Answer:

A simple truss is a structural system made up of straight members connected at their ends by joints. It is one of the most common types of structural systems used in civil engineering.

Internal Stability of a Truss:
Internal stability refers to the ability of a truss to resist internal forces, such as axial forces and moments, without collapsing or deforming. In simpler terms, it means that the truss should be able to maintain its shape and support loads without any member buckling or failing.

Reasoning:
A simple truss is considered to be internally stable due to the following reasons:

1. Equilibrium: A truss is designed in such a way that it satisfies the conditions of static equilibrium. This means that the sum of forces acting on any joint should be zero, and the sum of moments acting on any joint should also be zero. By satisfying these equilibrium conditions, the truss remains stable and can withstand the applied loads.

2. Method of Joints: The method of joints is commonly used to analyze simple trusses. This method assumes that the joints are perfectly rigid and transfers the applied loads to the truss members. By solving the equilibrium equations at each joint, the internal forces in each member can be determined. If the truss is internally stable, the calculated internal forces will not exceed the strength capacity of the members.

3. Member Forces: In a simple truss, the internal forces (axial forces) in the members are either tension or compression. These forces are distributed along the length of the members, and as long as the members are capable of resisting these forces, the truss remains internally stable. The design of the truss ensures that the member forces do not exceed the material strength limits.

4. Member Connections: The connections between the truss members are typically designed to transfer the internal forces between the members efficiently. Welded or bolted connections are commonly used, ensuring that the forces are transmitted without causing any significant deformation or failure.

Conclusion:
Based on the above reasoning, it can be concluded that a simple truss will always be internally stable. The design of the truss, the method of joints, and the distribution of internal forces ensure that the truss can withstand the applied loads without collapsing or deforming.