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Re: what good is "percentage error"?





On Tue, 13 May 1997, Roger A. Pruitt wrote:

Mike, you are being too hard on Frank. Don't kill the messenger. Take your
anger out on all of the chemistry departments around the world that grade
this way. Also, what are we to do about chemistry students in our classes
who want to "weigh" in mass units? It is an imperfect world we live in. We
do the best we can, and spend alot of time correcting misconceptions placed
in our students by others.

Roger


So what's wrong with "weighing" in mass units? If it's done thoughtlessly,
by habit, I might be concerned. If it's done by the student who realizes
that it's a waste of time to multiply everything by g just to get the
"accepted" form of weight, I'd say it is an example of thinking ahead, and
to be commended.

I've had students who do an experiment, say the classic balanced forces on
a force table, who insist on expressing everything in force units even
though the weights they use are marked in grams. I point out that they are
wasting time to do this first, when they could express forces in a
convenience unit "gram-weight" and convert to force units at the very end.
They respond "But aren't all forces "supposed" to be expressed in
Newtons?" (They are afraid they will "lose points" if they don't use
Newtons in all the calculations. Where did they get that idea? High
school, I'll bet.) I just shake my head in wonderment at such naivete.
Some just don't "get it", don't realize that if they have understanding,
they needn't be slaves to recipes and blind application of sterile
procedures.

I've even had students do a homework problem, where all data was in
English units, and express their answer in metric units! Worse, they will
convert *each* piece of given data to metric, then do the arithmentic! My
view is, if the problem uses unit system X, then express the results in
unit system X unless specifically asked to do otherwise. Why do
unnecessary labor? Most problems which give data in mixed units will
specify somewhere what units are desired in the answer. If not, the author
of the problem is negligent. The only purpose I san see for such problems
is to deliberately give students practice in unit conversions.

-- Donald

......................................................................
Dr. Donald E. Simanek Office: 717-893-2079
Prof. of Physics Internet: dsimanek@eagle.lhup.edu
Lock Haven University, Lock Haven, PA. 17745 CIS: 73147,2166
Home page: http://www.lhup.edu/~dsimanek FAX: 717-893-2047
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