Equilibrium States: Forces in Non-Rigid Systems

This lecture covers the principles of equilibrium states and forces in non-rigid systems, focusing on the application of the principle of virtual work. The instructor begins by reviewing the concept of work done by forces and introduces conservative forces, emphasizing their path independence. Examples include potential energy associated with gravitational forces and springs. The lecture then transitions to the principle of virtual work, explaining that for a mechanical system in equilibrium, the virtual work done by external loads vanishes during arbitrary virtual displacements. The instructor illustrates this with examples, including a drawbridge system, where the equilibrium position is determined by analyzing forces and displacements. The discussion extends to reaction forces and internal loads in rigid structures, highlighting the method of removing supports to create a hypostatic system. The lecture concludes with a demonstration of how to apply these principles to solve problems involving equilibrium conditions in various mechanical systems, reinforcing the importance of understanding kinematically admissible displacements.