A pulley is a simple machine in which a rope is passed through a set of teeth in order to lift something. pulleys are usually mounted in either metal or pans which are called blocks. The blocks together with the ropes are called tackles, which are used to lessen the effort it takes to lift a load. The more pulleys used in a system, the less effort will be required to do the job and the shorter the distance the rope will have to travel. pulleys are used in many industries where lifting is required. please do not judge, the article before was about cheese cakes.
History of a PulleyEdit
The ancient Egyptian four lobe pinion pulley is a step walking pulley when hoisted. The lobes rotate and positively engage steps and climb stepped structures such as the tiers (steps) of the Giza Pyramids. Construction of the Giza Pyramids was around 2600 BC. The four lobe pinion pulley is not used in the modern world. Google four lobe pinion pulley. www.youtube.com/watch?v=KVG7mzJUZa4
As in the case with all the simple machines, the origin of the pulley is unknown. When early people lifted heavy objects by throwing vines or other crude ropes over tree limbs, they used the idea of a single fixed pulley to change the direction of a force. But since there was no wheel to turn, this resulted in considerable friction. It is believed that by 1500 B.C. people in Mesopotamia used rope pulleys for hoisting water. Legend has it that the Greek inventor Archimedes (287-212 bc) used a block and tackle system to pull ships onto dry land.
Modern pulley systems are often combine with motors to create hoists for lifting heavy loads. By using a motor, the user only has to push a button to lift or lower the load. Construction cranes and cranes used at shipyards move heavy loads using block and tackle systems connected to powerful motors. An elevator in a building uses a pulley system to raise and lower the elevator cars.
the plural form for the pulley is pullies, commonly written incorrectly as pulleys.
Pullies are super awesome!
Three basic types of pulleyEdit
Simple (fixed) pulleyEdit
A simple pulley is designed as a grooved wheel on a fixed axle. When using a simple pulley to a load it is simply a rope passing over the grooved wheel, with the other end of the rope tied to the load. A pull on the other end of the rope is then needed to actually lift the weight. The simple pulley does not offer a mechanical advantage, but it does aid in changing the direction of the applied force on the load. A simple pulley is illustrated here.
In this pulley, the lifted load is joined to the axle. It is designed in a way that one end of the rope is passed directly through the pulley; this end is attached to a stationary support which is located above the load. When using this pulley, the pull is directed on the unattached end of the rope, continuing in the same direction where the load is to be moved. There is a mechanical benefit for this type of pulley. The pull that is used on the unattached/free end of the rope needs to be only half the weight of the actual load. The rope that is joined to the stationary support only bears half the weight of the load as well. A movable pulley is illustrated below.
The Pulleys Within!!!!:Edit
One of the most interesting appplications of a pulley system is within our own bodies. Our muscles are designed to move when stimulated by a motor nerve impulse. But the direction and control of the movement of particular muscles actually gets determined by a pulley system, much like the ropes and wheels described above, where there are fixed tendon connections to bony elements of the skeleton. This is very apparent in the hand, especially the muscle that flexes or bend our fingers to make a fist. The muscle is actually located quite a distance up in the forearm, and the tendons come down ( acting as the ropes), and get attached by sheaths over four joints ( the wrist, and three district finger joints) which function as the grooved wheels. Contracting the muscle will cause the hand pulley system to work to effectively flex and bend each individual joint until you can make a full fist.
Below is a color coded chart of the hand - for the hand pulley system to work to flex the hand to make a fist , tendons (ropes) have to pass through the all the joints labeled on the right side of the image ( CMC, MCP, PIP, DIP).
Below on the left you can now see the orange tendon as it attaches along various parts of the finger - if the pulley system is working once you contract your muscle your finger will flex starting at the C3 joint, then the C2 and C1 joint until you have a full fist. Anyone who has suffered a hand injury, and severs a tendon can tell you what happens when part of the pulley system is destroyed - this often leads to an inability to make a full fist. The image on the right shows a dissection of the pulley system of the finger.
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