CHAPTER XXIII. 



FARM MACHINERY. 







FBICTION. 



It has never been practicable to devise a machine which 

 could transmit the energy imparted to it without sustain- 

 ing a certain amount of loss through friction and in some 

 forms of machines the loss of power through friction is 

 necessarily very great under the best management. In 

 other cases ignorance of the laws of friction or carelessness 

 leads to much larger losses than are necessary. 



On the other hand friction may be a very essential con- 

 dition to the accomplishing of important results. How es- 

 sential it is in walking we appreciate when we attempt to 

 move over very smooth ice and it is the friction of the 

 drivers of the locomotive upon the rails which enables it to 

 haul the enormous loads it does. In transmitting power 

 by means of belts it is friction which enables it to be done. 

 The service of nails and screws in holding parts together 

 depends upon the amount of friction developed in forcing 

 them home. 



676. Friction Between Solids. When one surface rests 

 upon another there is a tendency for the inequalities of 

 one to fit into those of the other, producing an interlocking 

 not very unlike, except in degree, what would be produced 

 by putting the cutting edges of two saws together. When, 

 such an interlocking has occurred it is only possible to 

 move one surface over the other by either separating the 

 two surfaces slightly or else by tearing off the interlocking 

 portions, and it is the separating of the two bodies or the 

 abraiding of these inequalities which causes the chief part 



