Pulley systems ease lifting with ropes over wheels. Single pulleys change force direction; fixed pulleys change direction; movable pulleys reduce effort. Adding pulleys creates mechanical advantage.

Pulleys are wheel shaped with a groove that allows a cord or chain to sit inside the groove. A single pulley changes the direction of force, making pulling down easier than lifting up.

This article was originally published with the title “Changing a Four-Crown to a Single-Crown Pulley” in SA Supplements Vol. 56 No. 1444supp (September 1903), p. 23134 doi:10.1038 ...