however, only the symbols are used and must be known by anyone attempting to trace out a locomotive
circuit.
1.21. WORK AND POWER
Work and power are often confused. Work, the result of an applied force which results in
motion, is the product of force times the distance along which it moves, or Work = Force x Distance.
Power, the rate of doing work, has the element of time that work does not; power equals work divided
by time, or
. Work is expressed as foot-pounds while power is expressed as foot-
pounds per second. Work done on a body results in an increase in potential energy, kinetic energy, or
heat of friction. In the illustration shown in figure 1.13, energy is contained in the bucket of water.
Potential energy is that possessed because of the water's position. Since the bucket of water is 10 feet
high and there are 20 pounds of water, the potential energy is 20 x 10 = 200 foot-pounds. If the water
runs down the pipe toward the pump it becomes kinetic energy, that is, energy in motion. If the 20
pounds had moved in a horizontal line for 10 feet, no more than 200 foot-pounds of work could have
been done. Since the potential energy of the water has not changed, the work has all gone into the heat
of friction.
1.22. MEASURING CURRENT
An ammeter, used to measure the quantity of current flowing in a circuit, is connected either in
the main power generating circuit or in one of the traction motor circuits. If the latter prevails, other
traction motor circuits carry an equal amount of current. Each ammeter is equipped with a shunt--a
bypass carrying most of the current--and the total current load passes through either the ammeter or its
shunt. The shunt is designed to work with the ammeter so that there is a relation between the current
flowing through it and the current flowing through the coil of the ammeter. A pointer is attached to a
coil which turns against a spring so that deflection is proportional to the current. The dial over which
the pointer swings can be marked to read amperes or quantity of current flowing.
In addition to having figures showing the current in amperes, the ammeter may be marked in
minutes, indicating the maximum time the locomotive may be operated at a certain load.
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