block and tackle

block and tackle

Combination of pulleys with a rope or cable, commonly used to augment pulling force. Two or more of the pulleys are attached to a fixed block, and the remaining pulleys are free to move as well as rotate. A block and tackle can be used to lift heavy weights or to exert large forces in any direction. Higher force ratios may be obtained by the use of more pulleys, but this advantage may be offset by increased friction.

This entry comes from Encyclopædia Britannica Concise.
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