Re: [Phys-L] defining energy

[Richard Tarara <rtarara@saintmarys.edu>]

If you just 'define' work as "the means by which energy is transferred 
from one object to another and/or from one form to another" it is a 
little cleaner.   Defining energy is still a problem--the 'ability to do 
work' definition is pretty good for my world/national energy course, but 
ultimately it boils down to a bookkeeping system for keeping track of 
properties of nature that are conserved but moved and transformed by 
work. The Feynman 'Dennis the Menace' story is useful at this level (and 
beyond), and appears in Volume//one of the lectures but also in the 
Kirkpatrick and Francis textbook.  I'm sure someone will provide an 
incomprehensible (to 11th graders) more formal definition!  ;-)

rwt

On 10/29/2013 11:48 AM, Philip Keller wrote:
> Hello,
>
> I am going to be teaching this topic to my 11th graders soon.  I have a
> question about the definition of energy.  I know that the "ability to do
> work" definition runs into trouble when you consider heat, engines and 2nd
> law issues.  But what if I turn the definition around.  Instead of saying
> "energy is the ability to do work", I want to say:
>
> Work is defined to be the product of force and displacement (in the same
> direction).  Then, in different contexts, you can show that work = delta
> (some quantity).  Any such quantity is referred to as [blank] energy.  Fill
> in the blank with an adjective that fits the context.
>
> So "energy" is not the ability to do work, but energies are the quantities
> that are changed by work.
>
> Does this definition pass muster?
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--
Richard Tarara
Professor of Physics
Saint Mary's College

free Physics educational software at
www.saintmarys.edu/~rtarara/software.html