Graduate Fellows in K-12 Education

Transcription

1 Lesson Title: The Earthquake Machine Discipline Focus: Earth Science Grade level: Middle school Length of lesson: 45 minutes Graduate Fellows in K-12 Education Stage 1 Desired Results Content Standard(s): MN Standard Recognize that major geological events, such as earthquakes, volcanic eruptions and mountain building, result from the slow movement of tectonic plates. Understanding (s)/goals Students will understand: 1. that earthquakes are a result of motion along a fault plane 2. motion along plate can be either small incremental or large one time motions. 3. large earthquake are a result of large motions along the fault planes. Essential Question(s): with thousands of earthquakes everyday why do we only feel a few? what controls the strength and intensities of earthquakes? what do friction and elasticity come into play? Student objectives (outcomes): Students will be able to: 1. understand why most earthquakes are under 3.0 Mw and are unfelt and many times undetected. 2. what causes large earthquakes. Performance Task(s): Students will be a one meter section of carpet (somewhat rough) and a wooden block with sandpaper on one side and smooth on the other. The wooden block has an eyelet screw and is attached to a rubber band tied to a string. Students pull the string in 1 cm increments and measure the distance the block moves using the smooth and sandpaper sides. Students record these measurements and graph the results before answering the questions. Stage 2 Assessment Evidence Other Evidence: This exercise should be taught soon after discussing the different layers of the earth and the differences between elastic and brittle materials. Stage 3 Learning Plan Learning Activities: Materials for each group: One meter piece of carpet (using the somewhat rough backside)

2 Wooden block with an eyelet connected to a rubber band tied to a 25 cm string Metric ruler Attached sheet Background: Tectonic earthquakes are caused by a sudden slippage along the boundary between two plates. The type of motion that occurs between two plates is used to classify faults as strike-slip, thrust (reverse) and normal. Typical rates of plate motion are a few cm per year. Why then, might someone ask, do destructive earthquakes occur in which many meters of fault slip happen so quickly that the vibrations are recorded by seismographs all around the world and are sometimes strong enough to destroy nearby buildings and bridges? This is a result of friction and elasticity. Shallow portions of the plates are relatively cool, two plates act brittle and cannot flow past each other. The faults instead tend to stick or lock up for years or centuries at a time. Each year the portions of plates near locked faults deform elastically by a few more cm. The more the plates are bent and deformed, the greater the force is on the fault (shear stress). Eventually the force is sufficient to make the plates break free of one another and the elastic energy that has been stored up is released as frictional heating on the fault and ground vibrations. (seismic waves). This process of faulting is called stick-slip or elastic rebound. Procedure: In this lab, one student will be the puller, one will be the observer, and two or three will take notes. The puller will start with the rubber bands pulled out so that there is almost no tension on the block. This initial position on the meter stick of the leading edge of the block and the leading end of the string of rubber bands needs to be recorded by the recorders. Then when everyone is ready, the puller will move the end of the rubber bands 1 cm and then count out loud, "one, move the end of the rubber bands 1 more cm and then count out loud, "two," move 1 cm, count out loud, "three" and so forth. Initial position Intermediate position The observer will read out loud the position of the block at its initial position and then

3 after each movement that the puller makes and the recorders will write these numbers down. Do this three times on the sandpaper side and three times on the smooth side. Using the data from the recorder, make a graph of the position of the block versus the position of the end of the rubber bands that was being pulled. Now that you have an idea about how the lab works, discuss what you think is going on. How is friction related to the movement of the block? Do you expect the motion of the block would be the same if the experiment were repeated? Repeat the experiment twice more (for each side), each time changing the puller, observer, and recorder assignments (you do not need to make a graph unless you have very different results). After you have completed this answer the questions on the back.

4 The Earthquake Machine Name Directions: In this lab, one student will be the puller, one will be the observer, and two or three will take notes. The puller will start with the rubber bands pulled out so that there is almost no tension on the block. This initial position on the meter stick of the leading edge of the block and the leading end of the string of rubber bands needs to be recorded by the recorders. Then when everyone is ready, the puller will move the end of the rubber bands 1 cm and then count out loud, "one, move the end of the rubber bands 1 more cm and then count out loud, "two," move 1 cm, count out loud, "three" and so forth. The observer will read out loud the position of the block at its initial position and then after each movement that the puller makes and the recorders will write these numbers down. Do this three times on the sandpaper side and three times on the smooth side. Using the data from the recorder, make a graph of the position of the block versus the position of the end of the rubber bands that was being pulled. Now that you have an idea about how the lab works, discuss what you think is going on. How is friction related to the movement of the block? Do you expect the motion of the block would be the same if the experiment were repeated? Repeat the experiment twice more (for each side), each time changing the puller, observer, and recorder assignments (you do not need to make a graph unless you have very different results). After you have completed this answer the questions on the back.

5 1. Describe the sequence or steps leading up to the block moving. 2. Where did the energy that made the block move come from? Where might this same energy come from in the Earth to create an earthquake? 3. After using the Earthquake Machine model, refine your definition of an earthquake based on the model. 4. What did this model allow you to see that you don t think you would be able to see if looking at a real fault. 5. How might this model be like/unlike an actual fault and earthquake? 6. How would you modify the model so that it no longer stored energy? How do you think your modification would impact the models overall operation?