Book 12, Question 30
Why Do Seismographs Draw Squiggles?
A seismograph has a heavy weight that tries to stay still. When the ground shakes, the frame moves, but the weight does not. A pen draws the difference as a squiggly line.
More fun facts
- Seismographs record how the ground moves during an earthquake.
- Inside is a part called a seismometer, often a heavy weight hanging on a spring or a pendulum.
- When the ground shakes, the whole instrument shakes too, except the weight, which tends to stay still.
- The recorder notes the difference between the still weight and the shaking frame, and that makes the squiggles.
- When the ground is calm, the line is nearly straight; when it shakes, the line wiggles.
- Older seismographs drew on a turning drum that slowly moved sideways, so the pen did not trace the same circle over and over.
- The first seismograph was built in 1890.
Sources: U.S. Geological Survey, U.S. Geological Survey
Questions kids ask
Are the squiggles still drawn on paper?
No. Earthquake recordings are digital now, and there are no more paper recordings.