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: The force applied to a plane divided by the area of the plane. COMPRESSIVE STRESS: The stress generated by forces directed toward one another on opposite sides of a real or imaginary plane. TENSILE STRESS: The stress generated by forces directed away from one another on opposite sides of a real or imaginary plane. SHEAR STRESS: Stress (force per unit area) that acts parallel to a (fault) plane and tends to cause the rocks on either side of the plane to slide by one another. STRAIN: The result of stress applied to a body, causing the deformation of its shape and/or a change of volume. ELASTIC RESPONSE: The deformation of a body in proportion to the applied stress and its recovery once the stress is removed. ELASTIC LIMIT: The maximum amount of stress a material can withstand before it deforms permanently. DUCTILE RESPONSE: The permanent deformation, without fracture in the shape of a solid.