GROUP MEMBERS: Grp. Leader:

Haseeb Faisal Others:

Ahsan Tariq (010)

Waleed Khursheed

Abdullah Mehmood

Abyaz Zahid

Faiza Mobeen

PULLEY DESIGN

Topics To Cover : Introduction to Pulley.

Construction and Design.

Types:

I) Single Fixed Pulley.

II) Movable Pulley.

III) Block And Tackle

Applications

Introduction:History: Starting with the basic topic,pulley is

originally a simple machine.It was possibly created by Archimedes in B.C times. It's original use was to lift the buckets of water.

The term "sheave" can also be used to refer to a pulley.

What Are Pulleys: 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 in orderto transport people or things.

Pulleys mostly changes the direction of force to make things work easier

It is a collection of one or more wheels over which

you loop a rope to make it easier to lift things

If you want to lift a really heavy weight, there's only so much force your muscles can supply, when if you're the world's strongest man but if you use a simple machine such as a pulley you can effectively multiply the force your body produces.

Pulleys can be used everywhere to help make tasks easier. In addition to lifting things pulleys can also be used together with the other pulleys to transport the heavy objects .They can also be used to provide power from one shaft to another.

Construction:PARTS:

Pulleys are nothing but, Gears without teeth.and instead of running togetherdirectly they are made to drive one another by Cords Ropes, Cables Belting of some kinds.

To be a pulley a simple machine musthave a rope or belt.

A Simple pulley is made up of TWO MAIN PARTS:I. A pulley wheel that can spin around,II. A rope that goes around it.

One cannot work without the other.a pulley has a groove around its rim. This stops the rope from sliding from side to side. The

groove also helps to grip the rope. Pulleys are modified levers; their fulcrum is at their center.

The Main Part Of Pulley is BELT.Belts are looped over pulleys and may

have a twist between the pulleys and

the shafts need not be parallel. In

TWO PULLEY SYSTEM

the belt can either drive the

pulleys normally in one direction

(the same if on parallel shafts),

or the belt may be crossed, so that

the direction of the driven shaft is

reversed.

A conveyor belt is one application where the belt is adapted to continuously carry a load between two points.

TYPES:

FLAT BELT

ROUND BELT

V-BELT

PULLEY WITHOUT WHEEL:

You can make a pulley without a wheel. However there would be a friction between the rope and the metal and the rope would not be easily moved.

Forces Involved: The weight of the load does not change, it is the

same for each trial.

The output force will be the force required to hold the load still– it does not change since the weight remains the same

As more strings are added, the input force required to achieve the same output force decreases.

Types Of Pulley:

There are three types of pulleys Fixed pulley Movable pulley and block and tackle,

I will be describing the first type. The main aim of fixed pulley is it changes the direction of the force you exert by pulling, so you can pull down to move an object up.

In this fixed pulley system, you pull down on one side

of the rope and the other side goes up. You use the same amount of force to pull down as you would to lift the object yourself. However, you have changed the direction of the force..

A fixed pulley is useful because when

you pull down, you can use your body’s own

weight to add to the push.

In contrast, when you exert a force upwards by

lifting something, you also have to lift the weight of

your own arms. Now I will describe the mechanical

advantage of fixed pulley but first we have to know

what is mechanical advantage. As the name suggest it

involve machine.

Mechanical Advantage: Work done in a task is the force applied multiplied by the distance over

which it was applied. The work required to complete a particular task is fixed. Machines provide us a mechanical advantage by decreasing the input force but increasing the distance. The formula for mechanical advantage is:

Mechanical Advantage = Output Force/Input Force

A mechanical advantage of 1 means that the input force is equal to the output force. A mechanical advantage greater than 1 means that we can accomplish the work with lesser force but exerting it for a greater distance.

Movable Pulley: A movable pulley is a pulley that is free to move up and down, and is

attached to a ceiling or other object by two lengths of the same rope. Examples of movable pulleys include construction cranes, modern elevators, and some types of weight lifting machines at the gym.

For Example: Using the screws and your screwdriver or drill, attach one fixed pulley

to a point slightly off-center on one of your 2”x4” plank. Feed the rope through the pulley. Feed one end of the rope through a moveable pulley. Attach the end of the rope fed though the movable pulled to the 2x4

plank, about 1 foot away from the fixed pulley. Set the wooden plank between two high surfaces so the pulleys are

facing down. The movable pulley will hang down like this. Attach the handle of the toolbox to the movable pulley. Place different objects in the toolbox until it is heavy. Weigh the

toolbox on the scale.

Results will be: The fixed pulley will make the toolbox most difficult to lift. The moveable pulley will make the toolbox easier to lift. The compound pulley system will make the toolbox easiest to lift.

Mechanical Advantage

Movable pulleys give you a mechanical advantage, which is measure of performance for machines. Having a mechanical advantage means the force applied by the system is greater than the force you put in. In a pulley system, this means the pulley can lift the object with a greater amount of force than you apply to the rope. This allows you to lift heavy things more easily.

Block And Tackle: A Good way To Pull Heavy Loads. DEFINITION:- A block is a set of pulleys or "sheaves" mounted on a

single axle. The assembly of two blocks with a rope threaded through the pulleys is called tackle.

Block And Tackle System are among the simplest and most useful machines that man has ever invented. Both are used for lifting loads and for controlling the motion of a rope or cable. A block is a set of pulleys designed to rotate separately but along the same axis; such a construction is often referred to as a block and tackle, and may be rigged in different ways, for many purposes.

Gun tackle Gyn tackle Double tackle And others

Working:

A block and tackle is a system of two or more pulleys with a rope or cable threaded between them, usually used to lift or pull heavy loads.The pulleys are assembled together to form blocks and then blocks are paired so that one is fixed and one moves with the load.

Generally, Block And Tackle are used to change the direction of an applied force.

Example: This arrangement actually does change things in an important way. You can

see that the weight is now suspended by two pulleys rather than one. That means the weight is split equally between the two pulleys, so each one holds only half the weight, or 50 pounds (22.7 kilograms). That means that if you want to hold the weight suspended in the air, you only have to apply 50 pounds of force (the ceiling exerts the other 50 pounds of force on the other end of the rope). If you want to lift the weight 100 feet higher, then you have to reel in twice as much rope 0- 200 feet of rope must be pulled in. This demonstrates a force-distance tradeoff. The force has been cut in half but the distance the rope must be pulled has doubled.

Applications: Single Fixed Pulley:

Wells use the pulley system to hoist the bucket out of the well.

Flagpoles use pulleys in order 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.

Rock climbers use pulleys to help them to climb

This kind of pulley system is used in some elevators. The elevator has cable attached to it that goes up, around a pulley, then comes down

Movable Pulley:

ESCELATORS Are example of moveable pulley used for transporting people from one side to other.

Modern cranes are also examples of moveable pulley.

The pedaling system of a bicycle is a moveable pulley.

Some elevators and cable cars use moveable pulleys.