(a) A uniform metal bar, initially unstretched, has sides of length w, x and y, as shown in [Fig. 3.1]. The bar is now stretched by a tensile force F applied to the shaded ends. The changes in the lengths x and y are negligible. The bar now has sides of length x, y and z, as shown in [Fig. 3.2]. (b) A copper wire is stretched by a tensile force that gradually increases from 0 to 280 N. The variation with extension of the tensile force is shown in [Fig. 3.3].