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CHAPTER VIII 



THE FORCE FACTOR 



THE method of rating a motor in horse-power gives us no 

 indication of its ability to accelerate, although the function 

 of accelerating may be the most important that it is called 

 upon to perform. We shall find it convenient to be able 

 to describe a motor in terms of a unit that shall be indepen- 

 dent of speed and that will tell us to what extent a motor 

 is able to accelerate under given conditions. This must 

 be a force unit and not a power unit. 



If a pulley of d centimetres diameter is placed on the 

 shaft of a dynamo of induction factor M, carrying a current 

 of c amperes, the tangential force at the rim of the pulley 

 is given by 



T= McW dynes (91). 



TTCL 



If d = -W~ centimetres, this may be written 



7T 



T=Mc dynes ... (92). 



The force of a dynamo may thus be defined as a force of 

 Me dynes at the rim of a pulley 10 7 centimetres in cir- 

 cumference. We shall call Me the force factor of the 

 dynamo. 



