Everyday Life & Technology
How does a pulley system work?
Several pulleys and a rope: Puschel follows how a pulley system shares the load.
The short answer
In a pulley system, several sections of rope can support a load. This can reduce the pulling force needed. In return, you pull a longer length of rope. One fixed pulley only changes the pull's direction.
An imagined Wusel scene
Puschel and Flauschi investigate
At the table model, Puschel pulls the rope a long way down, but the light load rises only a little. Flauschi marks start and finish with paper strips. They can see the trade: more rope travel for less pulling force.
They rest the load back on the table.
Try explaining it
What is the trade-off in a force-saving pulley system?
Choose a), b) or c), then explain your choice.
- a)The same pulling force for longer rope travel, with no force advantage.
- b)Less pulling force for more rope travel.
- c)Less pulling force for a shorter rope travel.
Show the explanation
Correct: b): Less pulling force for more rope travel.
In a pulley system, several sections of rope can support a load. This can reduce the pulling force needed. In return, you pull a longer length of rope. One fixed pulley only changes the pull's direction.
Word help
- friction
- An effect between touching surfaces that resists sliding between them.
Explore in more detail
Here you will find longer explanations and further details. You can explore them together.
Understand step by step
How it works – simply explained
A pulley redirects pulling
A rope runs over a wheel. A fixed pulley can let you pull down while a load moves up.
Several rope sections share support
In a suitable system, several rope sections support a moving pulley and share the load. Less pulling force is needed.
Less force means more distance
Raising the load requires pulling a correspondingly longer rope length. Friction adds losses. Pulleys do not create free energy.
Half the force, twice the rope distance
In an ideal model, two rope sections support a moving pulley. Ignoring friction, about half the pulling force is needed, but roughly twice as much rope must be pulled as the load rises. Saving force is not the same as saving distance. This is a model, not an instruction to hang loads or ropes.
References for this explanation: [1]
The key points again
Discovery 1
A fixed pulley can change the direction of a pulling force.
Source: [1]
Discovery 2
Suitable moving pulleys share a load between supporting rope sections, reducing the required pull.
Source: [1]
Discovery 3
You must then pull more rope. Friction also matters: a pulley does not create free energy.
Source: [1]