Elasticity is the property of the body by virtue of witch the body regain its original configuration (length, volume or shape) when the deforming forces are removed.
Fundamental reason of Elasticity
In a solid, a large number of atoms or molecules are arranged in a ordered fashion and each molecule is acted upon by the forces due to the neighboring molecules. The solid acquire such a shape that each molecule is in the state of stable equilibrium. When the body is subjected to a deforming force, the molecules are displaced from their positions to stable equilibrium and the intermolecular distances get changed. As a result of this change in intermolecular separation, intermolecular force are developed in a direction opposite to that of deforming forces i.e. restoring forces start acting on the molecules. [When the solid is subjected to some extensional force (compression force) within elastic limit the inter molecular separation becomes greater (smaller) than equilibrium separation and inter molecular force of attractive (repulsive) nature get developed]. When deforming force is removed, it is these restoring forces which drive the molecules back to their original positions and the body comes back to its natural form.
Perfectly elastic body
It is that the body which perfectly regains its original form on removing the external deforming force from it e.g. quartz.
It is that the force which when applied changes the configuration of the body.
It is the body which does not regain its original form at all on the removal of deforming force from it e.g. quartz.
It states that within elastic limit stress is directly proportional to strain.
It states that if gravity effect is neglected, the pressure at every point of liquid in equilibrium of rest is same. Pascal’s law also states that the increase in pressure at one point of the enclosed liquid in equilibrium of rest is transmitted equally to all other points of liquid provided the gravity effect is neglected.