In economics, it refers to how changing one variable changes others.
The response of the quantity demanded with a change in price.
Seat belts are made from polyamide which has a good elasicity.
The EI value is the the relationship between design of a shape and the strength of the material the shape is to be produced out of. E = Modulas of Elasticity I = Inertia Value For example if a two tubes of the same diameter and wall thickness, one made from Aluminium and one made from Steel, the Steel tube will be stronger. The inertia value of the tube will be the same, but when multiplied by the Modulas of Elasicity the steel one will be significantly higher. Modulas of Elasticity of Aluminium T6-6063 = 65500N/mm2 Modulas of Elasticity of Steel (Mild) = 205000N/mm2 Approx Figures. EI Values are commonly used for calculating deflection amounts for self supporting glazing bars and lintels etc.