A Measurement of Newton's Gravitational Constant

Physical Review D (Impact Factor: 4.86). 10/2006; 74(8). DOI: 10.1103/PHYSREVD.74.082001
Source: arXiv

ABSTRACT A precision measurement of the gravitational constant $G$ has been made using a beam balance. Special attention has been given to determining the calibration, the effect of a possible nonlinearity of the balance and the zero-point variation of the balance. The equipment, the measurements and the analysis are described in detail. The value obtained for G is 6.674252(109)(54) 10^{-11} m3 kg-1 s-2. The relative statistical and systematic uncertainties of this result are 16.3 10^{-6} and 8.1 10^{-6}, respectively.

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    ABSTRACT: We review the G measurements with time-of-swing method at HUST. Two independent experiments have been completed and an improved experiment is in progress. The first G value was determined as 6.6699(7)×10(-11) m(3) kg(-1) s(-2) with a relative standard uncertainty (ur) of 105 ppm by using a long period torsion pendulum and two cylindrical source masses. Later, this result was corrected to be 6.6723(9)×10(-11) m(3) kg(-1) s(-2) with ur=130 ppm after considering the density distribution of the cylinders and the air buoyancy, which was 360 ppm larger than the previous value. In 2009, a new experiment by using a simple block pendulum and spherical source masses with more homogeneous density was carried out. A series of improvements were performed, and the G value was determined to be 6.67349(18)×10(-11) m(3) kg(-1) s(-2) with ur=26 ppm. To reduce the anelasticity of the torsion fibre, fused silica fibres with Q's of approximately 5×10(4) are used to measure G in the ongoing experiment. These fibres are coated with thin layers of germanium and bismuth in turn to reduce the electrostatic effect. Some other improvements include the gravity compensation, reduction of the coating layer effect, etc. The prospective uncertainty of the next G value is 20 ppm or lower.
    Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences 10/2014; 372(2026). DOI:10.1098/rsta.2014.0141 · 2.86 Impact Factor
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    ABSTRACT: Before this Theo Murphy Meeting, my working hypothesis was that human activity during the measurement of G significantly affects the measurement itself. Noise caused by the gravity gradient of humans was indeed the reason why in one experiment the apparatus was raised 3 m above the floor. The meeting convinced me that all experimenters took adequate precautions against gravity gradients caused by human activity. During the meeting, another concern arose: was the cycle time between two states of the experiment so long that the environment changed significantly in the meantime? Once again, it appears that the experimenters were appropriately cautious. After the meeting, it became clear that ageing effects in thin, stressed wires could be an issue. I conclude with a speculation about a future 'atomic' value of G.
    Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences 10/2014; 372(2026). DOI:10.1098/rsta.2014.0021 · 2.86 Impact Factor
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    ABSTRACT: We have recently completed a measurement of the Newtonian constant of gravitation G using atomic interferometry. Our result is G=6.67191(77)(62)×10(-11) m(3) kg(-1) s(-2) where the numbers in parenthesis are the type A and type B standard uncertainties, respectively. An evaluation of the measurement uncertainty is presented and the perspectives for improvement are discussed. Our result is approaching the precision of experiments based on macroscopic sensing masses showing that the next generation of atomic gradiometers could reach a total relative uncertainty in the 10 parts per million range.
    Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences 10/2014; 372(2026). DOI:10.1098/rsta.2014.0030 · 2.86 Impact Factor

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