Introduction to Pulleys
Before moving onto a single fixed pulley and its meaning, it is better to understand what a pulley is. You all must have come across a pulley at some point in your lives. Pulleys are used to pull water out of wells, in cranes, and in many other day-to-day applications. You also must be familiar with the fact that pulleys are used to pull heavy things. However, the physics behind them remains a mystery to most of us. A pulley is just a simple machine. It goes back to the ancient Egyptian era between 1991–1802 BCE and Mesopotamia in the early 2nd millennium BCE. No one knows who exactly discovered the pulley, but it has been in use for a long time now.
Archimedes’s name is associated with the compound pulley, and he was one of the first people to fully exploit the potential of pulleys. It is said that he used to move massive ships by using a block and tackle system of pulleys which he invented. By now, the usefulness and history of a pulley must be apparent to you. We’ll look at the single fixed pulley in detail throughout this article.
Defining Pulleys
We have looked at a simple introduction to pulleys, and now we’ll look at the definition of pulleys in physics. A wheel on an axle or shaft known as a pulley is used to transmit power from the shaft to the cable or belt as well as to sustain movement and direction change of a taut cable or belt.
In the instance of a pulley supported by a frame or shell that does not provide power to a shaft but is used to guide the cable or exert force, the supporting shell is referred to as a block, and the pulley is referred to as a sheave.
A pulley changes the direction of force applied by anyone, and this principle is exploited to lift anything with a bit of ease. A pulley may have a groove or grooves between flanges around its circumference to help identify the cable or belt. Pulleys are often used in various combinations with other pulleys, and each combination provides some sort of advantage to the users. These combinations of pulleys are known as pulley systems. A pulley system can be driven by a chain, cable, rope, or belt.
In daily life, pulley systems are utilised for everything from lifting large objects to running generators. The fundamentals of mechanics, which are essential to understanding physics, are what pulleys teach most importantly. The development of the current industrial sector depends on the use of pulley systems, which are widely accepted. Belt-driven generators and alternators utilise pulleys.
Image: A Pulley
Types of Pulleys
Pulleys are used in a lot of different ways and so this divides pulleys into different types which are mentioned below. Pulleys can broadly be divided into five types.
Fixed Pulley
As the name suggests, the wheel and axle of a fixed pulley remain in place. The force acting on a rope or belt that moves around a stationary pulley changes its direction. This is the simplest type of pulley.
Movable Pulley
An axle in a movable block is a part of a movable pulley. A single movable pulley has a mechanical advantage of two and is supported by two different sections of the same rope. When you use a movable pulley, the drum moves as you move the weight. Although the force you must exert does not alter, the burden will "feel" lighter than it actually is.
Compound Pulley
In a compound pulley system, there is a fixed pulley and a moving pulley. As a result, not only does the weight "feel" lighter, but the force's direction can also be altered. Although this kind of arrangement makes it relatively easy to move huge weights, the trade-off is that significantly more motion is needed to complete the task.
Cone Pulleys
Another customised pulley system that integrates the fundamental mechanics of a pulley system while permitting mechanical alterations is the cone pulley. Cone pulleys are made by stacking several pulleys with a progressively smaller vertical circumference.
Block and Tackle Pulley
A certain kind of compound pulley called a block and tackle can significantly minimise the amount of labour needed to lift a big object. Many fixed and movable pulses are arranged parallel to one another in a block-and-tackle pulley system; Movable pulleys are aligned with movables and fixed pulleys are fixed. It is believed that Archimedes is the one who invented this type of pulley.
Image: Types of Pulleys
Single Fixed Pulley
We have looked at the different types of pulleys. The first type was the fixed pulley, and a single fixed pulley is just that type of pulley. It is just a single pulley that is fixed on an axle and is used to pull a load by the application of force through a string or a rope. The basic example of this type of pulley is the pulley on a well that is used to pull water. A single fixed pulley is the simplest type of pulley.
A pulley with the drum fastened to a single point is referred to as a fixed pulley. The amount of force needed to lift or move an object is the same as when you lift it by hand, but you may vary the force's direction by using the fixed pulley. This means that the fixed pulley does not reduce the effort, it just changes the direction of the force.
For instance, if you're linked to a bucket that is taking water from a well, you can pull firmly in one direction while lifting the bucket horizontally rather than vertically, which is more comfortable. Although it is easier to lift, the water bucket still feels the same weight. The pulley on a well is one of the single fixed pulley examples.
The mechanical advantage M, of a pulley is defined as:
$M=\dfrac{\text{Load}}{\text { Effort }}$
Image: Single Fixed Pulley
From the above image, we can see that the load is W and the effort is P. However, since the tension across the string is constant, this means that the load is equal to the effort. So, the mechanical advantage will be 1.
Conclusion
A pulley is a straightforward machine made of wood or metal that lifts large objects using a wheel and rope. For carrying small loads, plastic pulleys are also available on the market today. It can freely spin around an axis that runs through its centre. A pulley changes the direction of force and, in doing so, eases the movement of any object. There are different types of pulleys. A single fixed pulley is the simplest type of pulley where the pulley is attached to a fixed axle and it cannot move. It does not reduce effort; it only changes the direction of motion. The mechanical advantage of a single fixed pulley is 1.
FAQs on Single Fixed Pulley for JEE
1. Why is a single-fixed pulley used?
Although it doesn't quite lessen effort, the single fixed pulley aids in adjusting the direction of effort. Applying force in a downward direction is significantly easier when using a single fixed pulley, which is frequently done. Although it provides an efficiency of 100% ideally, it has no meaning because the load and the effect are the same. But it does provide us with the opportunity to apply the force in a direction that is ideal for us.
2. How are pulleys used for speed reduction?
Under the same shaft power, two identically sized pulleys connected by a belt will rotate at the same speed. When a larger pulley is turned by a smaller one, the larger one moves more slowly but with greater shaft power. A truck in low gear, with its engine running quickly but its wheels moving slowly, would be an example of a vehicle having significant power at reduced speed. Alternately, when a larger pulley rotates a smaller pulley, the smaller pulley turns more quickly but with less force applied to the shaft.
