# Automation of the Cavendish Experiment to 'Weigh the Earth'

## TL;DR

This paper presents a simple, inexpensive automated method for collecting data in the Cavendish experiment using phototransistors and multiplexers, achieving a measurement of G within 5% of the accepted value.

## Contribution

It introduces a novel automation technique for the Cavendish experiment that requires no moving parts and simplifies data collection.

## Key findings

- Achieved measurement of G within 5% of the accepted value.
- Demonstrated effective capture of damped harmonic oscillations.
- Provided a cost-effective and straightforward automation approach.

## Abstract

We describe a simple and inexpensive method for automating the data collection in the well-known Cavendish torsion balance experiment to determine the gravitational constant $G$. The method uses a linear array of phototransistors and requires no moving parts. Multiplexers and a data-acquisition device are used to sample the state of each phototransistor sequentially. If the sampled phototransistor is illuminated by the laser spot, the position and time are recorded to a data file. The recorded data does an excellent job of capturing the damped harmonic oscillations. The resulting data were analysed to extract an experimental value of $G$ that was within 5% of the accepted value.