[Phys-L] Re: infinite sig. figs.

[Rick Tarara <rtarara@SAINTMARYS.EDU>]

That's fine in the classroom and for working problems, but what about the
laboratory.  To be sure, if you are going to be training scientists and
engineers, then at some point you need to get sophisticated about
uncertainties and error analysis (random versus systematic errors for
example).  However, the first time in the lab (say HS or Gen-Ed college), I
would argue that what you want to stress is that each measurement is done
with an instrument that has a finite precision but that should always be
read to that precision.  Then, armed with measurements that are limited in
their accuracy/precision, if you are to produced derived quantities with
those measurements, the calculator or computer (or your paper math) can
produce numerical values that must be adjusted (usually truncated) to
reflect the confidence one has in the accuracy of the derived quantity--(are
all those digits SIGNIFICANT?)  Our first lab of the semester is an example
of this where we try and determine what a number of objects are made from by
using the physical property of density and our direct measurements of mass
and the dimensions of the objects.

I hate to be a broken record here, but some of the students at this level
have a lot of trouble going from millimeters to centimeters and virtually
none can go directly from cubic centimeters to cubic millimeters.  Providing
a simple set of rules (significant figures) AND then assessing that the
students understand the reason for the use of these rules, can work to get
the main points through.  I'm not sure if JD's approach would work as well
here.  For those who despise and have tanked sig figs, are you successful
with HS and non-science students in getting across these ideas without
'strict' rules?

Rick

*********************************************************
Richard W. Tarara
Professor of Physics
Saint Mary's College
Notre Dame, Indiana
rtarara@saintmarys.edu
********************************************************
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----- Original Message -----
From: "Anthony Lapinski" <anthony_lapinski@PDS.ORG>
To: <PHYS-L@LISTS.NAU.EDU>
Sent: Friday, September 23, 2005 9:30 AM
Subject: Re: infinite sig. figs.


> I agree here, I don't even discuss significant figures in my class. I want
> them to learn physics, not get bogged down with how to round a final
> answer. To me, it's the process over the product that's important. Not the
> "accuracy" of the answer. Rounding to one or two decimal places is fine
> with me. As long as you solve the (math) problem correctly, you understand
> the physics of what's going on.
>
> Forum for Physics Educators <PHYS-L@list1.ucc.nau.edu> on Friday,
> September 23, 2005 at 10:04 AM -0500 wrote:
> > <snip>
> > all calculations, even those involving "real-world" examples, are to be
> > carried out to three decimal places
> > <snip>
> >
> > Well, I admit to doing this.  For my case, to answer Joel, 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.
> >
> > Why?
> >
> > (1) 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?
> >
> > (2) 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?
> >
> > (3) Three significant digits are generally satisfactory for typical
> > problems on exams and problem sets.  They are many enough to show what
> > needs shown, and few enough to be convenient.
> >
> > I suspect the AP folks are thinking the same thing.  Don't throw sig-fig
> > stuff or error analysis baggage on every problem.  Just test the
> > physics.
> >
> > Michael D. Edmiston, Ph.D.
> > Professor of Chemistry and Physics
> > Bluffton University
> > Bluffton, OH 45817
> > (419)-358-3270
> > edmiston@bluffton.edu
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