A differential is a gear train with three drive shafts that has the property that the rotational speed of one shaft is the average of the speeds of the others. A common use of differentials is in moto
Differential unit for a rear-wheel drive car, built by ZF c. 2004
Differential gears (in yellow) in a punched tape reader, built by Tally c. 1962
Illustration of a ring-and-pinion differential for a rear-wheel drive vehicle
Schematic diagram of a ring-and pinion differential
South-pointing chariot
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The south-pointing chariot was an ancient Chinese two-wheeled vehicle that carried a movable pointer that indicated south, no matter how the chariot turned. Usually, the pointer took the form of a dol
Exhibit in the Science Museum in London, England. This conjectural model chariot incorporates a differential gear.
An image of a south-pointing chariot from Sancai Tuhui (first published 1609)
Children's instructive toy chariot in Chinese display at Expo 2005 in Japan