Re: Swartz letter in AJP (work-energy theorem)

[Brian Whatcott <betwys1@SBCGLOBAL.NET>]

At 02:55 PM 9/1/2004, you wrote:

> >> /// I am reminded
> >> of a somewhat similar confusing item in the high school text,
> >> _Foundations of Physics_,
> >> 2nd ed, by Lehrman and Swartz. On p.45 of the _Teacher's Guide_ for that
> >> text, one finds
> >> "The cavalier way in which we treat the difference in definition of
> >> speed and velocity is
> >> very deliberate. It is a reaction to certain situations in our own
> >> experience where knowledge
> >> of the defined difference became  the essential feature of motion study
> >> to be tested with
> >> true-false questions."

> >> Hugh Logan
> >> Retired physics teacher
> >
> >
> > I can see why the quoted use of "cavalier" led to student difficulty.
> >  It means quite the opposite of the writer's intended value, where
> > cavalier is "off-hand, curt, supercilious" [COD]
>
> However, I thought Lehrman and Swartz's usage might fit in with one of
> the M-W (online) dictionary entries for "cavalier" used as an adjective:
> "marked by or given to offhand and often disdainful dismissal of
> important matters" -- perhaps with the emphasis on "offhand" rather than
> "disdainful." The reader of the text (not the _Teacher's Guide_ in which
> the intent is "deliberate") might think the important matter of the
> distinction between speed and velocity has been dismissed in an offhand
> manner. In 1970, I could only think of a gentleman on a horse, perhaps
> disdainful of those beneath him. I remained silent rather than display
> further ignorance. In the AJP article, Cliff Swartz wrote, "You don't
> plug friction into the wall socket or feed it gasoline or steak.
> Certainly it cannot do negative work, a concept that can only bewilder
> the innocent." Is Swartz being "cavalier" in his dismissal of negative
> work, while admitting that
> (if I interpret him correctly) juniors might use it?
>
> Hugh Logan
> Retired physics teacher


It seems to me that the L&S text in question treated the difference
between speed and velocity carefully.
 (Does the sub-conscious register "cavalier" as "carefully-er"?)
 I have not read it, true: but almost every physics text makes a big
 deal of the difference.
(Nevertheless, physics teachers almost always want to use the
term 'velocity' where speed is in fact the term in question.)


You quote Swartz in this way: "You don't  plug friction into
the wall socket or feed it gasoline or steak...."
This is a standard argument against "reification" of the kind that
  Jim Green champions, from time to time.
I take a different view: I see all physics, perhaps all science as a
 kind of reification of model entities: cost, value, interest, work,
 energy, entropy, enthalpy, friction and so on.
I do not rebel at the naming of defined concepts - I take it that
this concretion is what enables students to grasp the models in
 question - it allows the physical manipulation of terms.

About negative work: in the world of the accounts clerk, a debit
in one column is the credit in the other with an opposite sign.
I fancy the student has a more concrete conception of coinage,
for example.
 You have 'em or you don't.
 Owing money as an example of negative coins, has a conceptual
precipice for them, at times, I think.



Brian Whatcott    Altus OK    Eureka!