CREAMERY BUTTER MAKING 191 



FRICTION : ITS ADVxVNTAGE AND DISADVANTAGE. 



The resistance produced by one body sliding over 

 another is called friction. No matter how smooth a sur- 

 face may appear it always contains irregularities (molec- 

 ular) which are not unlike the teeth of a saw, though so 

 small as to render them invisible to the naked eye. When- 

 ever, then, two surfaces are put together they inter- 

 lock and when made to slide over each other produce 

 friction. 



Friction as Applied to Belts. Practical application 

 of friction is made in transmitting power by means of 

 belts. Without friction such transmission would be im- 

 possible. The highest efficiency of belts is obtained where 

 there is no slipping or stretching, conditions made possi- 

 ble by observing the following points : 



1. Use only good leather belting. 



2. Avoid too slack or too tight belts. 



3. Run belts with the hair side next to the pullev. 



4. Cover face of pulley with belting and have the 

 hair side out. 



5. Keep belts dry and flexible. 



Size of Belting. A two-ply belt may be subjected to 

 an effective tension of 40 pounds per inch of width with- 

 out straining it. In determining, therefore, the width of 

 a belt for a given horse power the eiTective tension of the 

 belt must be considered. Further, since a fast running 

 belt is capable of transmitting a greater horse power per 

 given width than a slow running belt, the speed of the 

 belt must also be considered. Hence the following 

 formula : 



