Concurrent Forces and Lami's Theorem

A set of forces is said to be concurrent if all their lines of action pass through one common point (they need not lie in the same plane); when concurrent forces do lie in one plane, they are called coplanar and concurrent.

Analysing a point held in static equilibrium under three such concurrent, coplanar forces is a very common situation in mechanics — a hanging swing, a sling shot, a signboard suspended by two cables, etc. The most convenient tool for such problems, avoiding the need to resolve ever …