What happens to a rubber band when you stretch it and let go? It deforms but regains its original nature when you stop applying force. But suppose you try to bend an aluminium rod using your arm strength. You somehow do manage to bend it a little and then stop applying force. Does the rod regain its original shape? Of course not.
This difference in the behaviour of the materials is based on their elastic and plastic nature. The rubber band has high elasticity. Elasticity is the ability of a body to resist any permanent changes to it when stress is applied. The body regains its original shape and size when stress application ceases.
All materials have an elastic limit beyond which, if continuous stress is applied, they will start losing their ability to exhibit perfect elastic behaviour and start deforming. In contrast, plastic deformation is the non-reversible deformation of solid materials on the application of forces.
Looking at the elasticity at the atomic level, solids are made of atoms (or molecules). They are surrounded by other such atoms, which are held in a state of equilibrium by interatomic forces. When an external force is applied, these particles are displaced, resulting in the deformation of the solid. When the application of the deforming force is stopped, interatomic forces drive the atoms to regain their state of equilibrium.
The concept of elasticity is an idealisation as no material is perfectly elastic. For example, if you use a hair tie to groom yourself, you may have noticed that its size tends to deform after prolonged use. After a point, it may snap as well. This is because the hair tie eventually loses its elastic nature.
Important Points on Elastic Behaviour of Solids
- An elastic body is one that regains its original shape and size when deforming forces are removed
- A plastic body is one that succumbs to deforming forces (however small) and cannot return to its original shape and size
- Elasticity is the property of a body to regain its original shape and size when deforming forces are removed. It exhibits an opposition to change.
Frequently Asked Questions – FAQs
Q1
What is an example of elastic behaviour?
When we stretch a slingshot, the force we applied allowed it to stretch, but when we removed the force, the deformation reverted to its original shape. This property is known as elasticity.
Q2
Do solids have elasticity?
Yes, non-Newtonian fluids, like viscoelastic fluids, which are not solids, may also display elasticity under certain circumstances.
Q3
What are examples of elastic materials?
Examples of elasticity are suspensions, steel, and rubber bands.
Q4
Why solids are more elastic than gases?
Solids have the smallest intermolecular gap between molecules and the strongest intermolecular force of attraction.
Q5
Do gases have elastic limit?
There is no elastic limit for gases.
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