CHAPTER XVI. 



FRICTION AND LUBRICATON. 



The rubbing of the surface of one body against 

 that of another produces friction. Friction varies 

 greatly with different materials, conditions of the 

 surfaces in contact and the weight bearing them 

 together. The friction between two pieces of pol- 

 ished steel is much less than between two pieces of 

 brick. 



The power expended in overcoming friction is 

 transformed into heat, and the greater the friction 

 between two surfaces the greater the quantity of heat 

 produced. 



Friction is caused between two surfaces by the 

 unevenness and roughness of the surfaces in contact. 

 No matter how smooth a journal or box may seem to 

 be, the surface is dotted all over with minute points 

 or projections, with indentations or depressions 

 between them. 



When the two metals of the journal come in 

 contact, the points of one of the bodies settle down 

 and fit into the depressions of the other, and when the 

 bodies are moved in relation to each other the points 

 cling fast, and some of them break off, thus wearing 

 the surface away. 



By the application of properly shaped particles 



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