Various forces offer resistance to the movement of a train on the track. These resistances may be a result of the movement of the various parts of the locomotives as well as the friction between them, the irregularities in the track profile, or the atmospheric resistance to a train moving at great speed. The tractive power of a locomotive should be adequate enough to overcome these resistances and haul the train at a specified speed.
Resistance Due to Starting and Accelerating
Trains face these resistances at stations when they start, accelerate, and decelerate. The values of these resistances are as follows:
Resistance on starting, R6 = 0.15W1 + 0.005W2 (25.10)
Resistance due to acceleration, R7 = 0.028aW (25.11)
where W1 is the weight of the locomotive in tonnes, W2 is the weight of the vehicles in tonnes, W is the total weight of the locomotive and vehicle in tonnes, i.e. W1 + W2, and a is the acceleration, which can be calculated by finding the increase in velocity per unit time, i.e., (V2 - V1)/t, where V2 is the final velocity, V1 is the initial velocity, and t is the time taken.
Table 25.1 summarizes the various resistances faced by a train.
Table 25.1 Details of various resistances