Physics · Mechanical Properties Of Solids · NEET
No. No real material is perfectly elastic or perfectly plastic. Every solid returns to its shape only up to a certain limit (called the elastic limit). Beyond that limit it stays partly deformed. A quartz fibre is close to a perfect elastic body, and putty or mud is close to a perfect plastic body, but neither is exact. NEET often uses the word 'nearly' or 'close to' for this reason.
In a spring (steel), the atoms are held by strong bonds that act like tiny springs. A small force pulls the atoms slightly apart, and when you remove the force the internal restoring force pulls them back, so the shape returns. In clay, the particles slide past each other and settle into new positions. There is no strong restoring force to pull them back, so the new shape stays. This is why steel is elastic and clay is plastic.
No, this is a common mix-up. Elasticity does NOT mean 'stretches easily.' It means the body RETURNS to its original shape after the force is removed. Steel stretches very little but is highly elastic because it recovers fully. Rubber stretches a lot but recovers less perfectly, so steel is actually MORE elastic than rubber. Read the linked page on 'why steel is more elastic than rubber' for the full reason.
No. Softness and flexibility are about how easily a body bends, not about whether it recovers. A thin rubber sheet is soft and flexible but still elastic because it springs back. Wax is soft and plastic. The test for plastic vs elastic is always the same: after you remove the force, does the shape come back (elastic) or stay changed (plastic)?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Elasticity is the property of a body to return to its original shape and size after the deforming force is removed. Plasticity is the property of a body to keep the deformed shape even after the force is removed. A rubber band is elastic; wet clay is plastic.
Elastic body: a steel spring or rubber band that springs back to its shape. Plastic body: putty, dough, or soft clay that stays in the new shape after you press it.
Elasticity comes from the internal restoring forces between the atoms or molecules of the solid. When a force deforms the body, the atoms are pushed out of their normal positions. The restoring forces try to pull them back, and when the outside force is removed, they bring the body back to its original shape.
The property of regaining shape is mainly discussed for solids because solids have a definite shape. Fluids (liquids and gases) do not have a fixed shape, but they do resist changes in volume, which is why we still talk about bulk modulus for them. In NEET the term elasticity mostly applies to solids returning to their original shape and size.
Elasticity is the foundation of the whole Mechanical Properties of Solids chapter. Understanding elastic behaviour leads to stress, strain, Hooke's law, and the three moduli (Young's, shear, and bulk). NEET regularly asks questions on the stress-strain curve, elastic limit, and comparing which material is more elastic, so this concept must be clear first.
