A seismograph is the device that scientists use to measure earthquakes. The goal of a seismograph is to accurately record the motion of the ground during a quake. If you live in a city, you may have noticed that buildings sometimes shake when a big truck or a subway train rolls by. Good seismographs are therefore isolated and connected to bedrock to prevent this sort of "data pollution."
The main problem that must be solved in creating a seismograph is that when the ground shakes, so does the instrument. Therefore, most seismographs involve a large mass of some sort.
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