Two different types of rubber are found to have the stree-strain curves shown in fig.

(a) In which significant ways do these curves differ form the stree-strain curve of a metal wire.
(b) A heavy machine is to be installed in a factory. To absorb vibrations of the machine, a block of rubber is placed between the machinery and the floor. which of the two rubbers A and B would you perfer to use for this purpose? why?
(c) Which of the two rubber materials would you choose for a car tyre ?

Explanation

(a) Since both the curves are not straight even for a very small region, hence Hooke's law is not obeyed even for small stresses. There is a large elastic region for both the materials but unloading. This frature is known as elastic hystersis. There is no permanent strain even for large stressess.
(b) The area of this hysteresis loop measures the amount of heat energy dissipated by the meterial . Since the areal of loop B is more than that of A, thererfore B can absorb more vibrations than that of A. Hence B is perferred.
(c ) In a car tyre it is desired to minimise the heating. Therefore rubber A would be perferred over rubber B.