[Illustration: FIG. 116.--A traveling crane.]
167. Measurement of Work. In Section 150, we learned that the amount
of work done depends upon the force exerted, and the distance
covered, or that _W_ = force x distance. A man who raises 5 pounds a
height of 5 feet does far more work than a man who raises 5 ounces a
height of 5 inches, but the product of force by distance is 25 in each
case. There is difficulty because we have not selected an arbitrary
unit of work. The unit of work chosen and in use in practical affairs
is the foot pound, and is defined as the work done when a force of 1
pound acts through a distance of 1 foot. A man who moves 8 pounds
through 6 feet does 48 foot pounds of work, while a man who moves 8
ounces (1/2 pound) through 6 inches (1/2 foot) does only one fourth of
a foot pound of work.
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