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Pulleys

A pulley consists of a rope (or a belt or chain) that passes around a wheel.

Fixed pulleys

An example of a fixed pulley would be a pulley at the top of a flagpole (see Diagram 9). Because of the pulley at the top, the person raising the flag can stand on the ground and hoist the flag by pulling down on the rope. Imagine how much harder it would be without a pulley - the person would need to climb up the flagpole with the flag!

Other examples of fixed pulleys include:

• the pulley at the top of a yacht mast. The deckhand can raise the sail up the mast by pulling down on the rope.

• the pulley at the end of the boom of a crane. The crane works by pulling upwards to lift the load.

Did you spot the two examples of pulleys in the Simple Machines Animation?

Moving pulleys

Diagram 10 shows one moving pulley attached to the engine (the load), and one fixed pulley attached to the support above. This type of pulley system is called a 'block and tackle', where 'block' refers to the pulleys and 'tackle' is the chain that the person is pulling to lift the engine.