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
James White's Dynamometer from A New Century of Inventions (1822)
Walter Hancock's Artillery Wheel with Driver allowing overrun on the outside of a curve
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
Differential (mechanical device)
…the ecliptic positions of the Sun and Moon, and thus the phase of the Moon. Around 250 AD Chinese engineer Ma Jun created the first well-documented south-pointing chariot, a precursor to modern inertial navigation systems. Its mechanism of action is unclear, though in the early twentieth century the engineer George…
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
An illustration of a differential between the drive shaft (at bottom right) and driving wheels of an automobile