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The Free-Fall Determination of the Universal Constant of Gravity

TitleThe Free-Fall Determination of the Universal Constant of Gravity
Publication TypeThesis
Year of Publication1998
AuthorsSchwarz, JP
Abstract

The Newtonian constant of gravity, G, is the constant of proportionality that scales the magnitude of the gravitational force between masses. G is the least precisely known of all fundamental constants. Recent high-precision experiments to measure G have produced highly discordant results, with values spread over a range of 0.7%. The situation is almost incredible; the second digit of the value is in contention and experiments disagree by as much as 50 of their individual error estimates.

We have developed a new determination that uses an absolute free-fall gravimeter to sense the gravitational attraction between a known source mass and a falling test mass. We use a one-half metric ton source mass whose position is alternated from above to below the dropping region, either decreasing or increasing the observed acceleration of the test mass. The source mass generates a differential signal of 8 parts in 107 of the local acceleration due to the Earth. This method is independent of many of the systematic errors associated with the traditional torsion balance experiments upon which the accepted value of G is based.

Using this "free-fall" method in two data runs of approximately two weeks, we have found a value of G at the level of 1100 ppm. Our value is: G = (6.6873 ± 0.0076) x10-11 m3/kg-s2. This value lies in the approximate center of the range of recent results.