Rubber is the first material that comes to mind when the word elasticity is mentioned. However, all solids possess this property to a certain degree, though it most cases it is barely noticeable. The only metal in which elasticity is very well developed is steel and even then it must be hardened steel. This is produced by rapidly cooling or quenching red-hot steel in cold water, a process called tempering. Tempered steels are hard and brittle but very elastic. Springs are nearly always made of tempered steel which has been gently reheated, a process that destroys some of the elasticity but makes the steel softer and tougher.
Extension and load
There comes a point at which the wire or strand begins to stretch much further than Hooke's law would predict for the extra weights added. Moreover, when the weights are removed it no longer reverts to its original length. The point at which this happens is called the elastic limit. The amount of extension increases rapidly after the elastic limit has been reached until the wire suddenly parts at the yield point.
Molecular explanation of elasticityThe elastic properties of materials are due to forces acting between atoms or molecules. The reason why rubber can be stretched so much is that it is built up of long molecular chains, most of which are folded like tangled ropes. When the material is stretched the chains simply straighten themselves out and when the force is removed they revert to their original tangled state. Many other materials, such as wood and silk, are built of chain molecules, but in most cases strong links between the chains prevent them from curling back upon themselves, so that elasticity is not pronounced.
Related category PROPERTIES OF MATTER
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