Re: Fuel Efficient Cars (was Oil Economics)

From: Kai Becker (kmb@kai-m-becker.de)
Date: Sun Feb 09 2003 - 06:07:01 MST

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    Am Samstag, 8. Februar 2003 22:23 schrieb Edwin Evans:
    > When a vehicle crashes, its size is the attribute of the vehicle that
    > most affects the occupants' injury risk.

    That equation has more variables. F1 racing cars show that humans can
    easily survive crashes with >200km/h in rather lightweight constructions
    (carbon fiber, aluminium, etc.), even if they drive into the sideline.
    The energy of the impact is used to crush and crumple everything else but
    the drivers cell.

    > If cars of the same mass crash into each other, each will undergo
    > identical speed changes.

    That's true, but says nothing about the effect of the crash on the
    passengers. A crash is an exchange of energy. The real scenario is not
    only determined by the masses of the two bodies, but also by their
    relative velocity to each other, the form of the bodies and the way the
    energy of the impact is distributed.

    Your own article says it: "However, the risk decreases as the common mass
    of the vehicles increases [...]. This effect is not because of the mass
    but because heavier vehicles are generally larger. The large size
    provides more crushable space and therefore more time for the occupants
    to decelerate."

    That's it. Its structure that matters, not mass. What is more efficient
    for chopping wood, an iron axe or a wooden club of the same mass? Hitting
    along the fibers or across? Why can a small bullet go through a steel
    plate, but not through a ligher Kevlar vest?

    To look on mass alone seems to be one of the positive feedback loops
    which normally lead to unwanted extremes. "Always drive a heavier car
    than the others" would probably lead to everyone driving a tank and
    therefore outweight the safety with several other disadvantages - e.g.
    heavy protective gear for pedestrians...

       Kai

    -- 
    == Kai M. Becker == kmb@kai-m-becker.de == Bremen, Germany ==
      "Any technology distinguishable from magic is insufficiently advanced"
    


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