Which of the following is NOT a common force acting on buildings?

Friction is not typically considered a common force acting directly on buildings in the same way that gravity, tension, and wind are.

Gravity is a fundamental force that affects all buildings, as it dictates the downward load that structures must support. Tension, which arises in materials when they are stretched, can occur in structural elements like cables in suspension bridges or reinforcement bars in concrete. Wind, another crucial external force, exerts lateral pressure on buildings, necessitating specific architectural designs to ensure stability and resistance to uplift or sway.

Friction, while present in the context of interactions between surfaces or materials—such as the sliding of structural elements against each other—is not classified as a fundamental force acting on the building itself. Instead, it plays a more secondary role in terms of motion and resistance rather than being a primary physical force that must be accounted for in the same way as the others mentioned. Thus, it stands out as the option that doesn't align with the more commonly referenced forces in structural engineering.