Food Rheology; Folding Fun

Erin K Beutel, College of Charleston

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Summary

In this activity students analyze the rheologic and structural properties of various foods (everything from pudding to white bread) and think about how they expect them to behave under lateral pressure and how they will affect each other. They design experiments, run the experiments and then do lab write-ups. Depending on your emphasis, you can use this to help teach folding mechanics, rheology, why beds deform the way they do, decollements (pudding works great), deformation mechanisms, folding and even more. It is a single lecture activity, though the lead-in lecture and activity and clean-up take about 40-50 minutes.

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Context

Audience

This activity is designed for an upper level (junior/senior) structural geology course, but could just as easily be worked into a lower level course on structure or tectonics.

Skills and concepts that students must have mastered

It is helpful before beginning this activity for students to have an understanding of fold terminology and rheologic terminology, though this can also be done as a 'discovery activity' where students describe what they see without knowing the words and then apply the vocabulary later.

How the activity is situated in the course

This is an in-class exercise that usually takes about 50 minutes (depending on how much material you have). I teach it about mid-way through my upper level structural geology class, but that also reflects the order in which I teach subjects, it could be done at any point in the class. I don't recommend expecting to lecture much afterward though, sugar highs still affect undergraduate students.

Goals

Content/concepts goals for this activity

You can change the goals of this activity to suite what you are covering at the time, it shows so much that I think covering them all becomes overwhelming.
  • rheology
  • deformation mechanisms
  • mechanisms of folding
  • material relationships
  • folding versus faulting
  • parasitic folding (you MUST use a fruit roll-up surrounded by pudding for this to work)
  • effect of . . . on deformation
  • decollements
  • mountain building

Higher order thinking skills goals for this activity

  • Formulation of Hypothesis (students predict how the materials will deform and affect the surrounding materials based on their observations)
  • Hypothesis Testing: Students design their own tests to determine the answers to their hypotheses (for example, if they want to know how overburden affects the deformation of lower beds, they have to decide how best to test this).
  • Critical Evaluation/Analysis: Students must then look at their results and decide what they are seeing (why beds are deforming in a particular manner).
  • Lab Report: Students then must write a lab report describing their findings
  • Visual Analysis: Students must learn to look closely at the deformation while it is occurring and afterward to analyze the mechanics of what is going on.
  • Synthesis of Ideas: Because this activity addresses everything from decollements to mountain building to rheology and overburden, it requires students to put together ideas they learned from many different lectures (or if they haven't had the lectures, from many different skill sets/observations).

Other skills goals for this activity

Group Work (usually teams)
Writing Lab Reports

Could include presenting results depending on how you angle the activity (if you have different people use different materials they could think-pair-share their results).

Description and Teaching Materials

In Class Activity: The Rheology of Food

Materials:
Pudding
Frosting
Fruit Roll-ups with plastic (separate)
White Bread
Graham Crackers

Optional:
Wheat Bread
Peanut Butter
Applesauce
Cooked Pie Crust

Goal: To use food to understand how materials deform, how they affect each other, how they are affected by depth, and how a decollement forms. Major concepts include rheology, deformation, and folding and faulting mechanisms.

To Be Turned In: Each student is expected to turn in their own lab report on their experiments, including materials, material analysis, overall hypothesis and individual experiment hypotheses, experiment descriptions, results and conclusions. Figures are helpful.

Step 1: In teams of two collect your materials (you should have about 8 pieces of bread per team, 2 pudding cups, 4 fruit roll-ups, 6 graham crackers, a Dixie cup full of frosting, wax paper, paper towels, and a couple of spoons and knives). I strongly suggest that all items except for your notebook and a writing implement be removed from your desk.

Step 2: Describe the properties of each of the items collected, use every word in your vocabulary from visco-elastic to thin to sticky to slimy. You should have at least 2-3 adjectives for every material. Record these descriptions for your lab report later.
Option: Think about each of these materials as rocks, they have been deliberately chosen to deform rapidly so they won't exactly resemble rocks, but think of rock analogs that they might be close to. For example: Pudding might be a water saturated shale at depth.

