11 ! -II 10S8 OF UNIFORM MOTION J ' 



Hysteresis, arising from the fact of a definite torque 

 being needed to turn a mass of iron in a magnetic field ; 

 this always opposes the motion. 



If the torque assisting the motion \.-irtly balances 

 that ivi-timr the motion, the motion will be eith.-r 

 nothing or uniform ; uniform motion implies a balance 

 between the assisting and resisting torques, assuming that 

 motion has been establish^!. For it' tin- a.sisting torque 

 is greater than the iv>Utintf torque, there will IK- a Hurplus 

 available for acceleration. 



Take the case of a locomotive pulling a train ; if the 

 horizontal effort of the locomotive at the draw-bar is 

 greater than the frirtional n-i tin- train it will 



accelerate ; when the draw-bar pull is equal to the resist- 

 ance the motion will be uniform. If, before there is any 

 i, the draw-bar pull is only just equal to the resist- 

 ance the train cannot start. So in a motor, to effect a 

 start the assisting torque must be greater than the 

 resisting torque, leaving a surplus which we shall call the 

 'accelerating torque/ the motor will then speed up until 

 the assisting and resisting torque* balance, and uniform 

 motion U the result. 



If a motor with an armature of I! ohms resistance be 



connected to a line having a t-n-fn <>f / \..lt*. the greatest 



I 

 possible in rr-nt i* 'amperes. If the iinlurtion factor Of 



the motor be .V, the torque produced by this current in the 

 armature, as given by Filiation >, is 111 me li-|xiindi. 



If the load is greater than this amount the armature cannot 

 move; if it in le** than thin the difference is availab 

 JDoeleration. ami ti will |H-M| up until the tonjue 



