Re: Impulse

[Larry Cartwright <exit60@CABLESPEED.COM>]

What they've done to dashboards is far less important to crash survival
than what they've done to the entire structure of the front end (and
rear end).  The structure of a modern automobile is a series of "crumple
zones" designed to collapse in a very predictable manner, spreading the
impact forces of a head-on collision over a longer period of time than
ever before.  First the bumper, then the shock-absorbers behind the
bumper, then the engine compartment; the passenger compartment itself
will start to deform with 30-40 mph barrier collisions.

Collision-safety engineering is all about reducing impulse.  You can't
do much about the forces involved, so you try to increase the time of
impact as much as you can.

Here's an interesting (IMO) statement from the "Real-life Safety"
engineering group at Saab:  "When other vehicles are involved, the
intensity of the crash forces is usually about half the level of the
forces generated at the same speed against a barrier.  Accidents
involving actual impacts against rigid objects at speeds above 40 mph
(equivalent to about 80 mph car to car) are extremely rare."

There is serious speculation that the retaining wall collisions which
caused the recent deaths of racing drivers Dale Earnhardt, Adam Petty
and Kenny Irwin were exacerbated by structural bracing which was added
to the front ends of their cars.  All three had very similar
triangular-framework stiffening modifications to reduce the amount of
front end flex as the car makes high speed turns.  With 3 high-echelon
high-visibility deaths in 10 months, racing teams are re-thinking front
end rigidity.

Wear those seatbelts!  They reduce the impulse some, too; but mainly
they keep you from leaving what automotive engineers call the "safety
box".

Best wishes,

Larry

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Larry Cartwright   <exit60@cablespeed.com>
Retired (June 2001) Physics Teacher
Charlotte MI 48813 USA
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"Information is not knowledge,
 knowledge is not wisdom,
 and wisdom is not foresight.
 Each grows out of the other
 and we need them all."
            (Arthur C. Clarke)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Chuck Britton wrote:
> The FIRST padded dash boards were covered with foam rubber. Then the
> accident watchers noted that there was an INCREASE in concussions.
>
> Dashboards were quickly converted to CRUSHABLE padding that prevents
> the rebound. Having the head bounce BACK after the initial impact was
> a BAD thing!
>
> The crushable dashboard applies the same force for LESS time than the
> bouncy dashboard.