Investigation of Newtonian Forces on Plate Tectonics

This activity is designed for students to develop two models of motion and forces acting on plate tectonics. They will need to apply Newtonian Laws (especially #3: For every action, there is an equal and opposite reaction) to Earth materials. After the lab, students should be able to explain plate tectonics at a point on Earth's crust. Concepts learned include Newton's Third Law. Also, students will be able to explain folding in the Earth's crust. Vocabulary to be reviewed includes synclines, anticlines and forces of compression.

This lab is appropriate for a class of about twenty middle school students that can be assigned to small groups. While studying plate tectonics, students will be able to review the forces of Newton's Third Law. Also, if you are teaching the physics of forces and Newton's Laws, this is a good review of plate tectonics. The lab can be conducted in one forty-five minute class period following related lecture topics. Set up preparation and clean-up are fairly easy, and supplies are readily available.

After a class discussion reviewing Newton's Third Law and plate tectonics, students will be divided into small groups (4-5 students each, if possible). Two of the students will work with colored clay, layering it to model Earth's crust, and two students will use springs and balls to represent a singular point on Earth's crust.

Materials:
-Set of atomic model springs and balls (at least 12 balls and 17 springs-colored)
-Soup can or rolling pin
-Clay, modeling, 4 colors
-8 1/2"X 11" sheets of plain paper
-Knife, plastic
-Newspaper
-Pencils colored
-12" ruler
-Poster board (1 strip 5cmX 15cm)

Clay group: Use modeling clay of one color to form a long cylinder, and place the cylinder in the center of the glossy side of the poster board strip. Mold the clay to the strip. Try to make the clay layer the same thickness all along the strip; you can use the rolling pin or soup can to even it out. Pinch the sides of the clay so that the clay is the same width and length as the strip. Your strip should be at least 15 cm long and 5 cm wide. Flip the strip over on newspaper laid across your desk. Carefully peel the strip from the modeling clay. Repeat steps 3-5 with the other colors of clay. Each person should have a turn molding the clay. Each time you flip the strip over, stack the new clay layer on top of the previous one. When you are finished, you should have a block of clay made of four layers. Lift the block of clay, and hold it parallel to and just above the tabletop. Push gently on the block from opposite (long) sides. Use the colored pencils to draw the results of pushing the model. Use the terms syncline and anticline to label your diagram. Draw arrows to show the direction that each edge of the clay was pushed.

Model group: Using 12 balls and 17 springs, connect to make a 3 ball X 4 ball mat. This model should be in one plane (i.e. flat on the table). Trace this model onto sheets of paper on table. If possible, color the drawing to match the model colors. If you don't have colored balls, simply number the paper tracings 1-12. Partner one then places each of her hands on the edges of the model (as is done in the clay group) and pushes (applies force) towards the center of the model. Each hand should only move about two centimeters towards center. Partner two then traces the new ball position over the original drawing and labels the colors or numbers accordingly. After tracing, partner one applies additional force (approximately another two centimeters towards center) and another tracing is taken. If possible, repeat these steps with additional force.
Upon completion, have partners explain steps and procedures to small group. Compare and contrast clay model forces with ball-spring model forces. Have students complete the analysis questions and write a conclusion.

Lab Analysis:
1. Draw a Venn diagram comparing/ contrasting the two models
2. What happened as force was applied to the clay model? To the ball-spring model?
3. Describe the difference between the forces applied to each. (Think: What size is each model representing?)
Conclusion: Summarize how the forces you applied to each model relate to the way tectonic forces affect rock layers. Be sure to include synclines, anticlines and compression.

This activity is adapted from "Oh, The Pressure!" by Daniel Bugenhagen, Yutan Jr-Sr High, Yutan, Nebraska. This lab is published in Holt, Reinhart, Winston Earth Science, 2005.

I have used the clay model activity ("Oh, The Pressure!") with students and it continues with a procedure for students to model faults and observe hanging walls and footwalls. After taking a Physics course recently, I thought it would be an appropriate place to review Newton's Laws, since my eighth graders haven't had any Physics for two years. If you have time, however, the fault portion of the lab is easy (www.HoltReinhartWinston.com). I have not yet done this activity with ball-spring models, but I think a review of free body diagrams- for both instructor and students- is a good idea. The ball-spring models represent one point on Earth's surface, and should help students visualize how all points move together to produce synclines and anticlines.

Student work to be handed in will include lab questions and answers, including a Venn diagram, and a summarizing conclusion. Students will be evaluated individually on lab write-ups and final chapter written assessments. Group discussion will allow for topics to be clarified.

9.II.E.1-2 Forces of Nature