One of the most important properties of materials in many applications is strength. two of the qualitative measures of the strength of a material are tensile strength and shear strength. the tensile strength of a material is the amount of force needed to pull the material apart perpendicular to a cross section, such as pulling on a rope. the shear strength is the amount of force needed to rupture the material when a force is applied parallel to the cross section, such as breaking a pencil overhanging a table edge. both tensile strength and shear strength have units of pressure, because they represent the force that must be applied per unit area in order to break the material. the importance of knowing the tensile strength and shear strength of a material is evidenced by the number of machines and companies specializing in determining these properties. many types of materials and objects are tested, from fabric and metal to nuts and bolts. it is always comforting to know that the tensile strength of the rope holding you above the ground can support your weight. shear strength needs to be found for bridges, the floors of multilevel buildings, and the joints where the wings join the body of an airplane. without the experimental determination of these properties, trial and error would be the only other method of determining these values, a process that would be dangerous to life and limb.