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Gawnsoft
Guest
On Thu, 11 Mar 2004 16:53:52 GMT, Trevor Barton <[email protected]>
wrote (more or less):
>On Thu, 11 Mar 2004 16:05:08 GMT, Simon Brooke wrote:
>> The first one is, do cycle helmets offer sufficient extra protection
>> to offset the increased risks (larger size -> greater angular
>> acceleration, more likely to hit things) they cause, or not?
...
>I keep seeing this large size/greater angular acceleration thing
>and I can't help commenting on it, because it seems to me to be
>a red herring, and if it's not a red herring it's unclear at best.
>
>If the helmet is bigger, for the same lateral velocity of impact,
>the angular acceleration will probably be lower for a helmeted head
>all else being equal. That's because the helmet has a larger radius,
>and therfore for the same linear velocity at the edge needs a smaller
>angular velocity, therefore the shock loading on the brain is likely
>to be lower. That assumes the same coefficient of friction between a
>head and the road as between a helmet and the road.
>
>On the other hand, the helmet is larger, and you therefore need less
>torque to angularly accelerate (?) the head if the mass and rotational
>inertia is the same. However, the mass isn't the same, although the
>mass of the helmet is light and most of the mass is concentrated in the
>centre so the rotational inertia is probably pretty similar.
It' sthat there's a greater moment arm, and so collisions which would
not otherwise have cause the head to be rotated about the axis of the
neck will cause such motion.
--
Cheers,
Euan
Gawnsoft: http://www.gawnsoft.co.sr
Symbian/Epoc wiki: http://html.dnsalias.net:1122
Smalltalk links (harvested from comp.lang.smalltalk) http://html.dnsalias.net/gawnsoft/smalltalk
wrote (more or less):
>On Thu, 11 Mar 2004 16:05:08 GMT, Simon Brooke wrote:
>> The first one is, do cycle helmets offer sufficient extra protection
>> to offset the increased risks (larger size -> greater angular
>> acceleration, more likely to hit things) they cause, or not?
...
>I keep seeing this large size/greater angular acceleration thing
>and I can't help commenting on it, because it seems to me to be
>a red herring, and if it's not a red herring it's unclear at best.
>
>If the helmet is bigger, for the same lateral velocity of impact,
>the angular acceleration will probably be lower for a helmeted head
>all else being equal. That's because the helmet has a larger radius,
>and therfore for the same linear velocity at the edge needs a smaller
>angular velocity, therefore the shock loading on the brain is likely
>to be lower. That assumes the same coefficient of friction between a
>head and the road as between a helmet and the road.
>
>On the other hand, the helmet is larger, and you therefore need less
>torque to angularly accelerate (?) the head if the mass and rotational
>inertia is the same. However, the mass isn't the same, although the
>mass of the helmet is light and most of the mass is concentrated in the
>centre so the rotational inertia is probably pretty similar.
It' sthat there's a greater moment arm, and so collisions which would
not otherwise have cause the head to be rotated about the axis of the
neck will cause such motion.
--
Cheers,
Euan
Gawnsoft: http://www.gawnsoft.co.sr
Symbian/Epoc wiki: http://html.dnsalias.net:1122
Smalltalk links (harvested from comp.lang.smalltalk) http://html.dnsalias.net/gawnsoft/smalltalk