Wheel and Axle
Man's Way of Helping Himself
The wheel and axle consists of a large wheel and a small axle so fastened that they rotate together.
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.
For example, in a wheel and axle of radii 20 and 4, respectively, a given weight at P
would balance 5 times as great a load at W
FIG. - The wheel and axle.