| Chronology | Current Month | Current Thread | Current Date |
| [Year List] [Month List (current year)] | [Date Index] [Thread Index] | [Thread Prev] [Thread Next] | [Date Prev] [Date Next] |
"significant figures". (What's a "figure"?) So maybe I'll join a
(highly) modified version of John Denker's "stamp out sig figs"
crusade after all."
Michael Edmiston writes:_______________________________________________
... I tell the students to carry out the calculations entirely in
the calculator, or Excel, or if using paper write down intermediate
results to 5
significant digits... and then report the final answer rounded to
3-significant digits.
I'm not quite as explicit, but I do say that answers should be
reported to a reasonable number of significant digits and I further
suggest that, when in doubt, three is almost always a good compromise.
[BTW, I do prefer the phrase "significant digits" to the phrase
"significant figures". (What's a "figure"?) So maybe I'll join a
(highly) modified version of John Denker's "stamp out sig figs"
crusade after all.
"Stamp out sig figs; hail sig digs."]
... I don't want them to waste time worrying about precision and error
analysis on problem sets and exams for which error analysis is not the
point of the problem. If the goal is to learn the physics (or test the
physics knowledge of the student) why throw extra non-physics hurdles in
front of the student?
Exactly.
... I don't have to worry about how I give my data. I can write 2 m/s
rather than writing 2.00 m/s. Why throw extra hurdles at myself when I
am writing exams and problem sets?
Well ... I confess that this makes me cringe a little. I don't want
to burden students with the extra overhead of worrying too much about
issues of precision, but I still think we ought to set a good
example. If we give a piece of data in a problem as "2 m/s", then I
think a student has every right to give the final answer to 1
significant digit. Indeed, I think a student really OUGHT to do so.
In such a case, you might choose not to take points off for an answer
given to 3 sig digs, but IMO it would be quite wrong to take points
off for an answer given to 1.
At the same time, values like "2.00 m/s" raise other questions in my
mind, especially when other pieces of data are similarly formatted.
How likely is it that the initial velocity was 2.00 m/s, the mass
5.00 kg, and the force acting on it 8.00 N? For that reason I
usually give my data to two or three sig digs and avoid ever giving
values with two zeroes after the decimal place. Then students who
give their answers to two sig digs get full credit as do those who
give one extra sig dig.
--
John "Slo" Mallinckrodt
Professor of Physics, Cal Poly Pomona
<http://www.csupomona.edu/~ajm>
and
Lead Guitarist, Out-Laws of Physics
<http://www.csupomona.edu/~hsleff/OoPs.html>