164. Wheel and Axle. The wheel and axle consists of a large wheel
and a small axle so fastened that they rotate together.
[Illustration: FIG. 112.--The wheel and axle.]
When the large wheel makes one revolution, _P_ falls a distance equal
to the circumference of the wheel. While _P_ moves downward, _W_
likewise moves, but its motion is upward, and the distance it moves is
small, being equal only to the circumference of the small axle. But a
small force at _P_ will sustain a larger force at _W_; if the
circumference of the large wheel is 40 inches, and that of the small
wheel 10 inches, a load of 100 at _W_ can be sustained by a force of
25 at _P_. The increase in force of the wheel and axle depends upon
the relative size of the two parts, that is, upon the circumference of
wheel as compared with circumference of axle, and since the ratio
between circumference and radius is constant, the ratio of the wheel
and axle combination is the ratio of the long radius to the short
radius.
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