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
Resistance Due to Friction
Resistance due to friction is the
resistance offered by the friction between the internal parts of locomotives
and wagons as well as between the metal surface of the rail and the wheel to a
train moving at a constant speed. This resistance is independent of speed and
can be further broken down into the following parts.
Journal friction This is
dependent on the type of bearing, the lubricant used, the temperature
and condition of the bearing, etc. In the case of roll bearings, it varies from
0.5 to 1.0 kg per tonne.
Internal resistance This resistance
is consequential to the movement of the various parts of the locomotive
Rolling resistance This
occurs due to rail-wheel interaction on account of the movement of steel
wheels on a steel rail. The total frictional resistance is given by the
R1 = 0.0016W
(25.1) where R1 is the frictional resistance
independent of speed and W is the weight of the train in tonnes.