How does a seismograph detect and record seismic waves?

I'm not exactly sure but maybe this will help you out>

By having the needle move along with the earth shaking and records how uch the earth shook on a piece of paper

i know its not the best but at least its something:)

Generally, it consists of a pen attached to a fixed base which has paper placed on top. During an earthquake, the base and paper move and the pen does not. This records the spikes and movement of an earthquake.

False. Direct observation is NOT the simplest and most effective method to determine population size.