What is a Pulley?
A pulley is a wheel that carries a flexible rope, cord, cable, chain, or belt on its rim. Pulleys are used individually or in combination to transmit power and motion. Pulleys with grooved edges are called sheaves. In belt drives, pulleys are attached to shafts at their axles, and power is transmitted between the shafts by endless belts running over the pulleys.
One or more independently rotating pulleys can be used to gain a mechanical advantage, particularly when lifting weights. Pulleys are assembled to form a block and tackle in order to provide a mechanical advantage to apply large forces. Pulleys are also assembled as part of belt and chain drives in order to transmit power from one rotating shaft to another
The Greek mathematician Archimedes (3rd century BC) is said to have used compound pulleys to pull a ship onto land. In Roman Egypt, Hero of Alexandria (c. 10-70 CE) identified the pulley as one of six simple machines used to lift weights.
Plutarch’s Parallel Lives recounts a scene where Archimedes proved the effectiveness of compound pulleys and the block-and-tackle system by using one to pull a fully laden ship towards him as if it was gliding through water.
What Are the Uses Of Pulleys?
The original primary use for pulleys was to make it easier to lift heavy items. A pulley is a simple machine made with a wheel and a rope, cord, or chain.
Pulleys can be found everywhere to help make tasks easier. In addition to lifting things, pulleys can be used singly or with many pulleys working together to transport people or things. They can also be used to provide power from one shaft to another.
Examples Of Pulleys In Everyday Life
Examples of pulleys include:
- Elevators: Elevators work via a powerful electronic pulley system. Elevators make use of a system of several pulleys and counterweights to provide the lift system with both power and safety.
- Wells: Old-fashioned “wishing well” style water wells use a simple pulley system to hoist the bucket out of the well.
- Exercise equipment. Most weight-lifting exercise equipment uses pulleys to control the angle at which weights are lifted while keeping the weights themselves in a dedicated location. This makes the process of weight lifting safer and more effective for the user than free weights maybe if used improperly.
- Construction Pulleys. Construction pulleys are some of the most basic and common pulleys, good for viewing the basic functioning of this simple machine. These pulleys consist of a wheel track that can be raised to great heights, and fitted with chains or rope attached to hooks.
- Theater Systems. In theaters, curtains and fly systems operate using a system of multiple pulleys. These pulleys are located high above the stage where the audience cannot see them and operated from the side of the stage to raise and lower curtains and pieces of scenery during a theatrical performance.
- Cargo lift system. A cargo lift system that allows for items to be hoisted to higher floors is a pulley system.
- Blinds on windows. Blinds on windows operate using a pulley system to move the blinds up and down. You pull the cord on the blinds and the pulley system causes the blinds to open or close.
- Flagpoles. Flagpoles use pulleys to hoist the flag up or to bring it down. You pull the string on the pulley and the flag runs up or down the pole.
- Cranes, Bulldozers, and Escalators utilize pulley systems to function.
- Garage doors, Sailboats, engines, extend ladders, and Rock climbers, all Use pulley systems to work safer and more effectively.
These are all examples of pulleys. A cable system makes it easier to lift or move objects. Pulleys are required to move and lift very heavy or large objects. The simple principle behind pulleys makes them one of the most effective tools out there.
How do pulleys work?
A pulley is a simple machine that consists of a rope and a grooved wheel. The rope fits into the groove in the wheel and pulling the rope turns the wheel. Pulleys are commonly used to lift objects, especially heavy objects. The object lifted by a roller is called a load.
A pulley with a wheel allows you to reverse the direction of your lifting force by pulling down on a rope (looped over the wheel) and lifting your weight. With a two-wheel pulley, you reduce the force you use to lift the same weight. You lift the weight at half-strength.
The more wheels you have, and the more times you loop the rope around them, the more you can lift.
A pulley is just a grouping of one or more wheels over which a rope (or a sturdy chain for heavier objects) is looped. Scientists call these “simple machines” because they allow humans to multiply the forces that allow us to lift a heavy weight. Using a roller greatly multiplies the strength of your physical exertion.
A pulley with a wheel allows you to reverse the direction of your lifting force by pulling down on a rope (looped over the wheel) and lifting your weight.
With a two-wheel pulley, you reduce the force you use to lift the same weight. You lift the weight at half-strength. This is known as the Mechanical Advantage (ME) and your two-wheeled pulley gives you an ME of two.
The bigger your Mechanical Advantage, the less force you need to lift a weight.
The more wheels your rope can wrap around, the more weight you can lift. This type of pulley system is often referred to as a pulley system and usually consists of a rope wound around two axes several times.
As you pull on the rope, the lower and upper axes slowly come together, increasing your ability to lift the object.
Material Use For Pulleys
Pulleys can be made from a variety of materials, including cast iron, cast steel or pressed steel, wood, and paper. The cast material should have good friction and wear characteristics. The pulley made from pressed steel is lighter than cast pulleys, but in many cases, they have less friction and can produce excessive wear.
