AL Phy: Measuring Young's modulus of copper

Question

As a parameter of mechinacial property, why is Yong modulus (defined by stress/strain )more useful than force constant (defineds by force/extension ) for material selection?

Answer 1

Be aware that you are going to select a material, not to select a specific size of a given material.

The force constant of a given material depends on the dimensions of it (length, diameter etc), but the Young's Modulus only depends on the nature of the material.

For example, the Young's Modulus of steel is a constant figure, but the force constant of a steel wire of, say 1 metre long and 0.05 mm square cross-section, is different from another steel wire of the same material but with dimensions of, say 2 metre long and 0.01 mm square cross-section.

Perhaps you have learnt that the force constant k and Young's Modulus E are related by the following equation:

k = EA/L
where A is the cross-sectional area (in m^2) and L is the length (in m).