Mechanics (Statics) — Equilibrium of a rigid body under the effect of coplanar forces meeting at a point

About this lesson

This unit covers the equilibrium of a rigid body under the effect of coplanar forces meeting at a point. It begins with the simplest case of equilibrium under two forces, stating the conditions (equal magnitude, opposite direction, same line of action). It then extends to three forces, introducing the triangle of forces rule, Lami's rule, and the theorem that three non-parallel forces in equilibrium must have lines of action meeting at a point. The unit also covers equilibrium of a set of coplanar forces meeting at a point, using the condition that the algebraic sum of components in two perpendicular directions is zero. Worked examples and exercises involve bodies like spheres, rods, and weights suspended by strings, often with smooth walls or pulleys, and require finding unknown forces, tensions, reactions, or angles.