A pulley is a system consisting of usually a rotating wheel with a curved rim which is mounted on a hook or base for stability. A rope, belt, or chain can move along the wheel's rim to change the direction of a pulling force. Examples are a flagpole and a curtain rod.
A "single-fixed pulley" is a pulley that is attached to an object.
A "single-moveable pulley" is a pulley that is attached to a wire or rope so that it can move with the wire or rope.
A "single-fixed pulley" gains nothing in force, distance or speed, but it changes the direction of the force. A system of pulleys may be used to improve leverage in lifting weights, thereby reducing the force
required to move an object.
Engineers use pulleys in all sorts of applications. Here's your mechanical challenge for the day:
- Design a pulley system that uses two pulleys to lift up a soda bottle vertically over a distance of 2 metres. Use your sketchbooks to sketch your ideas.
- Draw a plan for using four pulleys instead to lift your soda bottle, and answer the following questions:
- Do you expect the force you will have to apply to move the bottle will be reduced? By how much?
- Do you think that adding ten more pulleys would make a difference? Why, or why not?
- Do you think the size of the pulley impacts how much force is needed to lift the bottle? Why, or why not?
- Do you think the smoothness of the rope or twine pulley impacts how much force is needed to lift the bottle? Why, or why not?
- Can you think of examples of three machines that incorporate pulley systems?
- Can you think of engineering problems that were solved through the use of a pulley or a pulley system?
- Can you find any examples of pulleys in your school, home, or community?