From: Gary Horne (gary.horne@excite.com)
Date: Thu Sep 28 2000 - 13:53:38 PDT
Message-ID: <25135960.970174418076.JavaMail.imail@digger.excite.com> Date: Thu, 28 Sep 2000 13:53:38 -0700 (PDT) From: Gary Horne <gary.horne@excite.com> Subject: Re: pinhole Sig figs & averaging
My understanding of significant figures is that the last digit is the
"unsure" value. If I measure a weight that is 23 g, then it could be 24 or
22 or maybe even 20 grams. I'm sure of the tens place, but the one's case
is "unsure". In your example, the weights may measure as 2 and 3 grams, but
both are unsure measurements. In that light, the average of two items that
are about 3 grams equaling about 3 grams is correct.
If, however, one is sure that the weight is about 2 grams, she should write
2.0 with the tenths place being the "unsure" value. Likewise with 3.0. In
that case, the average is 2.5, and again, makes sense.
At least, that is my understanding, but I admit that significant figures
gave this non-chemist a lot of trouble as well.
-gary
On Thu, 28 Sep 2000 13:26:45 -0800, Pinhole Listserv wrote:
> I've been thinking about significant figures a lot recently, and
> contemplating when scientists do and don't use them. Here's a simple
> example.
>
> If you had two objects with masses of 2 g and 3 g, and you wanted to find
> their average, I think that most chemists would report the average mass
as
> 2.5 g. But according to sig fig rules, their average mass should be 3 g.
> That seems slightly insane to me: the idea of averaging 2 g and 3 g to
get
> 3 g is very weird to me, as well as my students.
>
> Advice?
>
> -Geoff Ruth
> Leadership High School
> 300 Seneca Avenue
> San Francisco, CA 94112
>
>
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