Theory of Machine
In a screw jack, the effort required to lower the load W is given by

P = W tan(α + φ)
P = W tan(α - φ)
P = W tan(φ - α)
P = W cos(α + φ)

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Theory of Machine
In a hydrodynamic journal bearing, there is

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

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