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Pulley

Pulley - Meaning, Types, Advantages, Formula and Applications

Have you ever wondered how the mechanism for drawing water from good works? Or how can one pull applications or lift objects with ease? Introduced first in 1500 B.C, the pulley is one of the most widely used to lift or pull heavy loads. In simple words, the pulley mechanism helps lift heavyweight objects that bare hands cannot lift with very little force. In this article, we discuss the definition of the pulley, various properties of the pulley mechanism, etc.

The pulley can be defined as a mechanical device that consists of a wheel and a rope. The rope is connected to the wheel as it is surrounding the wheel and its rim; It can be freely rotated around the wheel’s axis, passing through the center. Thus, the rope is the pulley's driving element. This helps lift heavy loads from the ground level. The pulley wheel is fixed to a hinge and rotates on an axle or shaft, and the object is loaded or tied to the other end of the rope. Hence, when the rope is pulled from the other side by the application of force, the object is lifted.

Advantages of Pulley

  1. By application of little force, heavy objects can be lifted.
  2. It is a cheaper and more efficient method as compared to other assemblies.
  3. No separate lubrication is required.
  4. It is noise-free while operating and acts as a support for long-distance moving ropes.

Types of Pulley

Based on the applications and different types of assembly, pulleys can be divided into the following categories:-

  1. Fixed Pulley
    In Fixed Pulley, the entire assembly is mounted on a high platform with an axle with bearings at the center. The wheel is fixed such that it rotates at its center point. The rope is passed circumferentially with the object lifted and loaded at one end while the other is free.
    Pulleys mounted in wells are examples of Fixed Pulley.

  2. Movable Pulley
    In a Movable Pulley assembly, the wheel is mounted on an axle that is free to move. Here, the pulley is not fixed around its axle when it carries the load. These pulleys are often attached to an object and multiply the force being applied by the user at one end. The movable pulley does not change the direction of the object. It is helpful to pull up heavier loads as the operator has to exert less force and the resultant force on the load is the multiplication of the operator’s force.

  3. Compound Pulley
    A combination of both fixed and rotating pulleys is known as a Compound pulley. In Compound Pulleys, there are several fixed pulleys connected to rotating pulleys and vice versa. In this case, a compound pulley is formed when a moving pulley has its rope connected with a fixed pulley. This mechanism changes the direction of the load to be lifted and requires less force to lift heavy objects.

Formula of Pulley

As we know that a pulley is a mechanical device that can help lift heavyweight objects, there are several kinds of pulley formulas one can utilize while measuring the effectiveness of the pulley. To calculate the mechanical advantage of the pulley system, we can use any one of the following formulas:-

  1. Mechanical Advantage = Load / Effort
  2. Velocity ratio = distance (effort)/distance (load).

We can also calculate the mechanical advantage of a pulley with the help of the number of loops in the system. In a single loop system, the effort required to pull the weight is equal to the weight itself. By introducing another loop of rope (adding another wheel attached to the first wheel by using an additional rope), the effort required to pull the same weight becomes half as compared to the previous arrangement assembly.

Further on, if we add another loop, the effort now becomes one-third compared to the first arrangement assembly, and therefore, the mechanical advantage is 3. Hence we can conclude that to increase the mechanical advantage, more pulleys can be added. However, it has to be noted that after a certain number of pulleys, the mechanical advantage does not change and becomes constant.

Applications of Pulley

Several applications of the pulley are as follows:-

  1. It is widely used to draw water from wells.
  2. This assembly is widely used in elevators and shifts
  3. Several gym equipment use pulleys.
  4. It is also used to lift heavy objects at a construction site
  5. Flagpoles bind, curtains are also among the several applications of the pulley.
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