Design and Implementation of Automated Data Acquisition Method for Historic Cavendish Experiment*

The gravitational constat, G, is essential for explaining and modeling gravitational attraction between any two objects with mass. The Cavendish Experiment was first performed in the late 18th century, and the value of G has been well established and confirmed since that time. This experiment is still used in physics teaching laboratories, allowing students to learn important lessons about experimental techniques. The goal of this research project was to automate the data collection and analysis using a PASCOTM apparatus modeled after the original Cavendish design. The instructional apparatus relies on observing the position of a laser beam reflected from a small mirror attached to an oscillating torsional pendulum. In this work, the older observational method was replaced with photosensors and an Arduino interface to automate the determination of laser position and pendulum oscillation times. A circuit was designed and tested for the array of interfaced photodiodes. A peak-detection code was written to process voltage values from the photodiodes and determine when the laser was at the center of a photosensor, allowing for positional information as a function of time. To improve experimental results, additional measurements of the mechanical apparatus were done, and three different methods were used to determine G. A Python code was developed to calculate G for the three methods, including error propagation. Reasonable values for G were found for two of the three methods