A few butterflies and many moth species spin a silk case or cocoon prior to pupating, while others do not, instead going underground. A butterfly pupa, called a chrysalis, has a hard skin, usually with no cocoon.
4. tension - (physics) a stress that produces an elongation of an elastic physical body; the direction of maximum tension moves asymptotically toward the direction of the shear. natural philosophy, physics-the science of matter and energy and their interactions; his favorite subject was physics.
Stress = Force/Area. Strain = A change in shape or volume in response to a stress. Stress is the cause, strain is the effect! There are three types of stress : 1) Compressive stress Forces that squeeze or push toward one another from opposite directions (cause shortening or flattening).