Which type of stress is created by forces pulling away from each other?

The correct choice is twofold: tensile stress specifically arises when forces are applied in a manner that pulls materials apart. This kind of stress occurs when an external force generates a stretching effect along the length of a material, leading to deformation as the material tries to respond to the applied forces.

In understanding tensile stress, it's important to recognize its significance in materials engineering and structural analysis. The design and integrity of various structures depend heavily on the knowledge of how materials will behave under such forces. Assessing tensile stress is critical for ensuring that materials can withstand the operational loads without failure.

The other types of stress mentioned have different characteristics. Compressive stress occurs when forces push materials together, leading to shortening or buckling. Shear stress involves forces acting parallel to a material's surface, causing layers to slide past one another. Ultimate stress refers to the maximum stress that a material can withstand before failure but does not specifically describe the pulling forces responsible for producing tensile stress. Understanding these distinctions is vital for both practical applications and theoretical analyses in engineering.