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Nabiha Farrukh

on 27 March 2013

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Transcript of Pulleys

An amazing simple machine Pulleys Introduction History about pulleys Different types of pulley systems Different types of pulleys Experiment Conclusion There are 3 kinds of that Pulleys provide a mechanical advantage when lifting heavy loads, they make the job much
much easier.

Fixed Pulleys has an axle that is enchored in place,
it is used for changing the direction of the force on belts and ropes. This pulley spreads the weight of the load evenly.

Movable Pulleys has a free moving axle wich means when lifting a heavy load it has the ability to move the load around.

Combined Pulleys is combined with the fixed pulley and the movable pulley it is easier to handle because you use less effort to lift the load.
When more effort expended it reduces the loads weight by half. How a pulley works in real life! In conclusion we have descovered, that pulleys
are one of the most useful simple machines.
Some, can lift light objects like a flag, while others can lift bicycles, cages and even chandeliers up to the sealing. Pulleys are all around us. They make our everyday tasks alot easier. A pulley works by transferring energy to make it easier to move heavy objects. The purpose of a pulley system is to move heavy objects with less effort. Pulleys are an easy machine to make our life easier on a daily basis. Cranes are a great example of a pulleys without the simple mechanics we wouldn't be able to have the sky scrapers or buildings we have today. Mechanical advantage of a pulley To calculate the effort required to lift the load we divide the load
by the number of ropes (do not count the rope that goes to the effort). 1.1 Direct Pulley All this system does is change the direction of where the effort needs to be put in, instead of pulling the rope in an upwards direction it can now be pulled downwards which is usually more efficient. 2:1 Pulley System If we take a 1:1 system and turn it upside down it will result in a 2:1 mechanical advantage. Instead of the pulley being attached to an anchor it is now attached to the load (pulley A). On one side of the pulley the rope has been attached to a fixed anchor point, the rope on the other side of the pulley has been sent back down to the ground via a redirect (pulley B). 3:1 Pulley System First one end of the rope is attached directly to the load, this is then passed around an anchored pulley (pulley B) and returns back to the load where it is passed through pulley through pulley A which has been fixed to the load. 4:1 Pulley System This pulley system provides a 4:1 mechanical advantage. The user is required to apply a force of 25kg to raise this 100kg load, for every 4 metres of rope that the user pulls through the pulley system the load will only be raised by 1 metre. 5:1 Pulley System When the end of the rope is attached directly to the load this usually results in a mechanical advantage with an odd ratio. When the end of the rope is attached to a fixed anchor point this will normally result in a mechanical advantage with an even ratio. With this 5:1 pulley system the user is required to apply an effort of only 20kg to lift the 100kg load. From ancient times to today, the invention and improvement of the pulley have made human lives easier. They enabled humans to move large loads with a small amount of force. Without them, we would have less clothing, food, and shelter and everyday would be a struggle. Simple machines especially the pulley have been a very important part in moving forward with civilization, but how and where did this simple machine originate? Possibly by the 1500 BC people in Mesopotamia used pulleys for bringing up water. Archimedes invented the first compound pulleys from 287 BC to 212 BC. It was reported that Archimedes moved an entire warship by just using the pulley. Archimedes understood the concept of mechanical advantage and how to use it to move or lift heavy objects with less force. Archimedes knew that he could improve his mechanical advantage for lifting or moving an object by using pulleys. Mecahnical advantage of a pulley To calculate the effort required to lift the load we divide the load by the number of ropes (do not count the rope that goes to the effort).

The image on the right shows a four pulley system. The person lifting the 200kg load experiences a pull equal to only 50kg (200kg/4).
Using the four pulley system on the right, the person certainly experiences an advantage. We call this advantage the mechanical advantage and is calculated by dividing the load by the effort (load/effort). The pulley system offers a mechanical advantage of 4. How it works
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