GMTV, cycle helmets and shonky physics

[James Annan]

Tony Raven wrote:
> James Annan wrote:
>
>>
>> That seems unlikely, since the head is free to move (a modest
>> distance) within the car.
>>
>
> Not if the car is slamming backwards into the concrete barrier, as is a
> fairly frequent CART occurrence.
>
Even then, there is a headrest, plus the chair itself will probably move
a bit given the forces involved. And the head is cradled in a helmet
with straps and pads and stuff. I was just wondering what the 200g
number referred to, that's all.

James
--
James Annan
see web pages for email
http://www.ne.jp/asahi/julesandjames/home/
http://julesandjames.blogspot.com/

 

[Nigel Randell]

Tim Woodall wrote:
> On Fri, 01 Jul 2005 19:34:33 +0100,
> John Hearns <[email protected]> wrote:
>
>>I thought the measure of effectiveness was the deceleration
>>"Research has shown that decelerations of about 250-300g are the maximum
>>that can be tolerated by the adult head without leading to irreversible
>>injury. (g is the acceleration due to gravity, approximately 9.8 m/s2)"
>>
>
> This sounds way too high. The skull may be able to withstand that sort
> of acceleration but I can't believe the brain has a sufficiently rigid
> structure to be able to able to support itself at those sorts of forces.
>
> Hard disk drives, when powered off, are typically rated to 70g. I would
> be surprised if a brain could go any higher.
>
> Tim.
>

Head injury risk is usually assessed using a calculated criterion rather
than just an acceleration. This criterion takes into account the
magnitude and duration of the acceleration and is proportional to the
mean acceleration raised to the power of 2.5, and the duration of the
most damaging part of the event.

The acceptance standards are by no means uniform; for cars the head
injury criterion must stay below 1000 (dimensions unspecified), in
coaches the target is 500.

Where accelerations, rather than injury criteria, are used there are
also wide variations in measurements and target numbers. For racing
cars a headform impacing a steering wheel must not exceed 80g for more
than 3ms, whereas Snell B95 stipulates an absolute maximum of 300g for
the helmeted headform without specifying a 3ms cutoff value.

--
Nigel Randell