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.
In physics, tension describes the pulling force exerted by each end of a string, cable, chain, or similar one-dimensional continuous object, or by each end of a rod, truss member, or similar three dimensional object.ach segment of the rope is pulled on by the two neighboring segments with a force due to tension. Tension can change along the length of a rope, as it does along the grip of each of the tug of war team members.