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Re: emf and batteries



brian mcinnes wrote:
on 22/3/04 11:29 AM, Ronald Newburgh at rgnew@BELLATLANTIC.NET wrote:


The term emf is an historical fly in amber. Until the early 19th
century the terms force and energy were often interchanged. The Latin
for force is "vis" and the Latin for kinetic energy is "vis viva" or
living force. The
term emf referred to energy, or more specifically an intensive energy -
electrical potential energy per unit charge.



It's more like the second half of the 19th Century, that any distinction was
made. The details that follow owe much to Martin Bailyn's book A Survey of
Thermodynamics AIP Press, 1994..

The word energy comes form the Latin energia and the Greek energeia, with
meanings of agency, force

I'm fairly sure the use of the term and concept of vis viva predates
"kinetic energy".

Joule spoke and wrote about vis viva (or living force) as contrasted with
Leibnitz's vis potentia or vis mortua. (or attraction in space). He did
not use the terms kinetic energy or potential energy. Joule asserted that
when heat (sic) is added to a body it can become internal living force
and/or internal attraction in space .

Although Leibniz certainly wrote about vis potentia and vis mortua, he
is better known for adopting vis viva (also referred to in his writings
as vis motrix). Vis viva, equal to m*v^2 or twice what we now call
kinetic energy, was contrasted with m*v, what Newton referred to as
"quantity of motion" or "quantitas motus" and later called momentum (or
at least its magnitude.)There was a heated controversy between Leibniz,
DesCartes, and their followers, the Cartesians favoring "quantitas
motus" as the more fundamental quantity.

A web search for "vis viva" will lead to a number of discussions in the
context of Leibniz's work. Eric Weissenstein's web pages for Leibniz
(http://scienceworld.wolfram.com/biography/Leibniz.html) and
DesCartes (http://scienceworld.wolfram.com/biography/Descartes.html)give
a somewhat simplified discussion of the history. A more detailed
historical account may be found at
http://www.fisica.uniud.it/girepseminar2001/CS03/BAGNI_01_FINAL.pdf .
Weissenstein mentions in his Leibniz article that Christiaan Huygens
also investigated vis viva. A link to the Huygens article leads to
mention of Huygens' study of conservation of momentum in collisions.
There are many historical, philosophical, and theological articles on
the nature of the many concepts of "force" and related quantities
involving motion. Leibniz's vis viva was only a step along the way to
the energy concept. I don't think Leibniz or others of his era related
it to the internal energy of bodies, and I don't think there was a clear
connection with work.

Hugh Logan
Retired physics teacher