Application of ultrasonic sensor and Arduino in analysing motion of damped pendulum

Abstract

An easy-to-setup experiment designed to measure the period and air drag coefficients of a damped pendulum is reported. The setup is made up of a solid metal ball and cylindrical shells of various sizes to create air drag. An ultrasonic position sensor (HC-SR04) and an Arduino Uno board were located beneath the pendulum’s lowest position. The pendulum was released from a fixed height at a small initial angle. The periods of the oscillations involving different cylindrical shells were obtained from the time series plots of the pendulum’s position when the pendulum moves back and forth above the sensor. The drag coefficients were measured from five different values of string length. The coefficient was proportional to the size of the cylindrical shells and in agreement with the drag equation for a small Reynolds number.