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John Walkup
California State University-Fresno
Veteran instructor of physics at California State University, Fresno, with research interests targeting introductory physics students (even freshmen). Received PhD in atomic theory at the University of Oklahoma. Current research focuses on the fundamentals of statistical analysis, science lab procedures, and science pedagogy. Professional grant writer with over 200 grant submissions netting over $30 million in awards.
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Statistics in Physics Lab: Catastrophic Cancellation part of CUREnet:CURE Collection
Error analysis consumes much of the focus in introductory physics labs. Catastrophic cancellation is a spike in error that occurs when subtracting two measurements of roughly equal magnitude. Often termed loss of significance or subtractive cancellation, this effect can easily relegate experimental results to utter worthlessness no matter how precise the measurements. A lab activity that exposes the ill effects of catastrophic cancellation in experimentation was carried out by undergraduate students that employs the traditional elastic collision experiment performed in countless labs across the country. Traditionally, lab designers try to lower experimental error as much as possible for students to confirm conservation of momentum and kinetic energy. In this lab activity, however, the calculations performed by the students were purposely modified to generate ridiculous levels of error based on nothing more than the order in which experimental values were summed. Students learn that measurement is not the only source of error in an experiment; that is, the order in which mathematical operations are carried out not only introduces error into calculations, but that this error can completely obscure experimental results.