A crank is a mechanical device used to convert rotational motion into linear motion or vice versa. It typically consists of a handle attached to a rotating shaft, allowing users to apply force and create movement. Cranks are commonly found in various machines, such as bicycles, where they help turn the pedals, and in engines, where they convert the linear motion of pistons into rotational motion. Cranks can be simple or complex, depending on their application. They are often used in conjunction with other components, such as gears and levers, to enhance mechanical efficiency. Related devices include pulleys, gears, and levers, which work together in many mechanical systems.