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

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

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Theory of Machine
In a hydrodynamic journal bearing, there is

A thick film of lubricant between the journal and the bearing
No lubricant between the journal and the bearing
A very thin film of lubricant between the journal and the bearing such that there is contact between the journal and the bearing
A forced lubricant between the journal and the bearing

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