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# Pulley Systems.

Extracts from this document...

Introduction

Udit Aggarwal

Pulley Systems

A simple machine consisting essentially of a wheel with a grooved rim in which a pulled rope or chain can run to change the direction of the pull thereby lifting a load is called a Pulley. Pulleys can be used as Force Magnifiers. If there were no friction, using one pulley to lift a load of 1 N would need an effort of 1 N. The use of one pulley only changes the direction of the applied force.  If two pulleys were used, only an effort of 0.5 N would be needed. If three pulleys were used, only an effort of 0.33N would be needed. The efficiency of a pulley system is less than 100% due to friction.

Velocity ratio = Number of pulleys used / Number of ropes supporting the load

Types of Pulleys

There are two types of pulleys, which are given below with their definitions-

• Fixed Pulley: A fixed pulley has a fixed axle and is used to redirect the rope. A fixed pulley has a mechanical advantage of 1.
• Movable Pulley: A movable pulley has a free axle, and is used to transform forces - when stationary the total force on the axle balances the total force provided by the tension in the rope.

## Method

• I had set one pulley system and hung 1N load (100g) from it.
• Using a spring balance I had measured the effort which was needed to lift the load vertically through 10 centimetres.
• After the above, I had set up a two pulley system and hung a 1N load from it.
• Using a spring balance I had measured the effort needed to lift the load vertically through 10 centimetres.
• After the two-pulley system, I had set up a three-pulley system and hung 1 N load to lift the load vertically through 10 centimetres.

## Equipment

• Pulley systems (3).
• Clamp Stand.
• Weights.
• Spring balance.
• Rope.
• Pen.
• Paper.
• Ruler.

Middle

Lastly, as I had desired to achieve accurate results I had taken extra care with all the equipment while carrying out the experiment.

Effort (N)

## Accurate results from Computer

1

1.2N

1 N

2

0.4 N

0.5 N

3

0.38 N

0.33 N

#### Conclusion

From my results I have found out that the effort decreases when more pulleys are used. This is because the load is spread on all the pulleys.

Evaluation

I believe I have successfully accomplished the experiment with achieving the desired results although not the perfect results. I think my results were not accurate as compared to the results, from the computer, but according to the other groups, I have achieved respectable results. I think the main difference, which caused a barrier, leading me to inaccurate results, was Friction. I believe that I could have made my experiment accurate by lubricating the ropes and the wires that were to be used while accomplishing the experiment. If the friction was not present, I believe everyone have achieved the desired results.

Conclusion

Writing and drawing would be impossible in absence of friction between the pen and the paper.Without friction in between the saw and the wood, it would be impossible to cut the wood.The brakes of bicycles and automobiles would not work without friction between the rim and the brake shoe. To increase friction the brake shoes are made rougher.

Friction can be Increased or Decreased

Friction can be increased in specific cases by following methods-

1. Sand is spread on slippery roads to increase friction and to avoid slipping of wheels.
2. A greater force of friction is required between the ground and the soles of shoes worn by athletes and players. To increase the friction in the soles of the shoes, spikes are provided in the soles.
3. In certain moving parts of the machinery such as the belt and the wheel, a greater friction is required; therefore special materials can achieve it.

Friction can be decreased-

1. Lubrication, oiling, and greasing the parts of the machinery can reduce friction.
2. By using ball bearings, the friction between the moving parts of machinery is considerably reduced.

-  -

This student written piece of work is one of many that can be found in our GCSE Forces and Motion section.

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