A pulley is a device designed to lift very heavy objects. This simple machine is based on Archimedes’ principle, according to which a body can move from a point of support.
A pulley is nothing more than a grooved wheel that rotates around an axis. A rope passes through the channel that connects with the load to be lifted, while a certain force is applied to the other end of the rope.
The first pulleys were precisely designed by Archimedes in the 3rd century BC. C with the purpose of facilitating civil and military engineering works.
How a simple pulley works
A simple pulley has a wheel in which there is a groove around its perimeter and the wheel rotates on a central axis. This pulley allows you to change the direction and direction of the applied effort and the distance that the load travels is equal to the length of the rope picked up. This type of pulley constitutes an equal-armed lever, since the first effort to pull the rope coincides with the weight of the load. In this way, it is possible to lift weights comfortably, with little effort and moving an object at a certain height.
Other types of pulleys
When two pulleys are used it is called a mobile pulley. In this way, one of them is fixed and the other is mobile. The mobile pulley is the one that moves the load when the rope is pulled and thus the effort is considerably reduced, specifically to half of the fixed pulley.
Composite pulley systems are sometimes used to move large loads with as little effort as possible. These more complex systems are a combination of fixed and moving pulleys and are also known as hoists.
The different pulley systems allow multiplying a force as if it were a lever. Thus, the magnification of the lifting force or mechanical gain depends on the number of rope sections that support the load.
Other inventions attributed to Archimedes
In addition to the pulley system, Archimedes devised a method to calculate the volume of an object with an irregular structure or shape, as well as the famous Archimedes principle.
These theoretical advances allowed a whole series of inventions and gadgets of great practical utility, such as the Archimedean screw for engineering, the catapult as a weapon for war, and a type of crane (the Archimedean claw) that had the purpose of sinking the enemy ships. These and other machines were decisive for the development of civil engineering and also for war.
Photos: iStock – Jon Faulknor / LunaMarina
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