Mechanical Pulley Working Model

Quick Answer: The Mechanical Pulley Working Model is a bench-top physics apparatus that sets a fixed pulley beside a movable pulley on a rigid frame, with cords and weight pans. Students load the pans to compare effort with load and to see how a pulley system trades force against distance.

Fixed and Movable Pulleys Side by Side

In the listing image, the mechanical pulley working model has two upright rods joined by a cross-bar, carrying a red pulley fixed at the top and a second pulley that hangs in a loop of cord, each with a weight pan below. That arrangement lets a class study both basic pulley types on one stand. A fixed pulley only changes the direction of the pull: the effort equals the load, apart from friction, but pulling down to lift something up is often easier. A single movable pulley hangs on two supporting lengths of cord, so each carries half the load and the ideal mechanical advantage is 2.

The trade-off is distance. To raise the movable pulley by 10 cm, both supporting cords must shorten by 10 cm, so the effort end travels 20 cm. Work in equals work out in the ideal case, which is the point most lessons build towards. With real pulleys the measured effort is a little higher than half the load because of friction in the bearings and the weight of the movable pulley itself, and students can calculate efficiency as mechanical advantage divided by velocity ratio.

Because both pulleys are visible and the loads sit in open pans, it is easy to add masses step by step and record effort against load in a table. The number of pans, the masses supplied and whether extra pulleys can be added for a block-and-tackle arrangement should be checked when ordering.

Practical Work with the Pulley Model

• Measuring the effort needed to balance a range of loads on the fixed pulley and on the movable pulley
• Plotting effort against load and reading the effect of friction and pulley weight from the intercept
• Measuring the distances moved by effort and load to find the velocity ratio
• Calculating efficiency and discussing why it rises as the load increases
• Relating the model to cranes, flagpoles, well pulleys and window blinds

Specifications

Care & Handling

• Keep the cords free of knots and fraying; replace a worn cord before it snaps under load.
• Add masses gently rather than dropping them into the pans, which jolts the frame and swings the cords.
• Check that each pulley turns freely; a light drop of oil on a stiff axle, if the design permits, reduces friction readings.
• Store the model upright with the pans empty so the cross-bar is not left under strain.

Why Choose LabEquip

Physics departments buying mechanics lab equipment for simple-machines practicals usually want a set-up that several groups can repeat with consistent results. LabEquip lists this pulley model in its STEM kits range, next to the Electrical Lifting Crane Model, which shows a pulley at work in a powered lift. Send group numbers and any requirement for extra masses through our contact page.

Frequently Asked Questions

Why does the fixed pulley give no mechanical advantage?

The cord passes over a pulley that does not move, so the tension is the same on both sides. The effort therefore equals the load, apart from friction. What the fixed pulley offers is a change of direction, letting you pull down to raise a load.

Why is the measured effort more than half the load on the movable pulley?

Two things add to the effort. The movable pulley and its hook are lifted with the load, and the bearings have some friction. Allow for the pulley’s weight, or plot a graph of effort against load, and the slope comes close to one half.

What is the difference between mechanical advantage and velocity ratio?

Mechanical advantage is load divided by effort and depends on friction. Velocity ratio is the distance moved by the effort divided by the distance moved by the load, and depends only on how the cord is arranged. Their ratio gives the efficiency of the system.

Can the model show a block and tackle?

A block and tackle uses several pulleys so that more lengths of cord support the load, raising the ideal mechanical advantage to 3, 4 or more. Whether extra pulleys can be fitted to this frame depends on the version supplied, so check that at enquiry if you need it.

How should students record their results?

Use a table with columns for load, effort, effort distance and load distance. Increase the load in equal steps, read the effort when the system just moves steadily, and repeat each reading. Averaged values give a smoother graph and a more reliable efficiency.

Is the pulley model safe for younger students?

Yes, with sensible handling. The loads are small, but masses can fall on feet or fingers if a cord slips, so keep the model on a stable bench, stay within the load it is designed for, and never reach directly under a raised mass.

Last Updated: September 2026