From: SFPhysics@aol.com
Date: Tue Nov 13 2001 - 02:58:57 PST
From: SFPhysics@aol.com Message-ID: <f4.123807ef.292256f1@aol.com> Date: Tue, 13 Nov 2001 05:58:57 EST Subject: Value of delta v for a Concussion?
<< >
> 2. We are studying the impulse equation Ft = change in mv. My students
> were wondering what amount of force in pounds or Newtons it takes to knock
> out an average person and what amount may cause death in a car accident?
> Does anyone know the range or where I could find it?
> Eric Plett
> Junipero Serra HS
>>
Greetings Eric:
I had my Physics students work out the deceleration values for car crashes
and what would happen at various velocities. Unfortunately there are no
solid figures for what it takes to "knock out" an "average" person. This is
because to knock out someone you must cause the brain to accelerate violently
and strike the inside of the cranium. This can be a rotational or linear
motion since the head can move in several axis. When the brain does
accelerate or decelerate rapidly the nerve cells, connective fibres, and
blood vessels get injured which leads to the loss of consciousness and leaves
permanent damage which is cumulative. Each accident produces different
forces and everyone has a different tolerance to violent head movements
before damage makes you lose consciousness.
That being said you can go to research done by doctors who deal with sports
medicine injuries such as boxing. A skilled boxer may easily put 160g
acceleration on the skull of another in a linear blow and up to
16,000rads/s^2 for an angular acceleration which will generally cause
concussive knockout in the opponent. Where the figure of the impulse was
applied longer than 3ms the brain damage was more apparent. Loss of
conscious control was generally agreed to be in the range of 90-120g. (Dr.
Schwartz in Clin Neurosurg, 1966)
As to the question of what force would cause death, this is again a function
of where the force was applied to the head, for how long, and at what delta
v. Boxers have been killed with punches at the lower range of 50g. All it
takes is for enough blood vessels to be damaged and the blood pools in a
"subdural hematoma" which puts pressure on the brain coupled with the
swelling of the brain from broken capillaries and the brain squeezes itself
to death.
I hope that helps. I asked my students why boxers stepped back to "roll with
the punches" and they did the math to find out. That too is a good exercise.
Best wishes to all - the meteors are coming - the meteors are coming - don't
forget to remind your students to look up for the Leonids from the 14th to
the 20th of this month and hope for a spectacular meteor storm........
Al Sefl
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