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Compound Machines Science Projects
Using Pulleys

If you need to do a science project on simple machines or compound machines, you can use pulleys to construct variety of working models.

 Pulley is 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 and thereby lift a load. A wheel turned by or driving a belt is also called pulley. The plural of pulley is pulleys.
 A Simple Science Fair Project for Compound Machines. We can't say enough about the educational value of this pulley set. Its prize-winning design enables your children to learn mechanics and spatial perception. Watch as they are inspired to effortlessly incorporate these concepts into their creative ideas.   MiniScience Part# PP54_S2  In your compound machine project you may show how a set of pulleys may be used to lift heavy objects effortlessly. Show how pulleys are used to lift trucks, other heavy objects and people. Optionally use a spring scale to show how pulleys reduce the force needed to lift heavy objects.

This pulley set increases the force by about 4 times. For example you may show that a 4 kilogram weight can be lifted with about 1 kilogram force.

 Force and mechanical advantage Pulleys are clever devices that allow you to lift large weights with much smaller forces. The length of the string used to lift the pulley determines how much force is needed. For example three string lengths allow us to lift a heavy object with a force equal to 1/3rd of its weight.  Do some experiments and measure the force it takes to lift the pulley by attaching a spring scale to the end of the string.

Pulleys can be used to simply change the direction of an applied force or to provide a force/distance tradeoff in addition to a directional change.
 Pulleys are very flexible because they use ropes to transfer force rather than a rigid object such as a board or a rod. Ropes can be routed through virtually any path. They are able to abruptly change directions in three-dimensions without consequence. Ropes can be wrapped around a motor's  shaft and either wound up or let out as the motor turns.

Ropes also have the advantage that their performance is not affected by length.

A compound pulley `trades' force for distance through an action/reaction force pair. In a double pulley, as the rope passes over the pulley the force is transmitted entirely but the direction has changed. The effort is now pulling up on the left side of the bottom pulley.

The disadvantages of pulleys, in contrast to machines that use rigid objects to transfer force, are slipping and stretching. A rope will permanently stretch under tension, which may affect the future performance of a device. If a line becomes slack, then the operation of a machine may change entirely. Also, ropes will slip and stick along pulley wheels just like belts. One solution to the problems associated with rope is to use chain. Chain is pliable like rope, and is able to transfer force through many direction changes, but the chain links are inflexible in tension, so that the chain will not stretch. Chains may also be made to fit on gears so that slipping is not a problem.

Lifting Heavy Objects

A common way to lift heavy objects is with a block-and-tackle, a schematic diagram of which is below (usually an actual block-and-tackle has all the pulleys on the the same axle, but that's hard to draw). Suppose there is a heavy crate (mass 100 kg) attached to the lower pulleys. What force must be applied to rope R to lift the crate off the ground? Assume all the pulleys are frictionless and massless.
Among benefits of pulleys:

While searching the Internet about uses of pulleys, I came across a website that describes how homes and communities may be modified to adapt the needs of disabled village children. This seemed to be a very good science project idea for students who need to make a compound machine or show the applications of pulleys. With the help of pulleys a person can lift himself to an elevated area such as a three or second floor of a village house. A model of house may be made using wood sticks and cardboards. Pulleys are available at MiniScience.com and other science suppliers.

The purpose of this project is to show that a system of ropes and pulleys may be the best way for a person with strong arms to lift herself without help to a 'house on stilts'.

The 'lift' can be made with a platform so that the whole wheelchair can be lifted. But if the house is small and people cook and eat at floor level, it may be best to leave the wheelchair outside.

For people who do not have strong arms, you may use pulley blocks with 2 or more pulleys. For example a pair of pulley blocks with 3 pulleys in each will increase the force by 6.

Available Pulley sets for science fair projects:

 Two, single plastic pulleys can be combined to form a fixed/moveable block and tackle pulley system. These pulleys have sheaves with deep V-grooves with diameters of 50 mm. MiniScience Part # PP5_S2 In addition to the pulleys you will need a wooden frame or structure to hang your fixed pulley. You will also need Nylon Mason line #18 or any similar nylon string (Available from Hardware stores). This set will reduce the lifting force by about 50%.
 Two, double pulley blocks can be combined to form a fixed/moveable block and tackle pulley system. Each pulley block has 2 plastic sheaves (mounted side by side) with deep V-grooves with diameters of 50 mm. MiniScience Part # PP55_S2 In addition to the pulley blocks you will need a wooden frame or structure to hang your fixed pulley. You will also need Nylon Mason line #18 or any similar nylon string (Available from Hardware stores). This set will reduce the lifting force by about 75%.
 Two, quad pulley blocks can be combined to form a fixed/moveable block and tackle pulley system. Each pulley block has 2 plastic sheaves (mounted side by side) with deep V-grooves with diameters of 50 mm. MiniScience Part # PP5555_S2 In addition to the pulley blocks you will need a wooden frame or structure to hang your fixed pulley. You will also need Nylon Mason line #18 or any similar nylon string (Available from Hardware stores). This set will reduce the lifting force by about 87%. Pairs of triple parallel pulley blocks are also available: MiniScience Part # PP555_S2

Possibilities are unlimited. You can design your own compound machine using pulleys.

 The diagram in the right shows a pulley system using 2 single pulleys and 2 sheaves. The end of the string is connected to a spring scale in order to measure the force required to lift the heavy block. In this design the upper block (fixed block) is made of sheaves.
 Sheaves may be used in fixed blocks or may be used to construct pulleys or pulley blocks. In the middle of each sheave is a hole that can be used to nail it to a board or block.

 The picture on the right shows an elevator for lifting heavy loads. This is one of the best compound machines suggested in ScienceProject.com. In this design pulleys are used to reduce the lifting force as well as changing the direction of the force. This design also incorporate a wheel and axle.
 This elevator project in the right shows how pulley blocks may be made using sheaves. This simple design reduces the lifting force by 75%.  Compound machines are generally classified as engineering projects. If you need to do a compound machine project as an experimental project, you can use your elevator to lift different masses from 1 Lb up to 5 Lbs and use a 2000-gram spring scale to measure the lifting force. Your results table will show the lifting force for different actual weights. You can then use your results table to draw a graph.

We have the largest collection of pulleys for science fair projects and educational activities.

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