Re: Fwd: Audi A8 Achieves Highest Possible Safety Test Rating

[Robert Myers <rmyers@inetone.net>]

With apologies for the bandwidth,

Visualize it this way, Mike.  Imagine a car colliding with an immovable
barrier.  Metal deforming - all that sort of stuff.  How much damage will
be done to the car?  Dunno, but some more or less certain amount, right?
By measuring the damage done, we could in fact (and with enough data from
other crashes), make a rather close estimate of the vehicle's speed at
contact?  Correct?  The energy of the collision is being absorbed by the
metal of the car as the car "pushes" against the immovable barrier and the
metal "crunches".

Suppose another identical car traveling at the same exact speed
simultaneously strikes the same barrier from the opposite side.  The damage
produced is a function of the vehicle's speed - more speed --> more damage.
 If the second car were identical to the first one and traveling at the
same speed and striking the same barrier then the same amount of damage
would be done to it.  Make sense so far?

Are you still with me?  What did the barrier do in each case?  It stopped
the car.  How much work was done on the barrier?  The answer?  Zero.  The
barrier did not move.  Work is the product of force and distance.  The
force term is large but the distance moved is zero, therefore, their
product is zero.  How much work was done on the car?  This is more
difficult to answer, but the answer is not zero.  A force was applied
during the brief period that the car was stopping (and crumpling).  The
center of gravity of the car also moved at that time, therefore the work
done is a product of that force times that distance.  This is a bit of an
over simplification since the force will probably not be totally constant
during the crash.  This would require the use of calculus to get an exact
answer.  But...  The idea is the same.

Alright, now let's do another "experiment".  Imagine removing the barrier.
The exact same forces effecting the cars with the barrier will effect the
cars without the barrier.  They both stop in the same distance (the length
of their crumple zone for this particular energy of collision).  The exact
same amount of damage will be done in each case.  The time of crumpling,
the distance of crumpling, the deformation caused by the crumpling is
independent of whether the "barrier" is an actual concrete barrier or
another car.

Granted, two cars will release twice as much energy, but it will be
absorbed by two cars, not just one.

That help, Mike?

At 09:39 AM 9/16/98 -0700, you wrote:
>Robert Myers decided to speak these words:
>
>>None whatsoever, Richard, that is, if you are referring to the head-on
>>vehicle 35 mph crash being equivalent to the 35 mph barrier crash.  The
>>physics says that is a true statement.  Team Door Handle has nothing to do
>>with it.
>
>
>Im confused now.  Wouldnt the momentum of the two cars add together and 
>cause what would be equivalently a 70 mph collision?  What am i 
>missing...its been years since my last physics class...
>
>later...
>
>
>Michael Sheridan Williams

___
   Bob
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