# Short Demonstrations, Set #2

## Session #2, time slot #2 (Sunday 3:55) , repeated in Session #6 (Thursday 10:55)

**S2A: Guided-Discovery Activities for Teaching Stress and Strain (Ann Bykerk-Kauffman, California State University, Chico).**A classical way of guiding students toward an understanding of a theory is to have them work through the derivation of that theory. But the derivation of stress and strain theory requires a level of math well beyond that of most geology majors. Must we then settle for rote memorization? I don't think so. In this session, we will work through several activities that guide students toward discovering essential and useful aspects of stress and strain theory. For example, students discover that (1) the Mohr circle is simply a graph of all possible solutions to the stress equations (thus it is not a picture of something physical) and (2) in pure shear, material lines rotate in two directions but in simple shear, material lines rotate in only one direction.

**S2B: Association of Normal Faults with Large Scale Structures: Case Study of the Evolution of the Main Ethiopian Rift Valley (Ashenafi Tegene, Mekelle University, Ethiopia).**Normal faults can be associated with small scale or large scale structures that require extension.Rift zones are classical examples where normal faults occur as large regional systems.Case studies from the geological literature of the Main Ethiopian rift valley are fabulous for demonstrating how rift zones can be initiated, the association of initiation of Rifting with igneous activity, the architecture of early rifting as well as late rifting phase, the evolution of the rift, geologically recent faulting and igneous activity in the Main Ethiopian rift valley with their implication on extension.

**S2C: (Relatively) Painless Stress Tensors (Colin Shaw, University of Wisconsin, Eau Claire).**Do your students have difficulties with quantitative abstractions like tensors? If so, you may be interested in hearing about this graphical approach to visualizing stress at a point. The in-class activity builds on an intuitive understanding of the relatively concrete strain ellipse and progresses to increasingly abstract concepts that are necessary to understand how stress varies with orientation. A great segue into graphical (Mohr's circle) or algebraic (tensor) approaches to finding the traction on a plane.