Re: Uncertainty Question

[Mark Sylvester <msylvest@SPIN.IT>]

At 15:46 31/08/99 -0600, Ken Fox wrote:
> I admit it, as part of my required curriculum I have to teach more about
> uncetainties than I am confident about. The rules are inconsistent from
> text to text and common sense does not always prevail. Is there a simple
> guide book?
>
> Here is my current question:
> Measuring the density of a 3x5 card as an exercise in sig.fig.s and
> uncertainty. Some groups used a micrometer to measure the thickness,
> others made a stack of 50 and measured the group with a cm ruler. This
> group measured the stack as 1.23 cm =/- .03 cm. We divide by 50 for the
> stack. How do YOU report the uncertainty?

I say the uncertainty is .03/50 cm IF we are dealing with cards whose
thickness can be assumed identical and uniform.

In this case the uncertainty is probably due not only to the measuring
process but also to a variation in the thickness from card to card, and we
cannot know about this without measuring some individual cards.

Mark


Mark Sylvester
United World College of the Adriatic
34013 Duino TS
Italy.
msylvest@spin.it
tel: +39 040 3739 255