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.
How to Calculate Tension in Physics. In physics, tension is the force exerted by a rope, string, cable, or similar object on one or more objects. Anything pulled, hung, supported, or swung from a rope, string, cable, etc. is subject to the force of tension. Like all forces, tension can accelerate objects or cause them to deform.