Tabletop Earthquake Activity Name 6 th Grade PSI Score: / 8 points Background Information: Earthquakes most often occur at transform boundaries where there are large faults (or breaks) in the Earth s crust. The two large pieces of rock that meet at these faults are in motion and are constantly grinding against each other. Think of the surface of a rock. When you envision a rock, you probably think of a hard, jagged, rough surface. This is exactly what the rock that makes up the Earth s crust looks like. When these two massive hunks of rock move across each other, it is not a smooth motion. The two rock faces are pressed so tightly together that they get stuck on each other as they try to slide past. The longer it takes for these two slabs to break free from each other, the more energy it builds up. This is similar to shooting a rubber band. The longer you keep stretching the rubber band, the more energy it will release when it finally shoots! When the large pieces of the crust finally slide past each other, the energy that has built up is released. This energy is felt throughout the surface of the Earth as powerful vibrations. This is how an earthquake occurs.
Do This! Feel the palms of your hands. The surface of your hand is fairly smooth. Your hands will play the roles of our transform boundaries for this demonstration. Press the palms of your hands together lightly and rub them together. Would you say it is easy or tough to slide your hands past each other? Next, press your hands together as hard as you can. You should feel as though each of your hands is trying to push through the other. While still pressing your hands together strongly, try to slide your hands past each other as you did before. You may find that it s a little harder to do this now! Your teacher will now lead a short discussion on this activity. Materials for each group: - A flat table-top surface - 2 pieces of sandpaper of different grades - A 2 x4 block of wood approximately 6 long with a hook already screwed in one side - Two rubber-bands that are joined together - A 5 to 10 N spring scale
Procedure: 1) Ensure that you have all of your supplies and ensure that they are already properly set-up (in particular the wooden block and the rubber bands). 2) Place the wooden block on the table so that it is lying on its largest face. Place one side of the rubber bands around the hook. Each member of your group will take turns slowly and steadily pulling the wooden block across the table using the other end of the rubber bands. (Your teacher will show you the proper method of doing this!) 3) Select the finer of the two pieces of sandpaper (or the one that is not as rough) and place it down on the table. Place the wooden block on top of the sandpaper and place the rubber band on the hook again. While one person holds the sandpaper in place, another member of the group will steadily pull the block across the sandpaper. Answer Question #1 in Data/Analysis. 4) Now take the rougher piece of sandpaper and place it down on the table. Repeat the procedure from Step 3 on this piece of sandpaper. Answer Question #2 in Data/Analysis. 5) Repeat Steps 2 through 4, but this time you will be using a spring scale. Lay the block as before, and attach the hook of the spring scale onto the hook of the block. (Your teacher will demonstrate proper use of the spring scale!) You will do 3 trials for each surface: one practice and two that you will record. You will then average these two numbers. The force will be recorded in Newtons (N). Use this information to fill in the Data Chart in Question #3. Data/Analysis: 1) How does the amount of force you need to apply to the rubber band when pulling the block across the table compare to pulling it across the fine sandpaper? Which is tougher to do? Which one causes the rubber band to stretch further?
2) How does the amount of force you need to apply to the rubber band when pulling the block across the fine sandpaper compare to pulling it across the rougher sandpaper? Which is tougher to do? Which one causes the rubber band to stretch further? 3) Surface Force in Trial 1 (N) Force in Trial 2 (N) Average Force (N) Table-Top Fine Sandpaper Rough Sandpaper 4) Describe the behavior of the block when it was pulled across the tabletop. Did it move at a consistent, steady pace or did it make quick jerks forward?
5) Describe the behavior of the block when it was pulled across the rough sandpaper. Did it move at a consistent, steady pace or did it make quick jerks forward? 6) Imagine that as the block moves across the surface, an earthquake is the result. Which surface out of the 3 do you think would produce the earthquake that would measure the highest on the Richter Scale? Explain.