Automating data acquisition for the Cavendish balance to improve the measurement of G

The Leybold-Heraeus gravitational torsion balance is commonly used in undergraduate laboratories to measure the gravitational attraction between known masses to find the gravitational constant G. Because the difficult task of data acquisition reduces its usefulness, we have implemented a simple design that minimizes this task and achieves more accurate results. This design features a small car that tracks the oscillating laser with the use of a stepper motor and some simple control circuitry. Step counting yields the location of the reflected laser in time. (C) 2007 American Association of Physics Teachers.