Teach the Earth > Introductory Courses > Activities > Milky Way - Ductile and Brittle Demo

Milky Way - Ductile and Brittle Demo

Mark F. Wood
Jefferson Community and Technical College (JCTC)
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This activity was selected for the On the Cutting Edge Reviewed Teaching Collection

This activity has received positive reviews in a peer review process involving five review categories. The five categories included in the process are

  • Scientific Accuracy
  • Alignment of Learning Goals, Activities, and Assessments
  • Pedagogic Effectiveness
  • Robustness (usability and dependability of all components)
  • Completeness of the ActivitySheet web page

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This activity has benefited from input from faculty educators beyond the author through a review and suggestion process. This review took place as a part of a faculty professional development workshop where groups of faculty reviewed each others' activities and offered feedback and ideas for improvements. To learn more about the process On the Cutting Edge uses for activity review, see http://serc.carleton.edu/NAGTWorkshops/review.html.

This page first made public: Jul 7, 2008


Milky way candy bar is given to each student. They are told to bend it and write down what they observe. The activity takes an every day object and ties the geologic terms to something they have experience with.

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Introductory Physical Geology (majors or non-majors), Structural Geology

Skills and concepts that students must have mastered

No mastery is skills is needed; I give a lead-in discussion of ductile and brittle behavior. I link it to the stress / strain graph and after we discuss what happens and how it relates to the chart, what is ductile behavior and what is brittle, where the elastic limit is found and when we exceed the limit and what happens. This is then related to rock behavior.

How the activity is situated in the course

This is part of a sequence of exercises and demonstrations in my introduction to structural geology, the earth, and rock deformation. It is all tied to the stress / strain graphing of brittle and ductile behavior. This leads into structural geology, folds, faults and greater plate tectonics and mountain building discussions.


Content/concepts goals for this activity

The goal is to be able to better relate to the meaning of the graph and what stress and strain are. I find that relating rock behaviors to every day items help students to visualize and conceptualize the more complex ideas.

Higher order thinking skills goals for this activity

This is pretty basic stuff I work on in my class.

Other skills goals for this activity

I have tried to do this in groups as well and it works quite well.

Description of the activity/assignment

To prepare for this activity the students are to have read the chapter in the book relating to rock deformation. We have discussed metamorphism and have used a couple of other related demos. I relate ductile deformation to bending clay or a coat hanger and brittle to breaking a pencil or a plastic rod. I graph these on the black board and we discuss what might happen if we mixed materials or changed the temperature. I then break out the Milky Way bars and pass them out. They are to bend them in half and write down what they observe. Sometimes I break into groups to discuss if there is time otherwise we go over the behavior and pass in the assignment.

Determining whether students have met the goals

I determine the effectiveness of the assignment in several ways. First I note which students participate in the discussion and at what level (I grade daily discussion). Also I grade the work they hand in. I have several quiz and test questions directly and indirectly related to the activity.

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Supporting references/URLs

I learned part of this from my structural geology prof. Dr. Eric Frost currently at Santa Barbara. I've never seen another reference to it.

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