Measurement of gravitational acceleration using a computer microphone port

Abstract

A method has been developed to measure the swing period of a simple pendulum automatically. The pendulum position is converted into a signal frequency by employing a simple electronic circuit that detects the intensity of infrared light reflected by the pendulum. The signal produced by the electronic circuit is sent to the microphone port and recorded as a 16-bit wave file by common software. The wave file is then processed to obtain the signal period as a function of time by timing all zero crossings. From the obtained signal period as a function of time, an average value of the period is calculated. Using the calculated average period, it was found that the gravitational acceleration is (9.77 ± 0.03) m s−2. Noting that the G-type La Coste & Romberg G928 gravimeter obtains a gravitational acceleration of 9.78 m s−2, the present method offers very good accuracy, with a percentage error of about 0.1%.