Which type of stress acts perpendicular to a surface?

The correct answer is compression stress, which acts perpendicular to a surface. This type of stress occurs when forces are applied in such a way that they push or pull inward, leading to a decrease in volume. In geological terms, compression stress is responsible for the folding and faulting of rocks, which often occur in tectonically active regions where tectonic plates converge.

When analyzing the forces at play, compression stress affects the material uniformly across the surface, resulting in the rock being compressed inward. This is contrasted with other types of stress, such as tension, which pulls apart and acts in the opposite direction, and shear stress, which acts parallel to the surface, causing slippage or deformation.

Understanding these different stresses is crucial for interpreting geological features and phenomena, as well as for predicting how rocks will behave under various geological conditions.