1. Concept Overview
When a force acts on any material, it tends to change its shape or size. But many materials try to regain their original form once the force is removed. This tendency to return to the initial shape is known as elasticity. It is the reason why a rubber band snaps back, why a metal wire regains its length, and why bridges don't permanently sag under load.
Different materials have different degrees of elasticity. Some snap back easily, others only slightly, and some do not return at all. This behaviour depends on how strongly the internal particles are bonded.
2. Definition
3. Key Ideas Explained
3.1. Why Elastic Behaviour Occurs
Inside every solid, atoms and molecules are connected by forces that act like tiny springs. When a force stretches or compresses the material, these internal 'springs' resist and try to pull particles back to their original positions. This restoring action gives rise to elasticity.
The stronger these internal forces, the more elastic the material is.
3.2. Perfectly Elastic vs Real Materials
3.2.1. Perfectly Elastic Materials
These regain their exact original shape completely, even after large deformation. They are ideal and do not exist in real life. Examples used in theory: perfectly elastic springs.
3.2.2. Real Materials
Real materials show elasticity only up to a limit. If stretched too much, they do not return completely. Metals, rubber, wood, and plastic all behave elastically within certain limits.
3.3. Elastic Limit and Plastic Behaviour
Every material has a maximum limit up to which it behaves elastically. This is called the elastic limit. Beyond this limit, the material undergoes permanent deformation and does not return to its original shape. This non-reversible behaviour is called plasticity.
3.4. Relation with Stress and Strain
Elastic behaviour is observed when the stress applied on a material is proportional to the resulting strain. In this region, the material obeys Hooke’s Law, which is the foundation of elasticity. Although the formulas belong to later topics, the idea is simple: small forces cause small, reversible deformations.
4. Important Characteristics of Elastic Materials
4.1. Restoring Force
Whenever a material is deformed, a restoring force develops inside it. This force tries to bring the material back to its original state. Larger deformation produces a larger restoring force.
4.2. Elastic Fatigue
A material may lose part of its elasticity when repeatedly stretched or compressed many times. This is called elastic fatigue. For example, a repeatedly stretched rubber band becomes loose and does not return to its original shape perfectly.
5. Examples to Build Intuition
5.1. Rubber Band
A rubber band stretches easily and returns to its original size, showing strong elastic behaviour. However, if stretched too much, it becomes permanently longer or even snaps.
5.2. Metal Wire
A metal wire elongates slightly when pulled by a heavy weight, even if the change is extremely small. Once the weight is removed, it returns to its original length. This is why metals are considered highly elastic (much more than rubber, scientifically).
5.3. Spring
A spring follows elasticity closely. When compressed or stretched, it stores energy and then releases it to return to its natural length. This behaviour is the basis of Hooke's Law.