Research Of Fiber's Anelasticity In G Experiments

The Newtonian gravitational constant has been measured precisely by using torsion balances with the time-of-swing method. However, the experimental results of several groups are not consistent in the range of error. It means that there are some unknown system errors in experiments at present. Since Cavendish measured Newtonian gravitational constant by a torsion balance, it had been assumed that the spring constant of the torsion fiber was exactly a constant. In 1995, Kuroda pointed out that this constancy might not be valid due to the anelasticity of the torsion fiber, it is dependent on the frequency. So it is necessary to consider the effect of anelasticity.Springs made of real materials fail to obey perfectly Hooke's law in that, after deflection, they do not return to their unstressed state immediately and, when they are stressed, they do not reach their final state of strain immediately. Such materials are said to exhibit anelasticity.We have studied in detail about the internal friction and mechanics property of metals, then make a research to anelasticity based on the theory of G experiment, and consider the influence of anelasticity on the measurement of Newtonian gravitational constant. The following works are discussed in this thesis: The analysis of two anelasticity experiments recently showed that their experiments can not support their conclusions. Kuroda et al ignored that the effects of background filed in their experiment are changed; In Bagley and Luther's experiment the temperature is unstable, and not only one physical quantity affects quality factor Q. Based on the inelasticity model, we propose an experiment method to confirm whether the anelasticity is the main component to Q, and make some theoretical calculations.