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Re: momentum

We all "know" that the total energy is conserved before and after
a collision. We also know that the kinetic energy in such a
collision is not conserved because some of the original energy
appears as heat and some in the crumpled wreckage.

Let's discuss the latter product, the crumpled wreckage.
During the collision, a large force was applied to the fenders,
grille, hood, and other parts of cars involved. I assume that
the some of this kinetic energy caused crumpling of the body
parts by applying a force through a distance. Other than the heat
and sound energy that is produced during the crumpling, is any of the
original kinetic energy preserved in the tears, dents, and
broken glass of the wreckage?? If so, is it theoretically possible
to reclaim this energy??

Herb Gottlieb from New York City
Where we have a lot of wrecked cars in our junk yards and would
like to reclaim some of the energy in their dents and shattered glass)

On Fri, 02 Jul 1999 10:41:19 -0500 paul o johnson <pojhome@FLASH.NET>
writes:
Leigh

Whoa! Did you really mean to say that the energy in Herb's example is
NOT conserved? The system's kinetic energy is obviously not
conserved, but I sure hope its energy is. Can we not agree that the
word
"energy" without modifying adjective refers to total system energy?

poj
Collin County College

Leigh Palmer wrote:

The nearest equivalence I can think of is a head on collision
between two cars moving at 35 and a head on collision between
two cars, one of which is moving at 70 and the other at rest
*with brakes off*. You may supply whatever velocity units you
like above.

Herb's comment that energy is conserved is either trivial and
potentially confusing, or else it is wrong. Such statements
can only distract students from a correct line of reasoning,
and they already have enough distractions from their raging
hormones so that we need not provide gratuitous distractions.

Leigh