Certified Forester Practice Exam

Which type of stress is associated with forces causing one part of the wood to move parallel to the plane of contact?

1. Bending stress

2. Shear stress

3. Tensile stress

4. Compression stress

The correct answer is: Shear stress

Shear stress is related to forces that cause different parts of a material to slide past one another in a direction parallel to the plane of contact. In the context of wood, this type of stress arises when external forces are applied that create a tendency for one section of the wood to move sideways relative to another section. In wood structures, shear stress is particularly significant in cases where loads are applied horizontally, such as in beams supported at both ends. The wood must resist this sideways sliding motion, which can lead to shear failure if the stress exceeds the wood's shear strength. Understanding shear stress is vital for foresters and engineers working with timber, as they must ensure that their designs can withstand not only the vertical loads but also lateral forces that may cause shearing. In contrast, bending stress relates to the deformation of material when subjected to a load causing it to bend, while tensile stress refers to forces that pull materials apart along their length. Compression stress involves forces that push materials together. Each of these stresses affects wood differently depending on the type of force applied and the geometry of the structure.