A pulley is a simple machine consisting of a wheel with a grooved rim and a rope or cable that runs along the groove. It is used to change the direction of a force applied to an object, making it easier to lift or move heavy objects.
A pulley provides mechanical advantage by distributing the weight of an object across multiple ropes or cables, reducing the amount of force needed to lift the object. The more ropes or cables used in a pulley system, the greater the mechanical advantage.
There are three main types of pulleys: fixed, movable, and compound. Fixed pulleys have a stationary axle and are used to change the direction of a force. Movable pulleys have a moveable axle and are used to amplify force. Compound pulleys combine fixed and movable pulleys for even greater mechanical advantage.
The formula for calculating mechanical advantage of a pulley system is MA = (number of supporting ropes or cables) + 1. For example, a pulley system with 3 supporting ropes would have a mechanical advantage of 4.
Pulleys are commonly used in construction, elevators, cranes, and on sailboats. They are also used in exercise equipment, such as weight machines, and in window blinds and curtains. Pulleys are also found in the human body, such as in the knee joint where the patella (kneecap) acts as a pulley to help the quadriceps muscle straighten the leg.