A new determination of G

Abstract

A determination of G, the Newtonian constant of gravitation, has been made utilizing a new free-fall method. Traditionally this determination has been made using a torsion fiber which (functionally) eliminates g (the acceleration due to gravity) from the measurement process. In this determination, we explicitly use g to measure G. We do this by measuring the effect a large, yet moveable, mass has on the measured value of g. In this determination we use a FG-5 absolute gravimeter to measure g. This commercial instrument uses time-resolved interferometry of a freely falling "mirror" to determine g with a measurement accuracy approaching 1 part in 10/sup 9/. Together with the FG-5, we use a large and finely moveable mass which surrounds the dropping region. On twenty-minute intervals this mass is moved between positions just above and just below this region. As a result, the measured value of g is square-wave modulated with a peak-to-peak amplitude of approximately 80 parts in 10/sup 9/. This precisely measured difference together with a straightforward, though numerically involved, analysis of the effects of the mass in the two positions on the measured value of g determine G.