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.
1 Tension (physics) , a force related to the stretching of an object (the opposite of compression). 2  Tension (geology) , a stress which stretches rocks in two opposite directions.3  Voltage or electric tension. Tension (physics) , a force related to the stretching of an object (the opposite of compression). 2  Tension (geology) , a stress which stretches rocks in two opposite directions.