Brief description

A pulley is a simple machine consisting of a wheel on an axle or shaft that may have a groove between two flanges around its circumference. It is used to lift heavy loads or change the direction of an applied force.

Use / Function

• Lifting loads: Vertically moving heavy objects with less effort.
• Directional change: Redirecting a pulling force to a more convenient direction.
• Mechanical advantage: In compound systems (tackles), it reduces the force needed to lift a weight.
• Tensioning: Maintaining tension in lines or cables.

Operating principle

The pulley works by distributing the weight of the load over one or more sections of rope. In a fixed pulley, only the direction of the force is changed. In a movable pulley, the load is supported by two parts of the rope, effectively halving the required force. Compound pulleys (block and tackle) combine multiple wheels to further multiply the mechanical advantage.

How to create it

1. The Wheel: Carve a circular disc from a hard material (wood, metal, or stone). Create a groove around the edge to hold the rope.
2. The Axle: Create a central hole and insert a sturdy rod that allows the wheel to spin.
3. The Frame (Block): Build a housing that holds the axle and allows the pulley to be attached to a support.
4. Assembly: Mount the wheel in the frame, ensuring it rotates freely. Thread a rope through the groove.

Materials needed

• Wheel: Hardwood, bronze, or iron for durability.
• Axle: Steel or iron rod.
• Frame: Wood or metal plates.
• Rope: Flexible and strong (hemp, sisal, or other plant fibers).

Variants and improvements

• Fixed Pulley: Changes the direction of force but provides no mechanical advantage.
• Movable Pulley: Provides mechanical advantage by supporting the load with multiple rope segments.
• Block and Tackle: A system of two or more pulleys with a rope or cable threaded between them, used to lift heavy loads.
• Modern Pulleys: Use ball bearings to minimize friction and high-strength alloy materials for extreme loads.

Limits and risks

• Friction: Energy is lost due to friction between the wheel and axle, reducing efficiency.
• Rope Wear: Constant movement and friction can fray or snap the rope, leading to dropped loads.
• Overload: Exceeding the structural capacity of the frame, axle, or rope can lead to catastrophic failure.
• Misalignment: If the rope slips out of the groove, the system may jam or fail suddenly.