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 is a force.the pull at both ends of a stretched spring,string or rope is called tension.ension and compression takes place when an object has a force on  another object. The tension is when the force is causing a pulling  effect on part of the object. The comp â¦ ression is when the force is  causing a contracting effect on part of the object. Answered.