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An ideal block and tackle with a moving block supported by n rope sections has the mechanical advantage (MA), = =, where F A is the hauling (or input) force and F B is the load. Consider the set of pulleys that form the moving block and the parts of the rope that support this block.
The ideal mechanical advantage of the block and tackle is equal to the number of sections of the rope that support the moving block. In the diagram on the right, the ideal mechanical advantage of each of the block and tackle assemblies [7] shown is as follows: Gun tackle: 2; Luff tackle: 3; Double tackle: 4; Gyn tackle: 5; Threefold purchase: 6
A traveling block is the freely moving section of a block and tackle that contains a set of pulleys or sheaves through which the drill line (wire rope) is threaded or reeved and is opposite (and under) the crown block (the stationary section).
In sailing, a block is a single or multiple pulley. One or a number of sheaves are enclosed in an assembly between cheeks or chocks. In use, a block is fixed to the end of a line, to a spar, or to a surface. A line (rope) is reeved through the sheaves, and maybe through one or more matching blocks at some far end, to make up a tackle.
At the other extreme, when r is zero, the system becomes a simple gun tackle with a mechanical advantage of 2. Comparison of a differential pulley (left) and a differential windlass or Chinese windlass (right). The rope of the windlass is depicted as spirals for clarity, but is more likely helices with axes perpendicular to the image.
A crown block is the stationary section of a block and tackle that contains a set of pulleys or sheaves through which the drill line (wire rope) is threaded or reeved and is opposite and above the traveling block.
The correct pronunciation of this is "block and take-el" not "block and tackle" as one might expect. The spelling is fine, but the pronunciation is wierd. Sure, for oddball cases like this. Stan 13:36, 5 January 2006 (UTC) Maybe this should be phrased as the "official" pronunciation. Block and tackle is pronunced the expected way quite often.
block A pulley with one or more sheaves or grooves over which a line is roved. It can be used to change the direction of the line, or in pairs used to form a tackle. [2] block, fiddle A block with two sheaves in the same plane, one being smaller than the other, giving the block a somewhat violin appearance. block, snatch