Theory of Machine
The example of spherical pair is

Lead screw of a lathe
Ball and socket joint
Ball bearing and roller bearing
Bolt and nut

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Theory of Machine
The Ackerman steering gear mechanism is preferred to the Davis steering gear mechanism, because

Both (A) and (B)
The Ackerman steering gear is most economical
Whole of the mechanism in the Ackerman steering gear is on the back of the front wheels
The Ackerman steering gear consists of turning pairs

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Theory of Machine
For an isochronous Hartnell governor (where r₁ and r₂ = Maximum and minimum radius of rotation of balls respectively, S₁ and S₂ = Maximum and minimum force exerted on the sleeve respectively, and M = Mass on the sleeve)

S₂/S₁ = r₁/r₂
(m.g - S₁)/(m.g - S₂) = r₂/r₁
S₁/S₂ = r₁/r₂
(m.g + S₁)/(m.g + S₂) = r₁/r₂

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