Pulley System

What is A Pulley System?

You might have seen fictional characters who pull trucks with their hair and pull trains with their teeth. But you may not know that science can make you so strong. If you want to lift heavy weights, use the knowledge of science and do amazing things using a device called a pulley.

A pulley is a collection of wheels looped over a rope that is used to lift things.

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A pulley system is an easy way to lift heavy objects, as compared to lifting the object barehanded. A single pulley only serves to change the direction of the applied force. When two or more forces are used in a system, then the pulley not only changes the direction of applied for, but also multiplies the input force. If one fixed and one movable pulley is applied in a system, the system almost doubles the amount of force applied by a person.

Pulley System Physics

A wheel on a shaft or an axle is designed for supportive movement. It changes the direction of the belt or the cable and also transfers power between the shaft and the belt or cable.

A pulley system which has a support frame or shell doesn't transfer power to the shaft. It is used to exert force and guide the cable in a specific direction. The shell, which is used as a support in the pulley system, basically acts as a block. It is referred to as a sheave.

The circumference of the pulley system is surrounded by flanges which contain groove or grooves to locate the table and the belt. This system of a pulley is driven by a rope, cable, belt, or chain.

The pulley system is assembled in a way to ease the mechanical effort required to lift heavyweights.

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It is also assembled in a way such that the chain or belt will have high efficiency for transmitting power from one shaft to the other.

Pulley Mechanism

A pulley has a unique mechanism, which makes it easier to lift heavy loads with less effort; for this reason, it has become one of the most important tools in the engineering industry. It has a wide range of applications in different industrial machines.

The work of a simple pulley is to lift a heavy load with ease by using a rope and a wheel. However, there are some other types of pulleys which have a very complex mechanism. 

The working mechanism of different types of pulley systems is given here below:

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a. Fixed Pulley

The simplest type of pulley system contains a wheel that is not free to move and rotate in any direction; this is a fixed wheel. The amount of force applied to the pulley system is the same as the weight of the pulley. This pulley system requires very little space to operate and has the simplest mechanism among all pulley systems.

b. Movable Pulley

This is also a simple pulley, but the wheel of this pulley can both move and rotate. In this pulley system, less force is required as compared to the weight of the object, to lift the object. The wheel of this pulley system translates the motion of the pulley system. This pulley system is used in almost all kinds of pulley systems and hence is very common.

c. Compound Pulley

The combination of a simple pulley and a movable pulley is called a compound pulley. It is also called a combination of the pulley. It is oriented in such a way so as to reduce the effort to less than half of the weight of the load. Thus the pulley system is mainly used by cranes to lift heavy objects of steel and concrete in construction sites.

d. Block and Tackle Pulley

The block and tackle or just tackle is a pulley system that consists of two or more pulleys attached with a rope or cable and is used to lift heavy-weight loads. In this pulley system, the pulleys are assembled in the form of blocks. The blocks are then paired in which one pulley is fixed, and the other pulley moves.

Rope Pulley System

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Pulley in oil derrick

The above-mentioned figure is a hoist using a compound pulley system that has a yielding capacity of 4. The hoist consists of one single fixed pulley and two movable pulleys (which are joined with each other) attached to the hook. One of the ends of the chain of the pulley is attached to the pulley while the other is attached to the winch.

A rope and a pulley system contains a single rope that is used to transmit force from one pulley to another, either to move or lift a load. The rope used can be a light rope or a chain that can also be used. The Renaissance scientists have included this system of the pulley in the list of simple machines.

FAQ (Frequently Asked Questions)

1. Give some examples of the pulley system.

Ans- Some significant pulley system examples include:

● Multiple pulleys are used in elevators to take it up and bring down.

● A cargo lift system uses a pulley system to raise items to higher floors.

● Pulley systems are used in various exercise equipment to function. 

● Pulley is used in cranes of construction sites to lift and place heavy materials.

2. What is a block and tackle pulley system?

Ans- A block and tackles pulley works to reduce the amount of force needed to lift a heavy object like a crate to a greater extent. Standard pulley comprises a single when on an axle where a rope runs over it. A pulley here will change the direction of the force being applied to the object. 

Now, when we consider a system of the pulley, they form a block and tackle where multiple numbers of force acts to change the direction of the force. This means less force is needed for moving the object.

3. State the difference between pulley and sheave.

Ans- A pulley is among the six kinds of a simple machine, whereas a sheave is a part of the pulley system that rotates and is grooved inside it.

In case where there is no sheave in the pulley, there's a change in the force's direction to move the load, but this doesn't change the amount of force required. 

So, for each sheave used in a pulley, one requires just half of the original force to shift the position of the object.

4. Does a pulley cut-weight in half?

Pulley lets you split the weight for a length of time. As you pull one meter of the rope, the weight of the object increases, which is nearly half a meter in case this is the ratio, and so appears half as heavy.