MECHANICAL DEVICES UTILIZED IN POWER
One of the most important things in enginery is the capacity to determine the power developed. Although the method of ascertaining this appears to be somewhat complicated, it is really simple, and will be comprehended the more readily if it is constantly borne in mind that a certain weight must be lifted a definite distance within a particular time.
The Unit of Time.—The unit of time is either the second, or the minute, usually the latter, because it would be exceedingly difficult to make the calculations, or rather to note the periods as short as a second, and a very simple piece of mechanism to ascertain this, is to mount a horizontal shaft A, [Fig. 59], in bearings B, B, and affix a crank C at one end.
It will be assumed that the shaft is in anti-friction bearings so that for the present we shall not take into account any loss by way of friction.
A cord, with one end attached to the shaft and the other fixed to a weight D, the latter weighing, say 550 pounds, is adapted to be wound on the shaft as it is turned by the crank.
Knowing the length of the cord and the time required to wind it up, it will be an easy matter to figure out the power exerted to lift the weight, which means, the power developed in doing it.
Suppose the cord is 100 feet long, and it requires one and a half minutes to raise the weight the full limit of the cord. It is thus raising 550 pounds 100 feet in 45 seconds.