Pulley simulator

What this simulator shows

A pulley is a wheel with a rope running around it. Choose 1, 2 or 4 supporting ropes, then drag down on the picture or press Pull to lift the crate. With 1 rope, a single fixed pulley simply changes the direction of your pull. With 2 or 4, movable pulleys hang from the crate and share its weight between rope sections. A spring scale in your hand shows the effort force, and a ruler shows how high the crate has risen.

• Effort = load ÷ number of supporting ropes: 120 N, 60 N or 30 N here.
• Rope pulled = height lifted × number of supporting ropes.
• Less force always means more rope. The work done, force × distance, stays the same.
• The model ignores friction and the weight of the pulleys, so real pulleys need a bit more force.

Why hands-on helps

Children often see pulleys as magic: pull less, lift more. Pulling the rope and watching the hand travel four times as far as the crate makes the trade-off visible. Counting the rope sections that hold up the crate gives a quick way to predict the force for any pulley system.

Common misconceptions

The most common mistake is thinking pulleys reduce the work you do or give you free energy. They reduce the force, but you pull a longer length of rope, so the force × distance is the same. Another error is thinking a single fixed pulley makes lifting easier. It makes pulling more comfortable, because you pull down instead of lifting up, but the force is the same as the load. Children also sometimes count every piece of rope, including the one in their hand; only the sections holding up the moving pulley and load count.

A 10-minute pulley activity

• With 1 rope, lift the crate to the shelf. Note the effort and rope pulled.
• Switch to 2 ropes. Before lifting, ask the child to predict both numbers.
• Lift to the shelf and check. Repeat for 4 ropes.
• Make a table and ask: "What happens to the force? What happens to the rope?"
• Ask where they have seen pulleys: flagpoles, cranes, blinds, sailboats, elevators.

Where this fits in school

• US, grades 3 to 8: pulleys are part of many simple machines units in elementary and middle school science and engineering.
• England, Year 5: pupils recognize that some mechanisms, including levers, pulleys and gears, allow a smaller force to have a greater effect.
• England, Key Stage 3: pupils meet work done as force × distance, which explains why the pulley trade-off works.

Learning more

Forces and simple machines sit on Eurekami's science skill map, with lessons that draw and explain each setup. The division and multiplication used here also turn up in daily math practice.