• A pulley is a wheel with a groove along its edge, for holding a rope or a chain.
Figure 58: A pulley
• Pulleys are usually used in sets designed to reduce the amount of force needed to lift a load.
• A small pulley at the top of a flagpole helps in raising the flag.
There different types of pulleys:
• Fixed pulley
• Movable pulley
• Combined pulley
• A fixed pulley has a fixed axle.
• A movable pulley has a free axle.
• With a fixed pulley, the pulley is attached to a hook or a wall and doesn't move, like the clothesline pulley.
• A fixed pulley changes the direction of the force.
• For instance, we can pull down any object in order to lift something up, or we can pull the upper clothesline toward us in order to move the lower clothesline away from us.
• With a movable pulley, we can pull an object with less force for a longer distance to get the same work done.
• This lets us lift things that would be too heavy for us without a pulley.
• Usually, machines use a combination of fixed and movable pulleys.
• A combined pulley is a system of movable pulleys.
Figure 59: A pulley is used to lift a bucket of water from well, a flagpole pulley
Figure 60: Rock climber pulley, marine pulley