Maxwell Behavior of Cake

Christie Rowe, McGill University
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Summary

Uses 3 points of entry to introduce students to viscoelastic rheology: A hands-on exercise with cake as the deformable material, an accessible example of an artificial material, and using literature to apply the concepts to post-glacial rebound in the British Isles.

Context

Audience

I have used this exercise in undergraduate structural geology and undergraduate tectonics (both core courses in the geology major).

Skills and concepts that students must have mastered

It is good if the students have done some pre-reading on elastic, linear viscous and other rheology models (I usually assign a chapter on Rheology from a structural geology textbook). The math required is basic algebra, but this could be adapted for more rigorous treatment.

How the activity is situated in the course

A lab (one per week)

Goals

Content/concepts goals for this activity

This activity aims to build intuition by hands-on experimentation and relate that to quantitative investigations. Students should be able to describe qualitatively the relative roles of viscous and elastic deformation at different strain rates and relate this to short and long term effects in the lithosphere and asthenosphere.

Higher order thinking skills goals for this activity

The students are asked to draw parallels between analog and natural systems with Maxwell behavior, and then examine the application of this simple rheologic model to explain a set of geological observations. The exercise has 3 parts as written, it could be customized by using only 1 or 2 of the parts, or replacing part 3 with a different literature source (e.g. post-seismic mantle response).

Other skills goals for this activity

Critical reading of journal articles, working in groups.

Description and Teaching Materials


Viscoelastic Rheology of Cake (Acrobat (PDF) 219kB Jun16 12)
Also available in LaTeX format ( 10kB Jun19 12)


Teaching Notes and Tips

Different types of cake have different properties. See some notes from the classroom on my old geoblog at http://christieatthecape.blogspot.com/2009/08/cake-practical.html.

Assessment

After doing this activity, most students seem to understand the importance of stressing rate in determining whether a material will have an elastic or viscous response. I havent done any systematic pre/post testing or compared to students who just read or attend a lecture but the cake does seem to facilitate intuition-building.

References and Resources

My notes from running this as a practical exercise at the University of Cape Town. http://christieatthecape.blogspot.com/2009/08/cake-practical.html

Here are the papers cited in the assignment sheet (not necessary that the students read all of them)

Brooks, A. J., Bradley, S. L., Edwards, R. J., Milne, G. A., Horton, B., & Shennan, I. (2008) Postglacial relative sea-level observations from Ireland and their role in glacial rebound modelling. , (2), 175-192.

Cannelli, V., Melini, D., & Piersanti, A. (2010). Post-seismic stress relaxation with linear transient rheology. (2), 89-99.

Perutz, M. F. (1946). A description of the iceberg aircraft carrier and the bearing of the mechanical properties of frozen wood pulp upon some problems of glacier flow. (2), 95-104.
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