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# Re: Crib Sheets

I take a little different tact than Jack. My contention IS that IF you
really understand HOW an equation/definition works, THEN you will 'know'
it without memorizing it. Therefore we try to look at things like the
Coulomb's Law equation from the point of view that:

1) The force is an interaction between TWO charges.

2) That the strength of the Force (or Field) eminates (spherically)
symmetrically from each charge thus leading to the fact that this
strength drops as 1/r^2.

3) The above leads to a proportionality of the force to the product of
the charges divided by the square of the distance between them. The
proportionallity constant 'k' or (1/4piepsilon0) completes the equality.

4) Force (of course) is a vector quantity and that force is along the
line connecting the two charges and either attractive or repulsive
depending on the sign of the charges.

Having gone through all that--discussing AND quizzing the consequences--I
would HOPE and EXPECT students to 'know' the equation.

The problem with having them MEMORIZE ANY equation, is that if in another
situation, somebody CHANGES the symbols on them (say 'd' for 'r') they
get all confused. I HATE books that produce a separate set of kinematics
equations for projectile motion (with y's for the vertical motion and
substituting 'g' for the acceleration). This just reinforces student's
belief that physics is just a bunch of equations to be
memorized--specific equations for each problem. I force students to work
such problems with ONLY the 4 standard kinematics equations--WHICH I
constantly stress are all derived FROM the DEFINITION of acceleration!

BTW: Don't underestimate how confusing our 'standard' nomenclatures are
for students. e.g. 'c' as specific heat, 'c' as speed of light, C as
capacitance, 'k' for any and everything, etc. We've 'acquired' the skill
of carefully looking at the context to determine what a symbol stands
for--many students do not immediately master that skill!

Rick

On Thu, 28 Mar 1996, JACK L. URETSKY (C) 1996; HEP DIV., ARGONNE NATIONAL LAB, ARGONNE, IL 60439 wrote:

Hi all-
Comment stimulated by Richard Goode's posting:
************************************************************
I don't allow crib sheets in my physics classes. I do provide them with a
formula sheet that grows larger throughout the year. Each chapter, new
equations are added. No equations are ever removed from the list. They are
required to do any algebra to transform the basic equations. They are required
to know all relevant constants. Even with this aid, I find they spend less
time relying on the formula sheet as the year progresses.
***********************
I think that students should learn (by heart) principles, but not
definitions. So, in the year that I tried allowing crib sheets, I gave
the sudents the material that was permitted on the crib sheets. For
example, Q=CV defines capacitance, C. Nobody should be obliged to memorize
that, because logically it would have made as much sense to define Q=V/C.
On the other hand, all of the force laws are of the form:
^F = KQ_1Q_2^r/r^3, where ^r or ^F denote vectors
, the Q's are charges, and K is a constant that gets the units right. This
is a fundamental principle, like Newton's laws, that are worthy of
memorization.
Why do I believe this? Because these are things that I think
are important enough to be part of the culture of a person who has
been through my physics course. Otherwise, why bother?
A seventh-grade teacher once required me to memorize "Snowbound",
punctuation and all. "The sun, that brief December day, rose, cheerless,
over hills of gray, and, darkly-circled, gave at noon a sadder light than
waning moon;....." (and I'm quoting from memory - somebody can tell me
what I've gotten wrong after 61 years). That teachers taught me the
importance of punctuation as one of the tools of effective communication.
I am profoundly grateful to her for that lesson.
Moral: If it's really important, then learn it!
Regards,
Jack

***************************************************************************
Richard W. Tarara Updated software (3-15-96) now available
Department of Chemistry & Physics
Saint Mary's College
Notre Dame, IN 46556 FREE PHYSICS INSTRUCTIONAL SOFTWARE AVAILABLE AT
219-284-4664 http://estel.uindy.edu/aapt/rickt/software
rtarara@saintmarys.edu
****************************************************************************