proof forces parallel to members in simple truss

The video tutorial provides a formal proof that internal forces in simple trusses must be parallel to the members, based on three key assumptions: pin joints, no friction, and negligible mass. It explains the use of free body diagrams and equilibrium conditions to demonstrate that forces are purely axial. The tutorial also covers the importance of questioning assumptions and provides a step-by-step proof of axial forces in trusses.

What are the two conditions that must be satisfied for equilibrium in the context of the truss?

How does the proof demonstrate that the internal reaction force must exist in a specific direction?

Summarize the main conclusion of the proof regarding internal forces in simple trusses.