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THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1952 



the maximum displacement of the wire takes place. Above this ampli- 

 tude the wire begins to slip on the plastic and for a travel of 0.3 mil 

 inch there are indications that the point of contact between the wire 

 and the plastic has changed from one position to another. This agrees 

 with the idea that friction is due to a definite bonding between points 

 of contact of the two materials which is broken by their relative motion. 

 New points of contacts are then made and a stick-slip process occurs. 

 At 0.5-mil-inch motion a number of small contacts occur during the 



LENGTH OF TRAVEL 



IN MIL INCHES 



0.05 



0.15 



'^rtM 



0.75 



1.0 



Fig. 9 — Tangential forces measured for an 18,000 cycle oscillatory motion whose 

 total displacements in mil inches are shown by the values given. 