Types of Pulley
There are three main types of pulleys:
- Fixed pulley.
- Movable pulley.
- Compound Pulley.
- Cone Pulley.
- Block and Tackle pulley.
1. Fixed Pulley
A fixed pulley’s wheel and axle stay in one place. A fixed pulley changes the direction of the force on a rope or belt that moves along its circumference. A good example of a fixed pulley is a flag pole: When you pull down on the rope, the direction of force is redirected by the pulley, and you raise the flag.
A fixed pulley is a pulley with a drum attached to a single location. While the force required to lift or move an object is no different than lifting it by hand, the fixed pulley allows you to change the direction of the force required.
For example, if you’re attached to a bucket that pulling water from a well, you can pull sideways with a firm pull to lift the bucket more comfortably than if you were pulling a bucket of water up hand in hand vertically. The water bucket still feels like the same weight, but it’s more convenient to lift.
2. Movable pulley
A movable pulley has an axle in a movable block. A single movable pulley is supported by two parts of the same rope and has a mechanical advantage of two.
A movable pulley is one in which the drum moves as you are moving the load. There is no change in the direction of the force that you need to apply, but the load will “feel” lighter than it is.
If you were hauling a heavy hay bale up into the loft of a barn, for example, a movable pulley would make the load feel much lighter, although the direction you are pulling would be the same.
3. Compound Pulley
In a compound pulley system, there is both a moveable pulley as well as a fixed pulley. This means that not only does the load “feel” lighter, but you can also change the direction of the force.
Although this type of configuration makes it possible to move heavy loads very easily, the tradeoff is that considerably more motion is required to do the work.
4. Cone pulley
The cone pulley is another specialized pulley system that incorporates the basic mechanics of a pulley system while allowing for mechanical adjustments. Cone pulleys are essentially multiple pulleys of decreasing vertical circumference on top of each other, forming a cone shape.
This cone shape allows the pulley operator to transfer the speed of the pulleys’ movements, requiring less work with a smaller circumference, but also producing less work.
Multi-gear bicycles essentially operate on the same system; Cyclists can quickly shift between smaller gears that propel the bike at a slower speed, and more gears require more effort but move the bike more distances per revolution.
5. Block and Tackle pulley
A block and tackle are specific forms of compound pulleys that can dramatically reduce the amount of work required to move a heavy object. A block-and-tackle pulleys system consists of several fixed and movable pulses arranged parallel to each other; a Fixed pulley is aligned with fixed and movable pulleys with movables.
Each compound pair is associated with the next pair, and each set reduces the total work required. This pulley system is attributed to the popular ancient inventor and mathematician, Archimedes.
Advantages and Disadvantages of Pulley Drive
Advantages of pulley
- The main advantage of the use of pulleys is that the effort becomes less as compared to the normal lifting of weights.
- It reduces the amount of actual force required to lift heavy objects.
- It also changes the direction of the force applied.
- It also provides a mechanical advantage.
- There is a safe distance between the operator and the weight, which avoids any disaster.
- Pulleys are easy to assemble and cost-effective.
- Although the pulley system contains moving parts, once installed, they require less or no lubrication.
Disadvantages of pulley
- It makes use of friction while transferring motion hence there are chances of slip.
- It is not a suitable solution for very high-power transfer at high rpm.
- Lifting distance increases while taking mechanical advantage.
- Long-term fatigue and creep break the rope.
- If the rope usually slipped when it was being pulled to the sides.
- A comparison with gears is not reliable.
- A combined pulley system uses multiple wheels and extra ropes to support the weight of a heavy object.
FAQs.
A pulley is a wheel that carries a flexible rope, cord, cable, chain, or belt on its rim. Pulleys are used singly or in combination to transmit energy and motion. One or more independently rotating pulleys can be used to gain a mechanical advantage, especially for lifting weights.
Pulleys are made by looping a rope over one or more wheels. They are often used to lift heavy objects: pulling down on one end of the rope creates an upward pull at the other end. Looping the rope over more wheels increases the upward force.
There are five main types of pulleys:
1. Fixed pulley.
2. Movable pulley.
3. Compound Pulley.
4. Cone Pulley.
5. Block and Tackle pulley.
Pulleys are commonly used to lift objects, especially heavy objects. The object lifted by a roller is called a load. A pulley with a wheel allows you to reverse the direction of your lifting force by pulling down on a rope (looped over the wheel) and lifting your weight.
Examples of pulleys include:
1. Elevators use multiple pulleys in order to function.
2. A cargo lift system that allows for items to be hoisted to higher floors is a pulley system.
3. Wells use the pulley system to hoist the bucket out of the well.
4. Many types of exercise equipment use pulleys in order to function.
Archimedes. Historians, however, credit Greek mathematician, inventor, astronomer, engineer, and physicist, Archimedes, with the first documented compound pulley system in the third century BCE.
