Question

Two different types of rubber are found to have the stress-strain curve as shown in the fig. (a) and (b).

(a) In which significant ways do these curves differ front the stress-strain curve of a metal wire shown in.fig. (c)?

(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 prefer to use for this purpose? Why?

(c) Which of the two rubber materials would you choose for a car tyre?

Answer 1

(a) These curves differ from that of the fig (c) in the following ways:

(i) Hooke's law is not obeyed at all

(ii) There is no permanent strain even if a large stress is applied

(iii) When the stress is reduced, the material does not retrace its path back

(iv) Both the materials A and B exhibit elastic hysteresis

(b) To absorb vibrations, rubber B is to be preferred. It is because the area enclosed by hysteresis loop of this material is large.

(c) For making the car tyre, the rubber material should be such that it is not heated up quickly. For rubber A, the energy loss is small (because of lesser area of hysteresis loop). Therefore, material A should be chosen.