Also provided is a variable weight loading device on the sample holder for loading the sample holder such that a selected load can be applied to the sample normal to the friction surface, and a force measurement device for obtaining {HEAD ~ a measurement} indicative of {TAIL ~ the frictional force} resisting such relative movement between the sample holder and the friction surface effected by the motion device 
Also provided is a variable weight loading device on the sample holder for loading the sample holder such that a selected load can be applied to the sample normal to the friction surface , and a force measurement device for obtaining { HEAD ~ a measurement } indicative of { TAIL ~ the frictional force } resisting such relative movement between the sample holder and the friction surface effected by the motion device
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