Tension, Shearing and Compression Stresses


To observe how pressure can change the structure of rock such as in the formation of metamorphic rock


There are many forces that act on the Earth's crust. For example compression forces push or squeeze rocks together. Tension forces pull rocks apart and shearing forces twist and tear rocks. These forces move the rocks in Earth's crust and change their shape and structure. Many of the Earth's major landforms are formed by these forces. Have the students practice the three forces on a piece of paper. Lay the paper flat on the desk and have the push the two ends together. Ask if this is the Earth's crust what have you made? Mountains Compression Stress. Then have them hold the paper above their desk and have them pull the two ends of the paper apart until it rips. Tension Stress- Rift Valley or Spreading Center or a fault. The have them put one piece of the ripped paper back on the desk. Have them hold opposite diagonal corners and pull the top left corner towards the top of the desk and the bottom right corner towards the bottom of the desk. Not easy to coordinate. If the paper rips they have created Fault by Shearing stress.

Materials :

3 or four different colors of play dough or clay. Some clay is very hard to push and pull
A plastic knife
Wax Paper or something to cover desk surface
Two hands
Paper and pencil for recording data


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