Surface pressure measurements with a cylindrical rod

A schematic diagram of the experimental set-up is shown in Fig. 6.1. It employs a stainless steel rod of 0.5 cm diameter and length 3 cm. The rod is hung by a thread from under a standard bottom-loading balance (e.g., Shimadzu model EB-280) of sensitivity 1 mg. This balance rests on a platform that can be raised or lowered at speeds down to about 1.0 mm/min. On raising the rod, the balance reading increases steadily, reaches a maximum value (Wmax) and then falls. The maximum is approached slowly (i.e., over a period of approximately 10 sec for the last few mg) in order to obtain equilibrium measurements. From the value of Wmax the weight of the rod in air (W r0d) is subtracted, and the surface 

The theoretical basis of the method has been investigated in some detail by Padday et al. (ref. 380) who derived all the general equations needed for its application. Unfortunately, these general mathematical expressions tend to be complicated and rather incon- 

---