Answer:
The apparatus would need to be extremely delicate because of the very small values being measured, the gravitational attraction of two massive objects.
(I) the torsion constant, measuring the deflection of massive objects would be very small and difficult to measure accurately
(II) since all surrounding objects are massive, it is difficult to remove the effect of such objects from forces being measured
(III) to consider a massive object as having all of its mass at its center, the massive object would need to be uniform throughout - any nonuniformity of the object would affect the calculations
(IV) all physical measurements would need to be made with utmost accuracy because of the relatively small distances involved with regard to the extremely small force being measured
(V) today laser measurements would assist in measuring small deflections accurately
