Re: CONSERVATION OF ENERGY

[John Mallinckrodt <ajmallinckro@CSUPomona.Edu>]

Ludwik writes:

> I find your distnction between "heating" and "warming" very useful.
> Two different words ARE needed but warming is not necessarilly the best
> term because most people would identify it with "less intense heating".
>
> What about self-heating (as opposed to heating, which is impelled)?

Nah.  I'd like the term to refer to the result of *any* process that 
increases the internal energy of a system.  Heat and work do this 
equally effectively and it's never a "self"-contained process; it always 
involves the action of an external entity.  I suppose you could call it 
"energizing" but that makes far less contact with the average person's 
association of temperature with internal energy.  No, I still like 
"warming."

> I read Sherwood's paper again and noticed that he is indeed using the
> term warming in the way you defined it. This escaped me when I read the
> paper for the first time. I do not know how closely you followed this
> thread. Do you remember these statements?
>
> > Let us examine the term "thermal energy". This term is not in my
> > dictionary, nor should it be in that of any physics teacher. It is
> > a source of confusion .... and a barrier to conceptual grasp.

100% agreement here.
 
> > It [m*c*dT] should properly be called heat, since a process, though not
> > a uniquely specified one, is implicit. It is certainly not an energy.
>
> Bruce Sherwood (AJP, November 1984) would probably disagrees. On page 1002,
> half way between the equations (4b) and (5), I see the following sentence.
>
> > The net work goes solely into increasing the thermal energy of the ...

An unfortunate slip of the tongue by Bruce.  He certainly *meant* 
"internal energy" and I know and respect him well enough to suspect that 
he could easily be induced to disavow this term.

> ...
>
> More significant to me is his equation (5). It shows that the effective
> distance (for the work done on a sliding object) is equal to one half
> of the total sliding distance. Thus, if Bruce was asked to solve the
> hypothetical student problem (posted yesterday) he would probably say that
> the work done is mu*m*g*distance/2. Note that mu is the experimentally
> determined coefficient of kinetic friction. I am puzzled. I wish more
> people shared what they think a good student should be able to do after
> learning some physics in an introductory course.

I don't have the paper with me and haven't read it in some time.  But I 
think that the "half distance" rule is a special case in the model that 
is restricted to substance against *like* substance.  (Maybe you can 
check this.)  If one rubs a "stiff" substance against a "not so stiff" 
substance.  I would expect the "not so stiff" substance to move an 
effective distance *greater* than half the sliding distance and the 
"stiff" substance to move correspondingly *less* than half.  (Of course, 
your problem *does* involve like substances, but I'm more interested in 
the general case.)

> I hope you do not mind being "my generic phys-L-er". 

Fine, as long as you'll share me with the others.

> Why did I select you?

Yeah, why me?

> Because your message was the most recent in this thread, and because it
> referred to the article of Sherwood and Bernard.

Rat's. I was hoping that it was because it was so exquisitely executed.

John
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