A freewheel mechanism is a device that allows rotation in one direction while preventing it in the opposite direction. It is commonly used in bicycles, where it enables the rider to coast without pedaling. When the pedals are not being pushed, the freewheel allows the rear wheel to spin freely, making it easier to maintain speed without exerting energy. This mechanism typically consists of a ratchet and pawl system, which engages when pedaling forward and disengages when pedaling backward. The freewheel is an essential component in many machines, including automobiles and gear systems, providing efficiency and ease of use.