A sprocket is a toothed wheel that is designed to engage with something that will be pulled over the wheel as the wheel rotates. These wheels look a great deal like gears, but unlike gears, they are not designed to be meshed with other gears. The basic design of this simple mechanical device has been use around the world for quite a long time, and it has a number of applications, from advancing the film in throwaway disposable cameras to powering professional-class bicycles.
One of the most familiar settings for a sprocket is in the bicycle, where the device pulls a linked chain to transform the movement of the rider's feet into rotation of the wheels. The size can be adjusted to change the gearing of the bicycle for different cycling situations, allowing bicyclists to make their movements as powerful and efficient as possible. This design is also used on motorcycles and some other types of motorized vehicles.
Tracked vehicles like tanks and certain types of farm equipment also use them. In this case, the sprocket interfaces with the links of a track, pulling them as it rotates, and causing the vehicle to move. This design distributes the weight of the vehicle across the entire track, rather than focusing it on individual wheels, and as a result, tracked vehicles can traverse unstable ground more safely.
Another use for these devices can be found in film cameras, where they are used to hold the film in place and move it as photographs are taken. Sprockets are also used to thread movies on film. Certain types of printers may also use the design, with paper being equipped with small perforations that are threaded onto sprockets that move the paper through the printer as the print head applies ink.
One of the problems with the sprocket is that, if the material being threaded through the teeth runs off track, it can cause serious problems. These systems are often more difficult to repair than the alternatives, which is one reason that they have fallen out of favor in applications such as printers. Damage to the sprockets or the track of a tracked vehicle can render the machine useless until the damage can be repaired or addressed, and high speed failures on bicycles can turn the chain into a cracking whip that can cause serious damage or injuries to equipment and people.