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Re: Why work before energy in texts



"John S. Denker" wrote:

I stand by my assertion: Defining work in terms of potential energy
would be a blunder. Defining potential energy in terms of work
would be an even bigger blunder.

1) YES, work is defined as a dot product. But

PE_elctr==work done against a E (or -work by E).

Why is this a "bigger blunder"? In this case we declare
that PE_electr=0 when E=0. What is wrong in using the
above definition to demonstrate that potential energy
in a capacitor (parallel plates, as in a typical first
physics textbook) is equal to 0.5*C*V^2 ?

2) I have never seen a physics textbook in which the
first chapter is about money. (I do not understand
money very well. Sure I use it and I manage it at my
level but I am often puzzled. Physics is usually not
as complicated as economics.) But I am willing to
examine an introductory physics text in which energy
is introduced by analogy with money. I might even be
impressed and use the suggested approach.

3) We are not discussing zero temperature oscillators,
or other advanced QM topics. We are discussing an
introductory physics sequence.

4) In my classes F is first defined loosely as a
measurable push or pull of any kind. This is good
enough to solve static equilibrium problems. Later
Fnet becomes "the cause of an acceleration." Is using
the concept of force also a blunder? In going "from
known to unknown" should we teach force before energy,
or the other way around?

Should ALL mechanical problems be solved by energy
approaches because energy is "more basic" than F?
Why not? I am ready to accept this kind of physics,
but not before seeing a good textbook based on the
suggestion. I would not be confident enough to
develop my own (untried by others) method of
teaching elementary physics.
Ludwik Kowalski