1. Physical Models of Deformation
These slides may be used to introduce and guide discussion associated with the activity described in the Unit 2: Basic physical models exercise for student worksheet
Image source: Vince Cronin
Physical Models of Deformation
Version: Sept 10, 2015

2. Model 1: Rubber Bands
A simple example for illustration and practice calculating extension. This slide may also be used when discussing why the extension is uniform (step 5).
Image sources: Phil Resor (top), Vince Cronin (bottom)
We’ll start by calculating extension from changes in length (steps 1–5)

3. Model 1: Rubber Bands
Another example you may have students consider after they complete steps 1-5 of the worksheet
Thought Experiment: What if you started with the band stretched?

4. Model 1: Rubber Bands
We can also calculate the extension from the variation in displacement (Ub, Ur) with position (xr0, xb0)
This slide can be used to help explain the calculation of extension from displacements in step 6.
Image source: Vince Cronin

5. Model 1: Rubber Bands
What are the displacements and extension if you translate the rubber band?
Step 7 - translation

6. Model 2: T-shirts Now we’ll explore deformation in two dimensions.
Start with translation
This slide can be used to introduce the 2D analog model of t-shirt deformation. The instructor may wish to lead a class discussion of the first example (translation) after students have attempted it on their own to make sure that all students are clear about how to plot displacement vectors and the deformed shapes.

7. Model 2: T-shirts Continue with Rotation Dilation
Extension in one direction
Simple shear
A general deformation

8. 2D Deformation
A Final Challenge: How would you describe this deformation?
Northward translation + north–south shortening
This slide is meant to give students an opportunity to practice interpreting and describing deformation from displacement (or velocity vectors), a skill they will continue to develop in unit 4.
Note that the answer will appear on mouse click