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Re: Problem solving or playtime?



Another example for using strategies in plug-and chug to get right answers:
ignore any measurement with the number one (1). For instance, if you have
a nice traditional problem like a bullet striking an object that goes into
constant rotational motion you wind up solving a pile of algebra based on the
conservation of L that includes moments of inertia and the cross product.
These expressions are much easier when L = 1 or R = 1 or M = 1 or w = 1
and so forth because you can screw up many multiplications and divisions
(including powers) and still get the right anwsers due to the properties of
the number 1.

Golden rule -- don't use 1 as a constant in numerical problems if you
can avoid it. This neat factoid was shown to me by a TA (Melissa Dancy)
who was shown it by a student! I believe this strategy is widely-known
by my students.

Dan M

Dan MacIsaac, Visiting Assistant Professor of Physics, danmac@physics.purdue.edu
http://physics.purdue.edu/~danmac/homepage.html (yes, white socks)

Agreed. You have hit on a pet peeve of mine, the "imitative algebraic
problem solving technique". Another annoying trend in texts the use of
nice numbers (like 30 degree angles) which lend themselves to getting the
right answer using the wrong reasoning.

I recently made up a test and went to my old freshman physics text as a
source of questions. I was struck by the fact that so many of the
questions began with the word "show". I can't remember seeing any of those
in the texts we have used lately, but maybe we need to get back to more
non-numerical calculations.

J. D. Sample (501) 698-4625
Math-Physics Dept sample@lyon.edu
Lyon College
2300 Highland Road
Batesville, Arkansas 72501