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Re: [Phys-l] [PTSOS] significant figures



Why do HS teachers insist on teaching what must be unlearned?

I have never read an article in the scientific litt. that uses the concept of sig. figs., except possibly in the "The Physics Teacher".

Here's a link that gives the correct method of reporting error:

Measurements and Uncertainties versus Significant Digits or Significant Figures

bc




On 2010, Sep 09, , at 07:48, Dan Burns wrote:

I think it is a good thing for students to encounter significant figures somewhere in their high school science education. I am fortunate because my students get it in chemistry. In physics I tell them that “significant figures are not that significant”. They should be able to report the result of their analysis, like taking the slope of a line based on experimental data to a reasonable number of significant figures. This usually means about 3 or 4. I do not spend very much time on it.

I do stress recording measurements they make to a reasonable amount of digits. Can they measure something to within a mm?, 0.5 mm? 10 cm? How accurately can they measure time with a stopwatch? Try it and see.

Dan


On 9/9/10 7:15 AM, "Eric Plett" <eplett@serrahs.com> wrote:






Method one is correct until the sum is put into scientific notation. The final zero is a place holder. The answer is still 1.37*10^3 either way.

I go through significant figures briefly and then follow the AP Physics general guidelines of keeping 2-3 SF’s in their answers. Students are instructed to keep an extra SF (say 4) in their work leading up to the answer (rounded to 2 or 3 SF’s).

Eric Plett

From: PTSOS@yahoogroups.com [mailto:PTSOS@yahoogroups.com] On Behalf Of pmatsu1
Sent: Thursday, September 09, 2010 7:05 AM
To: PTSOS@yahoogroups.com
Subject: [PTSOS] significant figures



While I know the rules for the use of significant figures for addition / subtraction and multiplication / division, I am unclear about its use in calculations involving a combination of operations. As such, what are the "rules" for such operations. For example, in the problem:

(1.23 * 10^3) + (1.4 * 10^2) = ___ (in scientific notation)

method 1:

(1.23 * 10^3) + (1.4 * 10^2)
= 1230. + 140.
= 1370.
= 1.3 70 * 10^3

method 2:

(1.23 * 10^3) + (1.4 * 10^2)
= (1.23 * 10^3) + (0.14 * 10^3)
= 1.37 * 10^3

i.e. does the answer have 4 or 3 significant figures ?

also, as a 1st year physics teacher, i was wondering on the frequency of teachers to teach "propagation of errors" instead of / in addition to "significant figures" in regards to uncertainty. while i realize the former uses calculus, one could simply state the basis / rationale / motivation of this approach, avoid the actual math, and present the results for various situations.






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