. Electric railways, theoretically and practically treated . tant accel-eration. Such a constant force may be obtained by pass-ing a current of electricity of a constant value throughthe armature and field coils of a series railway motor. Thepull transmitted by the gears from the armature shaft tothe base of the car wheel is termed tractive effoit, meaninghorizontal pull. It is sometimes referred to as the drawbar pull. It bears a fixed relation to the torque or turningmoment of the motor armature. The force of gravity willaccelerate one pound ft. per second. The relation between accelera
. Electric railways, theoretically and practically treated . tant accel-eration. Such a constant force may be obtained by pass-ing a current of electricity of a constant value throughthe armature and field coils of a series railway motor. Thepull transmitted by the gears from the armature shaft tothe base of the car wheel is termed tractive effoit, meaninghorizontal pull. It is sometimes referred to as the drawbar pull. It bears a fixed relation to the torque or turningmoment of the motor armature. The force of gravity willaccelerate one pound ft. per second. The relation between acceleration A, force F, and massm, is expressed by the formula, F = in A. Substituting for mass its equivalent = > & ^ g F X = ^— w ANALYSIS OF TRAIN PERFORMANCE. 19 where A = the acceleration in feet per second per second, F = the tractive effort, or force apphed in pounds, w = the weight in pounds being accelerated. Substituting for A the acceleration in feet per second per second its equivalent a in miles per hour per second, we obtain. a =. 10 20 30 40 50 60 70 SO 90 100 110 120 130 140 150 160 AMPERES Fig. 9. —MOTOR ACCELERATION CURVE. A F a = za X Let W = the weiirht in tons = w 2000 F F W X X 2000 W .01098 FW It is obvious from the preceding equations that 91. i effort will accelerate one ton at the rate of i 31. perH. per 5. It is also evident that the rate of acceleration 20 ELECTRIC RAILWAYS. varies directly as the force applied and inversely as theweight of the body undergoing acceleration. Motor Acceleration. — A curve, termed motor accelera-tion curve, Fig. 9, may be plotted for a particular motor
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