physical properties

physical properties:_A set of pulleys assembled so that they rotate independently on the same axle form a block. Two blocks with a rope attached to one of the blocks and threaded through the two sets of pulleys form a block and tackle.^[6][7]

A block and tackle is assembled so one block is attached to fixed mounting point and the other is attached to the moving load. The ideal mechanical advantage of the block and tackle is equal to the number of parts of the rope that support the moving block.

In the diagram on the right the ideal mechanical advantage of each of the block and tackle assemblies^[5] shown is as follows:

• Gun Tackle: 2
• Luff Tackle: 3
• Double Tackle: 4
• Gyn Tackle: 5
• Threefold purchase: 6

Chemical properties:

Timing pulleys mate with same-pitch timing belts in synchronous drives. Some timing pulleys are designed with an inch-based pitch designation. Timing pulleys are used in power transmission systems where maintenance of speed ratio is an important design consideration. These synchronous belt drive systems are durable, highly efficient, and suitable for many different applications.

English pitch timing pulleys have a spacing or pitch based on inch (in.) measurements and a toothed, trapezoidal form.

• 0.080 in. (MXL)
• 0.0816 in. (40 DP)
• 0.200 in. (XL)
• 0.375 in. (L)
• 0.500 in. (H)
• 0.875 in. (XH)
• 0.250 in. (XXH)

English pitch timing pulleys with an MXL, 40-DP, XL, or L pitch designation are designed for light duty applications. By contrast, pulleys with an H, XH, or XXH pitch designation are designed for heavy duty use.

history of a pulley

A pulley is a wheel with a groove along its edge for holding a rope or cable. It is a simple machine that helps change the direction and point of application of a pulling force. Pulleys are usually used in sets designed to reduce the amount of force needed to lift a load. The magnitude of the force is reduced, but it must act through a longer distance. Consequently, the amount of work necessary for the load to reach a particular height is the same as the amount of work needed without the pulleys.
Pulleys can be found in many different applications around us. Not only are they used for the obvious lifting of objects, such as by cranes, but they are also used in modern automobiles and airplanes. Pulleys are also essential for most machines in some form or other.

As is the case with all the simple machines, the origin of the pulley is unknown. When early peoples 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 use resulted in considerable friction. It is believed that by 1500 B.C.E. people in Mesopotamia used rope pulleys for hoisting water. [1]

It is not recorded when or by whom the pulley was first developed. It is believed however thatArchimedes developed the first documented block and tackle pulley system, as recorded byPlutarch. Plutarch reported that Archimedes moved an entire warship, laden with men, using compound pulleys and his own strength.

TYPES OF PULLEY

• Fixed A fixed or class 1 pulley has a fixed axle. That is, the axle is "fixed" or anchored in place. A fixed pulley is used to redirect the force in a rope (called a belt when it goes in a full circle. A fixed pulley has a mechanical advantage of one.
• Movable A movable or class 2 pulley has a free axle. That is, the axle is "free" to move in space. A movable pulley is used to transform forces. A movable pulley has a mechanical advantage of two. That is, if one end of the rope is anchored, pulling on the other end of the rope will apply a doubled force to the object attached to the pulley.
• Compound A compound pulley is a combination fixed and movable pulley system.
  • Block and tackle - A block and tackle is a compound pulley where several pulleys are mounted on each axle, further increasing the mechanical advantage.

Pulleys are able to change the direction of the force.

Uses of Pulleys

Pulleys have been used for lifting for thousands of years. The most prevelant and oldest example are their uses on ships and boats. The block and tackle have been a key tool for raising sails and cargo. Another major use for pulleys is with cranes.

Pulleys have been used also in modern times with various machines and systems. Even in the space age, pulleys have been an important aspect for the construction and operations of spacecraft and aircraft. It is with a pulley system that rudders for an aircraft are controlled.

Pulleys are used in everyday life, from vehicles to moving equipment such as crane

simple machines

This article is about the concept in physics. For the Internet forum software, see Simple Machines Forum.

For a broader coverage related to this topic, see Mechanism (engineering).

Table of simple mechanisms, fromChambers' Cyclopædia, 1728.^[1] Simple machines provide a vocabulary for understanding more complex machines.

A simple machine is a mechanical device that changes the direction or magnitude of a force.^[2] In general, they can be defined as the simplest mechanisms that use mechanical advantage (also called leverage) to multiply force.^[3] Usually the term refers to the six classical simple machines which were defined by Renaissance scientists:

A simple machine uses a single applied force to do work against a single load force. Ignoring friction losses, the work done on the load is equal to the work done by the applied force. The machine can increase the amount of the output force, at the cost of a proportional decrease in the distance moved by the load. The ratio of the output to the applied force is called the mechanical advantage.

Simple machines can be regarded as the elementary "building blocks" of which all more complicated machines (sometimes called "compound machines"^[5][6]) are composed.^[3][7] For example, wheels, levers, and pulleys are all used in the mechanism of a bicycle.^[8][9] The mechanical advantage of a compound machine is just the product of the mechanical advantages of the simple machines of which it is composed.

Although they continue to be of great importance in mechanics and applied science, modern mechanics has moved beyond the view of the simple machines as the ultimate building blocks of which all machines are composed, which arose in the Renaissance as a neoclassical amplification of ancient Greek texts on technology. The great variety and sophistication of modern machine linkages, which arose during the Industrial Revolution, is inadequately described by these six simple categories. As a result, various post-Renaissance authors have compiled expanded lists of "simple machines", often using terms like basic machines,^[8] compound machines,^[5] or machine elements to distinguish them from the classical simple machines above. By the late 1800s, Franz Reuleaux^[10] had identified hundreds of machine elements, calling them simple machines. Models of these devices may be found at Cornell University's Kinematic Models for Design (KMODDL) website.^[11]

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