Pulley Systems: Single, Compound, Block & Tackle, Belt Drives

This lesson covers pulley systems and belt drives — mechanisms that transmit force and motion using wheels and flexible connectors (ropes, cables or belts). Pulleys are part of AQA GCSE Design and Technology (8552), Section 3.1.5.

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What Is a Pulley?

A pulley is a wheel with a grooved rim through which a rope, cable or belt runs. Pulleys are used to:

• Change the direction of a force
• Multiply force (reduce the effort needed to lift a load)
• Transmit rotary motion between shafts (belt drives)

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Single Fixed Pulley

A single fixed pulley is attached to a fixed point (e.g. a ceiling beam). The rope runs over the pulley.

Properties

Property	Detail
Mechanical advantage	MA = 1 (no force multiplication)
Direction change	Yes — pulling down on the rope lifts the load up
Effort required	Equal to the load (ignoring friction)
Distance moved	Effort distance = Load distance

Why Use a Single Fixed Pulley?

Although it does not reduce the effort needed, it allows you to pull downwards (using your body weight) to lift an object upwards. This is much more convenient than trying to push a load up directly.

Example: A flagpole — you pull the rope down at ground level, and the flag rises to the top.

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Single Movable Pulley

A single movable pulley is attached to the load itself. One end of the rope is fixed to a support point.

Properties

Property	Detail
Mechanical advantage	MA = 2 (effort is halved)
Direction change	No — you pull up to lift the load up
Effort required	Half the load (ignoring friction)
Distance moved	You must pull twice the distance the load moves

Why Use a Single Movable Pulley?

The load is shared between two rope sections, so the effort is halved. The trade-off is that you must pull the rope twice as far as the load travels.

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Compound Pulley (Block and Tackle)

A block and tackle system combines multiple fixed and movable pulleys to achieve greater mechanical advantage.

How It Works

Number of Rope Sections Supporting the Load	Mechanical Advantage	Effort Required
2	2	Load ÷ 2
3	3	Load ÷ 3
4	4	Load ÷ 4
6	6	Load ÷ 6

General Rule:

$MA = \text{Number of rope sections supporting the load}$MA=Number of rope sections supporting the load

$\text{Effort} = \frac{\text{Load}}{MA}$Effort=MALoad​

Worked Example

A block and tackle system has 4 rope sections supporting the load. The load is 400 N.

$MA = 4$MA=4

$\text{Effort} = \frac{400}{4} = 100 \text{ N}$Effort=4400​=100 N

However, you must pull the rope 4 times further than the distance the load moves.

If the load needs to be raised by 2 m:

$\text{Rope pulled} = 4 \times 2 = 8 \text{ m}$Rope pulled=4×2=8 m

Applications of Block and Tackle

Application	Why a Block and Tackle Is Used
Sailing	Adjusting sails requires multiplying the sailor's effort
Construction cranes	Lifting heavy building materials
Theatre rigging	Raising and lowering scenery, curtains and lighting bars
Rescue operations	Lifting casualties from ravines, buildings or water
Garage engine hoist	Lifting heavy car engines for maintenance