Use of pulleys
Pulleys have made our everyday lives easy, from pulling curtains to lifting machinery, pulleys are found everywhere. They are simple yet powerful devices, with small force you can move large objects. Pulleys have made heavy work more manageable.
Pulleys give an extra mechanical advantage as it reduces the force needed to pull weight, thus pulley is used for shipping and marine applications and as heavy machinery lifting. They can be used singly or with many pulleys to lift or transport things.
Some examples of pulley include – elevators, a cargo lift system, well, exercise equipment, crane, bulldozer, timing belts in cars, and escalators. Pulley is a cable system that has made moving things easier. They are important machinery needed to move or lift large or heavy items.
What is a Pulley? – Types, Uses, and Examples
A pulley is a simple machine that carries a flexible rope, cord, or chain on its rim. Pulley is used to transmitting energy and motion. Grooved rimmed pulleys are called sheaves. In belt drives, they are affixed to shafts at their axes, and the power is transmitted between the shafts, via an endless belt running over the pulley.
The end of ropes creates an upward pull; thus, they are used to lift heavy objects. If the rope is looped over several wheels, then it increases the upward force, and with two wheels one can lift something twice as heavy with the same force.
There are now plastic pulleys available to lift the small loads. This can be freely rotated about the axis running along the center, this changes the direction of force and makes it easier to lift something.
There are three types of pulleys:
- Fixed Pulley – It has a fixed axle.
- Moveable Pulley – It has a movable axle.
- Compound Pulley – It is a combination of both fixed and movable pulleys.
The primary use of a pulley is to lift heavy objects. A simple pulley is made with a wheel and rope, cord, or chain. Pulley based systems are very common, let us look up at some examples of pulley uses are:
- Curtain Blinds – Pulley is used for the curtain blinds and help in pulling the curtain up and down.
- Water well – This technique of collecting water from the well is quite famous in the countryside. A bucket is dropped into the well to collect water and pulled up using the pulley.
- Crane
- Sailing Boat – To move the boat around as desired.
- Sports equipment – Pulley are used for the functioning of sports equipment for muscle exercise. Pulley help to control the angle at which the weights are lifted.
- Elevators – They work on an electronic pulley system. Several pulleys are used, and the counterweights are used to provide the lift system with both power and safety.
- Construction – They are the most basic and common type of pulleys. The pulley is made of a wheel track that can be raised to a great height to lift heavy machinery and collect debris.
- Theatre systems – The curtain and fly system in the theatre operate using the system of multiple pulleys. They are located at a height and operated from the side of the stage to raise and low the curtains and prop pieces.
Some other pulley uses and applications are – motor pulley used in a sewing machine, sliding bathroom doors, cargo lifts, escalators, rock climbing, and flag hoisting.
How does a pulley work?
Pulley is a simple machine made of rope and a grooved wheel. The rope goes into the groove, and pulling the rope turns the wheel. The wheel allows reversing the direction of lifting force by pulling down on the rope and lifting the weight. Using the two wheels you can pull more weight with the same strength or lift the weight at half strength.
This means the more wheel you have, i.e., the more time you loop the wheels around, the more you can lift.
So, the benefit of a pulley can be maximized by grouping two or more wheels with a rope. This will multiply the forces and allowing us to lift heavyweight. A pulley with wheels reverses the direction of the lifting force by pulling down a rope (looped over the wheel) and lifting the weight.
A two-wheel pulley will lift the same weight in half strength, this phenomenon is called Mechanical Advantage. The more the wheels, the more ME in lifting weights.
Additional read: How do pulleys work?
Rope and pulley systems
The rope and pulley system is made with a single continuous rope to transmit a tension force around one or more pulleys to lift weights. They are also called block and tackle. Renaissance scientists have included this system in the list of simple machines.
Consider a set of pulleys forming the moving block and the parts of the rope that support this block. If there is a load W supported by the parts of rope p, then the force balance required to move the block shows that the tension in each part of the rope must be W/p.
Thus, force balance one the moving block shows that the tension on each part of the rope must be W/p. Input force on the rope T=W/p.
In the pulley operation, it is assumed that the pulleys and lines are weightless and there is no energy loss due to friction.
The forces on the moving block must sum to zero, and the tension on each part of the rope must be the same for each part. This means if there are two parts of the rope supporting the moving block then each part must support half of the load.
Belt and pulley systems
In the belt and pulley system, there are two or more pulleys in a common belt. In this setup, the mechanical power, torque, and speed is transmitted across axels.
If the pulleys have different diameters, then the mechanical advantage is realized. The belt sheave should be smooth so that we get the mechanical diameter approximate to the ratio of the pitch diameter.
Pulleys are widely used for factory line shafts and in the rotating brush of vacuum cleaners in belt sanders and bandsaws. The agricultural tractors in the 1950s used belt and pulley system, however, it is now replaced by other mechanisms.
There are cone pulley and step pulleys that operate on the same principle provide multiple drive ratios in the belt and pulley system.
Who invented the pulley?
This simple machine was invented 2000 years ago by a famous Greek scientist and mathematician Archimedes. He studied many fields of science and many tools to be used in everyday life and war. It is said he used pulleys to drag ships out of the ocean. There is also evidence of pulley uses in the construction of Stonehenge, in England.
How does it get power?
Pulley gets its power from distance, for example, in a 2-pulley system, the pulley uses half force to lift, but you will have to pull the rope for two meters to lift the object one meter. This depends on the concept of Work. It is defined as how much effort you use over a distance.
So, if you pull the rope in a 2-pulley system for a distance of 2 feet, with 1lb force then you did 2ft/lbs work. This will be the same as pulling a rope 1-ft with 2lb force.
Conclusion
The invention of the pulley has saved humankind. They have made it easier to lift heavy objects. With pulley construction work has become a lot easier, they help to pull large blocks upward. It has become easy to build large sailing ships and explore the world.
