The first gears were a natural development from the invention of the wheel. In early types of rotating machinery, the capacity of gears to shift and increase power from one component to another made them a favourate device from the 3rd century BCE onwards, and led to a multitude of practical applications.
Most gears consist of cogs (rotating "teeth") that mesh with other cogs. They help movement to be transmitted from an input source - such as flowing water to an output device, such as a pump, mill, or the hands of a clock. The position of the gears' teeth can vary, depending on the type of gear (see right ) . Sometimes the teeth are arranged along a linear rack or form a spiral along a shaft instead of being borne on a cog .
ADVANTAGES OF GEARS
The earliest gears were probably made from wood with cylindrical pegs for teeth . Various arrangements were used , depending on which of the gearing advantages was required . Firstly , the direction of power can be changed from the input to the output gear . For instance , where a horse was used to pull a horizontal wheel , a gear arrangement could be used to transmit the power to another wheel that then raised water vertically from a river . Secondly , gears can be used to change slow input speed into a fast output speed . The rotational speed of horse or water - powered wheels was often too slow for grinding grain or hammering metals , so gears were used to increase the speed to a usable level . Finally , gear sets can be used to change a small input torque ( rotational force ) into a larger output torque , effectively creating leverage . This is useful for purposes such as lifting heavy loads . The property of gears that allows the output torque and rotational speed to be different from the input is called the mechanical advantage . It is equal to the gear ratio : the ratio of the number of teeth in the driven gear to the number of teeth in the driving gear .
Mechanical clocks differ from earlier clocks such as those driven by water flow - in containing some type of oscillating mechanism . Gears are used in these clocks essentially as chains of counting devices , adding up the regular - timed pulses generated by the oscillator to mark the units of time . The final gears in the chain are attached to , and move , the hands of the clock Mechanical clocks first appeared in Europe during the 13th century .