HY-SR04 is a widely available ultrasound ranging module. It consists of two 40 kHz Piezo crystals,
where one acts as a transmitter and other as a receiver, and some electronics circuitry is inbuilt to measure the time
interval between a burst of sound transmitted and the echo received.
This module can measure distance with around 3mm Accuracy, and can be applied to study mass-spring systems, pendulums, and other similar mechanical systems.