A simple pulley is a machine that reduces the amount of work required to lift or move an object using only one rope, chain, or belt. It consists of a wheel, an axle, and a rope. Archimedes invented it in the 3rd century BC. One or more pulleys can be used to lift heavy objects. Using more than one pulley reduces the amount of force required to lift an object by half each time a pulley is added.
A simple pulley is one of six simple machines that are used on their own or as components in more complex machines. Unlike complex sheaves, simple sheaves use only one rope, chain, or belt to reduce the amount of work required to lift or move an object, no matter how many sheaves are used together. These machines are extremely useful for lifting or moving heavy objects. The simple pulley was invented by Archimedes in the 3rd century BC and has been adapted to many different uses, although its design has changed very little over the last few millennia.
A rope, a wheel and an axle are the components of a simple pulley. The wheel is attached to the axle, which is the center of the car and which allows the wheel to spin freely. The rope is then looped around the outside of the wheel so that it touches about 50% of the wheel’s circumference. Most pulleys have an edge with a lip or outer casing to keep the rope from slipping off.
One end of the rope is attached to an object that needs to be lifted and the other end to a person, animal, or other machine that will apply force to the object by pulling on the rope. All sheaves in a system are placed above the object to be lifted, with the lowest sheave directly above the object and the highest sheave at the maximum height to which the object can be lifted. With enough pulleys and a long enough rope, extremely heavy objects can be lifted with ease.
In a simple pulley system, one pulley can be used alone or several of them can be used together. If there are multiple sheaves in a system, they are vertically spaced from each other and the rope runs alternately from a higher to a lower sheave. A single simple pulley reduces the amount of work required to move an object by allowing a person to apply a force in a downward motion while lifting an object up. This action cancels the force of gravity acting on the object, making it easier to lift. Using more than one pulley reduces the amount of force required to lift an object by half each time a pulley is added, although a double rope is also required.
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