Pulleys change how we lift — Engineering, 7–10 years
A wheel with a groove guides a rope, changing the direction or amount of force needed to lift a load.
A wheel that guides a rope
A pulley is a grooved wheel with a rope running around it. Pulling down on one side can make a load rise on the other, so you can stand on the ground instead of above the load. Several pulleys can also share the load and reduce the force needed.
Why pulleys were useful
Before cranes and machines, people still had to raise stones, sails and buckets. Pulling down is often easier to control than pulling up, and a rope can take the effort to a safer place. Extra pulleys do not create energy; they exchange a smaller force for more rope to pull.
One fixed pulley and one moving pulley
Imagine a 20 kg load hanging from one moving pulley. Two sections of rope support it, so the load is shared between them. In an ideal model, you pull with about 10 kg of force, but you must pull 2 metres of rope to raise the load 1 metre. Friction makes the real pull a little harder.
The mistake: a pulley makes the load lighter
It feels as if the pulley has reduced the weight, because your hands need less force. The load itself has not changed: Earth still pulls on it just as strongly. The rope and pulleys share or redirect the force, while you usually pull a greater length of rope.
Pulleys in real life
A flagpole uses a pulley so someone on the ground can raise and lower a flag. Cranes use pulley systems to lift building materials, and sailing boats use them to adjust ropes. In lifts, cables and wheels guide the car and help balance its movement.
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