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MAKING A SIMPLE
A seismograph is an instrument that detects vibrations in the earth. We can make a very simple one in our classroom. It probably will not have the capability of detecting and locating an earthquake in another part of the world, but it will give us a glimpse of the way they work.
Place a pan of water on a table in such a way that a beam of sunlight strikes the surface of the water and reflects a spot of light on the ceiling or a wall. Stamp your foot on the floor and observe the spot of light. Look at the water.
The water in a lake or pond would behave similarly if there were an earthquake nearby. Every time there is a quake, vibrations travel through the ground and air to the water, and set up ripples on its surface. If the quake is weak, the shimmering is slight; if it is strong, the shimmering is much greater.
You can set up vibrations in many ways to further test your simple seismograph; e.g., clapping your hands together, closing a window or door, dropping a book, or playing loud music.
See if your seismograph is sensitive enough to detect the hum of a motor in a school appliance or the rumble of vehicles passing by the school.
Consider this: If you have ever gone to an outdoor rock concert, you felt the vibrations of the music in the ground where you sat. Does this mean that an earthquake could be caused by a loud rock concert?
How is it that deaf people can dance to music that is being played? Can they feel the vibrations caused by the music? They can feel the vibrations and the rhythm itself!
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