[Phys-L] Significant Figures

[John Sohl <jsohl@weber.edu>]

I always try to use a "reasonable tolerance" approach. I spend a few
minutes talking about how well we can measure things and that reported
values should be consistent with how well we know what we are doing. I
inform them that my grading will only take points off for sig. figs. when
the reported values are several digits too many or too few.

Then, some news report comes out that says something stupid like: "The new
roadway into the university's campus will cost $204,531.18 and will be paid
for by..."

When has any large project come in, on-budget, to an accuracy down to the
penny?????

On the bright side, I can show these articles in class and ask "what do you
think is wrong with this number?"

John

- - - -
John E. Sohl, Ph.D.
Professor of Physics
Weber State University
1415 Edvalson St., Dept 2508
Ogden, UT 84408-2508

Office: TY 326
voice: (801) 626-7907
cell: (801) 476-0589


>  *) Very often, in class and in the real world, it is not
>   necessary to quantify the uncertainty, so long as it is
>   known to be /small enough/ i.e. within tolerances.  Unless
>   and until you hear otherwise, you (the student) should
>   report temperatures within ±2 °C, mass, length, and time
>   within ±2%, et cetera.  Use as many or as few digits as
>   you please, so long as the bottom-line answer is within
>   those tolerances.
>
>   The tolerance-based approach allows everybody to focus on
>   the physics, rather than on useless side-issues.