Tommy Tomcat,
When the helmet breaks, it clearly does absorb a significant amount of energy that would have
otherwise been transfered to the head. Your statement that "When the helmet breaks it essentially
absorbs NO energy" is absolutely untrue from a physics standpoint (so where did the energy come from
to break the helmet if not the fall itself, Tom?). You are aware of the Laws of thermodynamics that
state that energy cannot be created or detroyed, only changed from one form to another. A broken
Puerto Rican cooler signifies a successful transfer of significant energy into a helmet and NOT the
head. Manufacturing a helmet that does not break might actually offer less protection than one that
does because it would absorb little energy yet transfer a lot to the head.
Such a safety design features are employed in the auto industry in their vehicles as the well-known
'crumble-zone' technology.
Consequently, current DOT certified helmets are actually DESIGNED and INTENDED to break in an impact
precisely for this very reason. Your argument that the styrofoam needs to be 'crushed' (i.e.
compressed) would not apply to a high speed impact, but would apply to a very low-speed impact.
Cycling accidents are exclusively high speed impacts and thus result in breakage instead of
compression (they are the same species of animal).
Your other argument that a helmet is designed to dissipate the impact forces over a larger area of
the head's surface area is correct and is a secondary safety mechanism of bicycle helmets.
Your final conclusion that a helmet is only good for preventing minor injuries and not serious
injuries is a completely unquantified conclusion that lacks any data and does not even feel
intuitively correct. I can assure you if the safety engineers from Bell, SNELL, DOT, and Mercedes
Benz, not to mention the head trauma physicians from the AMA came onto this forum, they would have a
field day debunking your unqualified answers with core facts and scientific and medical data that
dates back to the 1950's....that is, once they stopped laughing at your head injury.
There can be only one,
Café Actually Paid Attention in Physics Class
Tom Kunich wrote:
> "George Privon" <
[email protected]> wrote in message
news:[email protected]...
> >
> > Umm... I think you're the one that needs to review High School
> Physics.
> > The head just before impact has a certain amount of momentum. The crushing of the helmet (or
> > breaking as the case may be) disperses
> *some*
> > of the energy. This crushing/breaking of the helmet also lengthens
> the
> > time of the impact.
>
> Firstly, George, the only way that foamed plastic can absorb energy is by crushing. When the
> helmet breaks it essentially absorbs NO energy. Haven't you noticed that there are all sorts of
> stories about how people's lives were saved by helmets and the way they knew it was because the
> helmets were broken? I wonder why people think that would show that a helmet performed correctly?
>
> And helmets only rarely crush, especially modern helmets. Over time they've made these weird
> shaped monstrosities that don't have enough surface area for soft enough foam. So the foam they
> use is very rigid and with all of the vents in modern helmets they simply break apart in a fall.
>
> Now it isn't as if helmets do nothing at all. In a minor fall the helmet can help spread the
> force of an impact over a larger area of the skull which has some positive effect. But when the
> forces start getting high enough to cause impact damage to the brain the forces are altogether
> too high for 7 ounces of plastic foam which isn't designed properly in the first place to have
> any cogent effect.
>
> So the most you can expect from a helmet is that it will protect your somewhat from minor injuries
> but it will have no effect at all in serious injuries.
>
> > If you remember from physics - Force * Time = Change in Momentum. In
> a
> > collision like this the change in momentum is very large. The time
> is
> > very small. This generates an extrememly large force on the head. However, with a helmet the
> > time of the impact is lengthened so, the force isn't as large. Less force = less damage.
>
> The foam in a helmet will collapse to about 50% of its original thickness. The thick parts of a
> helmet are about an inch thick. The foam is supposed to collapse at an even 300 gees for a 13 lb
> head magnesium mold.
>
> You seem capable of doing the math.
>
> However, in real life there isn't a magnesium head mold. There is a head and inside of that head
> is a brain floating in a liquid that allows it to slosh around when accelerated. That sloshing
> around can be fatal even though there is no external damage.
>
> The long and the short of it is that the head isn't a block of metal (well, most people's aren't)
> and saving the skull from cracking isn't the only thing that is necessary to prevent fatal
> injuries.
