Pulleys help lift and guide — Engineering, 4–6 years
A rope around a grooved wheel can change the direction of a pull. With the right arrangement, several rope sections can also share the load.
A pulley guides a rope
A pulley is a grooved wheel with a rope running around it. Pulling one side makes the other side move. The wheel can let you pull down to raise something up, or help a rope travel smoothly around a corner.
Why use a pulley?
Lifting a bucket straight up can be awkward when the load is below your hands. Early builders and sailors needed to raise things high, such as stones, sails and baskets. A pulley lets them stand in a better place and pull in a useful direction; extra pulleys can reduce the force needed.
Raising a basket with a pulley
Tie a small basket to one end of a rope over a pulley. The basket hangs 1 metre below the wheel. Pull the free end down 1 metre; the basket rises about 1 metre. The pulley has not removed the weight, but it lets you use a downward pull while standing safely on the ground.
A pulley does not make a load weightless
It is reasonable to feel that a pulley makes lifting easy because the rope moves smoothly and the pull changes direction. A single fixed pulley mostly changes direction; it does not remove the load’s weight. The rope, wheel and fastening must still be strong enough.
Pulleys around us
You may find pulleys in flagpoles, window blinds, cranes, lifts and some playground equipment. They guide cables or help raise objects. Real machines may use several pulleys, motors and brakes, so their users can control heavy loads safely.
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