Elasticity (Physics)

Elasticity refers to that property of an object by virtue of which it regains its original configuration after removal a deforming force. Deforming force is the force which causes a change in configuration of an object when applied to it.

Important Notes on Elasticity

• The upper limit of the deforming force up to which a body regains its original configuration completely is called Elastic Limit. Beyond elastic limit, the body will lose its property of elasticity and will deform permanently.
• If a body regains its original configuration immediately and completely after removal of the deforming force, it would be called Perfectly Elastic Body. There is no perfectly elastic body but quartz fibre and Phosphor bronze are examples of near perfect elastic bodies.
• If a body does not regain its original configuration at all after the deforming force is removed, it is called perfectly plastic body. Examples of near perfect plastic bodies are wax, putty etc.
• When a ball falls, it is temporarily deformed. Because of elasticity, the ball tends to regain its original shape for which it presses the ground and bounces up.
• The materials which show large plastic range beyond elastic limit are called ductile materials, e.g., copper, silver, iron, aluminum, etc. Ductile materials are used for making springs and sheets. The materials which show very small plastic range beyond elastic limit are called brittle materials, e.g., glass, cast iron, etc.
• The materials for which strain produced is much larger than the stress applied, with in the limit of elasticity are called elastomers, e.g., rubber, the elastic tissue of aorta, the large vessel carrying blood from heart. etc. Elastomers have no plastic range.
• Elasticity of steel is more than that of copper and so for equal applied force, the elongation of steel spring is less than that of copper for same initial length. This implies that the steel spring can bear a larger tension before the elastic limit is crossed. Further, steel recovers its original state quicker than copper after the deforming force is removed. Due to this reason, steel is preferred in making springs in comparison to steel.
• Glass is more elastic than rubber because for a given applied force per unit area, the strain produced in glass is much smaller than produced in rubber.

Working of Crazy Balls

Rubber is a common visco-elastic material which means it is both viscous and elastic. Further, Rubber is also characterized by another property called resilience. Resilience is the ability of a material to absorb energy when it is deformed elastically, and release that energy upon unloading. Higher the resilience, higher is the bounce in a rubber ball, which means higher elasticity and lesser viscosity. We note here that the butadiene rubber has highest resilience property, followed by natural rubber.