Re: Sans Work, part 1 (Long and wordy)

[John Mallinckrodt <ajmallinckro@CSUPomona.Edu>]

One further note on Bob Sciamanda's discussion of the "MET" ...

Bob wrote:

> ...   For example, when an
> ice skater pushes off from a wall and thereby gains speed, the MET
> states that the line integral of the force of the wall on the skater is
> numerically equal to the skater's kinetic energy increase.  However, the
> wall has not given up any energy to the person; the wall has not lost
> any energy; the source of the skater's kinetic energy increase is body
> metabolism acting through body muscle forces.  The wall provides a
> "leverage fulcrum" against which these forces can operate;  in so doing
> the wall force takes measure (through its line integral) of the kinetic
> energy change.  In sum, the MET uses the line integral of the wall force
> as a measurement of the skater's kinetic energy change.  It says nothing
> about the source of this energy.  It is the FLT which performs this
> function.

I'd go a step further and argue that no "work-energy" type theorem
--including the FLT (whatever it is!)--should be interpreted as saying
anything whatsoever about "sources" of energy.  All such statements are
merely accounting devices that correctly and usefully "relate" the change
in some energy-like (or state-determined) quantity to a work-like (or
process-determined) quantity; they do no "assigning of sources".  

In the case of the skater I can show you one equation that will make it
look like the wall *gives* the skater his or her kinetic energy, another
that will make it look like the wall did nothing whatsoever, and yet a
third that will make it look like the wall *gets* the metabolic energy of
the skater.  All three equations are rigorously "true" within Newtonian
mechanics and I suspect I could get some very good physicists to vote for
any one of them as *being* the FLT!

John
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