We report in this paper the results of a measurement of the gravitational constant G obtained in a laboratory at distances of about 1 m, using a superconducting gravimeter. The instrument measured the gravitational effect due to an annular mass of about 280 kg moving up and down around the gravimeter. The experiment yielded for the gravitational constant the value G=(6.675+/-0.007)10(-11)Nm(2)/kg(2) which agrees, within its uncertainty, with the last CODATA value.
A geophysical experiment to check Newton's inverse square law is described. As a consequence, the value of the constant G at a 50 m effective distance is obtained. A project to measure G at a 1 m distance using a method different from those normally employed is also presented.
Here we report the results of a new analysis of the data obtained in the framework of an experiment consisting of the measurement of the gravitational signal induced by varying the water mass of a lake. A more precise calibration of the superconducting gravimeter used in the experiment has been performed with the use of an absolute instrument; furthermore, a knowledge of the absolute amplitude of the solid Earth tides of the station has been improved. The result of this analysis shows an agreement between data and Newtonian theory to within a 0.17% level.
We briefly describe a recent experiment aimed at verifying the dependence on the distance in Newton’s inverse square law. Then we present two new experiments for: (i) testing the previous result; (ii) making a measurement of the G constant by a method different from those normally employed.
A geophysical experiment consisting of the measurement of the gravitational effect produced by a large water mass was performed in order to verify Newton's law. The use of a superconducting gravimeter, the detailed analysis of the local tidal perturbation, the precise topographic and geological surveys lead to a precision of about 0.1% in the final result. The ratio between the measured and the expected gravitational effect differs from 1 by more than 9 standard deviations. This may be explained by adding to the Newtonian potential a Yukawa repulsive term. The experimental result leads to constraints for the relationship between the relative magnitude (alpha) of the new term and the range (lambda) of the interaction. In the region 20 m < lambda < 500 m, alpha ranges from 2.6% to 1.3%.
A superconducting gravimeter was used to monitor the tidal signal for a period of five months. The instrument was placed in a site (Brasimone station, Italy) chat-acterized by a low noise level, and was calibrated with a precision of 0.2%. Then tidal analysis on hourly data was performed and the results presented in this paper; amplitudes, gravimetric factors, phase differences for the main tidal waves, M2, S2, N2, 01, Pl, K1, QI, were calculated together with barometric pressure admittance and long term instrumental drift.
In May 1994 a first comparison campaign between a superconducting and the IMGC absolute gravimeter has been performed in Brasimone, near Bologna in Italy. The superconducting gravimeter was previously calibrated by means of a moving ring, the mass of which has been measured with the highest accuracy allowed by the actual technology. During the three days of observation with the absolute gravity meter, a maximum, a complete semidiurnal curve and a minimum of the tidal effect have been observed. These data have been used to compute the calibration factor of the superconducting gravity meter; it agrees in a rather satisfactory way with the results of the calibration with the moving mass.
