally or otherwise, I will
Bob continue to wear a helmet that may save my life.

That's a very big may. I prefer not to entrust my safety to what is
essentially a piece of polystyrene designed to absorb the kinetic energy
of a fall from head height. That's all it does.

all my helmet did for me when i was hit by a car was put a nasty big
hole in a windscreen of a car that ran a stop sign and collected me...
i was fine the driver was furious. bike trashed the bumper on the
car, bent the bonnet, hole in windscreen and i had to replace a
derailuer. anyone who prattles on that helmets do nothing obviously are
clinically insane. i'm quite willing to be unfashionable =P

cheers,

kim

More stats from another source.
Swedish statiscs from january 1997 - june 2000 shows that
91 people died while cycling in southern sweden. Only 7 wore helmets.
The statistics for helmet usage in the area around the period was 17-1
%.

Assuming that the helmet had no effect, the number of dead with helme
should have been 16, we have less than half that. That indicates tha
helmet does indeed work

--
Claes

"Resound" == Resound writes:

Bicycle helmets absorb kinetic energy (KE). The formula for KE
is:

KE = 1/2 * M * V^2


Resound That does make a bit of difference, dunnit? I do wonder how
Resound constant the energy dispersion of a helmet relative to
Resound speed is though. Probably not a squared function though.

No idea, I'm not an engineer. I've just got basic physics under my belt
and I can remember some equations and Google what I can't :-)
--
Cheers | ~~ __@
Euan | ~~ _-\,
Melbourne, Australia | ~ (*)/ (*)

"Theo" == Theo Bekkers writes:

Theo Resound wrote:
And, importantly, it's only recently that we've been moving at
greater than running speed. Hit the ground at 20kph and you're
okelydokely. Hit the ground at 40kph and you're much more likely
to break something important. Not always of course, but doubling
impact speed is always going to skew your results more than a
touch.

Theo Err, if you fall off your bike you will hit the ground at
Theo approx 20km/h regardless of the speed at which you are
Theo travelling. This is the design spec of bike helmets. Should
Theo you have a horizontal velocity of 40 km/h you will still hit
Theo the ground at 20km/h.

I don't think that's correct.

When there are two or more velocities what we have a vectors. We have
the horizontal component (40km/h) and the vertical component. The
vector simplistically is the root of the sum of the horizontal squared
and the vertical squared.

For the cited figures that gives a velocity of 44km/h on point of
impact.

A combination of kinetic absorption and friction dissipates the
velocity.
--
Cheers | ~~ __@
Euan | ~~ _-\,
Melbourne, Australia | ~ (*)/ (*)

"ritcho" == ritcho writes:

ritcho Euan Wrote:
Bicycle helmets absorb kinetic energy (KE). The formula for KE
is:

KE = 1/2 * M * V^2

ritcho This doesn't smell right - surely it is the distribution of
ritcho the energy of an impact through time and across an area that
ritcho determine the likelihood of damage. You have shown that the
ritcho distribution of energy through time is little changed,
ritcho especially for higher speed impacts, but not shown that
ritcho energy is dissipated across a wider area of the head.

It's kinetic energy. Area is not a factor in kinetic energy. It's an
absolute figure. A helmet has X kinetic energy absorption capacity.

ritcho For example, a 20kg plate can be supported by balancing it
ritcho on your head, but put a nail in the centre of the plate and
ritcho you'll pierce a nice hole in your head if you try to balance
ritcho it in the same way. This example says nothing about
ritcho velocity, but something about the distribution of force...

That's correct, force. That's different from kinetic energy and
depending what you're trying to calculate there are many different
equations.
--
Cheers | ~~ __@
Euan | ~~ _-\,
Melbourne, Australia | ~ (*)/ (*)

"Claes" == Claes writes:

Claes Euan Wrote:
"Claes" == Claes
writes:


Claes It seems that statistics can not solve this one. How about a
Claes simple test. You wear nothing on your head, I smack a
Claes baseball bat on your head, just hard enough to crack you
Claes scull, then we do a test with your head again, healed up and
Claes all, and smack at the same force, you think you head would
Claes not crack this time?
You would have to have a very fine gradient in the velocity of
the baseball bat.

