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Re: [Phys-l] formatting uncertainties



John D.,

Do you find any merit in discussing significant figure rules for the
simple silly but practical reason that students may be tested on them?
Also, for the reason that they may have to communicate with folks who
talk about those rules?

________________________
Joel Rauber
Department of Physics - SDSU

Joel.Rauber@sdstate.edu
605-688-4293



| -----Original Message-----
| From: phys-l-bounces@carnot.physics.buffalo.edu
| [mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf
| Of John Denker
| Sent: Wednesday, January 23, 2008 2:04 PM
| To: Forum for Physics Educators
| Subject: Re: [Phys-l] formatting uncertainties
|
| On 01/23/2008 11:09 AM, Rick Tarara wrote:
| > Having 4 'guard' digits in the
| > answer seems more confusing to me--does the student really
| understand
| > the level of uncertainty in the answer?
|
| a) Of course they don't understand it.
|
| b) If you take away the four guard digits, they still don't
| understand it.
|
| Combining (a) and (b), this seems like a vanishingly weak
| argument against the guard digits.
|
| The only way I can make sense of this situation is in the
| case where the cure is worse than the original disease. That
| is, if you round off sufficiently brutally that roundoff
| error is the dominant source of uncertainty, then you know
| what the uncertainty is. But why would you want to do that?
| Designing an experiment or a calculation such that roundoff
| error is the dominant source of uncertainty is the hallmark
| of bad design.
| Why should we tempt (let alone require) students to go down
| that rabbit-hole?
|
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