A wheel and axle behave as a continuous lever. The center of the axle corresponds to the fulcrum. A wheel and axle has a mechanical advantage if the radius of the wheel is the applied arm and the radius of the axle is the resultant arm. It does not
have a mechanical advantage when the wheel radius is the resultant arm and the axle radius is the applied arm, Figure 4.11.
The equation for determining the mechanical advantage is the same as the equation used for the three classes of levers.
Problem: How much force will it take to lift a 10.0-lb weight with a wheel and axle, used as in Figure 4.11, when the axle is 2.0 inches in diameter, and the wheel is 10.0 inches in diameter?
Solution: The first step is to rearrange the equation to solve for the applied force. Remember that the length of the force arm is the radius of the wheel and the length of the resultant arm is the radius of the axle. This gives us:
The wheel and axle is not normally used alone. It is usually used in conjunction with a gear reduction system to form a hand operated or electric motor winch found on boat trailers and other applications, Figure 4.12.
FIGURE 4.12. Wheel and axle used as a winch without a gear reducer.
FIGURE 4.13. A single pulley.
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