158 



AXLE FRICTION 



CH. X 



table, whether it is on its Mat face, its edee, or its 

 end. The friction, therefore, between an axle and its 

 box is directly proportional to the weight of the car- 

 riage without its wheels, and is not dependent upon 

 the length of the axle-arm. The absolute friction 

 of the axle depends very slightly upon the diameter, 

 but the resistance to the turning of the wheel due 

 to friction, acts at the surface of the axle with a 

 leverage which is represented by the radius (or 

 semi-diameter) of the axle-arm. If the axle is raised 

 off of the ground so that the wheel can revolve 

 freely, the force applied to the outside of the wheel 



to make it turn will be re- 

 sisted by the friction at r, Fig. 

 74, and the force will act with 

 a leverage RO. The longer 

 RO is, the less force will be re- 

 quired, applied at R, to turn 

 the wheel, and the loneer rO 

 is, the greater will be the re- 

 sistance of the friction. The 

 ease, therefore, with which the wheel can be turned 

 will depend upon the relation, or ratio between RO 

 and rO ; the larger the axle the greater the effect 

 of the friction, and its amount will be measured by 

 the ratio * R multiplied by a constant to be deter- 

 mined by experiment. 



This constant, or coefficient, usually designated f 

 by writers upon this subject, is found, for polished, 

 well-oiled metal surfaces, to have a value, according 



77777777777777777777777?. 

 Fig. 74 



