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.
I think Wikipedia's definition is actually pretty clear: In physics, moment is a combination of a physical quantity and a distance. Notable examples: The moment of force (torque) about a given axis is given by the force (physical quantity) times the perpendicular distance of the line of action from the axis.