In general, a friction test machine according to the invention comprises a sample holder configured to hold a sample in frictional engagement with a friction surface, and {HEAD ~ a motion device} for effecting {TAIL ~ relative movement} between the friction surface and sample holder in a first direction 
for effecting
In general , a friction test machine according to the invention comprises a sample holder configured to hold a sample in frictional engagement with a friction surface , and { HEAD ~ a motion device } for effecting { TAIL ~ relative movement } between the friction surface and sample holder in a first direction
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