= Normal versus resultant force in a frictional pinch
{title2=$N_{\min}=mg/[2(\mu\cos\alpha-\sin\alpha)]$}
For symmetric upper faces inclined by alpha from the vertical, inward normals push partly downward. Limiting upward friction gives vertical support $2N(\mu\cos\alpha-\sin\alpha)$. Balancing weight yields the displayed minimum normal grip. The corresponding minimum total contact magnitude per face is $N_{\min}\sqrt{1+\mu^2}$. It is achieved at the limiting <friction angle>. The formula assumes symmetric contacts with cancelling horizontal force and torque and positive denominator.
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