One mole of nickel (6 x 10²³atoms) has a mass of 59 grams, and its density is 8.9 grams per cubic centimeter so the center-to-center distance between atoms is 2.23 x 10⁻¹⁰ m. You have a long thin bar of nickel, 2.7 m long, with a square cross-section, 0.06 cm on a side.
You hang the rod vertically and attach a 27 kg mass to the bottom, and you observe that the bar becomes 1.38 cm longer. From these measurements, it is possible to determine the stiffness of one interatomic bond in nickel.
What is the spring stiffness of the entire wire, considered as a single macroscopic (large scale), very stiff spring?