Bicycle helmets absorb kinetic energy (KE). The formula for KE
is:

KE = 1/2 * M * V^2

It's tempting to think that a bicycle helmet that's rated for a
19 km/h impact will take 19km/h off of any impact speed and make
a difference. This isn't the case.

Let's say the mass is 10kg and the velocity is 19km/h. The
kinetic energy is 1805.

Now let's take an impact at 40km/h. The kinetic energy is 8,000.

So we take away the 1805 from the 8,000 which leaves 6,195.

Re-arranging the equation a bit we can find out how much speed
the helmet's taken off the impact. The effective speed of the
impact is 35.2km/h.

The higher the impact speed, the more ineffective the helmet is
and it's an exponential curve. At 60km/h the effective speed of
impact is 56.9km/h. At 80km/h the effective speed of impact is
77.7km/h

I ride consistently at speeds over 35km/h. A collision at that
speed whilst wearing a helmet would make the collision speed
29.39km/h. I don't think that's going to make a huge difference
to the extent of a head injury incurred, but that's a personal
judgement.

Add in the fact that I weigh considerably more than 10kg and that
makes a helmet almost irrelevant. -- Cheers | ~~ __@ Euan | ~~
_-\, Melbourne, Australia | ~ (*)/ (*)

Claes You argue ****e again I think. If you come to a dead stop a
Claes 50 km/h, the helmet will not save you, agreed. But that was
Claes never the case. You fronting with a car or truck, helmet will
Claes probably not save you either. The MAJORITY of accidents, in
Claes Sweden at least, are single accidents. The only force
Claes absorbed is head towards the ground. Lets assume head hits
Claes the ground at a VERTICAL speed of 20 km/h as stated before,
Claes and suddenly, the helmet makes sense.

You forgot the horizontal component, that can be significant. See
earlier post about vectors.

Claes You weighing more than 10 kgs is not relevant either in most
Claes cases. Your body is not a stiff metal rod connected to your
Claes head. You will not transfer the energy the same way so your
Claes example is ****e once again.

If I land head first on my head then a significant amount of my mass
will be transmitted through my head. Tell you what, drop yourself off
a ladder head first from two meters wearing a helmet.

Claes Your head weighs about 5 kgs. We can argue for ever about how
Claes the kinetics work, but that will not help. From sweden there
Claes is statistics, and we do NOT have a helmet law, that 40 % of
Claes the cycling accidents are head injuries where helmets COULD
Claes help. The MAJORITY, of accidents are single accidents
Claes too. That is sweden, so it seems like helmets could help. No?

Could of, would of. Those are not facts.
--
Cheers | ~~ __@
Euan | ~~ _-\,
Melbourne, Australia | ~ (*)/ (*)

"Claes" == Claes writes:

Claes More stats from another source. Swedish statiscs from
Claes january 1997 - june 2000 shows that 91 people died while
Claes cycling in southern sweden. Only 7 wore helmets. The
Claes statistics for helmet usage in the area around the period was
Claes 17-18 %.

Claes Assuming that the helmet had no effect, the number of dead
Claes with helmet should have been 16, we have less than half
Claes that. That indicates that helmet does indeed work.

Maybe it's because it's late, but I'm not following your math. Please
elaborate.
--
Cheers | ~~ __@
Euan | ~~ _-\,
Melbourne, Australia | ~ (*)/ (*)

"Claes" == Claes writes:

The human brain is not a vegetable. It's a highly sophisticated
organ which is highly protected by a thick skull and in-built
shock absorption. Comparing the two is like comparing apples and
oranges.

Claes He he, it was an example, nothing else, read it and apply
Claes "critical thinking" to it.

Please read http://www.cyclehelmets.org/papers/c2022.pdf

Then come back to me and explain to me the case for helmet
compulsion when it's proved beyond all doubt that helmet
compulsion discourages cycling and therefore increases the risk
per kilometer cycled because there are less cyclists on the road.

Claes Ehh, what that does that prove? You can not prove what would
Claes have happened without the helmets. Too many other variables
Claes change, and many are not included. That report is total BS.

You can't dismiss a report as total BS without substantiating that
claim. Which facts in the report do you question?
--
Cheers | ~~ __@
Euan | ~~ _-\,
Melbourne, Australia | ~ (*)/ (*)