- block and tackle
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the ropes or chains and blocks used in a hoisting tackle.[1830-40]
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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.* * *
▪ devicecombination of a flexible rope, or cable, and pulleys (pulley) commonly used to augment pulling force; it can be used to lift heavy weights or to exert large forces in any direction. In the Figure—> there are four freely rotating pulleys, two on the upper block, which remains fixed, and two on the lower block, which moves up as the load W is lifted; one end of the rope is anchored to the upper block. If the load W is lifted one foot, each of the four rope links will shorten by one foot so that four feet of rope must be pulled off by the effort F; consequently the force magnification and the mechanical advantage, neglecting friction, is 4. Higher force ratios may be obtained by the use of more pulleys, but this advantage may be offset by increased friction. See also wheel and axle.* * *
Universalium. 2010.