Variable Pulley

The use of moving pulley can save half the force and distance.

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What is …

The pulley whose axis position moves with the object being pulled is called moving pulley. The movable pulley is essentially a lever whose power arm is equal to twice the resistance arm (labor-saving lever). It can’t change the direction of the force, but it can save half of the force at most, but it doesn’t save work. A pulley block can be formed with a fixed pulley. It is a simple machine commonly used in daily life.

Characteristic

The use of moving pulley can save half the force and distance. This is because when the movable pulley is used, the hook code is suspended by two sections of rope, and each section of rope only bears half of the weight of the hook code. Although the use of moving pulley saves force, the distance of power moving is twice of the distance of hook code rising, that is, the distance of cost. You can’t change the direction of the force. Move with the movement of an object. In addition, the quality of the moving pulley itself can not be ignored in life, so extra work is done in the process of moving pulley rising to reduce the mechanical efficiency.

① Definition: a pulley that moves with a weight. (can move up and down, or left and right)
② Essence: the power arm is twice as much as the resistance arm.
③ Features: the use of moving pulley can save half of the force, but can not change the direction of power.
④ Ideal moving pulley (regardless of shaft friction and moving pulley gravity).

The variable pulley can be regarded as a labor saving bar

"The pulley whose axis position moves with the object being pulled is called moving pulley."

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"If the heavy object is directly hung on the pulley, the pulley will also rise when lifting the heavy object. Such pulley is called movable pulley."

ever-power

"The definition of moving pulley is that if the pulley moves, it is moving pulley, otherwise it is fixed pulley."

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The origin of history

On the drawing of pulley

The painting of pulley first appeared in an Assyrian relief in the 8th century BC. This relief shows a very simple pulley, which can only change the direction of force application. The main purpose is to facilitate the force application, and will not give any mechanical benefits. In China, the drawing of pulley device first appeared in Han Dynasty’s portrait brick and pottery well model. There is also a discussion about pulley in Mojing.

Pulley principle

Archimedes is said to have used a compound pulley alone to pull a large seagoing ship full of goods and passengers. In the first century, aleksandro’s Hiro analyzed and wrote the theory of compound pulley, proving that the ratio of load to applied force is equal to the number of rope segments bearing the load, namely “pulley principle”.

 

Lagrangian mechanics

In 1788, Joseph Lagrange, a French physicist, used the pulley principle to deduce the principle of virtual work in his great book M é canique analytic mechanics, which opened the prelude of Lagrange mechanics

Simple machine

The ancient Greeks classified pulleys as simple machines. As early as 400 BC, the ancient Greeks already knew how to use the compound pulley. In about 330 BC, Aristotle’s eighteenth problem in his book mechanical problems was devoted to the study of the “compound pulley” system. Archimedes contributed a lot of knowledge about simple machines and explained the kinematic theory of pulley in detail.

Virtual work principle of prototype

In 1608, in his book “mathematical collection”, the Dutch physicist Simon sphin showed that the ratio of the length of the moving path between the force application and the load of the pulley system is equal to the inverse ratio between the force application and the load. This is the prototype principle of virtual work.

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Mon – Fri — 8:00am – 5:00pm
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