Engineering Mechanics
In a screw jack, the effort required to lift the load is given by (where W = Load lifted, α = Helix angle, and φ = Angle of friction.)

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

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Engineering Mechanics
Non-coplanar concurrent forces are those forces which

Meet at one point and their lines of action also lie on the same plane
Do not meet at one point and their lines of action do not lie on the same plane
Meet at one point, but their lines of action do not lie on the same plane
Do not meet at one point, but their lines of action lie on the same plane

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