Linguistic difficulties (RE: Measuring Volts?)

[John Clement <clement@HAL-PC.ORG>]

> John Clement wrote:
>
> > ... Often college students have the same difficulty.
> > This difficulty of course happens in daily life.  For example
> people will
> > say you need a certain square footage of shingles to cover your
> roof, or the
> > yardage of material is ...
>
> The horror, the horror!
>
> I shudder to think of the difficulties faced by
> those who speak of yardage.
>
> We must punish them severely, lest they become
> emboldened to perpetrate even worse crimes, such
> as
>   -- using "moving forwards" instead of "moving forward".
>   -- using "entitled" instead of "titled".
>   -- using "over 10" instead of "more than 10".
>   -- pronouncing "Westminster" with three syllables.
>   -- opening their eggs on the wrong end.

Well Duh.  Of course this distinction is not important in ordinary
conversation, nor is it a difficulty in many situations.  However when
students say they are measuring cm instead of saying they are measuring
distance or height or ... this can be a sign that they are not making a
distinction between units and the general quantity.  When they fail to make
this distinction, they may have difficulty using the quantity in other
contexts.  I have observed that this usage correlates with lower thinking
skills.  Such students will then be more apt to not be able to distinguish
between N/kg and N.  They will say that the gravitational force on an object
is 9.8 N/kg rather than recognizing that they were telling me g which allows
them to calculate the gravitational force.  Unfortunately my usual tendency
to make far connections put together 2 thoughts that probably should not
have been in the same sentence where a literal meaning could be all to
easily drawn.  At that point I was thinking about how common speech brings
abstract concepts to a more concrete level.  Remember these posts tend to be
stream of consciousness rather than carefully crafted publishable arguments.

The usage of such terms as yardage blurs the distinctions between units and
the name for the quantity.  Of course it is not wrong, but it sets up
students for the misconception that units describe the measurement rather
than units are part of the description of the measurement.  As an example,
when they see that 1 N/kg = 1 m/s^2 they tend to think of it as being an
equation rather than a unit conversion.  They will dutifully write it down
and then try to use it in solving problems.  The common usage of units as
being the same as the quantity measured, makes the situation much more
concrete and allows concrete operational thinkers to deal with the concepts.
We need to help our students become formal operational thinkers rather than
trying to bring everything down to the concrete level.

As I also stated this is actually just part of the linguistic confusion, and
is not something to be overly concerned with, as there are much bigger ideas
that must be dealt with.  This situation is actually analogous to one of the
symptom of dyslexia, namely letter reversals.  This particular symptom is
actually just a sign of the overall confusion.  It decreases dramatically as
the dyslexic learns techniques to read and spell, without being treated
separately.

As to the distinction between voltage and potential difference, Priscilla
Laws has a nice passage in "Workshop Physics" on this very topic.  She
points out that physicists talk about potential difference, while
electricians say voltage.  She says that it is not wrong, just different
usage. She also points out that potential difference is the preferred usage
in class.   She also has a cute cartoon with a female physicist talking to a
puzzled garage mechanic.  The female is saying "I need a new battery, but
its terminal potential difference has to be at least 12 Joules per coulomb
with an internal resistance not greater than 0.1 ohms and a capacity of 100
Amp hours.  And would you have something with a transient suppression of
10,000 volts per second?".

Of course the same situation happens with amperage and current.  Amperage is
the more concrete term and current the more abstract term.  Students can not
see current so naming what they are measuring according to the units is very
natural.  And remember that both current and potential difference are
extremely abstract ideas which depend on being able to picture microscopic
things that you can not see.  Anton Lawson has shown that when students try
to learn concepts that depend on visualizing things that you can not see,
they have extreme difficulty.  He has proposed that there is another level
of thinking beyond formal operational that he has dubbed theoretical.
Students at that level find concepts based on unobservable entities much
easier.  Examples of such concepts include practically all of the quantities
that we commonly talk about in physics classes.  If you do not like this
idea, perhaps you should read some of his papers in Journal of Research in
Science Teaching.

John M. Clement
Houston, TX