A sprocket wheel is a wheel or disc, usually thin, that contains a series of teeth around its outer perimeter. These teeth are created to engage the links of a chain. Turning the wheel causes the chain to advance, usually activating either another sprocket wheel or some other type of mechanism. Such wheels are used frequently in manufacturing, but are also found in common consumer items, most notably bicycles.
Most bicycles have two such wheels. One sprocket wheel is attached to the front wheel of the bike, while the other is attached to the rear wheel, with a chain connecting the two wheels. The links of the chain are made to engage with the teeth on both wheels so that when one turns, the other also turns. The pedals are connected to one of the wheels.
When the rider turns the pedals, the first sprocket wheel turns. This causes two things to happen: first, it makes the front wheel of the bicycle turn; second, it causes the chain to advance, which turns the second sprocket wheel. This, in turn, causes the rear bicycle wheel to rotate.
Both bicycle wheels then turn at the same time, allowing the bike to move forward. The rider repeats the motion of turning the pedals, which repeats the chain and sprocket cycle. This keeps the bike moving forward. Pedaling faster makes the bike go faster.
If the chain disengages with the teeth of either of the sprocket wheels, the entire mechanism ceases to work. While the pedals will still turn one wheel, the other will stop and the bike will not move forward. The slipped chain must be reengaged with the teeth of both wheels before the bike can be operated properly again.
This same mechanism is used in many manufacturing processes, and sprocket wheels can be found in many types of machinery. Some machines use a two-wheel system similar to a bicycle, but three-wheel systems are also common. The point is to allow two or more points to turn all at once when one point is rotated. Connecting sprocket wheels of differing sizes can effect the way a machine operates and the speed of its operation.
Sprocket wheels are often metal, but can also be plastic or wood. They differ from gears, which look similar but are made to engage with one another rather than with a chain or belt. They also differ from pulleys, which can serve similar functions but are smooth rather than having teeth.