# PHYSICAL EXPERIMENT ON ELASTIC AND NEWTONIAN RHEOLOGY

Basil Tikoff, Vasileios Chatzaras
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#### Summary

Simple physical models with rubber sheet (elastic rheology) and clear silicon putty (silicon "goo"; linear viscous rheology) help students conceptualize and describe quantitatively strain and stress in rheologically distinct materials.

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## Context

#### Audience

The activity is used in undergraduate structural geology (course in geology and geological engineering majors).

#### Skills and concepts that students must have mastered

Students must understand basic concepts of strain, stress, and rheology (elastic and linear viscous). The activity should therefore be implemented after the students have been taught the corresponding chapters from a structural geology textbook. The math required is basic algebra.

#### How the activity is situated in the course

The activity comprises a stand-alone exercise during a lab (three hours per week).

## Goals

#### Content/concepts goals for this activity

The goals of the activity are:
1) Compare strain axes orientations in pure shear vs. simple shear
2) Describe stress and strain in materials with elastic vs. linear viscous rheology
3) Quantitatively relate strain, stress, viscosity, and strain rate
4) Visualize finite vs. infinitesimal strain

#### Higher order thinking skills goals for this activity

The activity helps students synthesize key concepts about stress and strain (infinitesimal and finite). Students have to draw parallels between deformation of the analogue materials and deformation in the lithosphere.

#### Other skills goals for this activity

Students have to work in groups.

## Description of the activity/assignment

To prepare for the activity, students do background reading on rheology from structural geology textbook. In the lab, students are provided with the required analogue model materials (rubber sheets attached to aluminum grips, silicon goo, and straw). Their task is to apply specific type of deformations on the materials, make measurements, and calculate properties of the deformation.

## Determining whether students have met the goals

The provided worksheet answers (qualitative and quantitative) are used to evaluate students' understanding of concepts addressed.