Theory of Machine
A disc is a spinning with an angular velocity ω rad/s about the axis of spin. The couple applied to the disc causing precession will be (where I = Mass moment of inertia of the disc, and ωP = Angular velocity of precession of the axis of spin)

(1/2). I ω ωP
Iω²
I ω ωP
(1/2).Iω²

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Theory of Machine
In elliptical trammels

Two pairs turning and two pairs sliding
All four pairs are turning
One pair turning and three pairs sliding
Three pairs turning and one pair sliding

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Theory of Machine
Open pairs are those which have

Surface contact between the two elements when in motion
Elements of pairs not held together mechanically
Point or line contact between the two elements when in motion
Two elements that permit relative motion

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