The Effect Of Seismic Noise On The Torsion Pendulum And The Study Of "Abnormal Mode" In The Determining G

The fact that the gravitational constant G is the least precisely determined constant among all the fundamental constants of nature shows that it still have many difficulties to improve the precision of determination of G. The difficulties in measuring G are mainly resulted from the extreme weakness of gravitational force and the measurement of the geometry of attracting and the attracted masses and the relative positions between them. Furthermore, the temperature drift, non-linear effect and seismic noise are also the reasons to limit the precision of G experiment.This paper mainly deals with the points about the effect of seismic noise on the determination of G. The response of the torsion pendulum when the support point is motivated by different force is simulated. The fluctuation of the period from the simulated data agrees well with the experiment data. The equation describing the dynamics of torsion balance and analysis solution has been proposed. We find the coupling between swing modes and the torsional mode. The analytic solutions show that the amplitude of this coupling mode depends on the amplitude of the swing modes and the frequency of the coupling mode is the linear combinations of the frequency in the two orthogonal directions in horizon. Our improved magnetic damper system can suppress the seismic noise, which is not only benefit for the determining G, but also can improve the precision of other gravitational experiment.