[MR] Heavy Helms and inertia

[Christopher M Faulcon]

There are a combination of factors at work in protecting the head.

In football, where the impact area is large, the 'feather' method works,
mainly by increasing the surface area over which the collision takes place,
and by increasing the amount of time the collision takes.

In SCA combat, on the other hand, the impact area is comparatively small.
Helms must therefore provide protective value through several methods,
mainly:
	1. Increasing the Surface Area.
	2. Making most collisions 'elastic', meaning they glance off and continue
moving in another direction.
	3. Minimizing the acceleration of the brain by increasing the mass of the
collision object.

In essence, helms work because they make the sword push the whole head, not
just the 1 1/8 inch stripe they hit, by having good glancing surfaces to
redirect the energy of the incoming blow, and by making sure that those
blows that do stick do minimal damage to the brain.

As any fighter can tell you, the blows that feel the hardest are those that
do not glance, as these blows tend to transmit the maximum amount of kinetic
energy to the target. The reason, then, that heavier helms are better, is
both to minimize the transfer of momentum, both from glancing blows (elastic
collisions), and those that 'stick' (inelastic collisions).

Martin Lochner
Seneschal, Trimaris
Physics Major, Duke University, Class of 1994

-----Original Message-----
From: atlantia-admin at atlantia.sca.org
[mailto:atlantia-admin at atlantia.sca.org]On Behalf Of Teleri Barod
Sent: Friday, September 28, 2001 10:49 AM
To: thumpa at mindspring.com
Cc: atlantia at atlantia.sca.org
Subject: Re: [MR] Heavy Helms and inertia



--- thumpa at mindspring.com wrote:
>

>
> Close... actually F=MA is mass times acceleration.
> Or you could say Force = Mass times Velocity squared
>

Milord?  I don't recall this one.  dv/dt isn't the
same as v^2.  In fact, if your velocity is constant,
the net force on an object must be zero, as there is
no acceleration at all - even if the velocity is
large.

Perhaps you were thinking of kinetic energy = 1/2 *
mass * velocity^2?

I think the momentum argument is the most compelling
for the heavy helm case.  My guess is that lighter,
more modern head protection uses energy dissipation
(the feather pillow one fellow mentioned).  The energy
of the blow goes into deforming the high-tech foam and
plastic of the helmet rather than your head.  Aren't
such helmets usually replaced after a serious blow?
I'm fairly sure this is the case with motorcycle and
bicycle helmets, and less sure for football gear.

I think, for what we do and how hard we hit, a heavy
steel helm is most practical and safe.



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