| 释义 |
pulley A grooved wheel around which a rope can pass. When supported on an axle in some way, the device can be used to change the direction of a force: for example, pulling down on a rope may enable a load to be lifted. If the contact between the pulley and the axle is smooth, the magnitude of the force is not changed. A system of pulleys can be constructed that enables a large load to be raised a small distance by a small effort moving through a large distance. In such a machine, the velocity ratio is equal to the number of ropes supporting the load or, equivalently, the number of pulleys in the system.
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