Step 3: Hypotheses/Designing the experiment.
A) What is the overall question that you are attempting to answer? Why are we doing this experiment?
B) Now, you need to come up with a list of things that may affect how beds deform (or this is done as a group in class ahead of time). Take these ideas and create 5 experiments to test them (you may chose a single aspect of how rocks deform and create 5 experiments to test it in different ways). For each experiment, write a hypothesis predicting your test.
a. For example: Thin beds deform differently than the surrounding thick beds when lateral pressure is applied.
i. Experiment 1: Layer a fruit roll-up between two pieces of white bread, apply lateral pressure. Hypothesis: The fruit-roll-up will not deform differently in this instance, it is too sticky and cannot slide between the bread.
ii. Experiment 2: Start with a piece of white bread, place a layer of pudding on it, put a fruit roll-up on it, add more pudding, add another layer of white bread, apply lateral pressure. Hypothesis: The fruit roll-up will slide on the pudding and have shorter-wavelength folds than the bread.
iii. Etc!
C) RUN EXPERIMENTS!!! Now is the time to run each of your experiments.
a. Hints:
i. If you plan the order of your experiments you can often reuse the bread (check it carefully for structural integrity, if it has failures, note them and then decide whether to use them—be sure and include in your report).
ii. DO NOT SMOOSH THE STACK WITH VERTICAL PRESSURE, it makes it almost impossible to see anything.
iii. Place the stack on a piece of wax paper and push in from the sides (you will be creating a fold), if you cover your hands with the wax paper as you apply gentle pressure it will mean less mess (the biggest culprit is the frosting).
iv. Apply GENTLE pressure the better to see things.
v. Be smart about your assembly, if you put the fruit-roll up or graham cracker in the center you won't see it, put it right at the edge so you can see it.
vi. DRAW YOUR EXPERIMENT before you apply the pressure—so you have a good record of what the layers were and how it looked. A quick sketch afterward is often useful when writing your lab report because it is easier to refer to a figure than to explain

D) Design a GIANT SANDWICH which tests many of your hypotheses together. You will be surprised at how some of them change in a larger setting. Watch out for the graham cracker. Run experiment! (Note: Eating the entire sandwich after you are finished is a recipe for much groaning and moaning, don't do it. However, graham crackers dipped in frosting are a tasty post-experiment snack.


Step 4: Results/Conclusions
Discuss your results with your classmates as you are doing your experiments, this is critical to really understanding what you are seeing. Then write up a lab report detailing your results and your interpretations of those results. Were your hypotheses correct? What really does affect how materials deform (this will be a long list). As part of your analysis section list the properties you tested (i.e. bed thickness, overburden, surrounding materials) and list how each one affected the deformation of the beds and how each one interacted with the other ones.
Step 5: Include figures or pictures where you can. Disgusting images are most appreciated.
Step 6: 2 pts extra credit for finding an image of a deformed fold that illustrates one of your results.





Teaching Notes and Tips

There is no teachers version of this activity, the student handout is what is basically needed. I strongly suggest trying it yourself so you can determine how drop hints as needed. The cool thing is that it really works, with stacked white bread the top layer often splits at the crest of the anticline and the lowest layers exhibit less deformation. The plastic from the fruit-rollup in a bread-pudding sandwich works great to show how a) parasitic folds form (not always, but sometimes works) and b) how disharmonic folding takes place and c) how beds slide past each other during folding. The graham cracker really messes things up, so I try and suggest they no use it all the time, though it also does a great job of disharmonic folding and changing the shape of the beds around it. I also usually start off the activity with an image of disharmonic folding (I stole it off the web so it is not included here) as a way of motivating the question.

Assessment

This activity is assessed through the students' lab reports. The lab reports will very clearly convey what concepts the students understood and which they did not. Depending on how one chooses to teach this they can be used to design a lecture to follow or to see where students did not understand the prior lectures. A test question with a picture of ______________ folding asking the students to explain what happened to each bed (why it looks that way) is very useful for seeing if they understood long term.

References and Resources