Main Page | See live article | Alphabetical index A block and tackle is a system of two or more pulleys with a rope or cable threaded between them, usually used to lift or pull heavy loads. The most common arrangement is to have a set of fixed pulleys all mounted on a single axle, and another set left to move. Each set is called a "block" (the rope is the "tackle"). The mechanical advantage of a block and tackle is equal to the number of lines running between the two blocks. For example, a block and tackle consisting of three fixed and three moving pulleys has six lines going between the pulleys, which gives it a mechanical advantage of 6. This enables the lifting of weights six times heavier than would be possible otherwise. The increased force produced by a block and tackle is offset by the increased length of rope needed. In order to raise a block and tackle with a mechanical advantage of 6 a distance of 1 metre, it is necessary to pull 6 metres of rope through the blocks. This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.