Re: [Phys-L] Sig Figs homework from my 7th grader

[Paul Nord <paul.nord@valpo.edu>]

Brian,

I'm not familiar with this method.  What did you do there?

I would have only added the errors in quadrature, not the values.

sigma = sqrt(0.005**2 + 0.0005**2) = 0.005025

I get 11.145 +- 0.005

Being less generous to the signifigance of the last digit, I would probably suggest:
sigma = sqrt(0.01**2 + 0.001**2) = 0.01005
and report:  11.14 +- 0.01

The answer in the book is 11.1

Paul


On Oct 9, 2013, at 10:26 AM, brian whatcott <betwys1@sbcglobal.net> wrote:

> On 10/9/2013 8:49 AM, Paul Nord wrote:
> > I know the answer the teacher wants, but i find it troubling...
> >
> > 10.53 + 0.615 = ?
> >
> > Share and enjoy,
> > Paul
> > _______________________________________________
>
> Supposing I were troubled by the desire to best represent the last figure uncertainty, I might proceed in this way:
> 10.53 +-0.005
> 0.615 +-0.0005
> ==============
> 11.1450   +-0.0050   +-0.0005   =   11.1445 to 11.1505 or  11.1475 +- 0.0030
>
> It is this last line that would prove worrying: why should the nominal value shift, when the last figure uncertainties are accounted for?
>
> Brian Whatcott   Altus OK
>
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