Re: Controversial Exam Questions - Not Ohm's Law

[Mark Sylvester <msylvest@SPIN.IT>]

At 16.56 11/05/00 -0500, Rick Tarara wrote:
> Before we reopen the 'what is weight' debate--I suspect Mark to be in the
> 'what the scale measures' camp and not the 'gravitational force due to the
> earth' camp--let me just comment that the exam question points to the
> problem of 'going one's own way' on these issues.

Actually, I'm in the "don't use the term without clarifying what you mean"
camp. The IB includes the following admirable statement in an appendix to
the subject guide:

<start quote>
Note: Different scientists and textbooks seem to use the term 'weight' in
different
conceptual senses, i.e., the sense of gravitational force and that of scale
reading on
weighing. The term weight seems not to be explicitly and unambiguously
defined in
science. We must learn to live with this, and deduce the meaning from the
context.
We should at least be aware of the different possible interpretations.

In teaching and in testing, we can make our intended meaning clear, by using an
explicit phrase where necessary. For instance, if we talk about the
'weight' of an
astronaut orbiting the moon in a spaceship we can elucidate further by
specifying
either 'the gravitational force due to the moon', or 'the contact force on
a supporting
scale', depending on which sense of weight we mean.

Given the degree of ambiguity possible, it is best to specify precisely
what is meant,
by using the appropriate phrase, rather than trying to let a single word do
it all, and
failing. Thus one could refer to: the gravitational force on the object due
to the
earth, or the resultant gravitational force on the object at a certain
point in space, or
the contact force between scale and object in a specified situation. The
meaning is
then clear with no ambiguity.
<end quote>

>  Certainly students taught
> that weight is what the scale reads (you really are weightless in orbit)
> will be at a disadvantage on this question (although there is no other
> 'better' choice than B, even from this viewpoint).

I think if you look at the question you'll agree that the other
interpretation (weight is the force that you exert on your support) leads
clearly to answer A.


>  The 'standard
> curriculum' is pretty much set by the consensus found in the popular texts.
> While individual texts certainly have errors, the disagreement (often seen
> on this list) with certain common approaches and/or 'facts' found in these
> texts usually fall into the 'well that's a different interpretation'
> category.  The interpretation is not necessarily wrong (and neither is the
> text-book approach) but if one's students are expected to take
> 'standardized' tests, one should be wary about teaching 'outside' the
> mainstream curriculum.

I think we've seen on this list that people give passionate arguments for
particular interpretations. Having taught exclusively IB physics courses
for many years, I'm very aware of the need for orthodoxy when it comes to
externally set examinations. With students who are on the whole very able
and who often have a strong background in physics, there is no problem
about making them aware of these different religions in physics. They don't
get confused, and there should not be exam questions that put them in a
dilemma for this kind of reason.

Mark





_____________________________________
Mark Sylvester
United World College of the Adriatic,
34013 Duino TS, Italy.
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