[Phys-L] let's define energy

[John Denker <jsd@av8n.com>]

On 09/25/2015 07:04 AM, Paul Nord wrote:

> I heard some good debate on the idea of making an "Energy Concepts
> Inventory" something like the FCI (Force Concepts Inventory).  The
> conclusion seemed to be that the sciences use the term energy in so many
> different ways that science needs to sort this out before we can expect
> students to clearly articulate these concepts.

1) Is this debate documented anywhere?  In particular, is
 there something that interested parties could read and 
 then cite?

2) How many different definitions of /physics/ energy are
 we talking about?  Is there more than one serious contender?

 I've been wrong about this sort of thing before, but I
 would hope the community could come to a consensus on
 how to define the /physics/ energy.

   This stands in contrast to things like:
    -- "adiabatic", where there are two long-established
     meanings, neither of which is particularly better or
     worse than the other.
    -- "heat", where there are at least four long-established
     and widely-used meanings, each of which has some merit
     but also some serious problems.  (Not to mention various
     vernacular and/or metaphorical usages.)
    -- etc. etc. etc.

3) Within "science" broadly, I know of two or three definitions
 of «energy» ... only one of which is the /physics/ energy.

 a) The /physics/ energy, as I understand it, is unique, well
  defined, and well behaved.  Here's how I explain it:
      https://www.av8n.com/physics/thermo/energy.html
  or equivalently
      http://www.av8n.com/physics/thermo/energy.html

 b) Meanwhile, there is also the Department of Energy «energy».
  This involves some notion of "available" or "useful" energy.
  This is important, but it's not the /physics/ energy.
  Definitely not.  When the DoE says "please «conserve» «energy»"
  they are not using the physics notion of energy *or* the physics
  notion of conservation.

 c) In dictionaries and in third-grade science books you often
  see energy defined as "the ability to do work".  This is a
  rough approximation to the DoE «energy».  It is absolutely 
  not the physics energy.  For details on this, see
     https://www.av8n.com/physics/thermo/energy.html#sec-workability

Note that the DoE «energy» is important.  I'm not saying 
it's wrong;  I'm just saying it's not the /physics/ energy.
Context matters.  In physics context you have to use the 
physics definition.

==========================

One of the things I don't like about the FCI is that it 
plays word games.  It sets up situations where it would
make sense to apply the vernacular definition of force,
and then penalizes students for doing so.  I can imagine
a cockamamie Energy Concept Inventory that pulled the
same sort of trick:  setting up situations where it
would make sense to apply the DoE definition of «energy»
and then penalizing students for doing so.  Please please
please let's not go there.

==========================

I leave it as a question:

  1) Does anybody have a problem with the definition and
   explanation of energy as I have presented it?
      http://www.av8n.com/physics/thermo/energy.html

  2) Does anybody know of any other viable, useful, or even
   plausible ways of defining the /physics/ energy?

  3) Does anybody know of any other vernacular notions 
   that commonly interfere with students' understanding
   of physics energy?  (I don't want a long list of
   misconceptions, just the truly /important/ ones.  Keep
   in mind the Anna Karenina principle:  Each student who
   is confused is confused in his own way.)