An example of this type of compression would be the pressure that chair legs exert on a wooden floor. Compression stress is measured in psi. Tensile stress elongates or expands an object. Measurements of tensile stress perpendicular to the grain are useful for quantifying resistance to splitting. Examples of such stress include splitting firewood, driving nails, and forcing cupped boards to be flat.
Tensile stress is measured in psi.
Shear stress involves the application of stress from two opposite directions causing portions of an object to move in parallel but opposite directions. Wood is very resistant to shearing perpendicular to the grain and this property is not measured via a standard test. Shear stress is measured in psi. Density is weight per unit volume. For wood, density is expressed as pounds per cubic foot, kilograms per cubic meter, or grams per cubic centimeter - at a specified moisture content.