Re: Impulse

[Larry Cartwright <exit60@CABLESPEED.COM>]

Stefan Jeglinski wrote:
> It is interesting, but pretty vague as stated. What are they trying
> to say exactly? In a "zeroth" approximation, other things equal, a
> car hitting a rigid barrier at 40 mph is equivalent to 2 cars, each
> travelling 40 mph, colliding head on. Equivalent here meaning damage
> to each car due to dissipation of its KE. It is true that the cars
> are "closing" at 80 mph, but "80" doesn't enter into any calculation
> of KE, to my knowledge.

That was my reading of it.  It was specifically talking about the
*forces* at impact.  I think they were looking for a way to say to the
(general public) reader "If you're driving 40 mph, and you have a
head-on collision with another car travelling 40 mph, then in your frame
of reference it looks like that car is coming toward you at 80 mph; but
the collision really only produces roughly as much force as hitting a
big tree at 40 mph."  You and I can confirm that by doing the math, but
it probably seems a bit non-intuitive to Joe Averagereader.

To me, the "interesting" part was the claimed *rarity* of high-speed
impacts with stationary objects.  I was under the impression there were
more than a few of those type of accidents.  I was probably wrong; that
happens a lot.

Best wishes,

Larry

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Larry Cartwright   <exit60@cablespeed.com>
Retired (June 2001) Physics Teacher
Charlotte MI 48813 USA
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