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

[Marty Weiss <martweiss@comcast.net>]

The study of conservation is vital to the study of energy and momentum.  But to ask what is the "nature" of the word energy is imo meaningless.  It is not a "thing" rather a construct that we base different concepts on:  electrical energy, heat energy, human energy, and a lot of other things.  So, when we talk about energy we can mean a lot of things depending on the context:  to say we lack energy today to do something;  or talking about what an an energy drink does;  or the energy in a gallon of gas that is useful for running a car;  etc.  

I would leave the "meaning" of the word to the philosophers and just spend our time on using the concept to solve the world's energy problems, or the physics of what happens to it in our calculations of motion, or momentum of the cars that collide.  The equations work and while I agree that equation solving without meaning is useless, I would argue that the "meaning" we should concentrate on with our students is in the conservation of the energy in the system, the "loss" of the energy from useful to wasted energy, or concepts like those, rather than what the word itself means. 
  
On Sep 29, 2015, at 2:26 PM, John Clement wrote:

> Really???  I would say that physics courses do not typically go into any
> detail about the "nature" of energy.  Often the word is just used in
> conjunction with equations that define how to calculate specific places to
> put energy, and that energy is then used in calculations.  The books often
> give a pat definition, which JD would usually reject.
>
> Indeed there is a lot of debate about the "nature" of energy.  Modeling
> takes a specific point of view by proposing a tentative model for energy.
> The model is that it is something that can be put into various places sort
> of like pouring a liquid into various containers.  Then the places are used
> as a label for where the energy is located.  The big concept that is then
> pushed is conservation, or the idea that you can figure out where the energy
> has gone.
>
> So I would say the sentence is essentially correct.  The number of opinions
> about this is likely to equal the number of opinions as to the "nature" of
> energy.  Indeed physics courses often never give any "nature" information
> about the quantities we deal with.
>
> Do physics books and teachers tell students the "nature" of momentum???  It
> is usually just presented as an equation that is then used for calculations.
> So students come up and ask "What is momentum?".  How would you answer it?
> Is it the original "quantity of motion"?  Indeed physical science generally
> just has them calculate mV, and leaves off the important idea of
> conservation.  This is stupid and non-productive.  Why should they just
> calculate something they have with no idea of why?
>
> John M. Clement
> Houston, TX
>
> > Another tip:  Don't start the body of the article with a 
> > sentence that is obviously false:
> > > > The nature of energy is not typically an explicit topic of physics 
> > > > instruction.
>
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