Consider a lamp hanging vertically from the arms with its upper end clamped. If the arm member is isolated and the two forces act at two points, A and B, with no load in between, it is called a two-force member. Here, the nature of the forces is either tensile or compressive. For the two-force member to be in equilibrium, the forces FA and FB must be equal in magnitude but opposite in direction. To satisfy the condition for the moment equilibrium, FA and FB must have the same line of action. Generally, a two-force member can have multiple forces acting on points A and B that are represented as the resultant force at points A and B. If the magnitude and direction of the force on one side are known, the force on the other side can be calculated. This reduces the number of unknowns from the equilibrium equation. The two-force member is not necessarily straight; it can be bent or curved and is used to analyze the structure of trusses, frames, and machines.