A rope pulley is a system that uses fiber ropes and wheels made of plastic, metal, wood, or other materials to lift or move objects. This system is sometimes known as a block and tackle, and the purpose is to transfer heavy loads through the system to make moving heavy objects against gravity much easier. The rope pulley system is generally inexpensive when compared to other pulley systems, and it comes in a variety of sizes, features, and included accessories depending on the intended use of the system.
The number of pulleys in a rope pulley system will vary according to the purpose of the pulley system. If too many pulleys are added, friction in the system will prevent much of the advantage of the pulley system, as the force exerted on pulling the rope through the system will increase. With the right amount of pulleys in the rope pulley system, however, the mechanical advantage of moving the object will be increased. If, for example, one pulley is used, the rope is considered to be in two parts; each part of the rope will lift a certain amount of weight, so the amount of weight that can be lifted will effectively be doubled by running the rope through the pulley. Two pulleys will split the rope into three sections, tripling the amount the system can move.
A rope pulley system can be used for a variety of light- to medium-duty projects, but when the weight of the object to be moved reaches a certain point, other materials besides rope are used. Metal cables are common, as are chains, for heavy-duty applications, though the amount of weight that can be carried by rope can be quite high, depending on the thickness and build of the rope. Metal cable pulleys work in a similar fashion as rope pulleys, though the pulley wheels will usually be stronger and made of more durable materials than rope pulley wheels will.
Rigging on ships often utilize block and tackle systems to lift the sails into place, as well as lower them back down to the decks. Rope pulleys can be used at home in the garage to hoist bicycles off the ground and out of the way, or to lift other commonly used items high up off the ground to maximize available floor space. Some rope pulley systems are even used on exercise equipment so a user can lift weights safely and effectively.