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The quntity stress is tension generalized to rigid bodies which can not only be stretched, but compressed and twisted. If we try to stretch a body, we say that is is under tensile stress . If we try to compress or squish a body, it is under compressional stress . If we twist, or shear a body, it is under shear stress . A material's strength usually varies depending whether it is under compressional, tensile or shear stress.