272 



MECHANICS 



consequently, .65 = tan a, and from a table of natural tan- 

 gents a = 33. 



The accompanying tables give coefficients of friction and 

 angles of repose of a number of materials. 



COEFFICIENTS OF FRICTION AND ANGLES OF 

 REPOSE FOR MASONRY MATERIALS 



Rolling Friction. The friction between the circumference of 

 a rolling body and the surface upon which it rolls is known as 

 rolling friction. It is due to the compressibility of substances, 

 the weight of the rolling body causing a small depression in the 

 supporting surface and a flattening of the roller. Its magnitude 





