Re: [Phys-L] let's define energy

[David Bowman <David_Bowman@georgetowncollege.edu>]

Regarding Diego's observation:

> ...
> "1. Thermal energy is less useful"
>
> I do not agree, if you want to take a bath is better to have
> water at 40C or so, than a charged battery.  ...

Of all the problems previously discussed concerning the oft-used definition of energy in terms of 'available' work those associated with defining it in terms of 'useful' work are even worse, and Diego's observation above illustrates this.  This is because not only are all the problems with the 'available' definition still present with the 'useful' definition, but there are even more problems with the 'useful' definition.  A main purpose of the science of physics is to attempt to understand the behavior of physical things in terms of objective notions, categories and processes.  The concept of 'usefulness' is extremely *subjective* in depending on many more idiosyncratic and internal things associated with an observer than merely how the observer's frame of reference is happened to be embedded in space-time.  If we must have some sort of definition for energy I think it is *really* bad form to try to define an objective property of a physical system (albeit with a particular value that happens to be reference frame dependent) in terms of other notions that are themselves manifestly and thoroughly subjective.  In art it may be okay to have a notion such as beauty being in the eye of the beholder, but in a science it is not ok to have something like energy be so subjective.

David Bowman