how a Seismograph is work.

The simplest form of a seismograph is a simple pendulum.When the ground shakes,the base and the frame of the seismometer move with it,but the pendulum bob remains in place.thus,there is a relative motion between the bob and the sharing ground.A pen pen below the bob records this motion on a paper that is moved by a rotating Drum.The recording is the seismogram.The science that deals with the seismic waves is called seismology and earthquake scientists are called seismologists.