From french poulie, a pulley It is part of the so-called simple machines . It is formed by a wheel mobile around a axis , which presents a channel in its circumference. That throat goes through a rope , at whose ends they activate the resistance and the power .
The pulley, in this way, allows to transmit a force and helps to mobilize a weight. For example: "The masons have installed a pulley to raise the materials to the top floor", "We would have to devise a pulley system to move these boxes", "The firemen armed a pulley and, in this way, managed to rescue the horse that was trapped in the swamp".
The elements of a pulley are the wheel (also known simply as a pulley) with a circumference in which the channel appears (which can be referred to as throat); the weapons (the armor that surrounds the pulley and has a hook at its end); and the axis (which can be solidary to the wheel or be attached to weapons).
When weapons are suspended at a specific point and do not experience any movement of translation, there is talk of a fixed pulley . On the other hand, if the weapons move vertically during use, the classification corresponds to a mobile pulley .
The pulleys can also act independently (simple pulley ) or in conjunction with other pulleys (combined pulley or compound pulley ). The most frequent design of the composite pulley is known as hoist : in this case, the pulleys are divided into two sets (one mobile and the other fixed) and in each set an arbitrary amount of pulleys is installed. According to this mechanism, the mobile group is joined by the load.
The history of the elevator
The pulley concept is used daily by a large part of the world's population, even without knowing it, since it constitutes one of the essential parts of the elevator. In fact, its origins date back to several centuries before Christ, although its form and the comfort with which it operated the first elevators certainly differed greatly from the present.
In ancient Egypt, for example, there were several systems based on the use of ropes and ramps to move the heavy and bulky stone bricks that were used to build the pyramids. Similar methods helped to maintain irrigation, bringing water from the Nile to the canals. It is fascinating to take into account that both creations took place more than a millennium and a half before Christ.
Later, less than three centuries of year zero, Archimedes designed and manufactured a prototype that was operated by pulleys and ropes. It is worth mentioning that given the absence of automation, it was always necessary for a person, be it the user or a servant, to take the exhausting work of operating the elevator, using his own physical strength. Taking this into account, it is not surprising that such an ancient invention took so many centuries to become immensely popular.
Unfortunately, and as is the custom of the human being, it was not long before he used the involuntary help of animals. On the other hand, there were hydraulic systems that used ferris wheels to operate elevators and forklifts. With the industrial Revolution, the elevators were modernized and began to take advantage of the steam for your propulsion. From that moment on, in just two centuries its design would be perfected at an unprecedented rate, as it happened with many other inventions. In cities where population density demands the construction of tall buildings, the elevator is a necessity; on the other hand, you doubt your safety in case of fire.
