Theory of Machine
Lower pairs are those which have

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

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Theory of Machine
The frictional torque transmitted in a flat collar bearing, considering uniform pressure, is (where r₁ and r₂ = External and internal radii of collar respectively)

(2/3). μ W [(r₁³ - r₂³)/(r₁² - r₂²)]
(1/2). μ W [(r₁³ - r₂³)/(r₁² - r₂²)]
(1/2). μ W (r₁ + r₂)
(2/3). μ W (r₁ + r₂)

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