How does a seismograph detect vibrations from the passing wave front of an earthquake?
A) The wave front seeks out the instrument which stops vibrating when the wave front reaches it.
B) The instrument is anchored to the ground or buried in a vault so that it is stationary with respect to the earth. When the instrument moves, the suspended mass inside is relatively stationary due to inertia. The relative motion registers the quake.
C) The instrument vibrates with the ground as it rolls along a track above the focus.
D) The whole instrument moves up and down (or back and forth) on the ground, so that it starts jiggling a little weight inside that trips the detector to record the earthquake.

Question

Quizplus · Accepted Answer

Seismographs work based on the principle of inertia. The instrument itself is anchored to the ground, and when an earthquake occurs, the ground moves. However, the mass inside the seismograph (often a pendulum or a similar suspended weight) remains stationary due to inertia. The relative motion between the moving ground and the stationary mass is what gets recorded, allowing scientists to measure the strength and characteristics of the earthquake.

How Does a Seismograph Detect Vibrations from the Passing Wave