Have the students calculate the uncertainty associated with each determination and express them as a result plus-or-minus an uncertainty. Then ask them if each result falls within the limits set by the other's uncertainty.
Good if yes, bad if no.
Note that this emphasizes that no one determination can be considered good or bad on its own. It's only in the context of a comparison with other determinations that this value judgment can be made. In other words, they can't have one determination be good and the other bad. Either the pair of determinations is a good pair, or it's a bad pair.
Further comparisons need to be carried out to determine if one of the two determinations was better than the other. For example you could have them compare KE, PE and total E graphs of a simple harmonic oscillator. Then adjust the value of k in the PE formula to make the graphs look "good". See for example the RealTime Physics lab on Conservation of Energy, Investigation 2. If you're using LoggerPro software you can make an adjustable parameter for k. I imagine a similar provision could be made in other data collection software packages.
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From: Phys-l on behalf of Paul Lulai
Sent: Sun 08-Feb-15 9:45 PM
To: Phys-L@Phys-L.org; phys-l@www.phys-l.org
Subject: [Phys-L] determine k
Hey.
I plan to have students determine spring constants by both standard hooke's law relationships and the oscillation of a mass on the spring.
How would folks on this list recommend determining and using uncertainty for a lab like this? How would one show that the two spring constant values are close enough to be considered reasonably consistent?
The two values are not likely to be exactly the same. Students doing these things for the first time often see any difference in values to mean that one value is good and the other bad, or that the simple average of the two is the best value.
Thanks for your input.
Paul.
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