Pulley

• The sheave, or pulley, typically is made of metal or a touch plastic, depending on the type of machine in which the pulley system is installed. For instance, metal is used in machinery where the pulley is subjected to high heat in order to prevent melting. The sheave is circular, and its size often depends on the machine as well as the load it is required to pull. The sheave sits upward on its side and has a hollowed-out grooved edge with sides on each. The rope or wire of the pulley system lies within this groove.
  
  

Rope

• The rope of a sheave system is run over top of the pulley wheel and lies in the groove on the pulley itself. The rope may be a standard rope; in some cases, it is made of strong metal wire. One end of the rope is used to hold the load of the pulley system. This is the item being hoisted by the power of the sheave system. The other side holds the effort, which is applied to get the pulley system to lift a load effectively. Without the effort, the force of natural gravity allows the pulley to stay in one position due to the load that is constant on one side of the pulley system.
  
  

Load

• The type of machine or the work the pulley is expected to perform depends on what the load of the pulley is. The load is applied to one side of the rope or strong wire on one side of the pulley system. For instance, in construction, a pulley system often is used to lift heavy wood or aluminum beams. In this case, the beam is the load the system is used to lift to where it is needed.
  
  

Effort

• Effort is the force applied to the other side of the rope or strong wire to lift objects to where they are needed. Without effort applied to the other side of the rope in a pulley system, gravity causes the load to remain on the ground. Therefore, the effort applied to the opposite side of the rope system must be heavier than that of the load for the sheave system to work effectively. The effort can come from a person in some cases, if the load being lifted isn't terribly heavy; the pulley allows the person to lift more than he otherwise could because of the leverage in the pulley system. In some cases, a machine must be used to make the pulley work; in this case, it is the machine that is creating the effort.