pulley block
Definition
Noun: A pulley block is a simple machine consisting of a wheel (or sheave) with a grooved rim, mounted in a frame or block. A rope, cable, or belt runs in the groove, allowing the device to change the direction of an applied force or to provide a mechanical advantage for lifting or moving loads.
Usage
A pulley block is used to redirect force, making it easier to lift heavy objects or to pull in a different direction than the applied force. - It is a fundamental component in systems like cranes, elevators, and sailing rigs. - Multiple pulley blocks can be combined to form a block and tackle system, which multiplies the applied force.
Examples
Advanced Usage
- Mechanical Advantage: When used in a system with multiple sheaves (a block and tackle), a pulley block can significantly reduce the effort needed to lift a load. The mechanical advantage is roughly equal to the number of rope segments supporting the load.
- Fixed vs. Movable: A fixed pulley block changes the direction of force but does not provide a mechanical advantage in force (though it may make the task more convenient). A movable pulley block, where the block moves with the load, does provide a mechanical advantage.
Variants and Related Words
- Block (noun): Often used synonymously with "pulley block" in technical contexts (e.g., "a snatch block").
- Sheave (noun): The grooved wheel within the pulley block.
- Block and Tackle (noun phrase): A system comprising two or more pulley blocks with a rope threaded between them, used to lift heavy loads.
Synonyms
- Pulley
- Sheave block
- Block (in mechanical/engineering contexts)
Related Phrases and Compound Terms
- Snatch block: A pulley block with a side plate that opens, allowing a rope to be inserted without threading it through from the end.
- Idler pulley: A pulley used to guide or tension a belt or rope without transmitting power.
- Crown block: A stationary set of pulley blocks at the top of a drilling rig's derrick.
Noun
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a simple machine consisting of a wheel with a groove in which a rope can run to change the direction or point of application of a force applied to the rope
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