Can internal restoring force is always equal and opposite to the deforming force applied on the wire? If not, when?

When two forces appiled on an object are equal and opposite, then the forces.

In case of vibration the restoring force is

Which quantity represents the normal force applied on unit area of a surface?

During vibration, the restoring force is

If the force of friction is equal to the force applied, then friction may be

The breaking force for a wire is F.What will be the breaking force for a single wire of double the thickness?

The radius of a copper wire is twice that of a steel wire. One end of the copper wire is joined with one end of the steel wire and the same tensile force is applied on them . If the length of the copper wire increases by 1% , what will be the percentage increase in the length of the steel wire? Given Young's modulus of steel is twice that of copper.