Explain how the vertical and horizontal components of an earthquake motion are detected on a seismometer.

A seismometer is an instrument used to detect and measure ground movements caused by earthquakes, explosions, or other seismic waves. In simple terms, it records the vibrations of the earth by analyzing the motion of a sensing mass mounted on a spring system inside the seismometer.

There are typically three main components in a seismometer: the sensing mass, spring system, and recording device. The sensing mass is a heavy weight that remains at rest due to inertia. The spring system connects the mass to a frame, which is fixed to the ground. The recording device measures the relative motion between the mass and the frame to determine ground velocity.

To detect vertical motion or shaking, the mass is mounted vertically above the frame, usually with a stiff spring supporting it. When an earthquake occurs and the ground starts to move vertically, the frame moves along with it. However, due to the inertia of the mass, it tends to remain stationary. This causes the spring to stretch or contract, which in turn causes the mass to move relative to the frame. The motion of the mass is then converted into an electrical signal by a displacement sensor, which is then recorded and analyzed.

To detect horizontal motion or shaking, the mass is mounted horizontally, with a spring attached to it laterally. When an earthquake occurs and the ground starts to move horizontally, the frame moves along with it. Similarly to the detection of vertical motion, the inertia of the mass causes it to remain stationary, leading to a change in the relative position between the mass and the frame. This change is also converted into an electrical signal through a displacement sensor, which is then recorded and analyzed. In conclusion, seismometers detect both vertical and horizontal components of an earthquake motion by utilizing the differences in motion between the sensing mass and the frame due to inertia. The seismometer measures these changes in position and converts them into electrical signals that can be analyzed to understand the magnitude and direction of the earthquake's motion.