We explain what a pulley is and what the history of this machine is. Also, the types of pulleys that exist and the parts that make them up.
What is a pulley?
It is known as a pulley a simple machine designed to transmit force and operate as a traction mechanism reducing the amount of force necessary to move or suspend a weight in the air. It consists of a wheel that rotates on a central axis and provided with a channel on its periphery through which a rope passes.
The pulley can further be defined as the fulcrum of a rope that moves around it without making a complete revolution ; such is the definition of the French scientist Haton de la Goupillière. Thus, a resistance or weight acts on one end of said rope, while a power or force acts on the other.
The use of pulleys It is very common in the construction fields loading or unloading of vehicles and many others, in which a system is required to move large weights with considerably less force.
For example, the mechanism designed to extract water from a deep well, so common in films and medieval imagery, consists of a bucket tied to a rope that passes through a pulley. Thus, by pulling on the free end, the water-filled (and considerably heavy) bucket can be raised to the edge of the well.
See also: Inertia
History of the pulley
Not much is known about the invention of the pulley. The only note about it that there is in Historical literature accuses Archimedes as its inventor although he could well have been just a student and enthusiast of its use.
Plutarch tells in his book parallel lives (100 BC) that the Greek Archimedes affirmed to the King of Syracuse, Hiero, to whom he united a bond of friendship, that given a force and a fulcrum, any weight could be moved even that of an entire Earth. His friend demanded a practical demonstration: he filled a royal navy ship with cargo and passengers and asked the philosopher to move it to a dry dock.
After designing the appropriate pulley system, Archimedes sat at a distance and almost effortlessly pulled a rope, causing the boat to rise and move so stably that it seemed to still be in the water.
Pulley types
There are two ways of classifying pulleys:
- According to your displacement. We can talk about pulleys fixed when they are suspended from a fixed point; either mobiles when it is a set of two pulleys: one fixed and the other mobile.
- According to their number Depending on whether it is a pulley acting alone or an interconnected set of them, we can talk about pulleys. simple or pulleys combined either compositerespectively.
Parts of a pulley
Every pulley is made up of four fundamental parts:
- Axis The fixed portion around which the pulley is inserted or suspended and which allows its free rotation. This is the immobile and central part.
- Tire The external area of the pulley, where the throat through which the rope passes is located.
- Body The middle part of the pulley, between the hub and the rim, designed to rotate under the action of force, provided with arms or ribs to facilitate its movement.
- Cube The internal part of the pulley (the cylindrical hole into which the shaft attaches).
