A fixed pulley consists of a wheel fixed to a shaft and is used in conjunction with a belt to transfer energy to another fixed pulley. A movable pulley consists of a shell, a movable wheel and a rope. Movable pulleys are also know as block and tackle.
Experts choose flagpoles as applications of fixed pulleys, while movable pulleys are utilized in modern elevators and weight lifting machines. According to Education.com, movable pulleys have a greater mechanical advantage, meaning that the input force is less than the force of the system. Although, experts say that movable pulleys require more rope pulls by the user as the weight has become lighter, but fixed pulleys require less pulls. According to TeachEngineering, fixed pulleys enable the user to take advantage of gravity, balance an object and help raise objects above one's head. Movable pulleys are useful to raising objects below one's head. Education.com lists a third compound, the multiple pulley, which is comprised of both fixed and movable pulley systems. These pulleys are easiest to lift objects, as the mechanical advantage increases in tandem with the inclusion of more ropes, as cited by TeachEngineering. Pulleys are one form of simple machines in addition to screws and levers.