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25.3: Pulley

Last updated

Aug 8, 2024
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- 25.2: Wheel and Axle
- 25.4: Lever

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A pulley is a grooved wheel mounted in a frame. Pulleys may be connected to other pulleys to form compound pulley systems that have a large mechanical advantage. One may use such pulley arrangements to allow just one or two men to lift a large, heavy object such as a piano or safe. (Figure $\PageIndex{1}$ )

Figure $\PageIndex{1}$ : Systems of pulleys. These systems have a mechanical advantage of (left to right): 1, 2, 5, and 6 , so that each example requires only $1 \mathrm{lb}$ of effort to lift $1,2,5$ , and 6 pounds, respectively. Note that the leftmost arrangement only changes the direction of the applied effort force, by allowing us to pull downward to lift the weight upward; it does not provide any mechanical advantage. (Ref. [17])

The mechanical advantage of a set of pulleys is equal to the number of strands $N_{R}$ holding up the resistive force:

$M . A .=N_{R}$

Therefore one can gain a larger mechanical advantage (and thus lift a heavier weight) by using more pulleys.

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